Download Page 1 Biology 3

GCSE Science:
Biology 3
Revision Book
Content
The Circulatory System
2
Investigating Stomata
21
Blood
3
Comparing Water Loss From Leaves
22
Red and White Blood Cells
4
Platelets and Plasma
5
Using a Simple Potometer to
Measure Transpiration Rate
Structure of a Leaf
The Heart
6
The Transpiration Stream
25
Blood vessels
8
The Active Uptake of Mineral Ions by
Plant Roots
26
The Eye
9
Plant Transport Systems
27
The Nervous System
10
Healthy Plant Growth
29
The Reflex Arc
11
Microorganisms and Disease
30
The Structure of a Reflex Arc
12
The Immune Response
31
Homeostasis and the Kidneys
13
32
Structure of the Kidney
14
Immunity
Vaccination
How do the kidneys remove urea and
excess mineral salts?
15
Antibiotics
35
Water Balance and Osmoregulation
16
Kidney Failure
17
Kidney Transplants
18
Investigating water loss in plants
19
Investigating the effect of antibiotics
on bacteria growing on agar plates
Growing Bacteria
Investigating the effect of temperature
on the growth of bacteria
Penicillin
Estimating the rate of transpiration
from a plant cutting
20
Using Microbes for Food Production
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40
1
Blood and Circulation
A Historical Perspective
In the early 1600s William Harvey, a physician to
King Charles I. suggested that blood circulated
around the body, flowing from the heart through
arteries and returning through veins.
Harvey’s Approach
Prior to Harvey’s discovery, it was thought
that the blood was formed in the liver, and
was used up as it went around the body.
Harvey used a scientific approach, which
included:
• Dissection of humans and other
animals.
• A detailed study of the structure of the
heart.
• Observation of living hearts in fish.
• Experiments on human circulation.
• Mathematical models.
Fig. 1
William
Harvey
Fig. 2 Harvey’s experiment on
human circulation.
The Human Circulatory System - A double circulatory system.
The blood must pass through the heart twice before completing one whole
circuit
of the body.
Pulmonary
The
Oxygen enters
circulation
the blood in the
Blood
pumped
Pri form the heart to
the lungs and
back to the heart.
Fig. 3
Diagram showing
a double
circulatory
system.
Oxygenated blood
lungs.
Right
side
Left
side
The Systemic
Circulation
Blood pumped
form the heart to
the body and
then back to the
heart.
Oxygen enters
the blood in the
lungs.
Deoxygenated blood
2
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Blood and Circulation
Blood
Blood is made up of
Red blood
cells
carry oxygen
White blood
cells
defend the
body against
pathogens
Platelets
clotting of
blood
Plasma
carries
dissolved
substances
Fig. 1 – Illustration of the components of blood.
Examining blood smears
(These are diagrams you should be able to label).
Fig 2. Micrograph of a blood
smear.
The centre of red blood cells
appear paler because they
have no nucleus and therefore
more light from the microscope
passes through them.
White blood cell
Platelet
Red blood cell
Fig.3 – Illustration of blood smear
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3
Blood and Circulation
Blood
Red Blood Cells.
These cells carry oxygen around the body.
They are flattened, biconcave, disc shaped
cells; they are red in colour because of a
pigment called haemoglobin. This joins with
oxygen to transport it around the body.
Red blood cells don’t have a nucleus.
Fig. 1 – micrograph of red
blood cells
Iron is needed to produce haemoglobin. If there is a shortage of iron a person
won’t have enough red blood cells, this is called anaemia, less oxygen will be
carried around the body.
White blood cells
These cells defend the body against pathogens (microbes that cause disease).
They are bigger than red blood cells, and have a nucleus, but don’t contain a
pigment so are colourless.
If you have an infection the number of white blood cells in you body increases
rapidly.
There are many types pf white blood cells, but you only need to learn about two
of them:
• Phagocytes – ingest and digest ‘foreign’ cells.
• Lymphocytes – produce antibodies and antitoxins.
Comparing red and white blood cells
(You should be able to draw, label and compare a red and white blood cell)
Red blood cells
White blood cells
Fig. 2 – side view (left )and front view (right) of
red blood cell (not to scale)
Fig. 3 –white blood cell (phagocyte)
(not to scale)
cell membrane
cell
membrane
No nucleus present
Regular disc shaped
Smaller than white blood cells
4
nucleus
Nucleus present
Irregular shape
Larger than red blood cells
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Blood and Circulation
.
Platelets
Platelets clot the blood.
When the skin is cut you bleed.
Platelets make the blood clot, forming
a thick jelly. This hardens to form a scab,
preventing bleeding and blood loss.
Fig. 1 – micrograph showing
red blood cells clotting.
The scab keeps the wound clean as new
skin grows underneath.
This prevents pathogens from entering the body and bacterial infection.
Fig 2. – Illustration of blood
clotting in a wound
Plasma
Plasma carries dissolved substances.
This is the liquid part of blood. It is pale yellow in colour and is 90% water.
Plasma carries many dissolved substances around the body:
•
•
•
•
•
Small soluble food molecules, e.g. glucose, amino acids, etc.
Waste chemicals produced by the body, e.g. carbon dioxide from
respiration and urea produced by the liver.
Hormones carried from the endocrine glands to their target organs,
e.g. insulin.
Antibodies produced by lymphocytes (white blood cells).
Mineral salts, e.g. sodium ions.
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5
Blood and Circulation
The Heart
Structure of the Heart
The function of the heart is to pump blood.
The heart is made of a special muscle called cardiac muscle.
There are blood vessels on the outside of the
heart – the coronary arteries.
These supply oxygen and glucose to the heart
muscle.
Without a steady supply of oxygenated blood
the heart muscle couldn’t keep contracting
and pumping blood.
If a blood clot blocks a coronary artery, the
heart muscles won’t get enough oxygen and
will stop working – this is a heart attack.
