2.49 – Understand why simple, unicellular organisms can rely on diffusion for movement
of substances in and out of the cell.
– Unicellular organisms can rely on diffusion for movement of substances in and out of
the cell.
– A transport system is not required because they have a large SA:Vol.
– The diffusion distance is short. Thus, diffusion occurs at a fast rate.
2.50 – Understand the need for a transport system in multicellular organisms.
– Multicellular organisms cannot rely on diffusion for the movement of substances in and
out of cells.
– Multicellular organisms have a small SA:Vol. Diffusion occurs at a slow rate.
– A transport system is required to speed up the transportation of necessary molecules
in and out of cells.
• Some multicellular organisms with a relatively large SA:Vol have a single circulatory
system (e.g. fish).
• Other multicellular organisms with a small SA:Vol have a double circulatory system
(e.g. humans).
FLOWERING PLANTS (2.51 – 2.56)
2.51 – Describe the role of phloem in transporting sucrose and amino acids
between the leaves and other parts of the plant.
– Source: An organ that produces more than it needs.
– Sink: An organ that consumes for growth or storage.
– Water from the xylem move to the phloem due to osmosis.
– A build up of turgor pressure causes the sucrose and amino acids to move to the sink.
– The phloem is made up of living cells arranged end to end, with joined cytoplasms.
• It transports sucrose for energy and amino acids for making proteins between the
leaves and other parts of the plant.
• Sucrose can be converted to starch for storage.
2.52 – Describe the role of xylem in transporting water and mineral salts from the roots to
other parts of the plant.
– The xylem consists of hollow, dead cells made of lignin.
• Water only needs to travel in one direction.
• Water and mineral salts dissolved in water can pass through the hollow areas.
– The xylem transports water and mineral salts from the roots to other parts of the plant.
2.53 – Explain how water is absorbed by root hair cells.
– Plant roots are covered by tiny hairs that increase the surface area for water / mineral
absorption.
– The specialised root hair cells penetrate through soil and reach soil water.
– Soil water is less concentrated than the solutes in the root hair cell, creating a waterpotential gradient.
– Water moves through the root hair cells by osmosis.
– The xylem then takes up the water.
2.54 – Understand that transpiration is the evaporation of water from the surface of a
plant.
– Transpiration: The evaporation of water from the surface of a plant.
• Heat from sunlight evaporates water in a plant. The steam leaves the plant via the
stomata.
2.55 – Explain how the rate of transpiration is affected by changes in humidity, wind
speed, temperature and light intensity.
– Humidity: High humidity decreases the concentration gradient around the leaf, thus
decreasing the rate of transpiration.
– Wind Speed: Wind removes any moisture on the surface of the stomata that might
otherwise reduce the concentration gradient and decrease the rate of transpiration.
– Temperature: High temperatures increase the rate of evaporation, thus increasing the
rate of transpiration.
– Light Intensity: The rate of transpiration is increased under intense light, because it
causes the stomata to open up more.
2.56 – Describe experiments to investigate the role of environmental factors in
determining the rate of transpiration from a leafy shoot.
– A potometer measures the rate of water uptake and the rate of transpiration of a leafy
shoot.
• Humidity: A polythene bag sealed around the plant to prevent water vapour from
diffusing away, keeping the humidity high.
• Wind speed: Use an adjustable fan to change the wind speed.
• Temperature: Use an adjustable heater to change the temperature.
• Light intensity: Use an adjustable lamp to change the light intensity
HUMANS (2.57 – 2.66)
2.57 – Describe the composition of the blood: red blood cells, white blood cells, platelets
and plasma.
2.58 – Understand the role of plasma in the transport of carbon dioxide, digested food,
urea, hormones and heat energy.
– The plasma transports carbon dioxide, digested food, urea, hormones and evenly
distributes heat energy around the body.
2.59 – Explain how adaptations of red blood cells, including shape, structure and the
presence of haemoglobin, make them suitable for the transport of oxygen.
