Biology notes

Biology Form 4 Notes (2003-2004)2005 Jordan Mifsud (4.8) 5.8

TOPIC 1: NUTRITION
The 7 Basic Food Substances
All the food we eat is made up of the following 7 basic substances:
1. Carbohydrates
2. Fats
3. Proteins
4. Vitamins
5. Minerals
6. Fibre
7. Water

Carbohydrates, fats, proteins and vitamins are organic substances because they
contain carbon in their molecular structure. Water and minerals are inorganic
substances since they don’t contain carbon.
Carbohydrates, fats and proteins are needed in bulk in our diet, while vitamins and
minerals are needed in smaller amounts.
A person whose diet lacks any of these nutrients suffers from malnutrition, and this
may give rise to a deficiency disease.
Food gives us energy. The amount of energy needed by our body isn’t the same for
everyone. The amount of energy needed to live depends on the person’s sex, job,
attitude, age and other factors like if the person is a pregnant woman.

1. Carbohydrates
Carbohydrates are organic substances made up of carbon, hydrogen and oxygen.
They are very important because they provide energy for the body. There are 3 types
of carbohydrates: sugars, starch, and cellulose.
A. Sugars
• Glucose (C6H12O6)
• Fructose (sugars in fruit)
• Sucrose (table sugar)

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• Lactose (found in milk)
• Maltose (found in barley grains)

B. Strach
• Found in bread, potatoes, rice, cereals etc. Plants store food as starch.

C. Cellulose
• Found in all unrefined plant food. An important source of fibre.

Carbohydrates are all made up of molecules of glucose bonded (joined) together. The
simplest form of carbohydrate is glucose. Two molecules of glucose joined together
with a bond, form maltose, lactose and sucrose sugars. Starch, cellulose and
glycogen are formed when 3 or more glucose molecules are joined together with
bonds.
Glucose’s molecule is represented by a hexagon:
A single sugar molecule is called a monosaccharide. Examples of monosaccharides
are glucose and fructose.
Glucose
Molecule

Sucrose, maltose and lactose are all disaccharides because they have 2 sugar
molecules bonded together.

Starch, cellulose and glycogen are all polysaccharides because they are made up of
3 or more sugar molecules bonded together.

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Carbohydrates are found in cereals, pasta, bread, fruit, potatoes sugary food such as
ice cream etc.

Glucose’s chemical formula is the following: C6H12O6.

Plants store food as starch, while animals store food as glycogen. Both glycogen
and starch are polysaccharides. Polysaccharides are NOT sweet but ARE insoluble.

2. Fats
• Fats are organic substances. Lipids are fats in a liquid state. Fats are useful
for our body, because they:
• provide energy,
• can be stored for later use,
• build up cell membranes,
• layers serve as an insulating layers under mammal’s skins and
• and oils on the surface of the skin makes the skin waterproof.

Fat is found in vegetable oil, milk, fried foods, eggs, beef etc.

The simplest fat molecule is made up of 1 molecule of glycerol and 3 fatty acids
bonded together.

Fatty Acids
Glycerol
Fatty Acids

Fatty Acids

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3. Proteins
Proteins are organic substances made up of hydrogen, carbon and oxygen,
nitrogen and sometimes they contain sulphur. Proteins are needed by the body to
grow and repair tissues (a cellular structure), they are components of cell
membranes, are used to produce enzymes (biological catalysts) and hormones.
The simplest possible protein is an amino acid, thus proteins are made up of amino
acids, which can be represented as any form of shape (circle, rectangle, square).

Amino acids are joined together by peptide bonds. When 2 amino acids connected
together with a peptide bond, a dipeptide forms. When 3 or more amino acids are
joined together, a polypeptide is formed.

Amino Acid Dipeptide Polypeptide

When proteins are heated, they are denatured; they change shape, its properties and
functions are destroyed. Food rich in proteins are milk, meat, eggs, nuts, fish etc.

4. Water
Water is vital for animals and almost all living organisms. It makes up to one third of
the human body mass. Water is an inorganic substance with the chemical formula
H2O.
Water is important for animals because it gives support to aquatic animals, gametes
(sex cells like sperms and eggs) travel in a watery medium, sweating has a cooling
effect on the body, and urine and tears are mostly made up from water. There is water
even in the joints, so that reduces friction when bones move. Even blood is partially
made up of water.
Water is also needed by plants, to make leaves turgid, guard cells move by osmosis
and water takes part in the chemical reaction in which plants make there food (by
photosynthesis). Some seeds germinate with the help of water.

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5. Minerals
Many minerals are important for our body. There are other trace elements not listed in
the table which are useful for other bodily functions.
Mineral Found in Use in the body Deficiency disease
Milk, cheese, Developing bones Rickets
fish, mineral and maintaining their
water rigidity. Forms
intracellular cement
Calcium and the cell
membranes, and in
regulating nervous
excitability and
muscular contraction.
Tomatoes, liver, Part of haemoglobin in Anaemia headaches,
Iron kidneys red blood cells. tiredness, and
lethargy
Many foods, Important for bones Osteomalacia
Phosphorous
e.g. milk and teeth. (rickets)
Salt, many Present in extra cellular Cramps
Sodium
foods. fluid, and regulates it.
Sea food, Needed to synthesize Goitre
Iodine drinking water hormones of the thyroid
gland.
Water, Builds a layer above Can lead to tooth decay
Fluorine
toothpaste enamel.
Most foods Important for Tremors and
Magnesium
metabolism. convulsions

6. Vitamins
Vitamins are very, very important for the body, but only in small quantities.
Vitamin Found in Use Deficiency disease
Liver, carrot Important for eyes. Night Blindness
A
Exophthalmia.

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Fish liver oil Healthy bones and Rickets.
D
teeth.
Milk, egg yolk, Healthy reproductive Sterility.
E
lettuce system.
Cabbage, spinach, Important for the Disorders in blood
K
fish livers coagulation of blood. clotting.
Pork, organ meats Catalyst in Beriberi;
lean meats, eggs, carbohydrate Disturbances,
leafy green metabolism, enabling impaired sensory
B1 vegetables, whole or pyretic acid to be perception,
enriched cereals, metabolised and weakness, periods of
berries, nuts, and carbohydrates to irregular heartbeat,
legumes. release their energy. and partial paralysis.
Liver, milk, meat, Serves as a Skin lesions.
dark green coenzyme-one that
vegetables, whole must combine with a
grain and enriched portion of another
cereals, pasta, bread, enzyme to be
B2
and mushrooms. effective-in the
metabolism of
carbohydrates, fats,
and, especially,
respiratory proteins.
Liver, poultry, meat, Works as a Pellagra Diarrhoea,
canned tuna and coenzyme in the mental confusion,
salmon. release of energy irritability, and, when
Niacin (B6) from nutrients. the central nervous
system is affected,
depression and
mental disturbances.
Citrus fruits, fresh Important in the Scurvy; Bleeding
strawberries, formation and gums
cantaloupe, maintenance of
C
pineapple, and collagen, the protein
guava. that supports many
body structures and

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plays a major role in
the formation of
bones and teeth.

7. Fibre
Fibre is mainly cellulose from plant cell walls. Humans cannot digest fibre, but it is
important because it helps food to pass from the gut, and prevents constipation.
Food rich in fibre are whole meal bread, bran, cereals, fresh fruit and vegetables.

Food Tests
Test for Starch: with Iodine solution. If result is positive, a blue-black
precipitate forms.
Test for Glucose: with Benedict’s Solution and the mixture is heated. If the
result is positive, an orange brown solution forms.
Test for Proteins: with Copper Sulphate and Sodium hydroxide. A purple
colour forms if the tested food contains proteins.
Test for Fats: with Ethanol (alcohol) A miillky whiite solution forms in
m ky wh te
presence of fat.
Test for Vitamin C: with DCPIP. A blue to a collourlless liquid forms in
co our ess
presence of vitamin C.

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TOPIC 2 ENZYMES
Enzymes are biological catalysts. A catalyst enhances the speed of a chemical
reaction. Thus, enzymes are catalysts, which enhance the speed of the chemical
reactions taking place in the body.