Fig. 1 – Illustration showing the outside of a human
heart. The blood vessels shown are the coronary
arteries.
Pulmonary artery
Valves prevent
Aorta
carrying deoxygenated
blood from the lungs to
the heart.
backflow of blood
when ventricles relax.
an artery carrying
blood to the body.
Pulmonary
vein carrying
Vena Cava
oxygenated
blood from the
lungs to the
heart.
vein carrying
blood from
the body
back to the
heart.
Right atrium
Valve
Right ventricle
prevents
backflow of
blood to atrium
when the
ventricle
contracts.
Fig. 2 – illustration showing
internal structure of the heart.
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Left atrium
Left ventricle
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Blood and Circulation
Facts you must learn about the heart:
•
•
•
•
•
•
•
•
•
•
The heart is divided into 2 halves.
Blood flows in one direction through each half of the heart.
There are valves between the atria and ventricles. These can close to
stop backflow of blood when the ventricles contract.
There are valves at the bottom of the bottom of the pulmonary artery and
aorta to prevent backflow of blood to the ventricles when they relax.
There are tendons attached to the valves so they don’t get pushed inside
out.
The right side of the heart pumps blood to the lungs.
The left side of the heart pumps blood to the body.
The atria (more than one atrium) have thin walls because they only pump
blood to the ventricles.
The ventricles have thick muscular walls, because when they contract
they have to pump blood out of the heart.
The left ventricle has a thicker muscular wall than the right ventricle
because it pumps blood to all parts of the body – the right ventricle only
pumps blood to the lungs.
Flow of Blood Through the Heart
•
•
•
•
•
•
•
•
The vena cava carries blood from the organs of the body to the right
atrium.
Blood passes through a valve to the right ventricle.
The right ventricle contracts, pumping blood through the valve into the
pulmonary artery.
The pulmonary artery carries the blood to the lungs where it is
oxygenated.
The pulmonary vein carries blood back from the lungs to the left
atrium.
Blood passes through the valve into the left ventricle.
The left ventricle contracts, pumping blood through the valve into the
aorta.
The aorta carries blood form the heart to the organs of the body.
QWC questions sometimes ask you to describe the flow of blood through the heart. Always check to see where
you need to start and finish.
Remember, you will lose marks by including irrelevant information!
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Blood and Circulation
Blood Vessels
Fig.1 – (Left to right) Illustration of an artery, capillary and vein (not drawn to scale).
•
•
Arteries have thick walls because they carry blood under pressure away
from the heart.
Veins have thins walls because they carry blood under low pressure back
to the heart.
Vein
Artery
Venule
Arteriole
Capillaries
Fig. 2 Illustration showing structural relationship between blood vessels.
Capillaries are the smallest blood vessels that carry blood through the organs of
the body.
• They form extensive networks so that no cell is far away from a capillary.
• Their walls are very thin to allow materials to diffuse easily between the
blood and the body cells.
Capillary
Fig. 3
Diffusion between
cells and
capillaries.
1 Oxygen and
glucose.
2. Carbon dioxide.
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Body cells
2
1
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Nervous System
The Eye
The eye is a sense organ that contains light receptors.
Tear
gland
behind
the
eyelid.
Eyelid - blinks to
protect the eye.
Iris - a coloured
muscle.
Pupil
Sclera
Fig. 1 – Front view of an eye in bright light (left) and in dim light (right). The iris
controls how much light enters the eye by changing the size of the pupil. This reflex
action protects the retina.
Internal Structure of the Eye
Iris – muscles that alter
size of pupil to control
amount of light entering.
Sclera – protective,
tough white outer
coat.
Choroid – a pigmented
layer which absorbs
light to prevent
reflection, also contains
blood vessels
Retina – light
sensitive layer
an image is
formed here,
impulses sent
to optic nerve.
Cornea – clear
part of sclera
allows light to
enter and
refracts light
entering.
Pupil – hole
in centre of
the iris which
allows light
to enter.
Lens – changes
shape to focus
light onto retina.
Blind spot – where the
optic nerve leaves the
eye, there are no light
sensitive cells here.
Optic nerve – carries
impulses from retina
to brain.
Fig. 2 – vertical section through the eye.
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9
Nervous System
The Nervous System
Central
nervous
system:
• Brain
• Spinal
cord
Humans have 5 sense organs connected to the
nervous system.
Each sense organ is made up of special cells
called receptors.
The receptors can respond to a certain
stimulus.
The receptors collect information from out
surroundings and pass the information as
electrical impulses along neurones to the
central nervous system.
Fig. 1
Illustration
of central
nervous
system
The central nervous system (the brain or
spinal cord) can then store the information or
decide on a reaction.
Reflex Actions
Reflex actions are:
• protective,
• automatic,
• fast.
Examples of reflex actions:
Reflex
Blinking
Change in pupil diameter
Withdrawal / pulling away
Sneezing
Knee jerk
10
Fig. 2 – Illustration of
a knee jerk reflex.
When the hammer
strikes the tendon
below the knee cap
tension increases in
the leg muscle,
causing it to
contract. This reflex
helps keep us
upright.
Explanation
Protection of the eye
Protection of the retina
Prevent harm to the body
Expel substances form the nose
Helps maintain posture
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Nervous System
The Reflex Arc
All reflex actions
follow the same
order:
5. Motor neurone
2. Receptor = skin
1. Stimulus
2. Receptor
6. Effector = muscle
3. Sensory neurone
4. Co-ordinator
5. Motor neurone
6. Effector
3. Sensory neurone
4. Co-ordinator
= spinal cord
7. Response
1. Stimulus = heat
Fig. 1 – A typical
withdrawal reflex
The co-ordinator is always either the brain or the spinal cord.
The effector is always a muscle or a gland.
