Cell Structure and Organization
A
cell is the smallest unit that can carry on all the processes of life.
All organisms are made of cells, organisms are made of several organ systems,
each organ system contains several organs, each organ contains several tissues;
each tissue is made of cells. Cells are very tiny they could be seen only
through a microscope. We have two types of cells:
- Planet Cells
- Animal Cells
As
you can see from the diagram, there are some features found in plant cells but
not in animal cells.
Features
found in both plant and animal cells:
- Cell surface membrane: This is a partially permeable membrane separating the
cell from the environment its made of lipid and protein, it controls
movement of substances in and out, its strong but flexible.
- Cytoplasm: This is a
jelly like substance, its made of mostly water and protein. Metabolic
reactions occur in it.
- Nucleus: This
determines how the cell behaves and it contains chromosomes made of
strings of DNA which also determines which proteins the cell should make
etc.
Features
found in only plant cells:
- Cell Wall: This is a
rigid layer surrounding the cell made of cellulose, it gives the plant its
shape and prevents it from bursting.
- Chloroplasts: They are
sacs which contain chlorophyll which is a green pigment that traps
sunlight for photosynthesis.
- Vacuole: This is a
large room in the center of the cell, it stores sugars and salts and
controls movement of water in and out of the cell.
Animal
cells store sugars in glycogen form but plant cells store it as starch. Animal
cells have an irregular shape but plant cells have a regular shape.
Both
types of cells contain Mitochondria these are structures
that convert chemical energy in foods to energy that could be used in moving,
dividing, etc., it is evidence that the cell is an Active Cell.
Specialised Cells:
Red Blood Cells:
All organisms are made of cells, organisms are made of several organ systems, each organ system contains several organs, each organ contains several tissues; each tissue is made of cells. Cells are very tiny they could be seen only through a microscope. We have two types of cells:
Red blood cells are
found in the blood of animals, its function is to transport oxygen from the
lungs to all the body cells, and carbon dioxide from the body cells to the
lungs.
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They
are adapted by four ways:
- They have a biconcave disc
shape that gives it a large surface area to carry more oxygen.
- They contain a chemical called
hemoglobin that combines with oxygen and carbon dioxide.
- They have no nuclease to carry
more oxygen and CO2
- They are tiny enough to squeeze
through capillaries.
Muscle Cells:
They are cells found
in muscles in animals, they contract and relax together to move the
organisms.
Their function is to contract to support and move the body. |
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They
are adapted by two ways, First, Is that they are made of contractile filament to help in contraction.
Second is it contains lots
of mitochondria
to supply the cell with energy.
Ciliated Cells:
Ciliated cells are present in the
trachea and bronchi of out respiratory system.
Their
function is to use their
cilia to move the mucus up the trachea to the throat. The mucus traps bacteria and dust
particles. When it reaches the throat, mucus is swallowed to the stomach where the acid kills
the bacteria.
They are adapted by the tiny hair like projections
called cilia which sweeps the contaminated mucus upwards.
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The
mucus is secreted by
goblet cells which are next to ciliated cells.
Root Hair Cells:
These are cells situated in the roots of plants. They contain
no chloroplasts.
Their function is to absorb water
and minerals from the soil. And to anchor the plant in the soil.
They are adapted by 3
ways. One, they have an
extension that increases the surface area for more water intake. Two, they have a large number of
mitochondria for respiration to become more active. Three a concentrated vacuole to help
absorbing water by osmosis.
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Xylem Vessels:
These are dead lignified cells that
exist in the stem of a plant.
Their function is to transport water and minerals from the roots to the leaves and the rest of the plant through the stem. And to support the plant.
Their function is to transport water and minerals from the roots to the leaves and the rest of the plant through the stem. And to support the plant.
They
are adapted by 2 ways. Firstly, they are hollow to allow water and minerals to pass through them with no resistance.
Secondly they are strong
and lignified to support the plant.
The Division Of Labour: the
specialization of cells to carry out particular functions in an organism.
Movement In And Out Of
Cells
Substance
move in and out of cells by three ways:
- Diffusion: The net movement of particles from a region
of their higher concentration to a region of their lower concentration
down a concentration gradient, as a result of random movement.
- Osmosis: The diffusion of water molecules from a
region of their higher concentration (dilute solution) to a region of
their lower concentration (concentrated solution) through a partially
permeable membrane.
- Active Transport: The movement of ions, in and out
of a cell, through a cell membrane, from a region of their lower
concentration to a region of their higher concentration, against the
concentration gradient, using the energy released by respiration.
Diffusion:
Diffusion is the process by which
oxygen enters the blood from the lungs, and by which carbon dioxide enters the
leaf from the atmosphere. There are many more
examples of diffusion in biology.
Diffusion
always takes place down a
concentration gradient, that means that the particles that diffuse try
to spread evenly in all spaces, so it moves from where it’s very concentrated
to where it’s not concentrated.
There
are some factors affecting the rate of diffusion, like the steepness of the
concentration gradient.
The steeper the gradient the faster the particles diffuse.
The surface area of the exchange membrane also affects the rate of diffusion. The larger
the surface area of the exchange membrane the faster particles diffuse.
Thickness of exchange membrane too determines the diffusion rate, the thinner
it is, the easier it will be for particles to go through it, the faster the
diffusion rate.
Temperature is another factor affecting the diffusion rate, increasing the
temperature will give particles more kinetic energy, making them move faster,
thus increasing the rate of diffusion.
Osmosis:
Osmosis
is the diffusion of water molecules. When we speak about osmosis, we don’t say
water concentration; instead we use the term water potential. A dilute solution means it has lots of water
molecules, and a high water potential. A concentrated solution has few water
molecules and low water potential. Osmosis has to take place through a
partially permeable membrane (or Semipermeable) this means that the Water
molecules move from a place of their high concentration to a place of
their low concentration through a membrane with pores in it that lets some
molecules through but not others.
The
diagram shows two solutions, one dilute and one concentrated, separated by a
semipermeable membrane. The solution on the right is diluted while the
concentration on the left is concentrated. The water molecules will move from
the right handside solution where they are very concentrated to the left
handside solution where they are of a very low concentration, osmosis took
place.
Osmosis happens all
the time in cells. If you place an animal cell in distilled water. Osmosis
will result in the water molecules moving from the distilled water where they
are very concentrated to the Cell Where they are of low concentration Through
the cell surface membrane. The cell becomes fat. As more Water molecules
enter the cell, the cell will eventually burst and die.
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If
we do the opposite, and place a red blood cell in a concentrated salt solution,
the water in the cell has a higher water potential that the concentrated salt
solution. Water molecules will move from the cell to the salt solution causing
the cell to become shrunken and shrivel as in the diagram.
Hypotonic Solution
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Isotonic Solution
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Hypertonic Solution
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Animal Cell
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Plant Cell
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In plant cells, if a plant cell is placed in distilled water, water molecules will move from the distilled water to the cell, the cell swells up and becomes turgid but it will never burst because plant cells are surrounded by cell walls, which are made of cellulose and is elastic, it will stretch but never break, the cell becomes turgid.
If
we place a plant cell in a concentrated salt solution whith low water
potential, water will move from the cell to the solution causing the cell to
become plasmolysed as in the diagram.
Active Transport:
Active
transport occurs in cells, it is basically the movement of molecules or ions
from a region of their low concentration to a region of their high
concentration (against the concentration gradient) using energy of respiration.
Active transport occurs in living, active cells only because it needs energy,
these cells usually have a structure called mitochondria which respires
producing energy to be used in active transport.
Active
transport happens in roots to absorb mineral salts from the soil. It also
occurs in the digestive system of mammals.
If
oxygen is absent, respiration won’t take place, active transport will stop.
Molecules are taken into the cell by protein carriers within the cell membrane.
Enzymes
What are enzymes?
Enzymes
are proteins that function as a biological catalyst.They are proteins in nature. A catalyst is a substance that speeds up a chemical reaction but isn’t changed by the reaction. Hydrogen peroxide (H2O2) is a substance that decomposes into Water (H2O) and Oxygen (O2) if it is left in room temperature for a period of time. This reaction could a long time, but it could be sped up if we add a catalyst. Each catalyst can catalyse a specific substance and nothing but it. The catalyst for Hydrogen peroxide is called Manganese4 oxide. If it is added we will get water and oxygen gas in a very short time, and the manganese4 oxide could be obtained again as it was, it remains unchanged. |
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How Do Enzymes Work?
Enzymes work the same way as catalysts do, they can work with only
one substrate and they can be used more than once.
Enzymes have a structure that is called active site. Only one
substance can fit into the active site to be digested, and it is the only
substrate that this particular enzyme works with.
The figure above shows the function of enzymes:
- The
substrate enters the active site of the enzyme.
- The
reaction takes place.
- The
substrate exits the enzyme as two simpler products.
You can also think of the way enzymes work as a key and a lock,
the key is the substrate and the lock is the enzyme. The key should be exactly
the right shape to fit in the lock, so does the substrate to fit in the active
site of the enzyme. The key could only open only one lock, and the lock could
be unlocked by only that key.
Enzymes are two types, Builders and Breakers. Builder enzymes do
the opposite of breaker enzymes. Breakers break large molecules into smaller
simpler ones, builders combine smaller ones to make large molecules.
Breaker enzymes are used in the digestive system to break down
large insoluble molecules into simpler soluble ones to be used by the body.
They are also present in cells that respire to break down sugars and oxygen
into carbon dioxide, water and energy. Builder enzymes are present in plants to
be used in photosynthesis, the opposite of respiration, in photosynthesis,
oxygen and water are combined together to form carbon dioxide and sugars.
Naming enzymes depends on the substrate they work on. For
example:
The sucrase enzyme works on sucrose.
The maltase enzyme works on maltose.
The sucrase enzyme works on sucrose.
The maltase enzyme works on maltose.
Enzymes are reusable and are only affected by the change in
temperature and pH.
Affect of temperature on the
enzyme’s activity:
Each enzyme has an optimum temperature, this is the temperature
at which the enzyme is most active, below this temperature the activity of the
enzyme decreases until it becomes inactive at low temperatures, above this
optimum temperature the enzyme becomes denatured and can no longer work.
At low temperatures the enzyme is and the substrate are moving
very slowly and collide weakly, the enzyme is said to be inactive and doesn’t
work. As the temperature increases, the enzyme and substrate gain more kinetic
energy and move faster colliding more, the enzyme becomes more active and the
reaction takes place. When the enzyme reaches it’s optimum temperature, it is
in its most active mood, if the temperature crosses the optimum the enzyme
begins to die and become denatured. The enzymes become denatured when the shape
of their active site changes as a result of high temperature, thus the
substrate cannot fit into the active site and the enzyme is useless.
Each enzyme has its own optimum temperature, enzymes in humans
have optimum temperatures of around 40 degrees. Plants have enzymes with
optimum temperature of about 25 degrees.
The Effect of pH on the
enzyme’s activity:
As in temperature, enzymes have an optimum pH. The pH is a
scale measuring the acidity or alkalinity of a substance or solution. The
scale runs from 1 to 14. pH 7 is neutral, below that it is acidic and above
that it is alkaline.
Each enzyme has an optimum pH, if this pH changes, the shape of
the active site of the enzyme is changed, thus the substrate will not be able
to fit in it, and the enzyme becomes useless.