Properties of Enzymes
Enzymes are proteins, therefore, they become denatured by heat, which means that
when heated above 40oC, they change shape and do not work anymore. When the
temperature is lower than normal, enzymes become inactive. Enzymes are specific,
which means that every enzyme catalysis only one type of food substance, for
example, the enzyme amylase catalysis only starch, and does not take part in any
other chemical reaction involving another food substance.
Enzymes do not take part in the proper chemical reactions (they do not react), they
just enhance the speed, and this property makes them used over and over again.
An enzyme catalysis a reaction involving a substrate; the particular nutrient the
enzyme acts on. When the reaction is complete, a product is produced. An example is
amylase acting on starch. Amylase, which is an enzyme, acts on its substrate
(starch), to produce a product (maltose), which is a simpler type of carbohydrate.
The rate of productivity by enzymes is very affected by temperature and by pH. The
graph shows the rate of the activity by the enzymes in relation to temperature. The
rate increases slowly when the temperature rises between 10oC to 40oC, but when the
temperature rises further, activity decrease drastically, because enzymes are being
denatured.

Effect of Temp. on Enzymes

6

5
mg of product per min.

4
mg of products per
3
minute
2

1

0
10 20 30 40 50
Temerature in degrees celcius

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The graph here below shows the sensitivity of enzymes to pH. It is a bell-shaped
graph, showing that the enzymes work best that at their optimum pH, which in this
case is pH 2.

Effect of Temp. onEnzymes
Effect of pH on Enzymes Optimum pH
12

10
activity of enzymes

8

6 activity of enzyme

4

2

0
0 0.5 1 2 3 3.5 4
pH

An example:

Amylase acts on Starch to maltose
produce

Enzyme Substrate Product

Enzyme

The Lock and Key Theory
The lock and key theory is how scientists believe
Substrate
enzymes catalyze their substrate. It is shown in this
diagram. The substrate approaches the enzyme, then
the substrate docks into the active site, where the Active Site

reaction takes place. After the reaction, the enzyme
releases the products. Reaction taking
place

Products leave
active site
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Economic Important of Enzymes
Enzymes can be artificially made and used in Biological washing powders. These
washing powders contain enzymes that work at a suitable temperature (e.g. 40oC) and
dissolve food stains from fabrics. They are specific to particular stains.
Protease is used for tenderising meat and removing hair from hides.
Amylase is used to covert starch to sugars to make syrups and juices.

Enzyme Inhibitors
There are some poisons, such as cyanide and arsenic that block the enzymes’ active
site, therefore the substrate cannot enter the active site and the reaction doesn’t take
place. Certain pesticides block the active site of pests’ enzymes so that its respiratory
system stops working and the pest dies.

Dentition
The teeth are made of hardest substance found in the body. Humans have 4 types of
teeth:
Incisors: Adapted for cutting food.
Canines: for holing and tearing.
Premolars: For chewing and grinding food.
Molars: For chewing and grinding food.

Humans aged 6 months begin to grow 20 milk teeth (baby) teeth. Once he or she is
an adult, 32 permanent teeth will be developed.
The tooth is made up of 2 sections, an exposed Crown and the Root which is
embedded in the gum. The enamel (calcium phosphate: CaPO3) is the upper part of
the crown. It is very hard. Then beneath it there is the dentin. The tooth is primary
made of dentin, which is a substance, similar to bone but harder. The central region of
the tooth is the pulp cavity. It contains the pulp, which is composed of connective
tissue with blood vessels, nerves etc. the pulp is connected to the blood capillaries,
which give nutrients and oxygen to the dental cells.
Tooth decay (dental caries) is caused by bacteria in the mouth which produce acids
to digest food stuck in and between the teeth.
To prevent tooth decay, varies activities must be regularly done:

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Brushing teeth with a fluoride toothpaste
Regular visits to the dentist
X-rays of the jaw to ensure that no cavity is being developed where the dentist
cannot see
Use tooth floss
Wash mouth with a suitable mouth wash

Herbivores have different a dental system since they eat only vegetable matter. In
herbivores, there is a gap called diastema between the incisors and the molars.
Instead of the upper incisors, herbivores have a hard pad to pull leaves and grass out
of the branches or soil. They have no canines and molars have a flat surface. Their
teeth have an open root, which means that they grow continuously. Carnivores’
molars have cusps, to ensure that food is better chewed. They have canines, and
upper incisors, while teeth have a closed root unlike herbivores. The following
article shows more clearly the difference between carnivores and herbivore dentition.

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Diastema

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TOPIC 3: FEEDING
Feeding can be divided into 4 types:
1. Saprophytic: Saprophytic organisms such as fungi and some bacteria (called
decomposers) that feed on dead decaying matter. Saprophytes are useful to
the environment because they recycle nutrients.
2. Parasitic: When parasitic organisms feed on or in another organism harming
it.
3. Holozoic (heterotrophic): Animals feed heterotrophically, because they must
search for their food. Herbivores eat vegetable matter and have special
bodily structures to help them digest cellulose. Carnivores eat meat and are
usually predators. Omnivores, such as humans eat both meat and vegetable
matter.
4. Holophytic (autotrophic): Plants feed with this type of feeding. They are able
to make their own food by photosynthesis.

Holozoic Nutrition
The digestive system can be divided into various stages, but it is basically divided
into 5 main stages:
1. Ingestion: food is ate, chewed and mixed with saliva.
2. Digestion: Begins from the mouth by salivary amylase (starch-breaking
enzyme) and continues till the duodenum (first part of the small intestine),
were enzymes break down food into simpler soluble products (Glucose,
amino acids, fatty acids and glycerol), stage by stage, and prepares nutrients
for absorption.
3. Absorption: the blood absorbs soluble products in the ileum (second part of
the small intestine).
4. Assimilation: the nutrients are then assimilated (taken to) various organs
around the body.
5. Defecation (Egestion): Undigested matter such as fibre is egested (moved
out) of the body. [Do not mix excretion with egesting or defecation! Excretion
is the removal of waste products made by chemicals reaction within the cells;
e.g. excreting urine].

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Now the 5 stages will be examined more in detail.
Ingestion
The first stage, ingestion, is the actual eating of food, i.e. using teeth.

Digestion
The second stage, digestion begins from the mouth. It is divided into 2 other parts:
1. Physical digestion: teeth crush food to increase surface area for enzyme
action to break down food.
2. Chemical digestion: food is mixed with enzymes and digestive juices to
breaks down food into the 3 soluble products of digestion. The chemical
digestion continues till the duodenum. Chemical digestion also begins in the
mouth. When food is mixed with saliva, the enzyme salivary amylase starts
breaking down starch into maltose

Chemical Digestion in more detail
Saliva contains salivary amylase, mucus, water and lysozyme (which is also an
enzyme) that kills bacteria. The food, after that it is chewed, forms into a bolus, (a
ball) of mixed food with saliva that goes down the oesophagus (or gullet). Between
the mouth and the oesophagus there is the epiglottis. The epiglottis is a flap that
closes so as to prevent food entering the windpipe (trachea).
The oesophagus is made up of two layers of muscle cells. On layer is circular while
the other runs lengthwise. When they contract and relax, they push down food
downwards in a movement called peristalsis. Therefore food does not go down by
gravity (astronauts would NOT survive in space if it would!). The food is pushed
down to the stomach.
The stomach is made up of layers of muscles that make it twist and squeeze so that
food is mixed with gastric juices. There are about 35 million gastric glands that
produce gastric juice. Gastric juice contains:
Pepsinogen: an inactive form of pepsin that is then activated by the
hydrochloric acid.
Pepsin: digestive enzyme, which breaks down proteins into smaller
polypeptides.
Mucus: Protects the stomach wall from being digested by the enzymes
(prevention of self-digestion).