– Red blood cells are enucleate (contain no nucleus). More haemoglobin can be
packed, allowing the cell to carry more oxygen.
– Diffusion occurs at a fast rate as red blood cells have a large SA:Vol.
– Red blood cells have a biconcave shape which allows efficient exchange of oxygen in
and out of the cell.
– Red blood cells are thin, providing a short diffusion distance to the centre of the cell.
Component Description Function
Red Blood Cells
(Erythrocytes)
Biconcave, disc-like cells
with no nucleus.
Transports oxygen around the body – contains mainly
haemoglobin which loads oxygen in the lungs and
unloads it in other regions of the body.＊
Phagocytes Much larger cells with a
lobed nucleus. Engulf pathogens by phagocytosis.
Lymphocytes
About same size as red
blood cells with a large
spherical nucleus.
Produces antibodies to destroy pathogens – some
lymphocytes persist in our blood after infections and
give us immunity to specific diseases (memory cells).
Platelets Fragments of other cells. Release chemicals to clot our blood when we cut
ourselves and create a wound.
Plasma Liquid part of blood
(mainly water).
Carries the blood around the body and also carries
dissolved nutrients, hormones, carbon dioxide and
urea; distributes heat around the body evenly.
2.58 – Understand the role of plasma in the transport of carbon dioxide, digested food,
urea, hormones and heat energy.
– The plasma transports carbon dioxide, digested food, urea, hormones and evenly
distributes heat energy around the body.
2.59 – Explain how adaptations of red blood cells, including shape, structure and the
presence of haemoglobin, make them suitable for the transport of oxygen.
– Red blood cells are enucleate (contain no nucleus). More haemoglobin can be
packed, allowing the cell to carry more oxygen.
– Diffusion occurs at a fast rate as red blood cells have a large SA:Vol.
– Red blood cells have a biconcave shape which allows efficient exchange of oxygen in
and out of the cell.
– Red blood cells are thin, providing a short diffusion distance to the centre of the cell
– Red blood cells have thin surface membranes which allow oxygen to diffuse through
easily.
– Red blood cells contain no mitochondria and respire anaerobically so none of the
oxygen is used up during transport.
2.60 – Describe how the immune system responds to disease using white blood cells,
illustrated by phagocytes ingesting pathogens and lymphocytes releasing antibodies
specific to the pathogen.
– Phagocytes ingest pathogens via phagocytosis.
• 1) The phagocyte detects the pathogen.
• 2) Pseudopodia, long extensions, surround the pathogen.
• 3) The pathogen is trapped in a vesicle.
• 4) Enzymes are secreted into the vesicle and destroys the pathogen.
– Lymphocytes release antibodies specific to the pathogen.
– Antibodies match to the antigens (‘markers’) of the pathogen.
• Antibodies cause pathogens to clump together. Phagocytes can then ingest them
more easily.
• Antibodies ‘label’ the pathogens so they are easily identified by phagocytes.
• Antibodies cause pathogenic cells to burst open.
• Antibodies neutralise toxins produced by pathogens.
2.61 – Understand that vaccination results in the manufacture of memory cells,
which enable future antibody production to the pathogen to occur sooner, faster
and in greater quantity.
– A vaccination results in the manufacture of memory cells.
– This enables future antibody production to the pathogen to occur sooner, faster and in
greater quantity.
– Vaccination: An injection of a weakened or dead pathogen into a person’s body.
2.62 – Understand that platelets are involved in blood clotting, which prevents
blood loss and the entry of micro-organisms.
– Platelets are involved in blood clotting, which prevents blood loss and the entry of
micro-organisms.
• Exposure to open air stimulates platelets to produce a chemical.
• The chemical causes fibrinogen (a soluble plasma protein) to change into fibrin
(insoluble fibres of another protein).
• Fibrin forms a network across the wound, trapping red blood cells.