Uses Of Enzymes In Seeds
Germination:
Seeds grow into plants by germinating. Seed germination involves
enzymes breaking the materials stored in the seed down to be used in growth,
energy and building cells. The seed contains stored substances such as:
- Starch: Starch is broken down by amylase enzyme
into maltose, maltose is then broken down by maltase enzyme into glucose
which is used in respiration.
- Proteins: Proteins are broken down into amino
acids by Protease enzyme, amino acids are used in building up cells and
growth.
- Fats: Fats are broken down into fatty acids by
lipase enzyme, they are used in making cell membranes.
In order for a seed to germinate, some conditions must be
present:
- Water: To activate the enzymes.
- Oxygen: To be used for respiration.
- Warm Temperature: For providing
the best conditions for enzymes to work and optimum temperature.
Uses Of Enzymes In Biological
Washing Powders:
Washing
powders contain detergents that help in cleaning clothes by dissolving stains
in water. Some stains are made of insoluble substance, these cannot be
removed by normal washing powders, instead, a biological washing powder is
used. Biological washing powders contain enzymes that break down the insoluble stain into smaller soluble substances, which are then dissolved in the water. For example, if your shirt gets stained by egg yolk or blood, there is an enzyme called protease in the washing powder that will break down the insoluble protein into amino acids, which are dissolved in the water and sucked away. Thus the shirt becomes clean. |
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The best removal of stains is maintained by providing the
optimum temperature for enzymes, presoaking to leave time for the enzymes to
digest, putting the suitable amount of the powder.
Use Of Enzymes In Food
Industry:
Enzymes are often used in the manufacturing of different foods.
Baking – Brewing – Cheese Making:
In
baking, both yeast and sugar are used. Yeast cells contain enzymes that
ferment sugar by anaerobic respiration producing carbon dioxide bubbles which
causes the dough to rise as in the photo.Brewing is the process of making wine or beer. In this process fermentation is Involved producing alcohol which and carbon dioxide that gives wine and beer its sparkle. In making cheese, an enzyme called rennin extracted in enzymes, helps by clotting milk. |
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Making Juices:
In
fruits such as apples or oranges, a substance called pectin holds the cells
together making it hard to squeeze them. An enzyme called pectinase digests pectin making it much easier to squeeze the fruit and to make the juice more clear than cloudy. |
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Making Baby Foods:
It is hard for new born babies to digest food such as high
protein foods. That is why foods like that are treated with proteases to break
down protein to amino acids, making it easier for newborns to absorb and
assimilate them.
Making Sugar:
Sugar producing companies get sugar from starch by using the
amylase enzyme to digest starch into maltose. For dieters a sugar called
fructose is very useful because it provides a sweater taste than other sugars
from a less quantity. Fructose can be obtained by using the isomerase enzyme to
convert glucose to fructose.
Meat And Leather Production:
Proteases are used to make meat less tough and acceptable for
consumers by treating cuts of meat.
In leather industries hairs are removed from animal skin by
digesting them using protease enzymes.
Enzymes Extraction:
The Enzymes used in the industries are taken from either fungi
or bacteria. This takes place in a Fermenter, this is a large sterilized
container with a stirrer, a pipe to add feedstock and air pipes.
The following steps take place:
The following steps take place:
- The
micro-organisms and the feedstock are added and the liquid is maintained
at 26 degrees and pH of 5-6.
- The
micro-organisms produce two types of enzymes, either extra-cellular or
intra-cellular.
- Extra-cellular
enzymes are extracted from the feedstock by filtering.
- Intra-cellular
enzymes are extracted by filtering the micro-organisms from the feedstock,
crushing them, wash them with water then extracting them from the
solution.
Enzymes And Antibiotics:
Antibiotics are powerful medicines that fight bacterial
infections. Micro-organisms are used for the production of antibiotics.
Some Antibiotics, like bactericides, fight bacteria by damaging
its cell walls causing them to burst and die. Other antibiotics interfere with
the protein synthesis and stop the bacteria growing.
Antibiotics have no effect on human cells because human cells
have no cell walls and the structures involved in protein production are
different than that of bacteria.
Antibiotics are obtained from sources like:
- Bacteria (Actinobacterium
Streptomyces): this bacterium
produces the antibiotic strepmycin.
- Fungi (Penecillum fungus): penicillin, the first antibiotic
discovered is produced by thing fungus.
Different types of penicillin are produced by different species
of the fungus. They are chemically altered in lab to make them more effective
and make them able to work with different diseases.
Steps of production:
- The
Fermenting tank in filled with nutrient solution of sugar (lactose) or corn
liquor which contain sugars and amino acids,
- Minerals
are added,
- pH
is adjusted around 5 or 6,
- Temperature
is adjusted about 26 degrees,
- The
liquid is stirred and air is blown through it,
- The
micro-organisms are added and allowed to grow for a day or two in sterile
conditions,
- When
the nutrient supply is decreased, micro-organisms secrete their
antibiotics,
- The
fluid containing the antibiotic is filtered off and the antibiotic is
extracted.
Nutrition
Nutrition is taking in nutrients which are organic substances
and mineral ions, containing raw materials and energy for growth and tissue
repair, absorbing and assimilating them. Nutrition is one of the
characteristics of living organisms. All organisms do it, they do it to obtain
energy for vital activities and raw materials needed for growth and repair.
Every
Individual needs to take in a certain amount of each nutrient daily,
depending on their age, size, sex and activity. There are 7 Types of nutrients, these are:
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Carbohydrates, proteins, fats and vitamins are all organic
substances. This means that they are made by living organisms (plants) and
contain carbon atoms in their structures. Plants make organic substances from inorganic
materials like carbon dioxide, water and inorganic minerals. Animals are unable
to do this.
Carbohydrates:
This nutrient is an organic compound composed of carbon,
hydrogen and oxygen.
Function:
It is used as an energy resource, essential in respiration to
release energy.
It is used in creating the cellulose, the substance forming cell walls of plant cells.
It is used in creating the cellulose, the substance forming cell walls of plant cells.
Carbohydrates are 3 types:
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Monosaccharides:
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Disaccharides:
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Polysaccharides:
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Monosaccharide and Disaccharides are sugars, they
are reducing for Benedict’s reagent, except for the disaccharide sucrose, it is
non-reducing.
Polysaccharides are not considered as sugars and don’t have a
sweet taste. Excess polysaccharides are stored in the liver and muscles.
Lipids (Fats):
These are composed of carbon, hydrogen and oxygen. But their
ratios are different than that of carbohydrates. One fat molecule is made of a
glycerol unit and three molecules of fatty acids.
Fats are essential in a diet because they are needed to:
- Release
high amounts of energy
- Make
cell membranes
- Store
them under the skin to insulate heat.
- Forming
a layer of fats around organs to protect them from damage
- Storing
energy (better than glycogen)
When fats are respired, they produce about twice as much energy
as carbohydrates.
Proteins:
These are also organic compounds; they contain the elements
Carbon, Hydrogen, Oxygen, Nitrogen and sometimes Phosphorus or Sulfur.
A molecule of protein is a long chain of simpler units called amino acids.
A molecule of protein is a long chain of simpler units called amino acids.
These amino acids are linked together by what's called “peptide
bond”.
Types of protein:
- Animal Protein: It contains the most biological value
because it contains all essential amino acids (Meat, Milk, Fish, Eggs
etc).
- Plant Protein: It contains a lower biological value to
humans because it contains fewer essential amino acids (Cereals, Peas,
Beans etc).
Needs of proteins:
- Making
and new body cells
- Growth
and repair
- Making
enzymes (they are proteins in nature)
- Build
up hormones
- Making
antibodies
Although proteins are needed in high amounts, the body will only
absorb as much as needed, so excess protein is delaminated in the liver and
excreted as urea.
Vitamins:
These
are organic, soluble substances that should be present in small amount in our
diets, they are very important though.Most of the amount of vitamins in our bodies was taken in as nutrients, the body its self can only make few Vitamins, so we have to have to get them from organisms that make them, such as plants. Each type of Vitamin helps in chemical reactions that take place in our cells.
Types Of Vitamins:
Vitamin C: This is
present in most fruits and vegetables specially citrus fruits like lemon and
oranges, however, it is damaged by heating so it these foods have no value of
Vitamin |
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C
if they are eaten cooked. Vitamin C is essential for the formation of Collagen, a protein that functions as cementing layer between cells, Vitamin C also increases immunity. Vitamin D: This is present in fish oils, egg yolk, milk and liver. Unlike Vitamin C, Vitamin D is made by animals as well as plants, this occurs when the skin is exposed to the Ultra Violet Rays of the sun. Vitamin D plays a big role in absorbing Calcium from the small intestine and depositing it in bones. So it is responsible for having healthy bones. |
Minerals (Inorganic Ions):
These are a lot of types, each needed in small quantities. Iron
and Calcium are the most important minerals, and they are needed in higher
amounts.
Types Of Minerals:
- Calcium: This mineral is needed for the formation
of bones and teeth as they are made of calcium salts, it also helps in
blood clotting and transmission of nerve impulses. Good sources of the
mineral Calcium are milk, dairy products and hard water.
- Iron: This mineral is needed for the formation
of the red pigment haemoglobin which is essential for the transport of
oxygen around the body in red blood cells. Good sources of Iron include
red meat specially liver and green leafy vegetables.
Roughages (Fibre):
Although roughages are not even absorbed by the body, they are a
very important nutrient in our diet. Roughages are mostly cellulose, which is
the substance that makes up the cell walls of plants we eat. We humans, have no
enzyme that could digest cellulose, that means that roughages enter the body
from the mouth, go through the digestive system, and out through the anus
unchanged. But as it goes through the digestive system, roughages take space in
the gut to give the gut muscles something to push against, this process of
pushing the food through the gut is called peristalsis, without roughages
peristalsis is very slow and weak. Quick and strong peristalsis means that food
stays in the alimentary canal for a shorter period, this prevents harmful
chemicals of certain foods from changing the DNA of cells of the alimentary
canal causing cancer, so roughages also helps stay away from cancer. Roughages
are found in leafy vegetables.
Water:
About
70% of your weight is water. Water is perhaps a very essential nutrient we
should take in. The functions of water include:
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Balanced Diet:
A
perfect diet contains all of the nutrients in reasonable proportions, not too
much and not too little. The perfect diet should also contain energy as much
as the total energy used by the individual.
Unbalanced Diet (Malnutrition):
Malnutrition
is eating inadequate proportions of food. In other words, an unbalanced diet
means it is rich in a nutrient and low in another, or even lacking of a
substance. There are lots of effects of malnutrition, such as starvation,
obesity or deficiency diseases. |
Starvation:
Starvationis a severe reduction in vitamin, nutrient and energy
intake. It is the most extreme form of malnutrition. In humans, prolonged
starvation can cause permanent organ damage and eventually, death. The term
inanition refers to the symptoms and effects of starvation. In case of
starvation the body tends to feed on its own self. When the glucose level is
decreased in the body, the liver breaks down fats to respire for energy, when
the body is out of fats, it starts respiring proteins from the muscles to
release energy.
Obesity:
is the opposite of starvation. It is eating too much of every
nutrient, especially carbohydrates and fats. Obesity doesn’t strike alone, it
brings with it several other diseases such as high blood pressure, cardiac
diseases, diabetes, stress on joints and bones as well as other psychological
issues like low self esteem and lack of confidence. To prevent obesity, you
have to control your carbohydrates and fats intake and exercise regularly.
Another consequence of malnutrition is deficiency diseases.
