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The Need for Food
Explain in simple terms why food is required by animals
Three examples of food types are:
Carbohydrates
Proteins
Fats
Animals need food to fight off illnesses. You are now going to investigate why animals
need specific food types.
Carbohydrates
Carbohydrates are used to provide energy for everyday
activities e.g. movement
Fats
Fats are used to provide the body with energy for heat.
This is important to animals such as humans as they must
maintain a constant body temperature
Proteins
Body cell only last for a certain length of time and are then broken down.
Proteins are needed to build new cells to replace those that are worn out or damaged.
Young children need more protein than adults in order to grow properly.
In some Third World Countries, young children develop Kwashiorkor,
disease caused by protein deficiency. Their stomachs swell because they
cannot get rid of fluid.
1
State the chemical elements present in carbohydrates, proteins and fats
All carbohydrates, proteins and fats contain the elements carbon, hydrogen and
oxygen.
In addition, proteiNs contain Nitrogen.
Describe the simple structure of carbohydrates, proteins and fats in terms of simple
sugars, amino acids, fatty acids and glycerol
Some CARBOHYDRATES consist of long chains of glucose molecules,
e.g. starch
The basic units are glucose
Glucose, a simple sugar, is also
an example of a carbohydrate.
FAT molecules are made up of a glycerol molecule joined to three fatty acid molecules.
Fat molecule
Basic units
Glycerol
fatty acids
PROTEINS are long chains of amino acid molecules.
Protein molecule
Basic units
The shapes represent amino acids.
In each protein there are many
different amino acids.
2
State that digestion is the breakdown of large particles of food into smaller particles
to allow absorption into the blood stream through the small intestine
Before food can be absorbed into the bloodstream, large food particles must be broken
down into small food particles
Explain that digestion involves the breakdown of insoluble food substances into soluble
food substances
Digestion is the breakdown of large insoluble food particles into small
soluble food particles that can be absorbed across the wall of the small intestine into
the bloodstream.
Digestion starts in the mouth and is completed in the small intestine.
During digestion all carbohydrates are broken down into glucose, all proteins are broken
down into amino acids and all fats are broken down into fatty acids and glycerol.
Describe the role of different types of teeth in the mechanical breakdown of food in a
herbivore, a carnivore and an omnivore such as a human
Different mammals eat different foods. Mammals are grouped depending on their diet.
Carnivores eat other animals e.g. lion
Herbivores eat plants e.g. sheep
Omnivores eat both plants and animals e.g humans
Mammals have 4 types of teeth Incisors
Canines
Premolars
Molars
Teeth are important for the mechanical breakdown of food
Omnivore e.g. human
Teeth can cope with
plant and animal
material
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Carnivore e.g. dog
Teeth are adapted
for killing other
animals and
tearing flesh
Herbivore e.g. sheep
Their teeth are adapted
for chopping and grinding
grass
Type of
tooth
Sheep
Dog
Incisor
Function
Chop grass
Biting
Canine
Chop grass
Stab and hold prey
Premolar
Ridged
Grind food
Ridged
Grind food
Shear
Molar
Function
Crack bones
4
Human
Function
Chisel like
Biting
Pointed
Tearing
Uneven
Crushing and grinding
Uneven
Crushing and grinding
Identify in a diagram/model the main parts of the human alimentary canal and
associated organs (mouth, salivary glands, oesophagus, stomach, pancreas, liver, gall
bladder, small intestine, large intestine, appendix, rectum and anus)
The gut is a tube about 7 metres long, running from the mouth to the anus. Part of the
tube is coiled up to fit inside your body. Each part of the gut has a different job to do.
Functions of the gut
Mouth – mechanical breakdown of the food
Oesophagus – connects the mouth and the stomach
Stomach – churns food
Small intestine – absorbs digested food products
Large intestine – absorbs water
Rectum – stores waste
Anus – waste is excreted from here
Appendix – function unknown
5
State the sites of production of the main digestive juices in a mammal (salivary glands,
stomach, pancreas, liver, small intestine)
Site of
Digestive juice
production
Salivary glands
Saliva
Stomach
Gastric juice
Pancreas
Pancreatic juice
Liver
Bile
Small intestine
Intestinal juice
Bile is stored in the gall bladder
Explain the mechanism of peristalsis
Food cannot move along the gut itself it has to be pushed.