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Nervous System
The Structure of a Reflex Arc
1. Stimulus = heat
3. Sensory nerve
Relay neurone
2. Receptor = skin
Synapse
4. Co-ordinator = spinal cord
6. Effector = muscle
5. Motor nerve
Fig. 1 – The structure of a reflex arc showing relative positions of each neurone.
Describing the path taken by a nerve impulse from the receptor to the
effector. (This is always a potential QWC question).
•
•
•
•
•
•
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The stimulus (heat) is detected by receptors in the skin.
The receptor responds and sends and electrical impulse along a
sensory neurone to the co-ordinator (the spinal cord).
The electrical impulse is passed to a relay neurone inside the spinal
cord and then on to the motor neurone.
Between each neurone is a tiny gap called a synapse.
The motor neurone carries the impulse to the effector (the muscle).
The muscle contracts and pulls the hand away from the stimulus; this is
the response.
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Role of the Kidneys in Homeostasis
Homeostasis and the Kidneys
Homeostasis means keeping the internal environment constant
Conditions inside the body must be kept stable.
Examples to learn:
• Water content of the body must be kept constant,
• Waste chemicals must be removed from the body,
• Body temperature must remain constant. (See Biology 1)
• Glucose levels must remain constant. (See Biology 1)
The Kidneys
The kidneys have three functions in the body:
1. Control of water content of the blood.
2. Removal of urea from the blood.
3. Removal of excess mineral salts from the blood.
The process of removing waste from the body is called excretion.
Structure of the Excretory System
The kidneys are about 12 cm long and 7 cm wide and are located in the
abdomen.
Vena cava
Aorta
Facts to learn:
(to the heart)
(From the heart)
Diaphragm
• Blood enters the
Kidney
Renal artery
Renal vein
•
•
Ureter
Bladder
•
Muscle
•
Urethra
kidney through
the renal artery.
Blood leaves the
kidney through
the renal vein.
The ureter is a
tube that carries
urine from a the
kidney to the
bladder.
The bladder
stores urine.
The urethra
carries urine
from the bladder
out of the body,
Fig. 1 – Relative position of kidneys, bladder and main blood vessels.
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13
Role of the Kidneys in Homeostasis
Structure of the Kidney
The kidney consists of two layers:
1. Outer layer – Cortex.
2. Inner layer – Medulla.
Medulla
Medulla
Cortex
Nephron
Cortex
Renal
pelvis
Ureter
Fig. 1 Trans section of kidney
Fig. 2 Dissected pig’s kidney
The Nephron
The nephrons remove urea, excess mineral salts and excess water from the
blood to make urine.
There are approximately 1,000,000 nephrons in each kidney. Fig. 1 shows their
location across the cortex and medulla.
Arteriole to the capillary knot
Arteriole from the capillary knot
Capillary knot
Bowman’s capsule
Renal artery
Renal vein
Collecting
duct
Urine passes
from the
nephron into
the
collecting
ducts.
Fig. 3
Structure
of a
nephron.
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Urine = water,
urea and
mineral salts
Capillary network
Tubule
There are two stages in the
production of urine by the nephron:
1. Ultrafiltration – filtration of small
molecules under pressure from
the capillary knot into the
Bowman’s capsule.
2. Reabsorption – useful molecules
are reabsorbed back into the
blood from the tubule.
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Role of the Kidneys in Homeostasis
How do the kidneys remove urea and excess mineral salts?
Arteriole to the
glomerulus
Capillary
knot
Bowman’n
capsule
Arteriole to the
glomerulus
Tubule
Urine
Capillary
network
Fig. 1 Schematic drawing of the
nephron.
Ultrafiltration
• The arteriole to the capillary knot has a
larger diameter than the arteriole from
the capillary knot, this increases blood
pressure in the capillary knot.
• Small molecules such as urea,
glucose, mineral salts, water and
amino acids are filtered under pressure
from the blood in the capillary knot into
the Bowman’s capsule.
• Large molecules, such as proteins, or
red blood cells are too large to be
filtered out of the blood.
Reabsorption
• Useful substances such as glucose
and amino acids are reabsorbed from
the filtrate in the tubule into the blood in
the capillary network.
• Excess mineral salts are also
reabsorbed.
• Water is also reabsorbed.
(See osmoregulation – page 16)
The table shows some differences in the composition of blood plasma and
urine:
Substance
Protein
Glucose
Urea
Mineral Salts
Blood plasma (%)
9.00
0.10
0.02
0.75
Urine (%)
0
0
2.00
1.25
Analysis of table:
• There is no protein in the urine because their molecules are too large
to be ultrafiltrated from the capillary knot into the Bowman’s Capsule.
• There is no glucose in the urine because it has all been reabsorbed
from the tubule back into the blood of the capillary network.
• The percentage of urine and mineral salts has increased because
some of the water in the tubule has been reabsorbed, therefore making
the filtrate flowing into the collecting duct more concentrated.
The presence of blood or cells in the urine would indicate kidney disease.
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15
Role of the Kidneys in Homeostasis
low concentration
Water Balance
The volume of water you take in has to equal the volume of water you lose.
We gain water:
 in food
 by drinking
 metabolic water (made during respiration)
We lose water:
 when exhaling
 by sweating
 in urine
 in faeces
Osmoregulation = controlling water concentration in the blood
The brain monitors the concentration of water in the blood.
Osmoregulation is controlled by the anti diuretic hormone (ADH). It is released
by the brain and is carried by the blood to the kidneys. The flow chart below
summarises the process:
Decrease in
concentration of
water in blood
Increase in
concentration of
water in blood
Too much salt in
diet / sweating
Too much
water
drunk
Brain secretes
less ADH
Brain secretes
more ADH
Normal water concentration
in the blood
Small volume of
concentrated urine
produced.
More water
reabsorbed back
into the blood
16
Large volume of
dilute urine
produced.
Less water
reabsorbed back
into the blood
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The Role of the Kidneys in Homeostasis
Kidney Failure
Kidney failure is a common disease that affects tens of thousands of people
each year. It is possible to live after one kidney has failed, but if both fail,
without treatment, the patient will die. It is possible to treat kidney failure by
kidney dialysis or by organ transplant.