These are results of a certain nutrient in the diet:
These are results of a certain nutrient in the diet:
- Scurvy is the deficiency disease of vitamin C.
Its symptoms include bleeding gums.
- Rickets is the deficiency disease of both
Vitamin D and Calcium. Bones are made of calcium which Vitamin D helps in
depositing in the bones, if any of both is lacking in the diet, rickets is
developed.
- Anemia is the deficiency disease of iron. The
amount of haemoglobin decreases causes short breath and tiredness.
- Kwashiorkor affects children whose diets are lacking
in protein. It causes weakness and tiredness.
Special Needs:
There are certain types of people whose diets need to be
different to normal ones.
Such as pregnant women, breast-feeding women or children going through puberty.
Such as pregnant women, breast-feeding women or children going through puberty.
Pregnant Women:
The diet of a pregnant woman needs to be very rich of certain
nutrients because she is not only feeding her self, she is feeding her baby as
well. In order for the fetus to develop well, it needs extra Protein, Iron,
Calcium and Vitamin D. Proteins are to develop the tissues of the fetus, Iron
is to make haemoglobin and to store in the liver, while Calcium and Vitamin D
are to develop the baby’s bones.
Breast-Feeding Women (Lactation):
Lactation means the production of breast milk. After pregnancy,
the mother breast-feeds the baby for about 6 months or more. Breast milk needs
to be high in Proteins, Calcium, and Vitamins to guarantee a healthy growth for
the infant.
Growing Children (Passing Puberty):
At some point, each child gets a growing spurt. This is a very
high growth rate that increases the child’s size and mass in a short period of
time. A growing child’s diet needs extra Proteins to develop cells and enzymes
because their metabolic rate is higher, Calcium and Vitamin D to develop bones
and Iron to make hemoglobin.
Food Additives:
These are chemical compounded added to foods by the manufacturer
because they have some benefits such as increasing the lifespan, prevent
rotting etc.
Most food additives are good, such as ones that add colors or flavors to foods. But there are others which have been proven hazardous to humans.
Most food additives are good, such as ones that add colors or flavors to foods. But there are others which have been proven hazardous to humans.
Good food additives include flavorings and colorings which are
used to make the food more appealing, antioxidants which prevent foods from
combining with oxygen and rot, and stabilizers which stops foods like ice-cream
from separating into water and fatty components.
Food preservatives though, are a widely used food additives which
increase the lifespan of foods, making it cheaper to store and transport.
However, scientists claim that some preservatives contain nitrites which
combine with chemicals making a substance (nitrosamines) that causes cancer in
animals.
Food Additives
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Advantages
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Disadvantages
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Microorganisms And Food Industry:
Production of Single Celled Protein (Mycoprotein):
Mycoprotein is a protein made from microscopic fungus. Humans
need large amounts of proteins in their diets, in some poor areas, sources of
proteins like meat are unaffordable, mycoprotein is used.
The process takes place in a sterilised container called
fermenter. The micro-organisms are grown in the fermenter and supplied with air
which contains oxygen for aerobic respiration, ammonia as a source of nitrogen
to be used by the micro-organisms to make proteins, and methanol which contains
carbon for the formation of carbohydrates.
Advantages of mycoproteins are that it is cheaper than any
source of protein but equal in value, and that it contains much less fats and
more roughages and carbohydrates
Production Of Yoghurt:
- Milk
is sterilised by boiling
- Certain
types Bacteria are added to the milk
- The
milk is kept warm to provide best conditions for bacteria growing
- Bacteria
respire producing lactic acid, thickening the milk and giving it the
pleasant flavour
- Yoghurt
is cooled and flavours or fruits could be added.
Food Tests:
Starch Test:
- Put
sample in a test tube
- Add
water to make it a solution
- Add
iodine solution
- Is
starch is present the solution changes colour from yellowish brown to Blue
Black.
- If
starch is not present the solution remains yellowish brown.
Reducing sugars (carbohydrates) test:
Note: This test is only applicable on all sugars (monosaccharide
and disaccharide) EXCEPT FOR SUCROSE.
- Add
sample to a test tube
- Add
Benedict’s Reagent
- Put
test tube in water bath for heating
- If
reducing sugars are present the solution turns from blue to
yellow,orange,red (fire colours)
- If
reducing sugars are not present the solution remains blue.
Proteins Test:
- Put
sample in a test tube
- Add
water to make a solution
- Add
Buiret Reagent
- If
proteins are present in the solution turns Purple
- If
proteins are not present the solution remains blue.
Note: Biuret Reagent is blue in colour and made of copper
sulphate and a small amount of sodium hydroxide.
Fats Test:
- Add
sample to a test tube
- Add
ethanol
- Add
water and shake well
- If
fats are present the solution becomes unclear
- If
fats are not present the solution remains clear
General Table:
Nutrient
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Test
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Colour
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Positive
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Negative
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Starch
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Iodine sol.
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Yellow / Brown
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Blue / Black
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Yellow / Brown
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Carbs
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Benedict’s
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Blue
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Red (fire)
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Blue
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Proteins
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Biuret reagent
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Blue
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Purple
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Blue
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Fats
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Ethanol/water
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-
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Cloudy
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Clear
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Animal Nutrition
Animals eat to grow, repair etc. They simply eat to live. In
this unit we will study how animals make use of what they eat. The journey of
the food from the mouth to the anus through the alimentary canal includes 5
steps:
- Ingestion: Taking in pieces of food into the mouth
- Digestion: The break down of large, insoluble food
molecules into smaller more soluble ones by chemical and mechanical means.
- Absorption: Taking the digested food molecules into
the cells
- Assimilation: Making use of the digested food
molecules for example to release energy or grow etc.
- Egestion: The elimination of undigested food
materials through the anus
*Don’t confuse egestion with excretion, excretion is to get rid
of waste products of metabolism.
The alimentary canal (gut or digestive tract) is made up of
several organs working together to perform all the processes mentioned above.
Starting with the mouth and ending with the anus.
The Mouth:
The mouth performs several functions:
Mechanical Digestion: The action of the teeth biting a small
piece of food from a large one is considered mechanical digestion, the teeth also
tears and grinds the food into a bolus to give it larger surface area for
faster chemical digestion.
Chemical Digestion: beneath the tongue lies a salivary gland
which secrets saliva into the mouth, this saliva contains water and mucus to
lubricate the food bolus and amylase enzyme that breaks down starch in the food
into maltose.
After this the tongue pushes the food bolus into the oesophagus.
The Oesophagus:
This
is a tube that transports the food from the mouth deep into the body to the
stomach.The food is pushed downwards by the muscles in the walls of the oesophagus, this process is called Peristalsis. Muscles contract and relax creating a wavy motion to push the food down. |
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The Stomach:
Here the food stays for a while. The stomach is a flexible bag
that performs both mechanical and chemical digestion.
Mechanical Digestion: The walls of the stomach contain muscles
that contract and relax together mixing the food with the content of the
stomach and turning it into liquid chyme, this process is called churning.
Chemical Digestion: The walls of the stomach also secretes a
liquid called “Gastric Juice” which contains Hydrochloric acid, Mucus, and
pepsin enzyme. The pepsin enzyme digests proteins into simpler polypeptides,
while the hydrochloric acid is to provide optimum pH for the enzyme and the
mucus is to lubricate the food and protect the walls of the stomach from the
acid.
After a few hours, the sphincter which is a muscular valve opens
allowing the food into the small intestine.
The Small Intestine:
The small intestine is where most digestion and absorption takes
place. It is divided into two sections, duodenum and ileum. The walls of the
small intestine contain several types of liquids that help in providing
suitable conditions and digest the food. These liquids are:
Bile Juice: it comes from the liver, stored in the gall
bladder. It is squirted along the bile duct in the duodenum. The bile works on
fats only, fats are very difficult to digest because they are very insoluble,
the bile contains bile salts that breaks fats into tiny droplets that float in
the content of the small intestine, making it easier for the lipase to digest
fats into fatty acids and glycerol, this process is called emulsification.
Pancreatic Juice: it comes from the pancreas and secreted
along the pancreatic duct. It contains enzymes and sodium hydrogen carbonate,
which neutralises the hydrochloric acid that was added to the food in the
stomach, creating better conditions for the enzymes to work. The pancreatic
juice contains the following enzymes:
- Amylase to digest starch into Maltose
- Trypsin to digest proteins to polypeptides
- Lipase to digest fats into fatty acids and
glycerol
Small intestine liquid: The small intestine itself also secrets a
liquid that consists of lots of enzymes to make sure carbohydrates, fats and
proteins are digested to their simplest form, these enzymes are:
For carbohydrates:
- Maltase to digest maltose into glucose + glucose
- Sucrase to digest sucrose into glucose +
fructose
- Lactase to digest lactose into glucose +
galactose
For Fats:
- Lipase to digest fats into fatty acids and
glycerol
For proteins:
- Protease for further digestion of polypeptides to
amino acids.
Absorption in small intestine:
Absorption in the small intestine takes place in the second
section, the ileum. The walls of the ileum are fully adapted for absorption.
The interior walls of the ileum is covered with a layer of villi, each villus
is covered with another layer of micro villi.
Each villi has a branch of blood capillaries in it as well
as a lacteal which is a lymph vessel, the lacteal absorbs fats and lipids with
vitamins dissolved in them into The lymphatic system.
Villi
and microvilli are adapted to absorption by:
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The Large Intestine:
By the time the food reaches the large intestine, there is not
much left of it, only some water, minerals, and fibers. The water and the
minerals are absorbed into the blood, while the fibers and dead cells of the
alimentary canal are stored in the rectum then excreted through the anus
(egestion).
Assimilation Of The Absorbed
Food Molecules:
After the food molecules are absorbed from the alimentary canal,
it is transported to the liver by a special blood vessel called The
Hepatic Portal Vein. The liver is an organ that is
considered a gland too. It carries out several jobs to “sort out” the food
molecules it receives. Each type of nutrient has its own fate in the liver.
Glucose: when the absorbed glucose reaches the
liver, the liver allows as much as needed by the body to pass to the
circulatory system to by used for respiration or other processes. The excess
glucose is converted to glycogen and stored in the liver cells, when the blood
is short in glucose, glycogen will be converted back into glucose and secreted
to the blood. Some glucose will also be converted to fats as an energy reserve.
These functions are controlled by the Insulin and Glucagon hormones which are
made in the pancreas.
Amino Acids: some amino acids will be used by the liver
cells to make proteins, the rest will be allowed into the blood stream to be
absorbed by the body cells which also convert it to proteins. If the body
contains enough amino acids, the excess will undergo a process called Deamination, this
involves the break down of amino acids into carbohydrates and amino group,
which is then converted to ammonia then converted into urea, which is part of
the waste product of the body, urine.
A part from sorting out food molecules, the liver performs the
following jobs too:
- Dealing with old red blood
cells:
The liver changes dead red blood cells to iron and bile. Iron is stored in the liver, large amounts of iron give it the red colour and used to build up new red blood cells. The bile is stored in the gall bladder to be used in digesting food again. - Detoxification:
The liver breaks down toxic materials such as alcohol which damages cells to fats. Alcoholics are known to have liver diseases. - Helps in generating heat:
The liver contains a very large number of cells, which means a lot of metabolic reactions take place in it producing lots of energy to warm the blood. - Making fibrinogen:
This is a plasma protein which helps in blood clotting when the skin is cut.