Muscles in the gut wall do this. Muscles behind the food
contract, muscles in front of the food relax. The action
of the muscles pushes the food along the gut. This muscular
pushing of food is called peristalsis.
State that different enzymes are responsible for the breakdown of carbohydrates,
proteins and fats
6
Give an example of an amylase, a protease and a lipase. State their substrates and
products.
Salivary amylase is an amylase enzyme produced in saliva by the salivary glands.
Salivary amylase is active in the mouth. Salivary amylase breaks large carbohydrates
such as starch into smaller molecules of maltose.
Pepsin is a protease enzyme that is produced in the stomach. Proteins are digested by
proteases into peptides which are then digested into the basic units amino acids.
The final stages of digestion take place in the small intestine. Bile (produce in the
liver but stored in the gall bladder) is added. Pancreatic juice is also added from the
pancreas and contains enzymes.
All carbohydrates are broken down into glucose
All proteins/peptides are broken down into amino acids
Pancreatic lipase is produced in the pancreas but is active in the small intestine. It
breaks a fat molecule into 1 glycerol molecule and 3 fatty acids. The fatty acids lower
the pH.
Site of
Enzyme group
Enzyme
Substrate
Product(s)
production
Salivary glands
Amylase
Salivary
carbohydrates maltose
amylase
Stomach
Protease
Pepsin
protein
peptides
Pancreas
Lipase
Pancreatic
fats
Fatty acids +
lipase
glycerol
7
Explain how contractions of the stomach help in the chemical breakdown of food
The stomach is a muscular bag. There is a muscle at
either end of the stomach that can close to prevent
food from passing in or out of the stomach.
The stomach produces gastric juices which contains
pepsin and hydrochloric acid.
The muscles of the stomach wall relax and contract which churns and mixes the food
with gastric juice, speeding up digestion.
Acid production by the stomach is needed as the enzyme pepsin is most active when the
pH is acidic.
Explain how the structure of the small intestine is related to its function
In the small intestine, the products of digestion pass into the blood.
The small intestine is adapted to its function of absorption.
 It is long
 It is folded which increases the surface area
 It has many finger-like projections which also increase the surface area
 The lining is very thin allow rapid absorption of digested food
 It has a good blood supply which means that absorbed food is taken away quickly
Explain how the structure of a villus, including the lacteal and the blood capillaries, are
related to the absorption and transport of food.
The finger-like projections are called villi.
8
The villi are adapted for absorption
 The walls are only one cell thick which allows rapid absorption
 They contain many blood capillaries
 They contain lacteals which are part of the lymphatic system
Describe the role of the large intestine in water absorption and elimination
The wall of the large intestine absorbs most of the water from undigested food into
the bloodstream.
The undigested remains (faeces) are passed out of the body through the anus, this is
called elimination.
Reproduction
In order to survive, members of a species must reproduce – produce new members to
replace the ones which die.
Describe the main features of sperm and egg
A sperm is the male gamete (sex cell)
The tail allows the sperm to swim.
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The female gamete is called the egg
Cell membrane
nucleus
cytoplasm
The cytoplasm contains the food.
The nucleus contains the genetic information
Feature
Sperm
Egg
Size
small
large
Can it move by itself?
yes
no
Does it have food store?
no
yes
10
Describe the process of fertilisation
Fertilisation is the fusion (combining) of one sperm nucleus with one egg nucleus.
A sperm reaches an egg and its nucleus enters the egg. The 2 nuclei fuse to form a
zygote (a fertilised egg cell). The zygote is the first cell of the new individual.
The egg then forms a fertilisation membrane that stops other sperm from entering.
The zygote divides and rapidly becomes a ball of cells.
State that in some fish, sperm are deposited in water adjacent to the eggs and that in
mammals, sperm are deposited in the body of the female
Fertilisation can be
external - outside the female’s body
internal - inside the female’s body
or
Most fish produce a large number of sex cells that are released into the water
where fertilisation occurs. Fertilisation is external. Courtship rituals make sure that
the male and the female sex cells are released near one another
Sperm are chemically attracted to the egg cells and swim towards them.
