Animal survival
3A The need for food
Why do living things need food in order to survive?
There are three main food groups.
Elements
present
Basic Units
Diagram
Carbohydrates
Carbon
Hydrogen
Oxygen
Fats
Carbon
Hydrogen
Oxygen
Glucose
molecules
Fatty acids
and glycerol
Gl
Gl
Gl
Gl
Gl
G
L
Y
C
E
R
O
L
Protein
Carbon
Hydrogen
Oxygen
Nitrogen
Amino acids
fatty
acid
fatty
acid
fatty
acid
Carbohydrates are needed for energy
Fats are needed for energy and for storage of energy.
Proteins are needed for growth and repair.
Mammal diets
Mammals are specially adapted for the wide variety of food
they eat. There are three main groups of mammals whose teeth
are specialised for the food they eat:
Herbivores
Herbivores eat vegetation such as grass, leaves and fruit.
Examples are cattle, zebra, camel, and sheep.
Herbivore teeth are specialised by the molars having ridges
which help to grind the food.
Carnivores
Carnivores eat the flesh of other animals.
Examples are lions, dogs, otters and seals.
Carnivore teeth are specialised by having sharp canine teeth to
stab and rip open their prey and by having sharp premolar and
molar teeth to slice through bones and flesh.
Omnivores
Omnivores’ diet is made up of both flesh and vegetation.
Examples are humans, chimpanzees, bears and pigs.
Omnivore teeth are not particularly specialised as their teeth
have to be able to cope with all kinds of food.
Why do you need to digest your food?
Your food is a mixture of solid and liquids containing vitamins,
minerals, fibre, and water as well as carbohydrates, fats and
proteins. The food materials have to reach every cell in your
body and are carried by the blood system. How does the food
reach your blood?
The following experiment was set up:
Visking tubing
represents gut wall
Starch and glucose
represents food
Water represents
the blood
When the surrounding water (blood) is tested for glucose and
starch it is discovered that only glucose has got through the
Visking tubing because it is a smaller molecule than starch.
Another difference between starch and glucose is that glucose
is soluble in water but starch isn’t.
Therefore only small and soluble molecules can pass through into
the bloodstream. Digestion is the breakdown of large and
insoluble foods into small and soluble molecules so that they can
be absorbed into the bloodstream through the gut wall.
The human gut
The human gut is sometimes called the alimentary canal. It is a
muscular tube about 5 metres long, running from the mouth to
the anus. Part of the tube is coiled up to fit into the body.
Moving food
Food cannot move along the tube itself. It has to be pushed.
Muscular contractions of the gut wall force food along. This
wave of muscular contraction is called peristalsis. The wall of
the gut constricts (gets narrower) behind the food to push it
along. Meanwhile, in front of the food, the gut gets wider to let
the food through.
The stomach
The stomach is a muscular bag. Its wall produces a gastric juice
which chemically breaks down some protein molecules. For
digestion to work properly the food needs to be thoroughly
mixed with the gastric juice. This is doe by the muscles in the
wall of the stomach contracting and squeezing and moving the
contents about.
Small intestine
After the food has been churned and mixed with the gastric
juices in the stomach for a while, the partly digested food is
moved, a small amount at a time, into the small intestine.
The final products of digestion are then absorbed through the
intestine wall. Absorption happens more quickly if the surface
area of the inside of the small intestine is increased.
Lining the inside of the small intestine are finger-like
projections called villi. There are 3 ways the small intestine’s
surface area can be increased:
1. the thousands of villi significantly increase the surface
area
2. the small intestine is the longest part of the gut.
3. the inside of the small intestine is folded.
Large intestine
Any undigested food leaves the small intestine and passes into
the large intestine. No digestion takes place here.
The large intestine removes a lot of water from the undigested
food. Once the undigested material (faeces) reaches the
rectum, they will be stored until they are eliminated from the
anus.
anus
Enzyme action
Digestion in the gut involves the chemical breakdown of food.
Each type of food is broken down by a different chemical, an
enzyme.