Teeth:
Teeth
are small, calcified, whitish structures found in the jaws (or mouths) of
many vertebrates that are used to break down food.Types of mammalian teeth:
Incisors:
They
are 4 in front of each jaw.They act like a blade to cut food(eg. To cut a bite of a sandwich) they have a (chisel-like surface).
Canines:
They
are two in each jaw.They are very pointed, in humans they are used for the same purpose as incisors. However in carnivores they are longer and sharper and used to kill the prey.
Premolars:
4
on the sides of each jawThey are used to cut and grind food.
Molars:
They
are 6 at the back of Each jaw, 2 of them are wisdom teeth. They have the same use as Premolars. |
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Note: remember that we have two jaws, so 4 incisors in each jaw
means that we have a total of 8 incisors in our mouth. We have 16 teeth in each
jaw, 32 in the whole mouth.
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The
tooth is divided into two parts, the crown and the root. Parts of the tooth: Enamel: Made of calcium salts, it is very strong. Dentine: It is covered by the enamel and surrounds the pulp cavity. The pulp cavity: It contains the nerves and blood vessels. The part of the tooth above the gum is called the crown, the part buried in the jawbone is called the root. The enamel covers the crown, the root is covered by cement. And the tooth is held in place by fibres. Tooth Decay: when we eat, some food particles stay in our mouth. Bacteria that lives in our mouth feed on these food particles, they respire anaerobically producing lactic acid. Like any acid, lactic acid reacts with the enamel and dissolves it away reaching the dentine, here we feel the toothache. |
Methods Of preventing Tooth Decay:
- Reduce
sugar intake to prevent bacteria respiring
- Brush
teeth to remove the plaque layer of bacteria and saliva on our teeth and
nuetralise mouth
- Use
toothpaste or water containing fluoride because it is absorbed by the
teeth and helps stopping the attack by acid
- Pay
regular visits to the dentist.
Adding Fluoride To Water
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Advantages
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Disadvantages
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Transport In Humans
The
human transport system is a system of tubes with a pump and valves to ensure
one way blood flow. We need a transport system to deliver oxygen, nutrients
and other substances to all our body cells, and take away waste products from
them. The oxygenated blood (high in oxygen, red in color) comes to the heart from the lungs in the pulmonary vein; the heart pumps it to the aorta (an artery) to the rest of the body. The deoxygenated blood returns to the heart from the body in the vena cava (a vein), the heart pumps is to the lungs to get rid of the carbon dioxide.
When the blood is flowing away from the heart, it has a very high pressure, when it is flowing towards the heart it has a lower pressure. |
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The Blood:
The blood is a fluid consisting of several types of cells
floating in a liquid called plasma.
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Red Blood Cells:
These
are one of the smallest cells in your body, they are round with a dent in the
middle, we call this shape a Biconcave disc.The function of the red blood cells is to transport oxygen from the lungs to the body cells. A red protein called Haemoglobin, when the blood reaches the lungs, oxygen diffuses from the alveoli to the red blood cells and combines with haemoglobin forming an unstable compound called oxyhaemoglobin. When the blood reaches the body cells, the oxyhaemoglobin is easily split into oxygen and haemoglobin again, the oxygen diffuses through the blood plasma to the cells. |
Red blood cells are fully adapted to their function by the
following characteristics:
- Biconcave
disc shape gives it large surface area to carry more oxygen
- Haemoglobin
to combine with oxygen
- No
nucleus that takes up space.
White Blood Cells:
White blood cells are one of the substances floating in the
blood plasma. They are completely different in function than red blood cells.
White blood cells are part of the Immune System, they play a big role in
protecting the body by killing bacteria which cause disease, also known as
pathogens. White blood cells can be distinguished from red blood cells easily
because they are much bigger, with a nucleus, and present in fewer amounts.
Types Of White Blood Cells:
Phagocytes:
They
kill bacteria by engulfing them, taking them in the cell then kill them by
digesting them using enzymes, this process is called phagocytosis. Most white blood cells are the phagocyte type. |
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Lymphocytes:
Unlike
phagocytes, lymphocytes have a large nucleus. They are produced in the lymph
nodes (in the lymphatic system). Lymphocytes kill bacteria by secreting
antibodies and antitoxins which kill the pathogens directly or make them
easier to kill. Each pathogen could be killed by a certain type of antibody |
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The Platelets:
Platelets are tiny cell fragments that prevent bleeding when the
skin is cut, and stops bacteria from entering our systems through the wound.
This works by blood clotting, when the skin is cut, some reactions take place
that results in platelets producing a protein, this protein will change the
fibrinogen (another soluble protein in the plasma) to insoluble fibrin. The
fibrin forms long fibres that clot together blocking the cut, thus preventing
any bleeding, this is called blood clotting.
Blood Plasma:
This makes up most of the blood. It is mostly water with some
substances dissolved in it, these include carbon dioxide, hormones, food
nutrients, urea and other waste products. The blood plasma transports
substances from one place to another.
Functions of the blood:
- Transportation
of R.B.C’s, W.B.C’s, oxygen, food nutrients, hormones, and waste products.
- Defence
against disease, by white blood cells phagocytosis and production of
antibodies.
- Supplying
cells with glucose to respire and keep a constant temperature.
Blood Vessels (Vascular
System):
This is a number tubes carrying blood away from and to the heart
and other organs. The main types are Arteries, Veins and Capillaries.
Arteries:
Their
function is to transport blood away from the heart to the lungs or other body
organs.The blood in the arteries always has a high pressure. The heart pumps the blood quickly into the arteries, resulting in the pressure, each time the ventricle of the heart contracts, the pressure in arteries increase, when the ventricle relaxes, the pressure falls. The lumen of arteries is also very narrow, adding to the pressure. |
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The structure is simple, beside the narrow lumen, the arteries
have a strong thick wall to withstand the pressure. Their walls are also
elastic and stretchable.
Brief description of characteristics of arteries:
- Transporting
blood away from the heart
- Always
in a high pressure
- Strong
but stretchable walls
- Narrow
lumen.
Veins:
Their function is to transport blood to the heart from the body.
The veins always always have a low blood pressure because by the
time the blood with high pressure reaches the veins, it loses most of the
pressure. This means that blood flows very slowly in veins, to help this, veins
lie between muscles so that the blood is squeezed when the muscles contract.
They have a simple structure. Because they have a low pressure,
they don’t need strong, thick walls like the artery, instead they have thin
less elastic walls. Their lumen is much wider too. Veins have a unique feature,
that is valves. Because blood in veins flows slowly with a low pressure, there
is a risk of a backflow, specially in veins that move blood upwards against
gravity, like the ones in the leg. The valves ensure that the blood is always
flowing in the direction of the heart. When the muscles squeeze the blood, the
valves are open the let blood through, when muscles relax, valves close to
prevent a backflow.
Brief description of characteristics of veins:
- They
carry blood to the heart
- Always
in a low pressure
- Thin
less elastic walls
- Wide
lumen
- Valves
present.
Blood Capillaries:
Blood capillaries are very we
Blood
capillaries are the smallest blood vessels in our systems. Their function is
to get blood from the arteries as close as possible to the tissues in order to exchange materials with the cells, and to link arteries with veins. When arteries come near and organ or a tissue, it divides into arterioles, these arterioles divide more into several blood capillaries that go through the tissue, this is when the exchange of oxygen and food nutrients with carbon dioxide and waste products such as urea take place by diffusion. |
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ll adapted to their jobs. They are one cell thick to reduce the
diffusion distance of materials for faster diffusion. They also have pores in
their walls between the cells, to allow the plasma to get out of the blood and
become tissue fluid.
The Heart:
The heart is a pumping organ that is responsible for the
movement of blood around the body. The function of the heart is to give the
blood a push, keeping it flowing around the body all the time. That is why the
heart is constantly working, if it stops for a minute, the other organs will
not receive any oxygen or nutrients, thus the body fails and the person dies.
The heart is located in the chest, the thoriac cavity between both lungs.
Structure:
The
heart is hollow, it has 4 chambers. Two of them are atria and two are
ventricles. One of each of these on each side. When looking at the diagram of
a heart, notice that your right is the left side of the heart, and your left
is the heart’s right, as if you are looking at your own heart on a mirror.The sides of the heart are separated by a wall called septum. Each side contains an atrium (at the top) and a ventricle (at the bottom), there is a valve between the atrium and the ventricle in each side, it is called bicuspid valve in the left side and tricuspid valve in the right side. There are several blood vessels associated with the heart, these are: |
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- The
Pulmonary vein, it transports oxygenated blood from the lungs to the right
atrium.
- The
Aorta, which is the biggest artery in the body, it transports oxygenated
blood from the heart to the rest of the body.
- The
Vena Cava, the biggest vein in the body, it transports deoxygenated blood
from the whole body to the heart.
- The
pulmonary artery, it transports deoxygenated blood from the heart to the
lungs.
Note that blood vessels entering the heart are veins, and the
ones leaving the heart are arteries. The left side of the heart always contains
oxygenated blood because it receives blood fresh from the lungs and pumps it to
the body, the right side always contains deoxygenated blood because it receives
is from the body. You can memorise this by the word LORD:
Left Oxygenated – Right Deoxygenated
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The
heart receives blood from the lungs at the left atrium and pumps it to the
body from the left ventricle, then it receives it again from the body
at the right atrium and pumps it to the lungs from the right ventricle. The
red shows oxygenated blood and the blue shows deoxygenated blood. Notice that the walls around the left ventricle are much thicker than the ones in the right ventricle. The reason for this is that because the left ventricle pumps blood to the whole body, so blood will travel a long distance, so it needs lots of muscles to contract and pump the blood more strongly. However, the right ventricle pumps blood the lungs which are very close to heart, the blood does not need to be pumped very strongly. |
Mechanism of the heart:
When the heart is being filled with blood (whether from the body
or the lungs), this is called the diastole. When the heart is pumping the blood
out of it (whether to the body or to the lungs), it is called the systole.
During diastole, the heart is getting filled with blood, the
blood enters the atria first, the atria contract to force blood into the
ventricles, both tricuspid and bicuspid valves are open to allow blood into the
ventricles and the semilunar valves are shut. Once the ventricles get filled
with blood, it is systole, the bicuspid and tricuspid valves get shut and
semilunar valves are open, the ventricles contract strongly forcing the blood
into the Aorta or pulmonary artery.
During diastole the semilunar valves are shut to keep the blood
out of the arteries. During systole the tricuspid and bicuspid valves are
closed, to prevent blood from flowing back into the atria when it is pumped.
The tricuspid and bicuspid valves are kept fixed by fibres called tendons, they
prevent the valves from opening in the opposite direction, allowing backflow.
The tendons also control the opening and closing of the cuspid
valves, when the tendons are loose, the valves are open. When the tendons are
tightened the valves close.
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Diastole |
Systole |
Ventricles: |
Relax |
Contract |
Atria: |
Contract |
Relax |
Cuspid
Valves: |
Open |
Close |
Tendons: |
Loose |
Tightened |
Semilunar
Valves: |
Close |
Open |
If you listen to your heartbeat, you will hear two sounds, one
low and one high. These are results of the systole and diastole. They are the
sounds of the cardiac valves opening and shutting.