In mammals fertilisation is internal as it occurs inside the female’s body.
11
Explain the importance of internal fertilisation to land-living animals
Internal fertilisation is essential for land living organisms as on land there is no water
to allow the sperm to swim to the eggs.
State that sperm cells are produced in the testes
The male reproductive system
Sperm cells are produced in the testes
During sexual intercourse the sperm enter the vas deferens/sperm ducts and are
released through the urethra, then the penis into the female’s vagina. They swim up
through the uterus into the oviducts (fallopian tubes)
12
State that eggs are produced in ovaries and are released into oviducts, where
fertilisation takes place
The female reproductive system
Eggs are produced in the ovaries and released at regular intervals into the oviducts.
Eggs cannot move by themselves. The oviduct moves the egg from the ovary towards
the uterus by the beating of hair-like cilia.
State that in fish, eggs are protected by flexible coverings and that the embryos
obtain food from enclosed yolk
Very few fish protect their fertilised eggs. Instead, the young fish develop inside a
flexible protective covering.
They obtain their food from the enclosed yolk.
13
Explain the relationship between the number of eggs/young produced and the degree of
protection afforded during fertilisation and development in fish and mammals
Internal fertilisation is more efficient than external fertilisation for a number of
reasons

The chance of fertilisation is greater as the sex cells are closer together when
released.
This means

Less sex cells need to be produced
In mammals, fertilised eggs develop inside the body of the female. In fish they develop
in the water.
Since fish eggs receive little or no protection many of the eggs may be eaten before
or after fertilisation.A fish has to release thousands of eggs to ensure that at least a
small proportion will survive into adulthood.
In contrast, animals that reproduce by internal fertilisation only need to release one or
a small number of eggs.
Describe how the fertilised egg passes down the oviduct and becomes attached to the
wall of the uterus, develops in the fluid of the amniotic sac and obtains food from the
maternal circulation
When the fertilised egg (zygote) is carried down the oviduct, it divides to produce a
ball of cells. When the zygote divides to form 2 cells, it is now called an embryo.
The embryo is carried to the uterus where it attaches to the wall of the uterus
(implantation).
14
The embryo develops in a bag of watery fluid called the amniotic sac which acts as a
cushion.
The mother’s and the embryo’s blood supplies are separate but in direct contact to
allow the exchange of materials.
Describe the structure and function of the placenta
Embryo mammals develop a placenta. It is attached to the placenta by its umbilical
cord.
15
Oxygen and dissolved food diffuse from the mother’s circulation to the embryo while
Carbon dioxide and other wastes diffuse in the opposite direction.
In addition, harmful substances in the mother’s body can cross the placenta
e.g. drugs, alcohol and nicotine, if the mother smokes
State that in a fish, like the trout, the young emerge from the eggs able to maintain
themselves
In fish the newly hatched young have no parental care. It feeds on the remains of its
yolk sac. When this runs out it starts to catch its own food.
State that at birth, the young of mammals are dependent on the adult for care and
protection
In mammals, the young leave the uterus at birth. It suckles milk from its mother.
It is dependent on its parents for care and protection for a long period of time.
Water and Waste
Identify the ways in which a mammal gains and loses water
In mammals the volume of water that is taken into the body must equal the volume
that is lost otherwise the cells in the body would be damaged.
Water gain
Mammals gain water in 3 main ways
Drinking
Eating
Chemical reactions
e.g
Glucose + oxygen  energy + carbon dioxide + water
Water loss
Sweat
Breath
Urine
Faeces
16
State that the kidneys are the main organs for regulating the water content in a
mammal
The kidneys are the main organs that a mammal uses to adjust the water content of its
blood. They do this by controlling the volume of urine produced.
Explain the role of ADH in the regulation of water balance
ADH (Anti-diuretic hormone) is produced by the pituitary gland in the brain. ADH
controls the volume of water is reabsorbed by the kidneys.
The brain monitors blood water levels. If the levels are too low, more ADH is
produced. This increases the volume of water retained in the body and results in less
urine being produced.
The effects are summarised in the table below.