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Hydrochloric acid (chemical formula HCl) kills bacteria and provides and
acidic, optimum pH for pepsin to work.
After 3 to 4 hours of digestion, food becomes chyme. At intervals it is passed into the
small intestine. The first part of the small intestine is called the duodenum. The
duodenum receives digestive juices for 3 different places: intestinal wall, pancreas
and the liver.
From the intestinal wall, mainly 5 enzymes are produced:
1. Trypsin: breaks down polypeptides into dipeptides.
2. Maltase: breaks down maltose into glucose.
3. Lipase: breaks down fats (lipids are liquid fats) into fatty acids and glycerol.
4. Peptidases: breaks down dipeptides into amino acids
5. Sucrase: breaks down sucrose into glucose
These enzymes are summarised below in the following table:
Enzymes from the
Substrate Product
Intestinal Wall

Trypsin polypeptides dipeptides
Maltase maltose glucose
Lipase fats fatty acids and glycerol
Peptidases dipeptides amino acids
Sucrase sucrose glucose

From the pancreas mainly 4 chemicals are produced:
1. Sodium hydrogen carbonate (NaHCO3): neutralizes acids from the stomach
and provides alkaline pH in the duodenum.
2. Trypsin: breaks down polypeptides into dipeptides.
3. Pancreatic amylase: breaks down starch into maltose.
4. Lipase: Breaks down fats into fatty acids and glycerol.
These chemicals are enlisted here below:
Chemicals from the
Function / Substrate Product
Pancreas
Sodium hydrogen neutralizes acids from the
carbonate stomach and provides
alkaline pH in the
duodenum

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Trypsin polypeptides dipeptides
Pancreatic amylase Starch maltose
Lipase Fats Fatty acids and glycerol

From the liver, the duodenum receives no enzymes, but gets bile. Bile is a green
chemical, which helps to break down large fat molecules for lipase to act on it: this
process is called emulsification. It has a detergent effect, and it is stored in the gall
bladder and it is secreted from the gall bladder to the duodenum through the bile
duct. Digestion ends here.
Food has been all broken down into their soluble products, glucose, amino acids,
fatty acids and glycerol. They can be now absorbed into the blood stream from the
ileum.

The liver
The liver is the largest internal organ in vertebrates. It does the following functions:
synthesis of proteins, immune and clotting factors, and oxygen and fat-carrying
substances. Its chief digestive function is the secretion of bile, a solution critical to fat
emulsion (emulsification) and absorption. The liver also removes excess glucose from
circulation and stores it until it is needed. It converts excess amino acids into useful
forms and filters drugs and poisons (alcohol, pills etc) from the bloodstream,
neutralizing them and excreting them in bile. The liver has two main lobes located
just under the diaphragm on the right side of the body.

The Ileum
The ileum is a very long part of the gut so that absorption takes places efficiently.
Here, soluble products: glucose, amino acids, fatty acids and enter glycerol enter the
blood stream through millions of small finger-like structures called villi. The villi are
tiny, to increase surface area for absorption. Each villus is covered with tiny ‘hairs’
called microvilli, that are actual villi but smaller, like root hairs on a root in plants.
Villi have a thin lining and a good blood supply to allow blood to absorb the soluble
nutrients. Food passes through the intestine with the help of muscular contraction
(peristalsis) of the intestinal wall, which is also moist to allow food to pass well and to
enhance the speed of absorption.

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Thin Epithelium

Blood Vessels (absorb
Lacteal glucose and amino acids)
(absorbs
fatty acids
and glycerol
The villus’s structure is shown here;
Glucose and amino acids are absorbed by the blood capillaries, which are very thin
blood vessels. Fatty acids and glycerol, being large molecules are absorbed by the
lacteal first before draining into the blood stream.

The Large Intestine
The large intestine is divided into the colon and rectum. The colon is the part where
water is absorbed. In the rectum, faeces (undigested food such as fiber) are stored
until it is egested out of the body through the anus, within 24-48 hours after eating.
The rectum wall is covered with a layer of mucus to ease the passage of faeces. This
process is called defeacation.

The Caecum and the Appendix
The caecum and the appendix are vestigial organs, i.e. they do not have any known
function in humans. In herbivores called ruminants, (such as rabbits) the caecum and
appendix contain cellulose-digesting bacteria that produce the enzyme cellulase to
digest cellulose in plant cells.
A summary of the digestive system

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Digestion in Herbivores
Herbivores such as cows, sheep and horses are called ruminants because they contain
a special digestive system. They have a special type of dentition, different from
carnivorous dentition, to allow them to extract grass from soil easily. Their small
intestine is about 40 meters long, to allow them to digest cellulose completely, before
it reaches the end of the gut.
Their gut contains cellulose-digesting bacteria. These bacteria produce the enzyme
cellulase that catalysis the reaction that breaks down cellulose into soluble sugar
(glucose). The bacteria gain shelter and protection as well as food from the ruminants
so their relation is a mutualistic one (both benefiting from one another).
These bacterial are housed in the caecum and appendix, so in the ruminants, they are
not vestigial organs as in humans.

Ruminants have a special type of stomach called rumen. The rumen is a large
stomach that contains 3 other chambers. While the ruminant is grazing, grass is
swallowed and enters the rumen. When the animals stops eating, it regurgitates the
grass (brings the already swallowed food back to its mouth), little by little to allow it
to be chew and swallowed properly and then the food enters into the other 3 chambers
to further digest the food before it goes into the small intestine.
The following article helps you understand how the ruminant’s digestive system
works.

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More information about the Liver

Liver

Hepatic Vein

Hepatic portal vein

Hepatic Artery

Gut

The liver receives blood mixed with the soluble products of digestion from the
hepatic portal vein. The liver receives blood rich in oxygen from the heart through
the hepatic artery. Then the blood leaves the liver through the hepatic vein which
also carries a lot of heat since inside the liver, a lot of chemical reactions occur.

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TOPIC 4: RESPIRATION

What is Respiration and Why do we need it?
Respiration is a chemical reaction catalysed by enzymes. It takes place in each
and every mitochondria of the cells. Respiration is done to obtain energy needed
by the body. For vital functions to take place, the body needs energy. It also needs
energy to keep a constant body temperature and to transport chemical messages.
Plants need energy for active transport to take place.

Gas exchange
Differences between respiration and breathing:
Respiration is carried out in all cells to obtain energy.
Breathing is the exchange of gases, in case of humans and other organisms, the
removal of carbon dioxide and obtaining oxygen.
In large organisms such as mammals, respiratory surfaces are required for gas
exchange (breathing, not respiration) to take place efficiently. In humans, like all
mammals, lungs are used for this purpose.
There are two types of respiration: Aerobic (oxygen involved) and anaerobic
(no oxygen involved).

Anaerobic Respiration
Anaerobic means without oxygen, and thus this type of chemical reaction involves
only sugars (obtained from digestion of food). Energy is released by the chemical
breaking of bonds in organic molecules (containing carbon) present in sugars and
other carbohydrates, obtained from digestion. There is more than one type of
anaerobic respiration; it depends on the organism.
One very common type of anaerobic respiration is alcohol fermentation
represented in this equation below:

C6 H 12 O6 → 2CO2 + 2C 2 H 5OH + energy ( 210 kJ )
This type of reaction (alcohol fermentation) is done by yeast. As it produces
alcohol, it is important for world economy for the production of beer, wine and
other alcoholic drinks. Yeast’s most important function is surely in the production
of bread. Anaerobic respiration is also important for the economy as certain

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anaerobic bacteria produce lactic acid, which is used to make butter, yoghurt
cheese and other dairy products. Some other types of bacteria produce methane
gas (CH4), a flammable gas used for cooking and fuelling machinery, lighting, and
used in the production of hydrogen, hydrogen cyanide, ammonia, ethyne, and
formaldehyde.
Anaerobic respiration takes place in humans as well. During strenuous exercise,
blood vessels cannot provide enough oxygen for muscle cells to do proper aerobic
respiration; in this case, anaerobic respiration takes place in the muscles. In these
reactions, lactic acid (slightly poisonous) is produced and can cause cramps. After
the exercise, the lactic acid is converted into carbon dioxide and water by oxygen.
This whole process is known as oxygen debt.

Making Bread
This is a simple method to make bread.
• Some yeast and sugar and mixed with a little warm water.
• After some time, the mixture froths and this indicates that yeast cells are
becoming active.
• The yeast liquid is mixed with flour, salt and warm water to make the
dough.
• The dough is then kneaded for a few minutes to ensure that all the yeast
and the rest of the ingredients and evenly distributed.
• The dough is left in a warm place for fermentation is take place. Yeast
produces alcohol and carbon dioxide and this gas causes the dough to rise.
After an hour, the dough should have doubled its size.
• The dough is baked in a hot oven and yeast cells die. Alcohol, with a low
boiling point evaporates almost immediately and the carbon dioxide leaves
the bread with small holes inside it.

Aerobic respiration
Aerobic respiration is the respiration, which involves oxygen. An example of
aerobic respiration is shown here in this equation:

C6 H 12O6 + 6O2 → 6CO2 + H 2O + [energy]
glu cos e oxygen → carbon dio xed water ( 2880 KJ)

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The enzymes catalyze the oxidation of glucose to form carbon dioxide and
water. 2830kJ of energy are released by oxidizing 180 grams of glucose. Energy
is stored in the body as ATP (adenosine triphosphate), because glucose alone
does not provide energy.
As enzymes catalyse this reaction, it is controlled also by temperature, so when
the body temperature rises above 40oC, respiration slows down because heat
denatures enzymes.