Coronary Heart Disease (CHD):
The
heart, like any other organ, needs a supply of blood containing oxygen
and nutrients. In fact, the heart needs a higher amount of blood supply
than any other organ because it is working all the time, and contains a lot
of muscles. The coronary arteries are those which supply the heart tissues
with blood, they branch from the aorta. CHD develops when cholesterol layers
build on the walls of the coronary arteries, partially blocking the path of
blood, thus this tissue of the heart is not supplied with oxygen nor
nutrients, so it stops working properly. If it is not treated at this age, a
blood clot may form near the partially blocked area, completely blocking the
artery, when this happens, the blood cannot function anymore, a heart attack
occurs, which is extremely fatal. The causes of CHD are mostly in the diet. A diet with lots of fats, increases the chance of cholesterol building up on the walls of the artery, causing CHD, Same thing with salts. Smoking also increases the rate of fat deposition. It was also said that Causes Of CHD are: |
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- Diet
full of fats increases the fats level in blood
- Diet
full of salts, salts can be deposited in the artery leading to CHD, same
as fats or cholesterol
- Smoking,
carbon monoxides increases fat deposition
- Stress
was also said to contribute to CHD by raising blood pressure
- Lack
of exercise, regular workouts improve the blood flow wearing layers of
fats or salts deposited on the walls of arteries away.
So to protect yourself from CHD you need to avoid diets full of
fats and salts, avoid smoking, try to be less stressed out, and exercise
regularly.
Tissue Fluid And Lymph:
Tissue fluid is a fluid surrounding the cells of a tissue. It
supplies them with all their needs of oxygen and nutrients, and takes away all
their waste products including carbon dioxide. Tissue fluid plays a very big
role in substance exchange between blood and cells.
Plasma from the blood capillaries move to the tissue through
gaps in the walls. They become tissue fluid. They exchange their content of
oxygen and nutrients with the cells and take carbon dioxide and waste products.
At the end of the capillary bed, the tissue fluid leaks back into the blood,
and becomes plasma again, but not all of it. A little of it is absorbed by the
lymphatic vessel and becomes lymph. The lymphatic vessel takes the lymph to the
blood stream by secreting them in a vein near the heart, called subclavian
vein. The lymph in the lymphatic vessels are moved along by the squeeze of
muscles against the vessel, just like some veins.
The lymphatic system plays a big role in the protection against
disease. It produces the white blood cells lymphocytes. Which kill any cell
with a different antigens than the ones in your body cells. So if bacteria get
into your body, your lymphocytes quickly recognise them as foreigners and will
divide and kill them.
Lymphocytes are considered a problem when it comes to organs
transplant. For example if someone (recipient) with renal failure receives a
kidney from another person (the donor), the cells of the kidney will have
different antigens than the other cells in the patient’s body. The lymphocytes
will consider the cells of the kidney an enemy and start attacking it, this is
called tissue rejection. Organ transplant is perfect in one case, this is when
the donor and the recipient are identical twins, because the antigens of their
cells perfectly match. In other cases the recipient is given immunosuppressant
drugs to actually weaken their immune system to prevent tissue rejection.
Brief Summary Of Functions Of The Lymphatic System:
- Production
of white blood cells lymphocytes
- Transport
of digested fats from villi to blood stream
- Transport
of lymph from the tissue fluids to the blood stream at the subclavian
vein.
Plant Nutrition
Plants are living organisms, they need food in order to keep
living. The way they obtain their nutrients however, is completely different
than that of ours. Plant make most of their nutrients by them selves, they just
need 2 raw materials, these water and carbon dioxide.
The leaf of a plant is considered the kitchen of it. It is where
food is made, later on you will see how the leaf is adapted to making food.
Upper Epidermis: it is a layer of cells that cover the leaf
and protect it, it is covered by a layer of wax calledcuticle.
Mesophyll Layer:
- Palisade Mesophyll: a layer of palisade cells which carry
out most of photosynthesis
- Spongy Mesophyll: a layer of spongy cells beneath the
palisade layer, they carry out photosynthesis and store nutrients.
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Vascular Bundle: it is a group of phloem and xylem vessels
that transport water and minerals to and from the leaves. Lower Epidermis: similar to the upper epidermis, only that it contains a special type of cells called guard cells. Guard cells are a specialised type of cells that control the passage of carbon dioxide into the cell and the passage of oxygen out of the cell by opening and closing the stomata (a hole in the leaf through which gases pass) so guard cells are responsible for the gas exchange. |
Photosynthesis:
Photosynthesis
means “making with light”. It is the process by which plants make useful
glucose out of the raw materials water and carbon dioxide, using light energy
from the sun.Water is essential for photosynthesis, it is sucked up from the soil by the roots and transported up the stem to leaves where it is put into use. Carbon dioxide, just like water is essential for photosynthesis. It moves into the leaf from the air by diffusion, through the stomata (tiny wholes in the leaf). Once carbon dioxide and water are present in the leaf, one condition for photosynthesis is needed, that is light. The two cells in the diagrams are called palisade cells (the rectangular one) and spongy mesophyl cell (the circular one), these are the cells where photosynthesis takeplace. They a structure called chloroplasts, these structures contain a green pigment named chlorophyll, this is to trap sunlight to be used in energy, a large number of chloroplasts is required for photosynthesis. |
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How photosynthesis happen:
- Carbon
dioxide and water enter the cell
- The
cell traps light energy using chloroplasts
- The
energy is used to split water (H2O) into hydrogen and oxygen
- The
oxygen is excreted outside the leaf to the atmosphere as a waste product
- The
hydrogen reacts with carbon dioxide forming glucose.
Overall equation for the Photosynthesis
Carbon Dioxide Supply:
The carbon dioxide moves to the leaf from the atmosphere by
diffusion through tiny holes in the leaf called stomata. Carbon dioxide is not
present in a high concentration in air, but compared to its concentration
inside the leaf, it is more in the air. This is because the cells inside the
leaf are always doing photosynthesis (at daytime), converting the carbon
dioxide into the glucose quickly, thus the concentration of it inside the leaf
decreases, making a concentration gradient for diffusion from the atmosphere to
the leaf.
Water Supply:
The water is absorbed by the roots of the plants, then they are
transported upwards through a hollow tube called the xylem vessel, till it
reaches the leaf where photosynthesis takes place, it enters the leaf through
holes in the xylem. Excess water leaves the cell through the stomata, this is
called “transpiration”
Sunlight Supply:
The leaves are always exposed to sunlight at daytime. The sun
penetrates the transparent layers on the leaf till it reaches the mesophyll
layer, where photosynthesis take place. Palisade cells are nearer to the
surface of the leaf than the spongy cells, so they receive more of the light
and make more photosynthesis.
Factors Needed For Photosynthesis:
- Water
- Carbon
Dioxide
- Light
Factors Affecting The Rate Of Photosynthesis:
- Amount
of water: the rate increases as it increases
- Concentration
of carbon dioxide: the rate increases as it increases
- Light
intensity: the rate increases as it increases
Plants at night:
At night, the plant performs several process to convert the
stored starch into many useful nutrients like:
- Sugars
for respiration
- Cellulose
and proteins for making cells
- Vitamins
to help in energy action
- Fats
as a long term storage material
- Remaining
starch is temporarily stored.
Mechanism of Guard Cells:
At daytime, the guard cells open the stomata to allow gaseous
exchange, this occurs according to the following steps:
- Sunlight
increases the potassium concentration in the vacuoles of the guard cells,
the water potential decreases making a gradient between the guard cells
and the surround epidermal cells,
- Water
moves by osmosis into the guard cells from the epidermal cells,
- The
water raises the pressure inside the guard cells,
- The
cell wall adjacent to the stomata is thicker and less stretchable then the
cell wall on the other side,
- The
pressure expand the whole cell except for the inner cell wall (adjacent to
the stomata) creating a curve and a pore between the two guard cells,
- The
stoma opens.
At night however, the mechanism is opposite:
- Potassium
level decreases in the vacuole of the guard cells,
- Water
potential increases in the cell and water diffuses out of it,
- The
guard cells straighten up because of low pressure closing the stoma.
Mineral Requirements:
The plant is also in need for mineral ions to control chemical
activities, grow, and produce materials. The most important minerals are:
- Mg+2
(Magnesium ions): they are important for the production of the green
pigment chlorophyll. Lack of it results in lack of photosynthesis and
wilting of the leaves,
- Nitrates:
these are the sources of nitrogen, they are required to make amino acids
and proteins by combining with glucose. Lack of it results in deformation
of the plant structure making it small and weak.
Both mineral ions are absorbed from the soil.
Fertilisers:
Sometimes
the soil is lacking of the mineral ions needed, this problem can be solved by
adding fertilisers to the soil. Fertilisers are chemical compounds rich in
the mineral ions needed by the plants. They help the plants grow faster,
increase in size and become greener, they simply make them healthier and
increase the crop yield. But there are disadvantages of fertilisers, such as:
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Green House:
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A
green house is a placed covered by transparent polythene. In green houses,
the limiting factors of photosynthesis are eliminated, and the plants are
provided the most suitable conditions for a healthy, rapid growth. The soil in green houses is fertilised and very rich in mineral ions, assuring healthy, large yields. More carbon dioxide is supplied to the crops for faster photosynthesis. The polythene walls and ceiling allow heat waves and light rays only to enter and prevent harmful waves, thus providing a high light intensity and optimum temperature, sometimes a heating system is used too. A watering system is also present. The disadvantages of green houses are that it is too small to give a large yield and that it is expensive. |
The Respiratory System
We rarely think about breathing unless we’re out of breath. The
act of breathing is part of the respiratory system, a complex process where air
travels into and out of the lungs.
Respiration is slightly different, where exercise causes muscles
to release energy in the form of glucose. Both systems are co-dependent,
especially when you’re playing sport and inhaling greater quantities of oxygen.
Human Respiratory System:
The
human respiratory system is made up of air passages, lungs and the
respiratory muscles. Nose: most breathing and gas exchange occur through the nose. It is lined by a layer of mucus and hair to trap the dust and germs in the air. It is also supplied with a dense network of blood capillaries to warm the air entering the body. Pharynx: Works together with the epiglottis to block the nasal cavity and the trachea during swallowing food, to prevent it from entering the respiratory system. Trachea (windpipe): this is a tube that connects the nasal cavity and larynx to the lungs. It is lined with a layer of ciliated epithelium cells and goblet cells which secrete mucus that traps bacteria and dust from inhaled air and gets moved upwards to the larynx by the cilia. |
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It is then either spit out or swallowed to
the stomach where it is eliminated by acid.
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Bronchi: when the trachea reaches the lungs, it is
divided into two tubes, one goes to the right lung and one goes to the left
lung. These are called the bronchi. The bronchi are then divided bronchioles
that extended deeper into the lungs.
Alveoli (air sacs): these are tiny bags full of gas; they are
present in the lungs in large amounts (several million alveolus in each
lung). They give the lungs a much larger surface area (about 70 m2) for
faster diffusion of gases between them and the blood. Rib Cage: the lungs are protected by this cage of bones. It surrounds all the thoracic cavity. They are 12 pairs of ribs; one pair extends from one of the first 12 vertebrae of the vertebral column. All of the ribs except for the last two pairs are connected to the sternum, the chest bone. Each pair of ribs is connected to the pairs above it and below it by muscle fibres called inter costal muscles. The rib cage and the lungs are separated by an elastic layer called pleural membrane, or pleura for short. It protects the lungs from damage caused by friction with the rib cage during breathing. Diaphragm: this is a sheath of muscles that separates the thoracic cavity from the abdominal cavity. Together with the ribs and the inter costal muscles, it plays a big role in breathing and gas exchange. |
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Gas Exchange (Breathing):
Breathing is different from respiration. Breathing is just the
exchange of waste gases from the body with fresh air from the atmosphere. The
action of breathing fresh air in is called inhaling; the action of breathing
waste gases out is called exhaling.