Amylase
Starch
maltose
Protein
Fat
Pepsin
Lipase
peptides
fatty acids and glycerol
The main digestive juices are produced by the salivary glands,
the stomach, the liver the small intestine and the pancreas.
Most digestive juices contain enzymes. Bile which is produced by
the liver and stored in the gall bladder, has no enzymes.
There are three groups of enzymes involved in digestion. Each
group of enzymes acts on a different type of food called a
substrate. Each substrate gets broken down by the enzyme to
substances called products.
Enzyme group
Amylases
Proteases
Lipases
Enzyme
salivary
amylase
pepsin
lipase
Substrate
starch
Product
maltose
protein
fat
peptides
fatty acids
Bile does not contain any digestive enzymes but it is necessary
for digestion. It emulsifies fats to make it easier for lipase and
other fat digesting enzymes to breakdown the fat molecules ie
Large fat
droplet
Small fat
droplets
Absorbing food
After enzyme action, the digestion products become absorbed
by the blood. Most absorption takes place in the small intestine,
mainly by the villi.
A villus
The villus is well adapted for the job of absorbing digested
food:
a)
its wall is only one cell thick allowing digested food to pass
through quickly.
b)
it has its own blood supply (blood capillary) to carry away
glucose and amino acids.
c)
the lacteal carries away fatty acids and glycerol.
Summary of digestion
Region
of gut
Digestive
juice
Mouth
saliva
Made by
Enzymes substrate product
in the
juice
Salivary starch
Maltose
amylase
pepsin
protein
Peptides
Salivary
glands
Stomach Gastric
Gastric
juice
glands
Small
Pancreatic Pancreas Lipase
intestine juice
bile
Large
intestine
liver
Its job is to absorb water
Fat
Fatty
acids
and
glycerol
Protease Peptides
amino
acids
and
glycerol
Amylase
maltose
starch
Its job is to emulsify fats
3B
Reproduction
All living things reproduce and produce offspring similar to
them. If living things did not reproduce, then their numbers
would decrease and they would become extinct.
Sperm and eggs
Sperm and eggs are called gametes. They are the specialised
cells involved in reproduction.
Sperm
Nucleus
the male sex cell
Can swim
Smaller then the egg
tail
Egg
The female sex cell
Contains a food store
Much larger then the sperm
cytoplasm
nucleus
Cell membrane
Fertilisation
Fertilisation is when one sperm fuses with an egg. The sperm
loses its tail and the male nucleus fuses with the female nucleus.
A membrane called the fertilisation membrane then forms
around the fertilised egg preventing other sperm from entering.
The fertilised egg is called a zygote.
A zygote
Fertilisation membrane
Internal and external fertilisation
Internal fertilisation is when sperm and eggs meet inside the
female’s body. All mammals, birds and reptiles and most land
invertebrates carry out internal fertilisation.
Eternal fertilisation is when eggs and sperm meet outside the
body usually in water. Fish, amphibians and water living
invertebrates carry out external fertilisation.
Internal fertilisation is more efficient because the eggs are
protected inside the female, fewer eggs are produced and the
gametes are closer together so the chances of fertilisation are
greater.
After fertilisation
After fertilisation the fertilised egg begins to divide. Cell
divisions continue until a ball of cells is formed:
Trout development
Trout breed once per year during the month of November. The
female makes a hollow in the small stones in the river bed. She
lays about 3000 eggs and then the male releases sperm onto
them. After fertilisation takes place, the trout eggs begin to
develop.
Newly hatched trout feed on yolk from the yolk sac. After the
yolk sac is used up, the young fish (fry) to feed on small water
animals. No protection is given to the trout embryo before and
after hatching.
The human female reproductive system
oviduct
The human male reproductive system
Human development
The ova (eggs) develop in the ovary. At puberty, an ovum is
released once a month. The egg passes through the oviduct
where it must be fertilised, and on into the uterus. If a sperm
fuses with an egg in the oviduct, the fertilised egg or zygote
starts to divide as it is passed down the oviduct. When the ball
of cells reaches the uterus, it becomes embedded or implanted
into the spongy wall of the uterus. The embryo will spend the
next 9 months developing here.