Dialysis
Dialysis restores the concentrations of dissolved substances in the blood
to normal levels.
How does a dialysis machine work?
Fig. 1 Illustration of
a dialysis machine.
The patient’s blood flows between semi permeable membranes (the dialysis
tubing). To ensure that useful substances such as glucose and salts are not lost
from the blood (by diffusion through the pores of the dialysis tubing), the dialysis
fluid contains the same concentration of useful substances as the blood plasma.
This ensures that only urea, and excess of mineral salts and water will diffuse
into the dialysis fluid. Dialysis treatment needs to be carried out regularly.
Equal concentration of useful
substances, e.g. glucose;
therefore no net diffusion of
glucose out of blood.
Fig. 2 Schematic
illustration of a
dialysis machine.
Blood and dialysis
fluid flow in opposite
directions to maintain
a concentration
gradient.
Constant circulation and changing of dialysis fluid
ensures concentration of urea is higher in the
blood.
Urea therefore diffuses out of the blood into the
dialysis fluid.
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17
Role of the Kidney in Homeostasis
Transplantation
The donor kidney is implanted at the bottom of the abdomen close to the
thigh and is connected to the blood supply of the recipient. The failed
kidneys are not normally removed.
To reduce the chance of rejection before a transplant:
• Doctors make sure that the ‘tissue type’ of the donor and the
recipient need to be similar. (Close family members are more
likely to have a similar tissue type to the recipient.)
To reduce the chance of rejection after a transplant:
• The donor must take drugs that suppress the immune system.
Comparing the advantages and disadvantages of dialysis and a kidney
transplant:
Dialysis
Temporary treatment
Diet restrictions
Patient must visit hospital several
times a week for treatment.
Non-invasive treatment
No drugs needed
No problems with rejection of
treatment
Kidney transplant
Potential to ‘cure’ problem for many
years.
Generally no restriction to diet after
treatment
Patient does not have to visit
hospital every week
Treatment involves major surgery
Patient must take drugs to suppress
immune system
New kidney may be rejected by the
body.
Kidney Transplants – ethical Issues
There are a number of ethical issues involved with transplants. Some to
consider are:
• Xenotransplants
• Kidney donor schemes, e.g. presumed consent in Wales
• Living donors
• Buying and selling of organs
• Availability of dialysis machines.
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Plants, Water and Nutrients
Investigating Water Loss in Plants
Investigation 1
1. Tie a polythene bag around the stem and pot of a plant.
(This prevents water evaporating from the soil in the pot.)
2. Place it inside a large bell jar that stands on a vaselined glass plate.
(This prevents exchange of gases with the outside of the jar.)
3. Leave in a partly exposed, sunny site.
4. Observe the bell jar after 24 hours.
Droplets
Bell jar
Plant
Glass
plate
Polythene bag
Result
Droplets of water have formed on the inside of the bell jar.
Conclusion
The water on the inside of the jar must have come from the plant because
no water can pass into the jar or evaporate from the soil.
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19
Plants, Water and Nutrients
Investigation 2 – Estimating the rate of transpiration from a plant cutting
Method
1. Cut a shoot from a plant and place
it in a measuring cylinder.
2. Pour a thin layer of oil over the
surface of the water.
(This prevents evaporation of
water directly from the surface of
the water.)
3. Weigh the whole apparatus.
4. Record the results in a table.
5. Leave for a period of time.
6. Weigh the apparatus again.
7. Calculate the change in mass.
(This experiment can be carried out
by studying change in volume of
water, however it is not as accurate.)
Results
The mass of the apparatus will have decreased.
Conclusion
The mass has decreased because water has been lost from the measuring
cylinder.
Because water couldn’t evaporate directly from the surface of the water it
must have travelled up the stem of the plant and evaporated from the
leaves. This movement of water is called transpiration.
Factors that could affect the result of the investigation:
• The humidity of the air, or any breezes in the room could affect the rate
of water loss from the cuttings.
• Healthy cuttings will lose water steadily; unhealthy ones may not work
so well.
20
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Plants, Water and Nutrients
Investigation 3 – Investigating Stomata
Method for an epidermal impression of leaf
1. The upper surface of a leaf is painted with a thin layer of clear nail varnish.
2. Leave for 10 – 15 minutes to allow the varnish to dry.
3. Remove the layer of varnish by attaching clear sticky tape to it, peeling it
from the leaf surface and sticking it to a microscope slide.
4. Observe the slide with a microscope and count the number of stomata in the
field of view.
5. Repeat steps 1 to 4 for the lower surface of a leaf.
6. Compare the results.
Fig. 1 Upper surface of a privet leaf
showing no stomata present.
Fig. 2 Lower surface of a privet leaf
showing stomata present.
Result
The lower surface contains the highest number of stomata.
Conclusion
The function of stomata is to allow gas exchange between the cells of the leaf
and the air, however water is also lost by diffusion through open stomata.
Having most of the stomata on the lower surface of the leaf shades them from
the heat of the sun, and is an adaptation to reduce water loss.
Guard cell
Nucleus
Chloroplast
Thick cell wall
Stoma
Thin cell wall
Fig. 3 Illustration of stomata. The differences in the thickness of the cell walls of the
guard cells cause them to change shape when their water content changes leading to
opening and closing of the stomatal pore.
The stomata are pores in surface of a leaf that allow water vapour to pass out.
They also allow gaseous exchange to occur.
A pair of guard cells controls the size of a stoma. These can change their
shape causing the stoma to open or close. This allows a plant to control how
much water is lost.
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21
Plants, Water and Nutrients
Investigation 4 – Comparing Water Loss From Leaves
Method
• Four leaves were removed from a green plant and their stalks covered with
Vaseline (this prevents water loss from the cut ends).