During Inhaling, the brain sends electric
impulses by nerves to the diaphragm and the inter costal muscles. The diaphragm
contracts becoming flatter. The inter costal muscles also contract and move the
ribs in an outer upwards directions. These actions expand the thoracic cavity
making the lungs expand, thus increasing the increasing the volume, with the
volume increasing the internal pressure decreases which makes air enter the
lungs through the mouth, nose and trachea.
During Exhaling, the diaphragm and the inter
costal muscles relax again, contracting the thoracic cavity thus squeezing the
air out of the lungs to the trachea and mouth and nose to the atmosphere.
Respiratory System in Action:
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Gas Exchange in Alveoli:
Each alveolus is supplied with blood capillaries. These come
from the pulmonary artery and they contain deoxygenated blood rich in carbon
dioxide. The concentration of oxygen is very high inside the alveolus and very
low in the blood, so oxygen molecules diffuse from the alveolus to the red
blood cells and combine with haemoglobin. At the very same time this occurs,
carbon dioxide diffuses from the blood to the alveolus because the
concentration of it is very high in the blood and low in the alveolus.
Adaptations of Alveoli:
Gas exchange happens because of several factors in the alveolus
and the blood capillaries that control the rate of gas exchange:
- Very
thin wall of both the alveolus and the capillary, they are one cell thick
which makes the diffusion distance shorter, increasing the rate.
- The
difference in concentration of gases between the alveolus and the
capillary is very large, increasing the diffusion rate of gases.
- The
alveolus are balloon shaped which gives it a very large surface area for
faster diffusion.
- The
walls of the alveolus are lined by a thin film of water in which gases
dissolve in during diffusion, this makes it faster.
Composition of Inspired and
Expired Air:
Gas |
Inspired
Air |
Expired
Air |
Oxygen |
21% |
16% |
Carbon
Dioxide |
0.04% |
4% |
Nitrogen |
79% |
79% |
Water
Vapour |
Variable |
High |
Lung Capacity:
When lungs of an adult are fully inflated they have a volume of
about 5 litres.
Tidal Volume: This is the volume of air breathed in and
out at rest, this is 0.5 litres.
Vital Volume: The maximum volume of air that can be
breathed in and out, at exercise for example is 3 litres.
Residual Volume: The lungs have to have a certain volume of
air inside them all the time to keep shape. This is the residual volume and it
is 1.5 litres. This air is renewed through breathing.
Aerobic Respiration:
A chemical, metabolic reaction that burns down glucose with
oxygen producing carbon dioxide, water vapour and lots of energy
Aerobic Respiration: the release of relatively large amounts of
energy in cells by the breakdown of food substances in the presence of oxygen.
Anaerobic Respiration:
Some organisms are able to respire and release energy when
oxygen is lacking. This is anaerobic respiration. These are like yeast,
bacteria and other organisms. Humans can also respire anaerobically for a short
period of time. The amount of energy produce is much smaller than that produced
during aerobic respiration though.
Anaerobic respiration: the release of relatively small amount of
energy by the breakdown of food substances in the absence of oxygen.
C6H12O6 (aq) + 6O2 (g) → 6 O2 (g) + 6H2O (l)
Anaerobic Respiration I
Yeast: Yeast
is able to respire anaerobically by breaking down glucose molecules into
ethanol and carbon dioxide.
C6H12O6 → 2C2H5OH + 6CO2
Ethanol is produced here, so it is a fermentation reaction. Do
remember that glucose is the only reactant.
Anaerobic Respiration in Humans:
When the amount of oxygen received by the muscle cells of the
body is not enough to carry out all respiration aerobically, the cells respire
anaerobically. But they cannot go like that for a long time. The anaerobic
respiration in humans is different than of yeast. Lactic acid is produced
instead of ethanol, and no carbon dioxide is produced.
C6H12O6 → 2C3H6O3
The lactic acid produced is very toxic and harmful to the body.
That is why it has to be broken down with oxygen as soon as possible. This is
called oxygen debt. Breaking down lactic acid releases energy too, if you add
up the amount of energy produced during breaking down lactic acid and anaerobic
respiration, you will find that it is the same as the amount produced during
aerobic respiration.
Effects of Smoking:
Short Term Effects:
- Cilia
can’t vibrate anymore, the air inhaled isn’t clean. Goblet cells release
more mucus which makes the trachea narrower.
- Nicotine
increases heart beat rate and blood pressure.
- Carbon
monoxide combines with haemoglobin instead of oxygen combining with it.
- Carboxyhaemoglobin
is formed which is stable.
- Less
oxygen transported to cells.
Diseases Caused By Tar:
Chronic Bronchitis:
- Tar
makes goblet cells in trachea produce excess mucus
- Mucus
falls into lungs
- Bacteria
in mucus breed causing infections like bronchitis
- The
layer of excess mucus lining the walls of the alveoli increase the
diffusion distance of gases making gas exchange slower
Emphysema:
- The
excess mucus lining the alveoli irritates it, causing strong coughs which
damage the alveoli.
- The
alveoli lose its shape and surface area making gas exchange much slower.
- This
cause short breathes and sounds while breathing.
Lung Cancer:
- When
tar reaches the lungs, it is absorbed by cells of the bronchi, bronchioles
and the lungs.
- The
tar causes excessive division and reproduction of these cells which
develops into cancer
- The
cancer can be spread to other organs too.
Diseases Caused By Nicotine:
Coronary Heart Disease:
- Nicotine
helps cholesterol deposition on walls of coronary arteries. This causes
atheroma.
- Carbon
monoxide also increases risk of blood clots forming which might results in
blocking the artery.
- Less
oxygen is delivered to heart cells, a heart attack or failure can take
place leading to death.
Excretion in Humans
Excretion
is the removal of toxic materials, the waste products of metabolism and
substance in excess of requirements from organisms. Metabolism is chemical
reactions taking place inside cells, including respiration. The body excretes three main waste materials. These are Carbon Dioxide, Urea and Water. Excretion is a very important feature to us because without it toxic substances will build up in our bodies and kill us. It also helps in maintaining the composition of body fluids. The Excretory System of humans is made up of 4 structures: Two kidneys, two ureters, a bladder, and the urethra. The kidneys act as a filter to filter the waste products from the blood, the ureters are tubes that transport the main waste products (urine) from the kidneys to the bladder, where it is stored until it is excreted out of the body through the urethra. |
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Formation of Urea:
- When
you eat a food high in protein, it is digested in the small intestine into
amino acids.
- The
villi on the walls of the small intestine absorb the amino acids into the
hepatic portal vein.
- Hepatic
portal vein is a special vein that transports digested material from the
small intestine to the liver.
- The
liver plays a big role in maintaining the level of protein in our body. It
absorbs all amino acids from the hepatic portal vein. If the body needs
proteins, they will pass through the liver into the blood stream to be
used by the body cells to make protein.
- If
the body does not need proteins. The liver will absorb excess amino acids
and break them down into carbohydrates and nitrogen. The formula of amino
acids is CHON; here we remove the nitrogen from the molecule, to get a
carbohydrate. This is called deamination. Nitrogen is made into urea which
is a nitrogenous waste product.
- The
products are then released to the blood stream.
Kidneys Structure:
A
kidney consists of two main structures:
The nephrone is the where filtration of toxic materials from the blood takes place. We have many of them in each kidney. In the centre of the kidney there is a cavity called the pelvis which leads to the ureter. |
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Structure of Nephrone:
The nephrone starts with a cup shaped structure called Bowman’s
capsule. Inside the Bowman’s capsule there is a very dense network of blood capillaries
entering as capillaries from the renal artery and exiting as capillaries from
the renal vein. This dense network of capillaries is called Glomerulus. The
rest of the nephrone is a long coiled tube where materials filtered from the
blood flow in. At some point the coiled tube becomes straight and is bent in a
U shape tube, this part is called loop of Henle and it is surrounded by a network of
capillaries from the renal vein, it is where reabsorption takes place. All
nephrones end at a large tube called the Collecting duct where content of the nephrones are
transported to the pelvis, to be secreted in the ureter.
Mechanism of the Kidneys:
Ultrafiltration:
The blood in the renal artery contains large amounts of urea,
glucose, water, mineral ions and some amino acids. When it reaches the
glomerulus, the high pressure of the blood and the concentration gradient of
these materials between the blood and the nephrone cause most of these
substances to diffuse from the blood to the bowman’s capsule and become content
of the nephrone, which is called glomerular filtrate (glomerular filtrate is a
mixture of urea, water, glucose and mineral ions that diffused from the blood
to the nephrone).
Reabsorption:
The glomerular filtrate moves in the nephrone till it reaches
the loop of henle, which is surrounded by a dense network of blood capillaries
of the renal vein. Here there is a concentration gradient of the content of the
content of nephrone between the nephrone and blood. Both diffusion and active
transport occur to ensure the complete reabsorption of valuable substances from
the glomerular filtrate back to the blood; these substances are glucose and
amino acids. Some water also moves by osmosis to the blood, as well as
minerals.
That leaves urea, excess water and minerals to continue in the nephrone till it reaches the collecting duct and the pelvis. This mixture is called urine. Urine is transported from the pelvis to the urinary bladder by the ureters. It is them secreted out of the body through the urethra.
That leaves urea, excess water and minerals to continue in the nephrone till it reaches the collecting duct and the pelvis. This mixture is called urine. Urine is transported from the pelvis to the urinary bladder by the ureters. It is them secreted out of the body through the urethra.
Dialysis:
If
a person gets a kidney failure, which means his kidneys cannot function
anymore, they have to wash their blood on regular basis with a machine that
is an alternative to the damaged kidneys. This process is called dialysis.
During this process, a tube is attached to the patient’s vein; the tube is
attached to the dialysis machine on the other end. There is another tube
coming out of the machine to the patient’s vein. The blood is sucked from the
patient’s vein, it goes through the machine, and out from the other side back
to the patient’s vein.When the blood enters the dialysis machine, it is very rich in waste materials (urea, excess water and minerals). The tubes inside the dialysis machine are made of a partially permeable membrane to allow diffusion. The tubes are also surrounded with dialysis fluid |
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which is the same as blood plasma. The
concentration of waste products in the blood is much higher in the blood than
in the dialysis fluid. This creates a concentration gradient, diffusion
occurs and waste products leave the blood to the dialysis fluid, which then
exists the machine and gets disposed. The dialysis fluid has to be renewed
continuously to keep the concentration gradient of waste products higher in
the blood, thus ensuring that all waste products leave the blood. The clean
blood is then returned to the patient’s vein.
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Homeostasis
The human body has the ability to maintain a constant internal
environment so that every organ and cell is provided the perfect conditions to
perform its functions. This is called homeostasis. There is no organ system for
this function. However, every organ plays a role in maintaining a constant
internal environment. For example the lungs are responsible for the supply of
oxygen to cells. The liver is to maintain a constant level of glucose and amino
acids, and so on..
Temperature Regulation:
A healthy human should have a body temperature of 37°C. If
the body temperature drops below 37°C, metabolic reactions become slower
because molecules move slower and have less kinetic energy. If the temperature
rises above 37°C, the enzymes of the body begin to get denatured and metabolic
reactions will be much slower.