Blood water
ADH level
concentration
Volume of water
Volume of urine Concentration
reabsorbed
produced
of urine
Too low
Increased
Increased
Decreased
Concentrated
Too high
Decreased
Decreased
Increased
Dilute
Identify the positions, and state the functions, of: the kidneys, renal arteries and
veins, ureter and bladder
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Part of urinary system
Function
Renal arteries
Carry unpurified blood to the kidneys
Kidney
Filter blood and remove waste substances
Renal veins
Carry purified blood from the kidneys to the rest of the body
Ureters
Carry urine from the kidneys to the bladder
Bladder
Stores urine
State that essential kidney functions are filtration of blood and reabsorption of useful
materials such as glucose
The kidney removes a poisonous substance called urea from the blood by the two
processes of filtration and reabsorption.
Filtration
All small molecules (glucose, water, salts, urea)in the blood pass through the filtering
unit into the kidney tubule.
Reabsorption
The useful substances such as glucose and water are reabsorbed back into the blood.
The waste substance urea is passed out in the urine.
18
Explain the process of urine production using a simple diagram of the nephron, to
include the Bowman’s capsule, glomerulus, blood capillaries and collecting duct
Urine is produced in microscopic structures called nephrons.
Each kidney has millions of nephrons.
Each nephron receives blood from the renal artery that ends in a glomerulus - a tiny
knot of blood capillaries surrounded by a Bowman’s capsule.
The blood is filtered in the glomerulus.
The filtrate collects in the Bowman’s capsule and enters the tubule.
Useful substances such as glucose, amino acids, water and some salt are reabsorbed
into blood capillaries which are closely wrapped round the tubule.
The waste, consisting of some salt, urea and water is urine.
The collecting duct collects the urine, taken to the ureters and then to the bladder.
State that urea is a waste product removed in the urine
State the source of urea in the body and describe how urea is transported to the
kidneys
Urea is a waste produced by the liver during the break down of excess amino acids.
Urea is carried from the liver to the kidneys by the blood.
19
Explain the implications of damage to the kidneys by accidents or disease
If the kidneys were damaged then the concentration of poisonous wastes in the blood
would build up to dangerous levels and the person would die without medical
intervention. We could survive with one working kidney.
Nowadays death can be prevented by
Kidney transplant: the person receives a donated healthy replacement kidney
Kidney dialysis:
blood is purified using a kidney machine, only waste is removed
Describe the relative benefits and limitations of replacement and “artificial” kidneys
Procedure
Advantage
Disadvantage
Kidney transplant
Person can lead a normal
life
Rejection may occur
Dialysis
Drugs taken to suppress rejection
lower the
body’s ability to fight disease
Shortage of donors
It is expensive to run
Saves lives
No problem with rejection
Person has to spend a lot of time in
hospital
Responding to the environment
All animals need to respond to their environment if they are to survive.
Give examples of environmental factors which affect behaviour
Three environmental factors which affect behaviour are:
Light
Humidity (moisture)
Chemicals
20
Describe the response of an animal to change in one environmental factor
A choice chamber allows us to look at the response of organisms to changes in
environmental factors. E.g. one half of the choice chamber is covered in black paper and
the other is left uncovered. Several woodlice are dropped in through the hole in the
middle. After a few minutes the woodlice are found to be in the dark part of the
chamber.
Explain the significance of given examples of response to environmental stimuli in the
life of the organism concerned
The response of animal to an environmental stimulus is important for its survival.
Woodlice are the prey of several predators. Their preference for the dark is an
advantage as it means that their predators cannot see them.
Woodlice move towards humidity as it will allow their gills to work more efficiently
Describe examples of rhythmical behaviour and in each case identify the external
trigger
Rhythmical behaviour in animals results from regular events in the environment.
The main features of rhythmical behaviour are:
–
it is regular
–
it is triggered by an external stimulus
–
it is controlled internally by the animal’s biological clock
e. g.
birds migrate in autumn which is triggered by decreasing day length
activity in shore animals is triggered by the movement of the tide
cockroaches have a daily activity cycle controlled by darkness
Explain the significance of given examples of rhythmical behaviour in the life of the
organism
Birds migrate so that there will be enough food for them to eat
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Many shore animals can only feed safely when covered by water and remain inactive
when the tide is out
Cockroaches are active at night so that they are not easily seen by predators
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