The lungs
The lungs are the respiratory surface of mammals, birds, reptiles and some
amphibians.
Voice box
(larynx)
Rings of Cartilage
Pleural membrane Trachea
Pleural fluid Bronchus
Alveoli

Bronchioles, terminal
bronchioles
Intercostals
muscles
Ribs

Space for Heart Diaphragm
Pulmonary Artery
Pulmonary Veins

The Air Passage
The air passes through a number of passages before it goes to the bloodstream to
be used up. First the air passes through the nose and through the trachea, which is
surrounded by rings of cartilage to stay stiff. The nose and trachea have special
cells on their walls. There are some cells with cilia; hair-like structures that are
continuously beating up and down. These trap germs as well as dust from the air.
Another type of special cells in the epithelium of the nose and trachea are the
mucus-secreting cells. These have a hole in them from where mucus is secreted.
After the trachea, the air passes through the bronchi, bronchioles, terminal

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bronchioles and finally to the air sacks, or alveoli. These alveoli are shown here

Blood capillary filled
with oxidized blood
(oxy-hemoglobin
Alveolus

Blood capillary with
Thin water deoxidized blood
film
in this diagram.

Oxygen and carbon dioxide are exchange in the alveoli by diffusion. Numerous
alveoli create a large surface area for gas exchange. Oxygen is carried in the red
blood cells (rbc) while carbon dioxide is carried in the plasma as Hydrogen
Carbonate (HCO3-) ions.
The alveoli are adapted for gas exchange by a number of factors:
1. They have a thin film of water to ensure good and fast gas exchange by
diffusion surrounds the alveoli. In fact, some of this water evaporates and
there is always some water vapour in our exhaled breath.
2. Alveoli are surrounded by a lot of blood capillaries
3. Blood capillaries are very thin to allow diffusion.
4. There are many air sacks for a large surface area.

Breathing

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While breathing in, the rib cage moves upwards and outwards, the diaphragm
flattens and the volume in the chest increases. Since the volume increases the
pressure decreases and the air is drawn into the lungs.
While you exhale, the rib cage moves inwards and downwards, the diaphragm
relaxes (dome shaped) and the volume in the chest decreases. Since the volume
decreases pressure increases and the air is expelled out of the lungs.

Smoking and its Negative Effects
Cigarettes contain 3 harmful chemicals: 1) Tar, 2) nicotine and while it is burning
it produces 3) carbon monoxide. Apart from these, the cigarettes contain many
other chemicals. Some of these are irritants. Irritants and chemicals that annoy
the lungs. Other chemicals are carcinogens; may cause cancer.
The smoke produced by the cigarettes is very harmful, it affects the epithelium in
two ways: it irritates the goblet cells, making them produce more mucus.
Secondly, it slows down, or even stops the beating of the cilia, so that they can no
longer sweep out the mucus. Coughing can only clear the build up of mucus in the
lungs. This is known as smoker’s cough.
Some diseases caused by cigarettes are bronchitis, emphysema and lung cancer.
Bronchitis: This disease results as much of the epithelium is damaged and
destroyed by the cigarettes’ smoke and irritants. Germs and irritants penetrate
deeper into the lung tissue and so the body’s defence cell move into attack. Their
remains, along with the mucus make up phlegm, which must be coughed and spat
everyday. Bronchitis causes more than a 1000 deaths every year and it is a
disease, which mostly causes loss of workdays.
Emphysema: Emphysema causes the walls between alveoli become torn and
broken, while the others left become thicker. This causes the lungs to have a
smaller surface area for gas exchange. The sufferer coughs and wheezes and
struggles for breath. This illness can cause permanent disability and eventually
death.
Lung Cancer: Carcinogenic chemicals (chemicals which can cause cancer)
cause lung tissue to divide in an uncontrolled manner. This growth is called a
tumour or cancer. The tumour spreads through the lung destroying other healthy
tissue. Cancerous cells may go into the bloodstream and secondary tumour may
arise. This disease, although it can be treated if detected in the early stages, it is

Page 24


usually found too late and the victim dies.

Other Lungs diseases
Pneumonia: Certain bacteria and viruses cause this illness. These cause the
alveoli to get filled with fluid and cell debris. Oxygen starvation results since a
much of the alveoli block gas exchange.
Tuberculosis (TB): It is cause by a bacillus (pathogenic bacteria). This disease
can be treated and cured nowadays. The germs doesn’t do much harm but
sometimes, the bacillus may spread out through the lungs causing sever damage.
Dust Diseases: These diseases are caused when large amounts of dust are breath
during work. Stonecutters, miners and asbestos workers may catch illnesses such
as silicosis, pneumoconiosis and asbestosis respectfully. Special precautions
must be taken because once caught, these diseases are incurable.
Air Pollution
The air is polluted by mainly 5 different gases: carbon dioxide, carbon monoxide,
sulphur dioxide, nitrogen dioxide and ozone. 4 of them are poisonous for the human
body, namely carbon monoxide CO, sulphur dioxide SO2, nitrogen dioxide NO2
and ozone O3.
Carbon dioxide CO2 is not a toxic gas in moderate concentrations, but it contributes
to global warming, thus it is a greenhouse gas (traps the sun’s heat, causing global
temperature to rise, changing climate and endangering animal and plant species).
CFC’s (chlorofluorocarbons) although not considered pollutants, convert ozone in the
protective ozone (O3) layer back into oxygen (O2), thus it makes a hole in this layer,
letting harmful ultraviolet rays from the sun penetrate the atmosphere, causing skin
cancer.
Sulphur Dioxide and Nitrogen Dioxide rise from industrial effluent and car exhaust.
They are both toxic gases and in order to block nitrogen dioxide from escaping into
the air, cars should be equipped with catalytic converters. These devices convert
nitrogen oxides and carbon monoxide into carbon dioxide, harmless nitrogen and
water, with the help of rare catalysts.
Carbon monoxide is also produced by cars and other burning sources that are not
properly ventilated such as gas heaters and fire places in enclosed rooms. It is a
harmful gas because it combines with the blood, preventing it from absorbing
oxygen. Even in small concentrations it may be fatal.

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Certain electrical machinery and photocopiers produce ozone (O3) gas. Although
ozone is useful in the ozone layer, which is 20-50 km above sea level, it is highly
poisonous and can contribute to acid rain.
Glossary For Half Yearly Terms To Study
Nutrition: the study of food.
Basic Nutrients: The 7 basic food substances that are: Carbohydrates, Fats,
Proteins, Vitamins, Minerals, Fibre and Water.
Carbohydrates: 1 of the bulk material of which food is made of. An organic
substance from which the body gets energy.
Fats: Made up of fatty acids and glycerol; another bulk material found in food.
Proteins: Substances made up of carbon, hydrogen, oxygen, nitrogen and
sometimes sulphur. Used for growth and repair or tissue.
Vitamins: Organic substances needed in small amounts by the body. Some are co-
enzymes and other help to prevent illnesses.
Minerals: Important substances needed in small quantities to prevent illnesses.
Fibre: An insoluble, non-digested substance used to sweep out undigested food
out of the body; roughage
Water: Very important chemical; the most abundant compound in the Universe
and in the body.
Sugars: Carbohydrates used to get energy.
Glucose: C6H12O6 Final product of digestion of carbohydrates.
Fructose: A sugar found in fruit.
Sucrose: Table sugar.
Lactose: Found in milk.
Maltose: Found in barley grains.
Starch: Found in bread, potatoes, rice and cereals. A chemical used by plants to
store food; an insoluble polysaccharide.
Monosaccharides: Sugar with one glucose molecule. Fructose is also a
monosaccharides.
Disaccharides: Sugars with more than one glucose molecule attached together by
bonds.
Polysaccharide: three or more sugar molecules are bonded together; insoluble.
Glycogen: The chemical used by animals to store food.
Glycerol: Part of the fat molecule.