Sometimes, the temperature of the area you are at is low enough
to decrease your body temperature. Sometimes it is high enough to raise your
body temperature. This is why the body has the ability to control its body
temperature. Our skin is responsible for this process.
The Human Skin:
The
skin is an organ that coats your entire body. The skin is made up of two
layers, the Epidermis and the dermis.The epidermis’s main function is to protect the dermis which contains most of the structures, and protect the body from ultra-violet rays. The surface of the epidermis is made of tough, dead cells. The dermis contains many useful structures. Hairs, sweat and sebaceous glands, sense receptors and erector muscles are responsible for controlling the body temperature. Blood vessels transport oxygen and nutrients to the cells of the skin. |
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A healthy body is continuously gaining and
losing heat. Metabolic reactions like respiration release a lot of heat
energy, muscular activity increase the metabolic rate and release more heat
energy. The body can also gain temperature from the surroundings like the sun
or by eating hot food. Heat is lost by the body through exposed skin by
conduction. If there is sweat or water on the skin, it will absorb body heat
to evaporate which drops the temperature. All these factors are normal
however, but it is considered dangerous when the body temperature keeps on
dropping or rising severely.
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Cooling Down the Body:
When
the body is overheated, the body takes several actions to drop it by trying
to lose heat in several ways:
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Heating Up the Body:
When
the body temperatures drop, the body takes several actions to regulate its
temperature by insulation to prevent heat loss and producing heat energy:
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How the Body Senses Change in
internal environment:
When the body’s internal temperature changes the temperature of
the blood changes with it. When the blood flows through the brain, a part of it
called the hypothalamus detects
the drop or rise in temperature. The brain then starts sending electrical
impulses to the rest of the body so that it works on heating or cooling its
self.
This process is called Negative Feedback. Negative
feedback is not
for change in temperature only though, it is for any change in the internal
temperature including the blood glucose level.
Regulating Blood Glucose Level:
For blood glucose level however, the pancreas is the organ which
monitors its level not the hypothalamus. When the blood flows through the
pancreas, the pancreas detects the level of glucose in it. If it is higher than
normal, the pancreas secretes a hormone called insulin.
Insulin flows in the blood till it reaches the liver. When it reaches the
liver, insulin hormone will make it convert excess glucose in the blood into
glycogen and store it in the liver cells. When the blood glucose level becomes
normal, the pancreas will stop secreting insulin so that the liver stops
converting glucose. If the blood glucose level decreases below normal, the
pancreas secretes another hormone called glucagon. When glucagon reaches the
liver, it makes the liver convert the glycogen it made from excess glucose back
into glucose and secrete it into the blood stream so that the blood glucose
level goes back to normal. When this happens the pancreas stops secreting
glucagon.
Normal Blood Glucose Level: 80-100 mg per 100cm3.
Co-ordination and Response
You have previously learned that one of the 7 characteristics of
living organism is irritability or
sensitivity. And this is the ability to detect a change in the outer
environment and respond to it. A change in the environment is also called a stimulus (plural stimuli). Actions taken by the body
in order to co-operate with a stimuli are called responses. The body detects a
stimulus by parts in the body called receptors and is
able to respond to it through other parts called effectors. Two
organ systems are continuously working to detect and respond to stimuli, these
organ system are called the nervous system and the endocrine system.
The Nervous System:
The
nervous system is a system of organs working together to detect and respond
to stimuli. The nervous system is made up of two systems, the Central
Nervous System (C.N.S) and the Peripheral
Nervous System (P.N.S) the
peripheral nervous system connects the central nervous system to the other
parts of the body.
Central Nervous System (CNS):
The
central nervous system is made up of the brain and the spinal cord. The
spinal cord is basically a big bundle of nerve cells running through a tunnel
inside the backbone which protects it while the brain is protected by the
skull. The central nervous system is what gives out orders to other parts of
the body to perform certain jobs.
The Peripheral Nervous System PNS:
The
peripheral nervous system is the other part of the nervous system. The main
job of the PNS is to detect stimuli and send impulses to the CNS according to
the stimuli. The PNS is made of receptors and nerves that carry the impulses. |
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Receptor cells are ones whose function is to detect something
about its environment. There are many receptors in the body that are able to
detect many changes like temperature, touch, light, sound and chemicals. There
are some organs in the body that are there to detect just one stimulus, like
the eye for example. These are called sensory organs and they can be defined as a group of
receptor cells responding to specific stimuli.
Effectors are the opposite of receptors. Receptors are two
detect the stimuli while effectors are two respond to it. Effectors are usually
muscles and glands.
Neurons (Nerve Cells):
Neurones are one of the most important structures of the nervous
systems. Neurones act as a wire that transmits electrical impulses all over the
body. Like a cable that consists of many wires, a bundle of neurones is called
a nerve. There are 3 types of neurones, each type is to transmit electrical
impulses from a specific place to another.
Motor Neurone: This is a neurone that transmits electrical
impulses from the Central nervous system to the effectors.
This neurone is made up of three segments; the cell body which
is the start of the motor neurone and is in the CNS, axon which stretches out
from the cell body all the way to end of the neuron, and the motor plate which
is the end of the neurone and is in the effector muscle.
Neurones have features that are common between most animal cells like a nucleus, cymiddlelasm and cell surface membrane, but they also have some exclusive features like the axon. The axon is an extended cymiddlelasm thread along which electrical impulses travel. Some motor neurones have axons of length 1 metre. Axons are coated by a layer of myelin called myelin sheath, this is an electrically insulating layer which is essential for the proper functioning of the nervous system.
Neurones have features that are common between most animal cells like a nucleus, cymiddlelasm and cell surface membrane, but they also have some exclusive features like the axon. The axon is an extended cymiddlelasm thread along which electrical impulses travel. Some motor neurones have axons of length 1 metre. Axons are coated by a layer of myelin called myelin sheath, this is an electrically insulating layer which is essential for the proper functioning of the nervous system.
Another exclusive feature of neurones is dendrites, these
are several short threads of cymiddlelasm coming out of the cell body. Their
function is to pick up electrical impulses from other cells.
The last exclusive feature of motor neurones only is motor end
plate. This is just the end of the axon which is in the muscle. It
passes the electrical impulses from the neurone to the muscle fibres.
Sensory Neurones: like other neurones, sensory neurones carry
electrical impulses from one place to another. But sensory neurones carry
electrical impulses in the direction different to that of motor neurones, from
the receptors to the CNS.
The sensory neurone’s shape is unique. This is because it is
made of a cell body, with two arms extending out of it. The first arm is the
axon which’s other end is in the CNS. The second arm is dendrite which’s other
end is in the receptor. The dendrite is similar in structure to the axon except
that it joins the receptor with the cell body. The electrical impulses of the
sensory neurone flow from the receptor, through the dendrite to the cell body,
then from the cell body to the CNS through the axon.
Relay Neurone: Relay neurones are located in
the CNS. Their job is to pass electrical impulses from the sensory neurone onto
the motor neurone, so it acts like a diversion.
Where neurones meet, they are not actually touching each other.
Instead there is a gap called synapse or junction box. When the electrical
impulses reach the end of a neurone, the neurone secretes a chemical
transmitter which passes by diffusion to the other neurone causing the impulses
to be carried from the first neurone to the second.
Reflex Arc (Nervous System in Action):
If your finger touches a hot surface, receptor cells in the skin
of your finger detect a stimulus, which is a sudden rise in the temperature.
The receptor uses the energy of the stimulus to generate electrical impulses.
These impulses are then carried by the axons of the dendrites of the sensory neurone
through cell body to axon and from the axon to the CNS. At the CNS the
electrical impulses travel through the synapse to the relay neurone, which
passes it onto the motor neurone. The nerve impulses are transmitted through
the axon of the motor neurone to the targeted muscle which contracts when
electrical impulses reach it, resulting in your finger being pulled away from
the hot surface. This pathway is called the reflex arc and
happens in about a fraction of a second.
Reflex Arc: RECEPTOR →
Sensory Neurone → CNS → Motor Neurone → EFFECTOR
Voluntary and Involuntary Actions:
The reflex arc is a reflex action. Reflex means it is
automatically done without your choice. This is because when the electrical
impulses reach the relay neurone in the CNS from the receptors, some impulses
are carried by other neurones to the brain, and some impulses are passes onto
the motor neurone to the effector muscle and the response takes place. The
electrical impulses going to your brain are much slower that the ones going to
the effector muscle directly. This is why the reflex action takes place before
you realise it, it is uncontrollable. Reflex actions are said to be involuntary
actions. Involuntary actions start at the sense organ heading to the
effector. They are extremely quick. Voluntary actions are the ones that you make the choice to
do. Like picking up a bag from the floor for example. Your brain sends
electrical impulses to the effector muscles ordering them to contract so you
could pick the bag up. Voluntary actions are slower than involuntary actions
and they start at the brain.
The Human Eye:
The human eye is a sensory organ. This means it is an organ of
tissues working together to detect and respond to a specific stimulus, which is
light.
Features of the Human Eye:
- Lens: changes shape to focus light on retina
- Ciliary muscles: contracts and relaxes to adjust
thickness of the lens
- Suspensory ligaments: loosens and tightens to adjust thickness
of lens
- Iris: widens and narrows to control amount of
light entering the eye depending on light intensity
- Choroid: middle layer surrounding the eye. It
contains many blood vessels
- Sclera: outer most tough, protective layer of
the eye.
- Retina: inner most layer. It is sensitive to
light and it is where the fovea is and it has rods and cons
- Fovea: very light sensitive spot
- Blind spot: Where the optic nerve touches the eye.
No light sensitive cells in this area.
How We See:
When the light hits an object, it is reflected in all
directions. When a light ray reflected from the object hits your eye you see
that object. At the back of your eye, there is a spot on the retina called the
fovea (blind spot). This spot is full of light sensitive cells. When the light
ray falls on the fovea, the light sensitive cells generate electrical impulses
that travel through the optic nerve to brain. When the electrical impulses
reach the brain, the brain generates the image you see. This all happens in
less than a fraction of a second.
But this is the general idea only. Light
rays enter the eye from every direction. If they are not focused on the
fovea, they will most probably not hit it and we won’t see. Here comes the
role of the front part of the eye. When the light ray hits the eye at an
angle, it first has to penetrate the cornea which refracts (bends) the light
ray inwards. The cornea acts as a converging (convex) lens. Then the light
penetrates the lens which refracts the ray a little more inwards focusing the
light ray on the fovea. And thus the light ray is focused on the retina. When
the ray hits the retina, the closer to the fovea the sharper the image is.
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Accommodation:
The angle at which the light ray hits the hits the eye depends
on the distance of the object. Every light ray that hits the eye needs a
certain amount of refraction in order to be directed to the fovea. This is why
the lens has the ability to widen and narrow according to the distant of the
object you’re looking at in order to make the light ray hit the retina at the
right spot. This is called accommodation. Light rays refracted from close
objects are diverging (spreading out), they need to be refracted inwards to be
focused on the fovea. When you look at a close object, it takes some time till
the vision becomes clear. This is because at first, the light ray is not
correctly refracted, so it hits the retina away from the fovea. The electrical
impulses are generated and sent to the brain which realises that the image is
not clear. The brain then sends electrical impulses to the ciliary muscles
making them contract. When the ciliary muscles contract the suspensory
ligaments become loose, this makes the lens become thicker and rounder for more
refraction of the light rays. Now the light rays are correctly refracted and
hit the retina at the fovea, the image becomes clear.