• Their surfaces were treated as follows:
o Leaf 1 – Vaseline on upper surface of leaf,
o Leaf 2 – Vaseline on lower surface of leaf,
o Leaf 3 – Vaseline on upper and lower surface of leaf,
o Leaf 4 – No Vaseline.
Fig. 1 – Appearance of leaves at start of investigation.
Fig. 2 – Appearance of leaves after 10 days.
Analysis
Leaf Appearance after 10 days
1
Slightly wrinkled
2
Almost fresh
3
Fresh
4
Wrinkled and dried out
Explanation
As there are far less stomata on the upper
surface of a leaf the Vaseline has only
prevented a small amount of water loss.
As most stomata are found on the lower
surface the Vaseline has prevented most
of the water being lost from the leaf.
The Vaseline has prevented water loss
through the stomata on both surfaces.
Water has been lost through the stomata
of both surfaces.
(This investigation can be done as a ‘stand alone’ or as a variation of “Investigation 2”
and “Investigation 5”.)
Quantitative or Qualitative Result?
The result in the table is a description and therefore can’t be graphed; this is a
qualitative result.
If the mass of the leaves were measured before and after 10 days and the
percentage change in mass was calculated we would have a result that could be
graphed; this is a quantitative result.
22
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Plants, Water and Nutrients
Investigation 5 – Using a Simple Potometer to Measure Transpiration Rate.
Plant shoot
Water reservoir
Tap
Capillary tube
Beaker of water
Scale
Bubble
Fig. 1 A simple potometer.
An air bubble is introduced into the capillary tube at the start of the investigation. As
water evaporates through the stomata of the leaves water is drawn up the capillary tube
causing the bubble to move.
The investigation makes the assumption that water uptake is equal to the transpiration
rate. However not all water is lost from the leaves, some is taken up by leaf tissue or used
for photosynthesis.
Method
1. Set the bubble to it’s starting position by using the tap to release water
from the water reservoir.
2. Measure the time taken for the bubble to move a set distance
OR
Measure how far the bubble moves in a set period of time.
3. Record the results.
4. Repeat the experiment.
Environmental factors that affect water loss from a plant
• Temperature – as temperature increases water molecules have more
kinetic energy and therefore move faster. This increases transpiration.
• Humidity - increasing humidity reduces the concentration gradient of
water between the air and the intercellular spaces in the spongy layer of
the leaf – this decreases the diffusion of water out of the stomata.
• Wind speed – increasing wind speed carries away more water vapour
from near the leaf surface and increases the rate of diffusion of water
vapour out of the stomata.
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Plants, Water and Nutrients
Tran section (T.S.) of a leaf
1. Epidermis
2. Palisade layer
Contains cells packed
with chloroplasts for
photosynthesis.
3. Spongy layer
Contains large air
spaces to allow
gaseous exchange.
4. Epidermis
5. Guard cells
Structure of a Leaf
6. Stoma
10. Cuticle
Waxy, waterproof layer
to reduce water loss
7. Xylem
Transports water
8. Phloem
Transports sugar
9. Air space
Allows gas
exchange
with leaf
cells.
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24
Plants, Water and Nutrients
The Transpiration Stream
There is a constant flow of water through a plant; this is called the
transpiration stream.
3. Water evaporates from
the leaf through the
stomata
6. Water evaporates from some of
the leaf cells, causing more water
to be pulled up the xylem.
2. Water is carried through
the plant by the xylem.
Water enters the root
hairs by osmosis.
Fig. 1 The transpiration stream
5. Water moves from cell to cell
in the leaf by osmosis.
4. Water molecules stick
together and this causes water
to be pulled up the xylem as a
column.
1. Water enters the plant
through root hair cells by
osmosis.
7. Water diffuses from the air
spaces in the spongy layer
out of the stomata into the
air.
2. Water moves from
cell to cell in the root
by osmosis.
3. Water moves into
the xylem by osmosis
Water
Fig. 2 Annotated illustration of the transpiration stream
Observation of root hair cells
Fig. 3 Root with root hairs
(left) and magnified view of
root hair (above).
Water enters the plant from an area
of high concentration of water in the
soil to an area of lower water
concentration inside the root hair cell,
through it’s partially permeable
membrane, by osmosis.
The increased surface area of the
root hair cell allows the plant to take
in more water faster by osmosis.
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25
Plants, Water and Nutrients
Active Uptake of Mineral Ions by Plant Roots
When the concentration of a material is lower outside the cell it must be actively
transported into the cell (sometimes referred to as active uptake).
Example – Uptake of nitrate ions by root hair cells
Fig. 1
High
concentration
of nitrate ions
inside plant cells. Diagram of a
plant root with
enlarged view of
a root hair cells. Low
concentration of
nitrate ions in
soil water.
•
•
Nitrate ions cannot move in by diffusion.
Nitrate ions must be actively transported from the soil water (an area of low
nitrate concentration) to the inside of the plant cells (an area of high nitrate
concentration).
During active transport, salts or ions are pumped from an area of low
concentration to an area of higher concentration.
This process requires energy released by the cell during respiration.
Factors that affect active transport:
• Active transport needs energy.
• Energy is released during respiration.
Any factor that affects the rate of respiration will affect the rate of active
transport, e.g.:
•
•
•
•
Glucose concentration – respiration needs glucose.
Oxygen – aerobic respiration needs oxygen.
Temperature – affects the enzymes controlling respiration.
Toxic substances – e.g. cyanide stops respiration.
Factors that affect active transport will have an effect on the rate of uptake of
ions from the soil into root hair cells.
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Plants, Water and Nutrition
Plant Transport Systems
Plants have two separate transport systems.
 Phloem vessels (tubes) – transport sugar and other substances that
are produced by cells to all the other parts of the plant.
 Xylem vessels (tubes) – transport water and mineral ions from the
roots to the rest of the plant.