• A clot is formed, which prevents further blood loss and the entry of microorganisms.
• The clot developed into a scab, which protects the damaged tissue while new skin
grows.
2.63 – Describe the structure of the heart and how it functions.
– Systole: Contraction of the heart.
– Diastole: Relaxation of the heart.
– The heart is divided into two halves by the septum.
– The four sections of the heart are: the left atrium, the right atrium, the left ventricle
and the right ventricle.
• The right ventricle pumps blood to the lungs only while the left ventricle pumps
blood to all other parts of the body.
– The walls of the left ventricle are thicker because pumping blood to all parts of the
body requires higher pressure.
• Bicuspid and tricuspid valves ensure that blood only flows in one direction only
• The walls of the atria are thin and can be stretched to receive blood as it returns to
the heart.
• The walls of the heart are made out of cardiac muscle, allowing the heart to pump
the blood at different pressures and speeds according to the body’s needs.
– Cardiac muscle can contract and relax continuously without being fatigued.
• The cardiac muscle has its own blood supply: the coronary circulation.
– Blood reaches the muscle via coronary arteries.
– Coronary arteries carry blood to capillaries that supply the heart muscle with
oxygen and nutrients.
– Blood is returned to the right atrium via coronary veins.
– The heart pumps blood through the cardiac cycle:
• 1) Blood enters the atria. Valves are closed so it cannot pass into the ventricles.
• 2) Atria contract, raising the blood pressure and opening the valves. Blood flows
into the ventricles.
• 3) Ventricles contract when they are filled with blood. Blood pressure rises and
closes the valves so blood cannot flow back into the atria.
• 4) Ventricles continue to contract and pressure continues to increase. Semilunar valves at the base of the aorta and the pulmonary artery are forced open.
Blood flows into these two arteries.
– The aorta is connected to the left ventricle. It pumps blood to all parts of the body.
– The pulmonary artery is connected to the right ventricle. It pumps blood to the
lungs.
• 5) The ventricles empty and higher pressure in the aorta and pulmonary artery
closes the semi-lunar valves. The cycle restarts as the atria is filled with blood.
2.64 – Explain how the heart rate changes during exercise and under the influence of
adrenaline.
– Adrenaline is a hormone secreted by the adrenal gland above the kidneys.
– Adrenaline creates a ‘fight or flight’ reaction.
• Breathing rate is increased and breaths become deeper. More oxygen is taken in.
• Heart rate is increased and blood is diverted to the muscles so they receive more
glucose and oxygen for respiration.
• Stored glycogen in the liver is converted back to glucose by the hormone glucagon
and is used by muscles for respiration.
• Pupil dilation occurs; pupils become larger and more light is taken in which
increases visual sensitivity to movement.
• Mental awareness and reaction rate is increased.
– During exercise, the heart uses more glucose and oxygen for respiration. It beats
faster, delivering more glucose and oxygen to muscle cells.
2.65 – Describe the structure of arteries, veins and capillaries and understand their roles.
– Arteries carry blood away from the heart to other organs.
• Arterial blood has a high pressure.
• Arterial walls are thicker to contain the blood pressure and have a thin endothelium.
• Arteries have a small lumen.
– Veins carry blood away from organs to the heart.
• Venous blood has a low pressure.
• Venous walls are thin and have a thick endothelium.
• Veins have a large lumen.
• Veins contain watch-pocket valves which prevent the backflow of blood.
– Capillaries carry blood through organs.
• Substances are transferred between the the capillaries and the organ.
• Capillaries are one cell thick to provide a short diffusion distance of substances.
2.66 – Understand the general structure of the circulation system to include the blood
vessels to and from the heart, the lungs, the liver and the kidneys.
– Vein: To the heart.
– Artery: Away from the heart.
– Lung: Pulmonary
– Liver: Hepatic
– Kidney: Renal
– Stomach: Gastric
– The hepatic portal vein lies between the gut and liver.