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Fatty acid: There are 3 fatty acids in a fat molecule.
Amino Acid: The final product of digestion of proteins.
Peptide bonds: the bond by which amino acids are attached.
Dipeptide: 2 amino acids attached together by peptide bonds.
Polypeptides: 3 or more amino acids attached together by peptide bonds.
Peptide Bonds: Bonds attaching amino acids together to form dipeptides and
polypeptides.
Foods rich in Protein: Meat, eggs, nuts.
Urine: The body’s excretorial waste.
Calcium: Found in Milk, cheese, mineral water; used for growth and repair of
bone and cartilage tissue. Prevents rickets; malformed bones.
Iron: Found in tomatoes, liver and kidneys. Part of haemoglobin in rbc. Prevents
anaemia (tiredness, headaches).
Phosphorous: Found in many foods; important for bones and teeth.
Sodium: Found in salt. Prevents cramps.
Iodine: Found in sea food, and drinking water. Helps to prevent goitre.
Vitamin A: Found in liver and carrots. Prevents night blindness (exophthalmia).
Vitamin D: Found in fish liver oil. Prevents richets.
Vitamin E: Found in milk, egg yolk, lettuce. Prevents sterility.
Vitamin K: Found in cabbage, spinach, fish liver. Important for blood
coagulation.
Fat soluble Vitamins: Vitamins A, D, E, K.
Water Soluble Vitamins: Vitamins B1, B2, B6, C.
Vitamin B1: Found in Pork, eggs, leafy green vegetables. Prevents beriberi
(weakness, irregular heartbeat, partial paralysis)
Vitamin B2: Found in liver, milk, dark green vegetables. Prevents Skin lesions.
Niacin (B6): Found in liver, poultry, canned tuna. Prevents pellagra (metal
confusion, diarrhoea)
Vitamin C: Found in citrus fruit. Prevents Scurvy. (bleeding gums)
Enzymes: Biological catalysts.
Denatured: Proteins like enzymes get denatured by heat (loses its properties).
Substrate: The food on which an enzyme acts.
Active site: Where the substrate enters.
Products: The substances released by the enzymes after the reaction is completed.

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Biological Washing Powders: Washing powders that contain enzymes.
Protease: An enzymes used for tenderising meat.
Amylase: Found in saliva and duodenum. Used in industry to convert starch to
sugars to make syrups and juices.
Cyanide: Enzyme inhibitor.
Arsenic: Enzyme inhibitor.
Incisors: Teeth adapted for cutting food.
Canines: for holing and tearing.
Premolars: For chewing and grinding food.
Molars: For chewing and grinding food.
Crown: The upper part of the tooth.
Root: The lower part of the tooth.
Dental Caries: Tooth decay.
Cusps: ‘hills’ on the teeth of carnivores and omnivores.
Saprophytic: When saprophytic organisms such as fungi and some bacteria that
feed on dead decaying matter. Saprophytes are useful to the environment because
they recycle nutrients.
Parasitic: When parasitic organisms feed on or in another organism harming it.
Holozoic (heterotrophic): Animals feed heterotrophically, because they must
search for their food. Herbivores eat vegetable matter and have special bodily
structures to help them digest cellulose. Carnivores eat meat and are usually
predators. Omnivores, such as humans eat both meat and vegetable matter.
Holophytic (autotrophic): Plants feed with this type of feeding. They are able to
make their own food by photosynthesis.
Ingestion: food is ate, chewed and mixed with saliva.
Digestion: Begins from the mouth by salivary amylase (starch-breaking enzyme)
and continues till the duodenum, were enzymes chemically break down food into
simpler soluble products, stage by stage, and prepare nutrients for absorption.
Absorption: the blood absorbs soluble products.
Assimilation: the nutrients are then assimilated (taken to) various organs around
the body.
Defecation (Egestion): Undigested matter such as fiber is egested (moved out) of
the body. [Do not mix excretion with egesting or defecation! Excretion is the
removal of waste products made by chemicals reaction within the cells; e.g.

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excreting urine.
Physical digestion: teeth to increase surface area for enzyme action to break
down food.
Chemical digestion: food is mixed with saliva and salivary amylase breaks down
some starch from the food (if there is) into maltose. The chemical digestion
continues till the duodenum.
Lysozyme: Chemical found in the saliva used to kill bacteria.
Oesophagus: Gullet.
Pepsinogen: an inactive form of pepsin that is then activated by the hydrochloric
acid.
Pepsin: digestive enzyme, which breaks down proteins into smaller polypeptides.
Mucus: Protects the stomach from being digested by the enzymes.
Hydrochloric acid (HCl acid): kills bacteria and provides and acidic pH for
pepsin to work.

From the intestinal wall:, Mainly five enzymes are produced:
Trypsin: breaks down polypeptides into dipeptides.
Maltase: breaks down maltose into glucose.
Lipase: breaks down fates (lipids) into fatty acids and glycerol.
Peptidases: breaks down dipeptides into amino acids
Sucrase: breaks down sucrose into glucose

From the pancreas mainly 4 chemicals are produced:
Sodium hydrogen carbonate (NaHCO3): neutralizes acids from the stomach and
provides alkaline pH in the duodenum.
Trypsin: breaks down starch into maltose.
Pancreatic amylase: breaks down starch into maltose.
Lipase: Breaks down fats into fatty acids and glycerol.

Liver: The largest and very important internal organ found in the body. Among its
functions, it produces bile, breaks down drugs and alcohol, and converts the final
products of digestion into glycerol for storage. The liver cells help the blood to
assimilate food substances and to excrete waste materials and toxins, as well as
products such as steroids, oestrogen, and other hormones. The liver also stores

Page 29


iron, vitamin A, many of the B-complex vitamins, and vitamin D.
Detoxification: One of the functions of the liver, where the liver breaks down
drugs.
Deamination: The destruction of red blood cells so that the body forms new ones.
This function is carried out by the liver, in fact, the liver is a source of iron.
Duodenum: The first part of the small intestine. It continues digestion of food and
it receives enzymes from the intestinal wall and from the pancreas. It receives bile
that the liver produced from the gall bladder.
Gall Bladder: An organ used to store bile.
Bile: A green chemical used for emulsification.
Emulsification: The process by which bile does detergent action on lipids. Fat
molecules are too large to be absorbed by the blood so it is broken down into
smaller molecules by the bile.
Hepatic Artery: The artery that gives blood from the heart to the liver.
Hepatic Portal Vein: The vein that transports blood rich in soluble products of
digestion from the ileum to the liver.
Hepatic Vein: The vein that transports blood from the liver to the heart.
Ileum: A long part of the gut where digestion stops and absorption starts.
Absorption is done by the villi surrounding its walls. It ends in the large intestine.
Villi: Small structures found on the walls of the ileum where absorption stakes
place. There are millions of them to ensure that all nutrients have been absorbed.
Microvilli: Even smaller villi on the large villi in the ileum.
Mucus-Secreting Cell: Cells present in the trachea, nose, stomach wall, the
intestinal wall and on the epithelium of the villi, also called goblet cells.
Epithelium: The first thin layer of cells of the villi and other small structures in
the body.
Lacteal: The structure found in the villi that absorbs fat droplets.
Venule: The vein that carries amino acids and monosaccharides. They are found
in the villi.
Arteriole: The vein that transports blood in the villi.
Appendix: A vestigial organ located the between the ileum and colon.
Caesium: Another vestigial organ located near the appendix.
Vestigial Organ: An organ that has no known functions. Vestigial organs found
in the body are the caesium and the appendix. Ancient human beings who ate

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mainly vegetable matter probably used these organs. Then, by evolution, these
organs ceased from being used. They were home to cellulose-digesting bacteria.
Large Intestine: Part of the alimentary canal. It is dividing into the colon and
rectum.
Colon: The first part of the large intestine where water and fluid are absorbed. It
ends in the rectum.
Herbivores: Vegetable eating animals.
Ruminants: Herbivores with a special type of stomach called a rumen.
Cellulose: A cellulose-digesting enzyme produced by certain bacteria found in
herbivores.
Mutualistic Relationship: A type of relationship between organisms where both
animals are benefiting from each other. An example of such relationships is the
relationship between the cellulose-digesting bacteria in the caesium and appendix
of ruminants.
Rumen: A large stomach with 3 compartments found in ruminants.
Regurgitation: Ruminants bring the food they have already eaten and swallowed
back to their mouth to continue chewing it.
Respiration: A chemical reaction catalysed by enzymes where (in case of aerobic
respiration) oxygen combines with glucose to form carbon dioxide, water and
energy.
Aerobic: A type of respiration where oxygen is involved.
Anaerobic: A type of respiration that does not involve oxygen and doesn’t
produce as much energy as aerobic respiration.
Mitochondria/Mitochondrion: An organelle found in all cells that do respiration.
Gas exchange: The process where oxygen is absorbed by the blood and carbon
dioxide is exhaled out of the body. Don’t mix gas exchange with respiration.
Respiration is a chemical reaction while gas exchange is just the exchange of
gases.
Organic Molecules: Molecule containing carbon.
Alcoholic Fermentation: A type of anaerobic respiration where alcohol is a
product of the chemical reaction.
Lactic Acid: An acid produced in muscle tissues during strenuous exercise when
there is lack of oxygen.
Oxygen Dept: When lactic acid is produce, a state called oxygen debt occurs,