After the human egg has implanted into the wall of the uterus,
it begins to grow and develop. A special structure called the
placenta develops, allowing the blood of the mother and the
blood of the embryo become very close without mixing. The
embryo is attached to the mother by the umbilical cord. The
placenta allows the mother and the embryo to exchange
essential materials.
Exchange at the placenta
Mother’s blood
Oxygen and food
CO2 and waste
Embryo’s blood
Oxygen and food pass from the mother’s blood to the placenta,
down the umbilical cord to the embryo.
Carbon dioxide and waste materials are passed along the
umbilical cord to the placenta and across to the mother’s blood.
During pregnancy, a mother should avoid alcohol and smoking
because the alcohol and nicotine can be passed through the
placenta to the embryo and affect its development.
Unlike the trout eggs, human eggs and embryos are well
protected during development by the amniotic sac and fluid, by
the uterus wall and the pelvic bones of the mother. After birth,
human babies are protected for many years by their parents.
Survival chances
During reproduction many sex cells and young are destroyed.
Only the ‘fittest’ survive to reproduce more of the offspring.
Species
No of
No of
No of
eggs
eggs
fertilised
produced fertilised eggs
diseased
Rabbit
8
8
0
Trout
3000
2000
200
Pheasant 15
12
2
Human
1
1
0
Frog
1000
750
50
No of
fertilised
eggs
eaten
0
800
2
0
200
No
of
young
eaten
0
850
3
0
400
%
survival
100
5
33
100
10
Mammals have the highest survival rate while fish have the
lowest. This is because fish and amphibians do not normally care
for their young, and therefore they have to lay many eggs in the
hope that some survive to adulthood.
Birds and mammal take care of their young before and after
birth so they do not have to produce as many eggs and their
young have a better chance of survival.
C
Water and Waste
Water gain
Our bodies gain water in three different ways:
Food
Water loss
drink
metabolic
Water
Our bodies lose water in four different ways:
Sweat
through
skin
urine
water
loss
faeces
breath
through
lungs
You gain and lose water in various ways. To maintain water
balance in your body, water gain must equal water loss.
The kidneys are the main organs for controlling the water
content of your bodies.
The urinary system
In humans the kidneys are solid, oval structures found towards
the back of the body below the rib cage.
The kidney has two main functions:
1.
2.
maintaining water balance
getting rid of poisonous waste substances from the
body
Filtration and absorption
Blood enters the kidney through the renal artery and leaves
through the renal vein.
The blood contains useful substances such as glucose and a
poisonous substance, urea. Somehow the kidney has to keep the
useful substances and get rid of the poisonous ones. The blood
entering the kidney is filtered removing water, useful
substances and harmful urea. Useful substances are then
reabsorbed back into the blood, leaving some water and the
urea. The amount of water reabsorbed depends on the body’s
requirements.
If we compare the blood going in and out of the kidney and urine
for the presence of glucose and urea:
Sample
Renal artery (in)
Renal vein (out)
Urine
Urea present?
Yes
No
yes
Glucose present?
Yes
Yes
No
This means that the kidney has removed the urea that was in
the renal artery coming into the kidney and placed it in the
urine. The renal vein leaving the kidney should be urea free.
No glucose should escape in the urine; it should be reabsorbed
back into the blood and leave in the renal vein.
To explain the process of filtration and reabsorption you have
to look at the kidney’s structure in more detail.
The kidney is made up of about one million tiny tubes called
nephrons that filter the blood and then reabsorb the useful
substances. Proteins are broken down to amino acids during
digestion. They can be used to build new cells or repair tissues.
Any extra amino acids not needed at the time are broken down
in the liver to a poisonous waste called urea and a carbohydrate.
The urea is transported by the blood to the kidney where it is
removed from the blood and leaves the body in the urine.
Below is a diagram of one nephron or kidney tubule:
1.
2.
3.
4.
5.
Blood is filtered through the glomerulus. All molecules
small enough pass through into the Bowman’s capsule eg
glucose, amino acids water and urea. Large molecules
like protein or blood cells do not get through.
As the filtrate moves along the nephron, useful
substances are absorbed back into the blood ie glucose
salt and water are reabsorbed.