Phloem and xylem vessels usually run together side by side.
Groupings of phloem and xylem vessels are called vascular bundles.
Vascular bundle
Fig. 1 – T.S. of a sunflower
stem showing positions of
vascular bundles.
Phloem vessels
Xylem vessels
Fig. 2 – T.S. of a sunflower
stem showing a single
vascular bundle.
Phloem Vessels
Phloem carries sugar from the photosynthetic areas to other parts of the plant.
Sugar is moved to other parts of the plant for use in respiration and converted
into starch for storage.
The transport of sugar is not fully understood so plant scientists are still
investigating it.
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27
Plants, Water and Nutrients
Xylem Vessels
The function of xylem vessels are:
1. Transport of water – from the roots to the rest of the plant.
2. Transport minerals – minerals such as nitrates phosphates and
potassium are transported by xylem around the plant dissolved in water.
3. Support the plant – the xylem vessels in the shoots and roots of mature
plants are inflexible and strong and give support to the plant.
Investigation into the movement of a dye through a flowering plant
1. Take a white flower with a long stalk, e.g. a chrysanthemum and cut the
stalk carefully lengthwise.
2. Put each half of the stalk into a measuring cylinder (or boiling tube)
containing either plain water or water to which food dye has been added.
3. Tape the measuring cylinders to a plastic tray so that they don’t fall over.
4. Leave the flower for a few hours.
5. Observe where the dye ends up in the flower head.
Fig. 1
Flower at
beginning.
Fig. 2
Flower
after a
few
hours.
Explanation
Water and dye are pulled up through xylem vessels.
When they reach the flower petals the water evaporates from pores in the
petal surface but the dye remains in the cells of the petals.
The petals become coloured as dye accumulates in them.
This procedure could be useful for producing quantities of unusually
coloured flowers.
The Importance of Water
Water is important to the plant for:
1. Use in photosynthesis;
2. Transport of minerals;
3. Support.
How does water support the structure of plant?
Water provides support due to the pressure of the vacuoles pushing against the
cell walls and this keeps the cells turgid and prevents cells becoming flaccid and
plants wilting.
Fig. 3 Turgid cell
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Fig. 4 Flaccid cell
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Plants, Water and Nutrients
Healthy Plant Growth
Plants can only grow well if they are in a soil rich in mineral nutrients.
Plant roots absorb the minerals from the soil and use them to produce materials
that they need to grow.
Three main minerals are needed:
 Nitrates
 Potassium
 Phosphates
Investigating Plant Nutrient Requirements
1. Three healthy plants of the same species and age are grown in an equal
volume of aerated mineral solutions.
2. After eight weeks the growth of the plants are observed.
Plant 1
Analysis
Plant
1
2
3
4
Plant 2
Description
Healthy growth
Poor growth
Yellowing of leaves
Poor root growth
Plant 3
Plant 4
Explanation
Complete solution of minerals
Nitrogen deficiency
Potassium deficiency
Phosphate deficiency
NPK fertilisers that contain nitrates, phosphates and
potassium can be added to soil to increase the mineral
content.
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29
Microorganisms and Disease
Microorganisms and Disease
Most microorganisms (microbes) are harmless and many perform vital functions,
e.g. recycling nutrients in the Nitrogen Cycle (Biology 1), food production (see page 40),
production of antibiotics (see page 39).
Some microbes are pathogens.
A pathogen is a disease-causing microorganism
Defending Against Infection
Your body has three lines of defence against infection by pathogens:
1. The skin stops microbes getting into the body.
 A layer of dead cells form a barrier around the body.
 There is also a community of microbes on the skin (the skin flora), that
makes it difficult for pathogens to become established on the skin surface.
2. Platelets stop microbes getting into the body through a cut.
 Platelets clot the blood in a cut and form a scab, keeping out microbes
(See page 5).
3. White blood cells defend against microbes that are inside the body.
White blood cells defend against microbes in three ways:
a. Phagocytes Ingest bacteria.
Microbe
Phagocyte
Phagocyte detects ‘foreign’
microbe.
Phagocyte engulfs microbe.
Phagocyte digests microbe.
b. Lymphocytes produce antibodies to inactivate bacteria or viruses.
Lymphocyte
produces antibodies.
Antibodies
Binds to antigen and destroy the
foreign cell.
Antigen
A molecule on the cell surface
that can be recognised by the
immune system.
Antibodies
c. Lymphocytes produce antitoxins that counteract toxins released by
bacteria.
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Microorganisms and Disease
The Immune Response
All cells have unique proteins on their surface called antigens.
The immune system will recognise any cells as ‘foreign’ if their antigens are
different to the ones on body cells.
‘Foreign’ antigens stimulate an immune response by the body.
Primary
Response
Antigen
1. Lymphocyte
recognises
‘foreign’ antigen.
2. Clones
differentiate.
Most develop
to form short
lived plasma
cells.
Lymphocytes
multiply to
form clones.
3. Plasma
cells
produce
antibodies
that will
destroy cells
carrying the
specific
‘foreign’
antigen.
Secondary
Response
4. Some
clones
develop into
long lasting
memory
cells.
5. Memory cells are long
lasting and if they come
across the same specific
antigen again they stimulate
an immune response.
6. Large
numbers of
plasma cells
develop
producing a
large
concentration
of antibodies
very quickly.
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7. More memory
cells produced.
This ‘boosts’
immunity.
31
Microorganisms and Disease
Immunity
Memory cells remain in the body and antibodies are produced very quickly if the
same antigen is encountered a second time.
This memory provides immunity following a natural infection and after
vaccination.
The response is highly specific to the antigen involved.
The graph below shows the body’s immune response when it comes across an
antigen for the first and second time:
Primary
response
Body encounters
‘specific antigen’ for the
first time stimulating an
immune response.
Secondary
response
Memory cells encounter the
same ‘specific antigen’
stimulating an immune
response.