Page 31


when after exercise the body continues breathing heavily so re gain all the oxygen
needed by the muscle cells to break down lactic acid in carbon dioxide and water.
Aerobic respiration: A type of respiration where oxygen is involved. An example
of this type of respiration is alcoholic fermentation.
Lungs: Major organs in some animals needed for gas exchange.
Trachea: Otherwise called windpipe. The second pipe from where air passes and
is filtered by cilia and mucus secreting cells. Rings of cartilage to make it stiff
surround this structure and so that it doesn’t get bent.
Bronchus: One of the pipes from which air passes before going inside the lungs.
There are two bronchi and they are attached to the trachea. Rings of cartilage to
make it stiff surround these structures.
Alveoli: Also called air sacks. The place where the actual gas-exchange takes
place. Tiny structures surrounded by many blood vessels to ensure that gas
exchange takes place rapidly and efficiently.
Pleural Membrane: A thin membrane that covers the inside of the ribs and the
outside of the lungs. A film of moisture between the two layers lets them slide
easily over each other as the lungs move.
Intercostals: Muscles between they ribs that contract and relax during inhalation
and exhalation.
Inhalation: Breathing in.
Exhalation: Breathing out.
Breathing: A series of movements made by intercostals, the rib cage and
pectorals to enable the air to get into the lungs. These movements are shown here
in this diagram.
Ribs: Bones surrounding the lungs.
Bronchioles: Small pipes from which air passes. These are found inside the lungs.
Pulmonary Vein/Artery: Blood vessels from which blood passes from and into
the heart. They are connected to the lungs and the heart.
Diaphragm: A muscle present only in mammals to ease inhalation and
exhalation. This muscle is found under the lungs.
Plasma: Part of the fluid in blood.
Hydrogen carbonate ions: Carbon dioxide is transported in the blood by this ion.
HCO3-.
Blood capillaries: Very, very small blood vessels that surround alveoli. They are

Page 32


very thin and tender and are found in many other places in the body.
Tar: A chemical found in cigarettes.
Carbon monoxide: A poisonous gas released by lightened cigarettes.
Nicotine: Colourless, oily, liquid alkaloid, C10H14N2 that constitutes the principal
active chemical constituent of tobacco.
Epithelium: A layer of cells that serves as a protective covering over a surface,
such as the outside of an organ or the lining of a cavity wall in the body.
Goblet Cells: Mucus secreting cells.
Diseases caused by smoking: Bronchitis, Emphysema and Lung Cancer
Other lung Diseases: Pneumonia, TB (Tuberculosis) and Dust Diseases.
Poisonous gases in the air: Carbon monoxide, sulphur dioxide, nitrogen dioxide,
ozone.

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Part 2 of Biology Notes (Rest of syllabus)

TOPIC 5: HOMEOSTASIS
KEEPING A CONSTANT BODY ENVIRONMENT

Introduction
There are mainly 4 organs that help the body to keep a constant body
environment: the lungs, the liver, the skin and the kidneys.

Lungs
The lungs are responsible to exchange of gases in the body. They exchange
carbon dioxide with oxygen from the air. Also, the lungs must provide the oxygen
with a temperature of around 37 degress Celsius so that chemical reactions
involving oxygen can take place.

The Liver
The liver is a major organ in the human body that makes a large amount of
chemical reactions that produce heat (chemical reactions that produce heat are
called exothermic).
Therefore, the liver produces all the necessary heat for the body to keep its
internal temperature around 37oC.

Skin
The skin is responsible for transferring excess heat from inside the body to the
outside environment. For that reason it is one of the organs that does homeostasis.
It also protects the body from germs.

Kidneys
The kidneys are responsible for osmoregulation, i.e. to control the amount of
water in the body, by filtering blood from salts, water and waste products (urea).
Blood is involved and so the kidneys are also part of homeostasis, because blood
transports heat and helps to keep the body at a constant temperature.

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The Excretory System
The excretory system is the system responsible for the disposal of waste material
produced by the body --Urine. The major organs in the excretory system are the
kidneys. The body can survive with just one kidney, but with none, the person
must use the kidney machine (explained in the following pages) or else he or she
dies. The function of the kidneys is to filter blood from urea (waste produced by
chemical reactions in the body) excess water, and excess salts. This process is
called ultra-filtration and it is done by nephrons (explained further in the
following pages)

The Kindey
The diagram below shows the kidneys, the bladder and blood vessels connected to
it.

Pyramid Medulla

Kidney Wall
Pelvis
Renal Vein
Renal Artery
Cortex

Urither

Renal Vein: The vein that transports blood OUT OF the kidneys. Blood in the
renal vein is deoxidized or reduced (without oxygen) and filtered by kidneys, thus
it is clean.
Renal Artery: The artery that transports blood INTO the kidneys. Blood in the
renal artery is full of oxygen but also full of waste (urea and salts) thus it has to
be filtered.

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Ureters: Carry urine (urea, excess water, excess salts) into the bladder.
Bladder: The structure, which stores urine before it is excreted out of the body.
Ring of Muscle: A ring of muscle that is kept closed before one goes to the toilet
to excrete the urine. They control the passage of urine out of the body.
Urethra: The last structure from which urine passes before going out of the body.

Renal Vein
Renal Artery

Right Kidney

Ureters

Bladder

Ring of Muscles

Urethra

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The Nephron

First Coiled Tubule (all
glucose re-absorbed) Second Coiled Tubule
(all useful salts re-
absorbed)

%

The nephron is the structure, half inside a pyramid and the other half inside the
cortex, where blood is filtered (ultra-filtered) from urea, excess water and salts.
The structure of the nephron is shown above.
Blood in the renal artery is oxygenated and with urea.
Glomerulus: A network of blood capillaries.
Selective re-absorption: Not everything is re-absorbed at once, but every tubule
re-absorbs a particular nutrient.
The renal artery is wider than the blood vessel through which it moves out. This
increases pressure in the glomerulus. The pressure causes some constituents of
blood to leak out of the capillary tube.
The filtrate contains glucose, urea, water and salts. Proteins and Erythrocytes
(red blood cells) are too large and they don’t pass through the capillary walls.
This filtration takes place on a microscopic scale. It is known as
ULTRAFILTRATION. This takes place in the Bowman’s capsule.
The First Coiled Tubule: Here, all the glucose that passed from the capillary
walls to the nephron is re-absorbed. In a diabetic person, not all glucose is re-
absorbed and it is found in Urine. Since each part of the nephron re-absorbs the
useful nutrients one at a time, it is called a selective re-absorption.
Loop of Henle: Here some water is re-absorbed. The amount of water re-absorbed
depends on the concentration of blood. If it is concentrated (has little water), a lot
of water will be re-absorbed. If it is not that concentrated it will re-absorb less

Page 37


water. The amount of water re-absorbed also depends on a chemical called ADH
(Anti-diuretic hormone). ADH is produce by the pituitary gland in the brain
and causes thirst; hence, more water will be re-absorbed by the loop of henle.
When there is a lot of ADH, urine is full of waste and with relatively few water.
When ADH is not found in the blood, urine is in large amounts, very dilute (full of
water) and with few waste.
Second Coiled Tubule: Here some salts (Na+, Cl-) are re-absorbed.
Collecting Duct: Here, urea, water and salts pass down the ureter into the
bladder which stores urine. Urine is a mixture of urea, water and salts.