For far visions it is the exact opposite. The rays reflected
from far objects are almost parallel. Very little refraction should be done.
The brain sends electrical impulses to ciliary muscles making them relax, the
suspensory ligaments now tighten up and pull the lens which become narrow.
Distance
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Ciliary muscles
|
Suspensory
ligaments |
Lens
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Near
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Contract
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Loosen
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Widens
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Far
|
Relaxes
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tighten
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narrows
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Rods and Cones:
The retina is full of light sensitive cells called
photoreceptors. There are two types photoreceptors, they are rods and cones.
Rods and cones are specialised types of neurons. They look alike but they are a
little different in function.
Rods are sensitive to dim light. At night or in dark places,
most light detection electrical impulses transmission is done by rods. Vitamin
A is essential for proper functioning of rods, if Vitamin A lacks it can lead
to night blindness. Rods are spread all over the retina.
Cones are sensitive to bright and coloured light. All cones are
packed in one area, the fovea.
The Pupil:
The pupil of the eye is the dark round area
in the centre of it. It is surrounded by a coloured ring structure called the
iris. The pupil and the together play a big role in protecting the eye from
damage by limiting the amount of light entering the eye. If too much light
fall on the retina, the rods and cones get damaged. The iris and pupil change
their size to smiddle that happening. The iris contains two sets of muscles; Circular and Radial muscles. Circular muscles
run around the iris and radial muscles run from the centre to the outside.
When circular muscles contract they make the pupil smaller. When the radial
muscles contract the stretch the pupil outwards making it wider.
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In bright light, too much light starts entering the eye, which
is dangerous for the rods and cones, which detect the high light intensity. The
rods and cones start a reflex arc by sending electrical impulses to the brain
via sensory neurone. The brain responds by sending electrical impulses to the
muscles of the iris via motor neurone. These impulses make the circular muscles
contract and the radial muscles relax limiting the amount of light entering the
eye, thus protecting the rods and cones from damage.
If you walk into a dark room, the rods and cones sense the
little amount of light. They start another reflex arc and send electrical
impulses to the brain which responds by sending electrical impulses the muscles
of the iris. The radial muscles contract and the circular muscles relax
widening the pupil to let more light in.
Antagonistic Muscles:
You have just learned that in order for the pupil to get
narrower or wider, two muscles work simultaneously, when one contracts the
other relaxes. Pairs of muscles like that are called antagonistic muscles.
The most known antagonistic muscle pair is the biceps and
triceps of the arm. The bi and the tri for short, they are what causes the
movement of the arm. They work simultaneously to bend or straighten the arm.
The biceps is located in front of the humerus bone of the upper arm. The biceps
is joined to the radius bone of the lower arm and the triceps is joined to the
ulna bone of the lower arm. Muscles are attached to bones by strong fibres
called tendons.
When
you want to bend your arm the brain send two electrical impulses, one to the
bi making it contract and one to the tri telling it to relax. When the bi
contracts, it becomes shorter pulling the bones to which it is attached close
and bending the arm. This causes the fibres of the tri to stretch while they
are relaxed. To straighten your arm, the brain send electrical impulses to both muscles making the bi relax in order to leave the muscle it is attached to free. The tri contracts and becomes shorter pulling the muscle it is attached to into place and straightening the arm. |
|
The biceps can be called a flexor because it flexes (bends) the
arm. The triceps can be called an extensor because it extends (straightens) the
arm.
Drugs:
A drug is a chemical substance that modifies and affects
chemical reactions of the body when taken in. Many drugs are useful to us like
antibiotics, painkillers and caffeine.
Some drugs however are abused by users to feel relaxed, or reach
euphoria. Euphoria is a state of mind at which the abuser feels extremely happy
and relaxed. These drugs include alcohol and heroin.
Alcohol:
Alcohol is a depressant drug. This means that it reduces the
activity of the brain and slows down the nervous system and reflex actions.
Alcohol can be extremely dangerous when the user is in a situation in which
they need fast reflex actions. Alcohol is addictive. The more you drink
it the more you need it. The user may reach a point where they cannot do
without alcohol, this is when they become alcoholics. Alcohol is broken down
into fats by the liver. If the abuser drinks too much alcohol, the cells of the
kidney may die shortening their life.
Heroine:
Heroine is a narcotic drug. This means that it relieves pain and
induces sleep. Heroine is extracted from a plant called opium poppy. Most
heroine abusers become addicts. For the addicts heroine become the number one
priority in their lives. They would do anything to get the drug even become
criminals and possess a threat to their society. If not rehabilitated, a
heroine abuser will end up homeless or dead. Some heroine users inject the drug
in their veins by an unsterilized, shared needle, this increases the risk of
getting AID/HIV.
The Endocrine System:
You
have previously learned that messages are delivered around body as electrical
impulses by the nervous system. Another way messages are transported around
the body is by chemicals calledhormones secreted by the endocrine system. Hormones are chemical substances produced by a gland, carried by the blood, which alters the activity of one or more specific target organs and is then destroyed by the liver. Hormones are produced in organs called endocrine glands which make up the endocrine system. The following diagram shows the glands of a human body. Glands are organs made of secretory cells which’s function is to produce hormones and secret them into the bloodstream. Glands have a dense network of blood capillaries in them to secret the hormones in. hormones are carried around the plasma like all other content of the blood but certain organs are able to use them, these are target organs. |
|
Gland |
Hormone
produced |
Function
of hormone |
Adrenal
gland |
Adrenaline |
Prepares
the body for activities that need energy and quick reflex actions |
Pancreas |
Insulin |
Makes
liver reduce blood glucose level |
Glucagon |
Makes
liver increase blood glucose level |
|
Testis |
Testosterone |
Produces
male secondary sexual characteristics |
Ovary |
Oestrogen |
Produces
female secondary sexual characteristics |
Progesterone |
Helps
control menstrual cycle and maintain pregnancy |
Adrenaline:
When you get a fright you feel some changes in your body like a
sudden increase in heart beat rate, blood flowing quickly in veins and your
breath becomes deeper and faster. This is because the fright you got caused the
brain to send electrical impulses to the adrenal glands making them secrete
adrenaline hormone in your bloodstream. Adrenaline is a hormone that is
secreted from the adrenal glands to prepare the body for situations that need
lots of energy and fast reflex action, like fights or running away for example.
Adrenaline’s main objective is to increase your metabolic rate so that you have
enough energy for fighting or running away etc. This is why adrenaline is
called the three Fs hormone (Fight, fright, flight). One of adrenaline’s target
organs is the heart. When adrenaline reaches the heart it causes the cardiac
muscle to contract and relax much rapider so that oxygen and glucose reach the
muscles of the body faster. Adrenaline also makes the liver convert glycogen
into glucose and secret it in the blood to be used in respiration. When
adrenaline reaches the diaphragm and the intercostals muscles of the ribs, they
make it contract and relax faster too to increase rate of breathing. These
changes cause an increase in the respiration rate so that lots of energy is
being released. Generally, adrenaline is secreted when you are nervous or
anxious.
Use of Hormones in Food Industries:
Technologies and science have advanced enough that we can now
gut much more money out of farming and animal keeping. Hormones are now being
used in farms to increase milk yields in cows and growth rate in cattle and
fish.
In farms, the cows are being injected with a hormone called
Bovine Somatotropin or BST. BST is a hormone that is naturally produced in
cows. The function of BST is to produce milk. Injecting cows with extra BST
will boost milk production and bring in more money for the farmers. Some people
however are against the use of BST and claim it is safer for both the cows and
the consumer to keep it natural and keep more cows if we want an increased milk
yield.
Growth hormones are also being mixed with the food fed to cattle
to increase their growth rate and make them grow larger. But again many people
are against this and prefer buying meat and fish that were naturally grown.
Comparing Nervous and Endocrine
Systems:
Nervous
System |
Endocrine
System |
Information
sent in form of electrical impulses |
Information
sent in form of chemical hormones |
Information
travel neurones |
Information
travel in bloodstream |
Information
travels extremely rapidly |
Information
travels relatively slow |
Information
is headed to one target (effector) |
Information
may be used by several targeted organs |
Electrical
signals have an effect that ends quickly |
Hormones
have a longer lasting effect |
Coordinates and Responses in
Plants:
Plants cannot move themselves to areas of preferable conditions.
This is why plants have the ability to detect a stimulus and respond to it by
growing or bending in its direction or away from it. These responses are called
tropisms. For example a plant tends to grow its stem in the direction of
sunlight for more photosynthesis, this is atropism. There
are two types of tropism, these are phototropism and geotropism.
- Phototropism: the response in which a plant grows
towards or away from the direction from which light is coming.
- Geotropism: the response in which a plant grows
towards or away from gravity.
A tropism can be either positive or negative. If a tropism is in
the direction of the stimulus, it is positive. If the tropism is away from the
stimulus it is negative.
For example, a plant’s shoot tends to grow in the direction of
sunlight, this is positive phototropism. But the plant’s root grows in the
opposite direction deeply into the soil, this is negative phototropism.
However, positive phototropism can also be described as negative geotropism
because it involves the plant growing in the direction opposite to gravity. And
negative photo tropism can be described as positive geotropism because it
involves the plant growing towards gravity.
Auxins:
Tropisms are controlled by a chemical called Auxin. Auxin
is a plant hormone. It is produced by cells at the tip of roots and shoots of
plants. At the tip of a shoot, there is an area in which cells are being
produced by dividing so that the shoot grows. Old cells do not divide, but they
grow longer instead. The growth of these cells longer is controlled by auxins.
Auxins is what makes the plant grows this is why a plant doesn’t grow if you
cut it’s tip off.
Auxins’ Role in Phototropism:
If the sun shines on the right side of a plant’s shoot, auxins
will accumulate on the dark opposite left side. Auxins accumulating there makes
the cells on the left side grow much faster than the cells on the right side.
When the left side of the shoot starts growing faster than the right side, the
shoot will start to bend to the right side towards sunlight. This is
phototropism.
Auxins’ Role in Geotropism:
Auxins tend to settle at the bottom end of the root. However,
this does not make the sells of the tip of the root grow longer. Instead,
auxins prevent the cells at the bottom tip of the root from growing, making the
cells at the middle of the root grow faster. When the cells of the middle of
the root grow faster, they push the root deeper into the soil and the root gets
longer. The root grows in the direction of the gravitational pull. This is
geotropism.
Roots show positive geotropism and negative phototropism because
they grow towards gravity and away from sunlight at the same time. Shoots show
positive phototropism and negative geotropism because they grow towards the
sunlight and away from gravity at the same time.
Advantages of Positive Phototropism:
- Leaves
exposed to more sunlight and are able to do more photosynthesis,
- Flowers
can be seen by insects for pollination,
- The
plant gets higher for better seed dispersal.
Advantages of Positive Geotropism:
- By
growing deeply into the soil, the root fixes the plant into the ground
firmly,
- Roots
are able to reach more water,
- Roots
have a larger surface area for more diffusion and osmosis.
Selective Weed Killers:
Auxins can be used to kill weeds that grow over grass or cereal
crops. If weed grows on crops, auxins are sprayed everywhere. Weeds absorb
auxins faster than crops or grass. Auxins accumulate in the weeds making them
grow very rapidly. Fast growth of weed kills it leaving the crops or grass
alive. Auxins are used ass selective weed killers.