Describing the differences between the primary and secondary response:
1. The primary response is relatively slow, with a delay before antibody
production, compared to the secondary response that is much faster.
2. The concentration of antibodies produced in the secondary response is
much higher compared to the primary response.
3. The concentration of antibodies stays higher for much longer in the
secondary response compared to the primary response.
Explanation of differences
The presence of memory cells able to detect a ‘specific antigen’ causes
antibodies to be produced very quickly and in large numbers if the same antigen
is encountered a second time – this is known as immunity.
Why do most people suffer from measles only once, but could suffer from
flu many times during their lives?
The ‘flu’ virus mutates rapidly giving rise to new strains with different antigens.
Because of this, different antibodies are needed and the memory cells
produced during the previous bout of ‘flu’ cannot recognise the new antigens.
The body therefore is not immune to the new strain of ‘flu’.
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Microorganisms and Disease
Vaccination
A Historical Perspective
Edward Jenner first used vaccination against smallpox.
He had heard that milkmaids who suffered the mild disease
of cowpox never seemed to catch smallpox, a disease that
caused many deaths at the time, particularly among children.
He suggested that the pus in the blisters that milkmaids
received from cowpox protected them from smallpox.
In 1796, he inoculated a healthy boy with pus taken from a
cowpox spot and the boy caught cowpox. A few weeks later
Jenner inoculated the boy again, this time with smallpox.
Fortunately for Jenner his theory proved correct and the boy survived.
Jenner’s methodology would be considered unethical these days.
How does vaccination work?
Some pathogens can make you seriously ill before the immune system gets a
chance to respond. Getting vaccinated against these diseases can greatly
reduce the possibility of dying or suffering permanent harm because of these
diseases.
It’s possible to get immunized against diseases by introducing a small
amount of dead or inactive pathogens into the body.
The antigens on these pathogens will cause the lymphocytes to produce
antibodies to destroy the pathogens. The immune system will also produce
memory cells that will recognise the specific antigens if they enter the body
again causing large numbers of antibodies to be produced rapidly.
Fig.1
Flow chart
illustrating
vaccination.
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33
Microorganisms and Disease
Are vaccinations Safe? The MMR Story
The MMR (measles, mumps and rubella) is a vaccination that protects against
measles, mumps and rubella (German measles). Measles and mumps can
cause brain damage and even death. Rubella (German measles) can damage
unborn babies. After the MMR vaccine was introduced the number of cases of
these diseases fell until almost no children died of measles or mumps.
In February 1998, Dr Andrew Wakefield published a paper in the medical
journal The Lancet. His research suggested that there was a link between the
MMR vaccine and autism in children.
The story drew a lot of interest from the media. People got worried and the
number of children vaccinated with the MMR fell.
Graph 1
As uptake of MMR
fell the cases of
measles increased.
By 2001 the percentage of children vaccinated fell from 92% to 75%. This
percentage of vaccination is not enough to support herd immunity in the
population.
How confident can we be with the validity of the research?
 The study included only twelve children.
 Dr Wakefield was paid £55 000 by the parents of some of the children to
help them prepare evidence against the MMR vaccine for a court case.
 Dr Wakefield had also been developing some treatments for measles
that would not have been used if people had more faith in the MMR.
How can reproducing research be of value?
 A large number of separate studies have been carried out since 1998.
 Thousands of children have been studied.
The conclusion drawn from these studies have shown that there is no link
between the MMR vaccine and autism in children.
This conclusion is based on thousands of repeat experiments and reproducing
research by separate research groups, and therefore is far more valid.
Unfortunately, children have been harmed and a number have died as a result
of poor research and irresponsible reporting by the media.
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Microorganisms and Disease
Antibiotics
An antibiotic is a substance produced by a microorganism to kill other
microorganisms. (e.g. Penicillin from the fungus Penicillium)
Antibiotics, including penicillin, were originally medicines produced by living
organisms, such as fungi. Antibiotics help to cure bacterial disease by killing
the infecting bacteria or preventing their growth.
Antibiotics do not kill viruses, because viruses live inside the host’s cells and so
an antibiotic cannot reach them.
Antibiotic Resistance
Resistance to a chemical poison is the ability of an organism to survive
exposure to a dose of that poison which would normally be lethal to it.
Antibiotic resistant bacteria can evolve by the overuse of antibiotics such as:
• Use of antibiotics in animal feed,
• Over-prescription by doctors.
Doctors are worried about resistance to antibiotics because some bacteria,
e.g. E. coli are common in humans and can cause serious illness or even death.
Fig. 1
How
antibiotic
resistance
develops.
MRSA (methycillin resistant Staphylococcus aureus) has developed resistance
to several antibiotics. Antibiotics are widely used in hospitals, especially to
prevent infections occurring from surgery. The bacteria originated in Australia
and within ten years had spread world-wide.
Methods used in hospitals to control MRSA are:
• Hand washing,
• Thorough cleaning of hospital wards,
• Use of alcohol gels or antibacterial gels,
• MRSA screening before surgery.
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35
Microorganisms and Disease
Investigating the effect of antibiotics on bacteria growing on agar plates.
Method
1. Grow a culture of bacteria, e.g. Micrococcus luteus, on a nutrient agar
plate.
2. Place a penicillin disc on the surface of the agar.
3. Label the Petri dish on the underside using a marker pen.
4. Seal the lid of the dish at either end with sticky tape.
5. Incubate the dish for 48 hours at 25OC.
6. Examine the dish and measure the diameter of the clear zone around the
disc.
7. Record the results.
8. Repeat the experiment.
9. Repeat steps 1 – 7 using a different antibiotic.
10. Compare the results.
Result from one Petri dish
Penicillin disc.
Area with no bacteria
growing.
P 1.5
Bacteria only
growing around
the edges.
Fig. 1 Effect of antibiotic
(peniciliin) on bacterial growth.
Diameter of clear
zone is measured.