Constituents of Blood and Urine
Substance Percentage in Blood Percentage in Urine

Water 92% 95%
Erythrocytes (red blood 7% 0%
cells)

Glucose 0.1% 0%
Salts 0.4% 0.6%
Urea 0.03% 2%

Page 38


The Skin
The skin is the organ responsible for: Protection, Sensitivity, and Temperature
Control (Homeostasis).
As a Protective Organ
The skin acts as a barrier against foreign bodies (germs). In some animals, it has the
same colour as its surroundings (camouflage), other animals are covered in spines or
produce an oil to make it water proof.
As a Sense Organ
The skin contains many receptors or sense organs (heat receptors, cold receptors,
pressure receptors, pain receptors, touch receptors) and these make the skin
sensitive.
As the Organ which Controls Temperature
Warm blooded animals are called Endothermic or homoeothermic (warm-
blooded). This means that they have a constant body temperature. Some animals have
blubber (thick fat layer) under their skin to keep warm in very cold weather; e.g.
Penguins, polar bears)
Ectothermic or poikilothermic (cold-blooded) animals have their internal
temperature controlled by their surroundings. In fact, some reptiles (cold-blooded
animals) stay long hours in the sun to heat up their bodies.

The Human Skin
The diagram below shows a cross section of the skin. The human skin has 3 layers:
the epidermis (made up of dead cells) the dermis (where there are the major living
cells and nerves) and the fat layer (full of fat for insulation).

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Hair erector
Oil

Temperature Control
When it is Hot When it is Cold
Skin loses heat Skin doesn’t lose heat
Sweating (oil glands produce sweat that Shivering takes Place (uncontrolled
passes through the sweat duct and constriction of muscles)
evaporates through the sweat pore)
Hair erector muscle relaxes and hair is Hair erector muscle contracts and hair
loosened and touches with skin so that no erects so that air and heat is trapped
heat and air is trapped. between the hair and the skin.
Blood vessels travel at the surface of the Blood vessels travel deep down the
skin. skin.
Vaso-dilation takes place (Blood vessels Vaso-constriction (blood vessels get
widen thus more heat is lost) narrower so that less heat is lost to the
environment.

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TOPIC 6 THE HEART
The heart is a 4 chambered double pump, responsible of circulating oxygenated
blood around the body and deoxygenated blood to the lungs. An adult heart pumps
about 5 litres of blood per minute. The heart, has 2 upper chambers called atria
(singular: Atrium) and 2 lower chambers called ventricles. The heart has 2 pumps
and circulates oxygenated and de-oxygenated blood. This is known as double
circulation.
Pulmonary artery Aorta (Blood to
(blood head and body)
Vena Cava to lungs)
(blood
Pulmonary vein
from head
(blood from
and body)
lungs)

Right atrium
Left atrium

Bicuspid valves

Tricuspid valves
Semi-lunar
Left ventricle valves
Right ventricle

Oxygenated Blood ‘Tendon’

Deoxygenated Blood
Aorta: The largest artery found in the body. It receives oxygenated blood from the
heart and then divides into many arteries all around the body.
Vena Cava: The largest vein found in the body. It transports de-oxygenated blood to
the heart from the rest of the body. De-oxygenated blood is then transported to the
lungs to be oxygenated.
Atrium: One of the upper chambers of the heart.
Tricuspid valve: A valve that lets blood to pass from the right atrium to the right
ventricle.

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Ventricle: one of the lower chambers of the heart.
Bicuspid valve: the valve that lets blood to pass from the left atrium to the left
ventricle.
Pulmonary Vein: The vein that carries oxygenated blood to the left atrium.
Semi-lunar valves: the 2 valves which let blood pass from the lower ventricle to the
aorta and the pulmonary artery.
Pulmonary Artery: The artery that carries deoxygenated blood from the heart to the
lungs.
Tendon: Special fibres in the heart muscle.

A Double circulation
This diagram shows the double circulation of the blood. The arteries are on the right
hand side of the diagram while the veins are on the left hand side.

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Biology for you Stanley Thornes (publishes) Ltd. © Gareth Williams


The following table shows the various blood vessels of the body, their route and
function. It is important to view the blood vessels shown here in the different organs
studied this year.

Blood Vessels
Blood Vessel Route Function
Hepatic Artery Heart Liver Carries oxygenated
blood from the heart to
the liver
Hepatic Vein Liver Heart Carries deoxygenated
blood from the liver to
the heart
Hepatic Portal Vein Ileum Liver Carries blood filled with
amino acids, glucose,
water, fatty acids and
glycerol and salts from
the small intestine
(Ileum) to the liver to be
stored
Renal Artery Heart Kidney Carries oxygenated
blood full of waste from
the heart to the lungs.
Renal Vein Kidney Heart Carries filtered blood
from the kidneys to the
heart.
Pulmonary Vein Lungs Heart Carries oxygenated
blood from the lungs to
the left atrium of the
heart.
Pulmonart Artery Heart Lungs Carries deoxygenated
blood from the heart to
the lungs
Aorta Heart Body Carries oxygenated

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blood from the left
ventricle of the heart to
the rest of the body
Vena Cava Body Heart Carries deoxygenated
blood from the body to
the right atrium of the
heart.

The Difference between Arteries and Veins
The main difference between arties and veins is that arteries carry blood from the heat
to all the other tissues in the body while veins carry blood from the body to the heart.
Usually, veins carry deoxygenated blood and arteries carry oxygenated blood. One
exception is that the pulmonary artery carries deoxygenated blood from the body to
the heart and the pulmonary vein carry oxygenated blood from the heart to the lungs.
Veins have valves so that blood goes in the right direction; arteries don’t have valves
because blood flows with a lot of pressure inside the arteries and backflow of blood is
impossible. Arteries have a thin lumen (inner structure of the blood vessel, where
blood passes) because blood flows with a high pressure and the walls have to be wide,
while veins have a wide lumen.
Arteries have an elastic wall, but veins don’t have an elastic wall.
Artery Vein

Thin Lumen
Wide Lumen

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Blood
Blood is the main fluid found in the body. The functions of blood are the following:
• The fluid that carries all the nutrients and oxygen around the body to all
cells
• Transports heat around the body
• Transports hormones
• Transports antibodies
• Important for excretion of urea, excess water and salts
• Blood clotting
• Controls the amount of water and chemicals in the body tissues

The body has about 6 litres of blood (9% body mass). There are 4 blood groups in
humans, namely A, B, O and AB (rarest) Blood is made up of Erythrocytes (Red
Blood Cells), Leucocytes (white blood cells), and Plasma.

Erythrocytes (red-blood cells)
Erythrocytes are numerous, have no nucleus and have a bi-concave shape (for a larger
surface area) to carry oxygen (O2) more efficiently.
Red-blood cells are made in the bone marrow and their life span is about 4 months.
Deamination (taking away iron from the red-blood cells, hence, destroying them to
be replaced by new ones) takes place in the liver.
Erythrocytes contain haemoglobin that when it is oxygenated, haemoglobin becomes
oxyhaemoglobin. Carbon dioxide travels in the plasma as (hydrogen carbonate ions)
HCO3- ions. This also helps erythrocytes to carry O2.
Carbon monoxide (CO) combines with the haemoglobin 300 times faster than O2,
thus it is very harmful. This gas is produced by cigarettes and burning of fuels such as
in cars.
People living in high altitudes have a greater number of Erythrocytes since less
oxygen is present in the air. Their body has adapted to the environment. This is
known as acclimatization.

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Cross section
Front view

These two diagrams above show erythrocytes, viewed from the front and a cross
section.

Leucocytes
Leucocytes are lager than Erythrocytes. They‘re colourless, and are made in the red
bone marrow and the lymph glands. There are various types of leucocytes:
Phagocytes and Lymphocytes are two of these types.
Phagocytes engulf the germs, which leaves remains of dead germs and leucocytes
called pus. The process by which phagocytes engulf germs is similar to the way
amoebas feed and is known as phagocytosis.
Lymphocytes produce antibodies, detect the germ’s antigen and it can either make
the germ burst, or clump together, or make them harmless.
Platelets are Fragments of cells also found in the blood.

Lobed Nucleus

Large Nucleus
Lymphocyte
Phagocyte

Plasma
Plasma is a sticky fluid, containing water, salts, food substances, urea, hormones,
platelets, prothrombin, blood proteins, fibrinogen (for blood clotting), globulin
(helps to destroy germs), albumin (makes blood thick and viscous).

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Blood Clotting
When a blood vessel is damaged, platelets enter the wound. Platelets activate
prothrombin into thrombin. Then thrombin activates fibrinogen into fibrin, which
is insoluble and forms solid threads that forms the cloth.

Platelets
Hemophilia is a genetic disease where blood fails to clot.