The nephron is surrounded by a network of blood
capillaries that carry the now cleaned blood away to
rejoin the renal vein.
the collecting duct now contains urine which is the urea
and some water. How much water depends on what the
body needs.
The urine is carried by the ureter down to the bladder
for storage. Eventually it is passed out through the
urethra.
Water regulation
No matter how much liquid the body gains, the kidney adjusts
urine output to maintain water balance. The regulation of water
balance by the kidneys is under the control of the brain. The
brain produces a hormone called ADH (anti diuretic hormone)
that controls how much water is reabsorbed by the kidney.
Water content of
blood too low
Water content of
blood too high
too much salt
or sweating
drinking
Brain produces
more ADH
Brain produces
less ADH
water content
of blood normal
High volume of
Water reabsorbed
by the kidney
Low volume of water
water reabsorbed
by the kidney
Low volume of
concentrated urine
High volume of
dilute urine
In other words
The lower the water content of the blood >>
The more ADH is released by the brain >>
The more water is reabsorbed by the kidney >>
And a small amount of concentrated urine is produced.
The higher the water content of the blood >>
The less ADH is released by the brain>>
The less water is reabsorbed by the kidney >>
And more dilute urine is produced.
When kidneys go wrong
If kidneys are damaged or diseased, they may cease to function.
This can lead to a build up of the poisonous waste urea in their
bloodstream. This can be fatal if untreated. If total kidney
failure occurs, there are two possible treatments. Each of these
treatments will save the life of the patient but there are
certain disadvantages to each form of treatment.
Treatment How it works
The blood is
Dialysis
filtered
through
a
machine over
a number of
hours several
times a week
to remove the
urea.
The
patient
Transplant receives
a
donor kidney
Advantages
It saves the
patient’s
life
allowing them
to live until a
donor kidney is
available to
Disadvantages
It’s expensive to
run. It limits the
patient’s lifestyle
A
successful
transplant
means
the
patient can go
back
to
a
normal life
The patient’s body
may reject the
new kidney. There
is a shortage of
kidney donors.
D
responding to the environment
Animals are continually being subjected to signs or signals
coming from the environment around them. Environmental
signals are called stimuli and the animal will respond to them in a
variety of ways.
The way in which an animal responds to a stimuli makes up an
animal’s behaviour. This behaviour is important for an animal’s
survival.
Some examples:
Woodlice
A woodlouse is the land’s equivalent of a shrimp. It has to keep
its self moist in order to breathe. It tends to stay in damp
dark places where it can breathe and avoid predators.
Flatworm
Flatworms live on the bottom of ponds and rivers.
They cannot see but are attracted by chemical signals from
their food.
Investigating the response of woodlice to light
We know that woodlice prefer damp conditions to dry and dark
conditions to light. Can we show this in an experiment?
Dark side
light side
Hole
sellotape
When woodlice are put through the central hole and all holes are
sealed with sellotape, they are left for awhile.
After 10 minutes you would expect to see more woodlice in the
dark side of the chamber. This is because in the wild they will
be safer in a dark place. You can also use this chamber to
investigate whether the woodlice prefer damp conditions to dry.
Rhythmical behaviour
Some environmental; conditions vary regularly eg light during
the day, dark at night, long warm days in summer and short cold
days in the winter. There are three main rhythmical changes in
the environment: daily, tidal and annual.
Daily
Some animals are nocturnal, some are diurnal eg owls usually
hunt at night whilst humans are usually active during the day.
The owls have less competition for food if they hunt at night.
Tidal
Seashore animals coordinate their activity according to high or
low tide.
Shore crabs tend to hide under rocks while the tide is out and
become active only when the tide comes in. This will happen
twice a day.
Annual
This is behaviour that usually occurs only at one specific time of
the year. The two best examples are courtship and migration.
Most animals only mate once a year often involving an elaborate
courtship. Many animals migrate long distances at certain times
of the year, usually in search of food or warmer living conditions
or a safe place to bring up young.
These two behaviours are predominantly triggered by changes in
the hours of light and dark.