Explanation
Penicillin is an antibiotic and has killed the bacteria in the clear zone and is
preventing any new growth.
There are bacteria growing around the edges because the effect of the penicillin
decreases with distance form the penicillin disc.
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Microorganisms and Their Applications
Growing Bacteria
Bacteria and fungi can be grown in Petri dishes containing nutrient agar.
Working safely with microbes requires the use of aseptic techniques - this
prevents microbes from the air contaminating the culture or microbes
from the culture contaminating the air.
Investigating the presence of bacteria in milk using agar plates
Method
1. Sterilise Petri dishes and nutrient agar
before use, e.g. in an
autoclave/pressure cooker at 121OC for
15 minutes - to kill any bacteria in the
agar.
2. Use an incubating loop to transfer a
sample of milk to the Petri dish.
The loop should be sterilised before
and after the transfer by heating the
loop until it glows red in a Bunsen
flame, to kill all the micro-organisms.
3. Wipe the surface of the agar with the
inoculating loop.
4. Secure the lid of the Petri dish with
strips of adhesive tape, to prevent
micro-organisms from entering or
escaping.
5. Incubate the agar plates at 25OC to
allow the bacteria to grow - pathogens
will not grow at this temperature.
6. After 48 hours examine the dishes and
count the number of colonies present.
7. Record your results.
8. Repeat the experiment.
Fig. 1 Culturing of bacteria using
9. Repeat steps 1 – 8 using different milk
aseptic techniques.
samples.
10. Compare the results.
11. The Plates and equipment should be
sterilised after use
Result
A single bacterium is too small to
be counted when it is placed on
the agar plate
Each bacterium grows into a
colony. The colonies can be
counted to find out the original
numbers of bacteria
Bacterial
colonies
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Fig. 2 Magnified view of one
bacterial colony. This
investigation assumes that each
colony has grown from an
individual bacterium in the
original culture.
37
Microorganisms and their Applications
Investigating the effect of temperature on the growth of bacteria
The graph below shows the growth of the bacterium Micrococcus luteus at
different temperatures:
O
4 C in fridge
O
-20 C in freezer
Description
• As the temperature increases the number of bacteria increases up to
37OC.
• Above 37OC as the temperature increases the number of bacteria begin
to decrease.
Explanation (This links with the work on enzymes in Biology 2)
• Cell metabolism (chemical reactions in cells) is controlled by enzymes.
• Increasing temperature increases the rate of enzyme-controlled reactions
therefore growth and reproduction of bacteria speeds up.
• Above 37OC the enzymes in cells begin to denature and therefore growth
and reproduction of bacteria slows down.
Application in Food Storage
• Most refrigerators are kept at 4OC. At this temperature bacteria
reproduce only very slowly, but they are not killed. The activity of any
enzymes in the food is also slowed down.
• The temperature of -20OC in the freezer stops the growth and
reproduction of bacteria, but it still does not kill them.
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Microorganisms and their Applications
Penicillin
Penicillin is a type of antibiotic that is produced by the fungus Penicillium.
It was first isolated in 1928 by Alexander Fleming from contaminated Petri
dishes. He succeeded in extracting some of the fungus and used it to treat an
infected wound. He called this extract penicillin. The technology at that time
was too limited to allow him to culture and study the fungus successfully, so he
saved the culture and moved on to a different research field.
These days the fungus Penicillium is grown in fermenters and the penicillin is
extracted from them.
Motor
Acid/alkali reservoir
___
to control pH
___
___
___
__
Nutrients in
Waste air out
Water jacket
to control
temperature.
Water out
Paddles
to stir
culture.
Cold water in
Sterile air in
to maintain
aerobic
conditions for
the fungus.
Tap for
draining
the culture
medium.
Air diffuser
to bubble the
air through the
culture.
Fig. 1 Typical plan of a fermenter used to produce Penicillin.
The Process
1. A starter culture of Penicillium is added to a culture medium containing
nutrients in a fermenter.
2. The fermenter allows fine control of the air supply, temperature and pH to
ensure optimal growth by the fungus.
3. The fungus grows and secretes the antibiotic into the culture medium.
4. When the incubation comes to an end the culture medium is filtered and the
penicillin is extracted from the filtrate.
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39
Microorganisms and their Applications
Using Microbes for Food Production
Three examples of foods produced by using microbes are:
• Bread
• Cheese
• Yoghurt
Case Study – Mycoprotein
Mycoprotein is the ingredient common to all Quorn™ products.
Mycoprotein, means ‘protein from fungus’.
It is produced using the fungus Fusarium that
grows and reproduces rapidly on relatively
cheap sugar syrup (made from waste carbohydrate)
in large specialised fermenters. It needs aerobic
conditions to grow successfully and can double
its mass every five hours.
The fungal biomass is harvested and purified.
Then it is dried and processed to make mycoprotein.
This is a pale yellow solid with a faint taste of mushrooms. On its own it has very
little flavour.
However, mycoprotein can be given a range of tastes and flavours to make it
similar to many familiar foods. It is a high-protein, low-fat meat substitute. So
vegetarians and people who want to reduce the fat in their diet plus people who
just like the taste use it.
Advantages of using microbes for food production:
•
•
•
Rapid and contained growth so minimum space is used.
A predictable product is made under controlled conditions.
Waste materials from other processes may be used as a food source for
the microorganisms, e.g. whey from the production of cheese, may be
used as a food source for the microorganisms.
Environmental Uses of Microbes
Microorganisms have an important role in decay and organic breakdown, e.g.
digesting all the foliage dropped by trees in woods.
Other examples of the environmental advantages of microbes are:
• Some micro-organisms are able to break down some plastics;
• Cleaning up pollution, e.g. oil eating micro-organisms that use oil as food;
• Production of biofuels by microorganisms, e.g. ethanol made from sugar
cane, sugar beet or corn. The sugar from these crops can be fermented to
ethanol by microorganisms.
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