Tissue Fluid
Tissue fluid is a liquid found around cells. This watery liquid keeps the cells in the
right condition, providing them with oxygen and all the necessary nutrients. Tissue
fluid is drained from blood capillaries. It is a yellowish in colour because it contains
urea when it is full of waste.
Useful substances pass from the tissue fluid to the cells and urea, excess water and
waste substances pass from the cells to the tissue fluid.
Tissue fluid drains in the lymph vessels. Lymph vessels transport the fluid called
lymph. Lymph vessels also have valves like veins do.
Along these lymph vessels, there are lymph nodes. Lymph nodes are structures that
produce cells similar to white blood cells that fight germs. When there is an infection,
these lymph nodes become swollen and painful. Inside them, bacteria and germs are
being trapped and killed by these cells.

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TOPIC 6 PHOTOSYNTHESIS
What is Photosynthesis?
Photosynthesis is a chemical reaction in which carbon dioxide and water is changed to
glucose by the action of chlorophyll and with sunlight energy.
light
6C 2 +6 2 → C6 12 6 +6 2
chlorophyl l

Carbon dioxide + Water Glucose + Oxygen

Raw Materials
Products

Water goes upwards from
the roots

Glucose goes downwards
from the leafs

Water is
absorbed by
the roots by
osmosis

Photosynthesis is performed by plants, green algae, and plant-like protists such as the
Euglena. To photosynthesize, a plant, or other heterotrophic organism, needs Carbon
dioxide, water, light and chlorophyll.
Plants store food as starch. Thus, after producing glucose, the plant transforms
glucose into starch, which is an insoluble polysaccharide, to be stored. Glucose goes
down the stem towards the roots in the Phloem vessels in the vascular bundles,
while water goes upwards the stem from the roots through the xylem vessels in the
vascular bundles.
To find out if the plant has performed photosynthesis, you must do a starch test on a
leaf. If the leaf has starch, then it must have photosynthesized but if the leaf has no

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starch, that means the plant has not photosynthesized and it used up all the starch it
had in the leaf to stay alive.

Testing a Leaf for Starch
1. Cut a leaf from a plant and boil it in a beaker with water to soften it.
2. Dip it in alcohol (ethanol) to decolorize it. The leaf must be put in a boiling
tube dipped in warm water. Don’t heat up the boiling tube with alcohol
because it is flammable.
3. Put the decolorized leaf again in the warm water to soften it again.
4. Put the leaf on a white tile and add two drops of iodine on the leaf.

Results for Iodine test
If the iodine turns blue-black, then the leaf has starch, hence it has photosynthesized.

De-starching
De-starching occurs when the plant doesn’t make any photosynthesis (e.g. because it
is in the dark) and so the plant uses its stored starch stored for energy. It turns starch
into glucose and uses it up.

The Importance of Photosynthesis
Photosynthesis is the process in which plants get the energy from. Without it, plants
wouldn’t exist. Thus photosynthesis is indirectly useful for other animals, which eat
plants.
Photosynthesis releases oxygen as a by-product of its reaction. Oxygen is used by
almost all living organisms for the breakdown of glucose and release of energy.

Inside a Leaf
Photosynthesis happens in plants, exactly in the chloroplasts that are found in leaves.
The green part of the plant is usually the leaf, and this is because chloroplasts have a
special green chemical called chlorophyll that converts sunlight into chemical
energy.
The following picture shows a cross section of a typical leaf.

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Waxy cuticle
Upper Epidermis

Palisade layer

Air spaces

Spongy layer

Lower epidermis

Stomata
Vascular bundle
(vein)

The waxy cuticle is the uppermost part of the leaf. It makes the leaf waterproof and
protects the leaf from losing water. It is transparent.
The upper epidermis is the second layer of the leaf, but the first layer that is made up
of living cells. The cells in this layer don’t have chloroplasts, so that light passes
directly into next layer;
The palisade layer is a thick layer of elongated cells packed with chloroplasts. It is
here that most photosynthesis takes place.
The spongy layer is characterized by air spaces between the cells, so diffusion of
gases takes place efficiently, as photosynthesis uses carbon dioxide and produces
oxygen. The cells in the spongy layer also have chloroplasts.
The palisade and the spongy layer are made up of cells called mesophyll cells.
The lower epidermis is similar to the upper epidermis, with the cells making it up
that don’t have chloroplasts, but this layer has stomata; tiny holes from which
exchange of gases takes place. Stomata are surrounded by two guard cells, which are
the only cells in the lower epidermis that have chloroplasts. These cells have thin cell
walls on the outer side but wide cell walls on the inner side.

The following picture shows the structure of guard cells:

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Stomata

Thick cell wall
Think cell wall

In the leave there are also vascular bundles (plant veins) that are made up of xylem
and phloem vessels. Water and soluble minerals pass from the xylem vessels while
sugars pass from the phloem vessels.

How are leaves adapted for photosynthesis
Leaves have numerous adaptations to ease photosynthesis.
They have a large surface area, for absorbing light and carbon dioxide.
Leaves are arranged so that they don’t over-shadow each other, and all of them
receive light.
They have a lot of stomata in the lower epidermis for gas exchange, carbon
dioxide gets in and oxygen does out while photosynthesis takes place.
Leaves are thin to allow fast diffusion of carbon dioxide.
The waxy cuticle and epidermis are transparent to allow light passage
throughout the leaf.
The place were most photosynthesis takes place; the palisade layer, is found
near the upper side of the leaf, were most of the light comes.
The palisade layer is made up of palisade mesophyll cells, which are packed
with chloroplast, and these organelles move around the cell so as to find the
best position to find light.

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There are air spaces around the spongy mesophyll cells to allow gas
circulation.

Glucose and sugars
In the chemical reaction of photosynthesis, glucose and other sugars are produced.
With these, the plant can do a number of things:
1. Respiration: like any other living thing, plants need energy. Plants and
animals do this my oxidizing glucose in the process called respiration,
releasing water and carbon dioxide.
2. Translocation: this means that the excess sugars produced by the leaves are
transported into other parts of the plant, through the phloem vessels, that
cannot make photosynthesis, such as roots, to supply their needs.
3. Production of cell material: from sugars, the plant can make other important
chemical and material such as proteins, fats and oils. In order to make some
of these materials, the plants must also have other minerals absorbed from the
soil such as nitrogen, sulphur and potassium. For instance, the plant must
have a supply of nitrogen in order to produce proteins.
4. Conversion to starch: Enzymes in the plant convert glucose into starch. This
is done so that glucose can be stored. Since glucose is soluble, it cannot be
stored; it can only be used straight away or transported. Thus the plant
converts it into starch, which is insoluble and stores it. Starch is stored in
special storage organs, which are formed by part of the plant swelling up.
These storage organs can be formed in roots, leaves or stems. When energy is
needed and no glucose is formed by photosynthesis, such as when it is dark,
the chain of glucose molecules, which makes starch, uncoils back into single
glucose molecules in a process called hydrolysis. When a plant performs
hydrolysis, starch is mobilised, which means it can now be moved or
transported in a solution since glucose is water-soluble.
5. Storage in germination structures: the plant stores some food for the next
generation by storing starch or fat in their seeds and fruits. When a seed
germinates, food passes from the seed to the new growing plant until it can
make its own food by photosynthesis. Some plants store food in tubers or
bulbs that can also germinate.

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Important Minerals for Plants
As mentioned above, apart from carbon dioxide and water, the plant needs other
substances important for the formation of other material. Some minerals needed by
plants are listed here.
Mineral Symbol Importance Deficiency
Nitrogen N To make amino Poor growth and
acids, proteins and chlorosis
chlorophyll (yellowing of the
leaf)
Potassium K Helps chlorophyll Abnormal leaf
and protein shape, chlorosis
formation,
resistance to
disease
Calcium Ca Formation of cell Abnormal leaf
wall cement in the shape, poor buds
middle lamella and slow growth
Magnesium Mg Centre of Chlorosis of old
chlorophyll leaves
molecule
Iron Fe Formation of Chlorosis of
chlorophyll young leaves
Sulphur S Formation of Chlorosis of
amino acids young leaves and
excessive root
growth
Phosphorous P Formation of ATP, Lack of energy,
DNA, for poor growth
respiration and
photosynthesis

If the soil is deficient in some of these important nutrients, one must add fertilizers in
order to replenish the soil with vital minerals. Fertilisers can be either artificial, such

Page 53

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