Transport Systems (Edexcel IGCSE Science (Double Award): Biology): Flashcards
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By which three processes do cells exchange substances?
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By which three processes do cells exchange substances?
Diffusion
Osmosis
Active transport
All across the cell membrane.
Why can unicellular organisms rely on diffusion alone?
They have a large surface area relative to their volume, so the distance from the surface to the centre is small.
Diffusion, osmosis and active transport through the cell membrane are therefore sufficient.
Give an example of a unicellular organism with no transport system.
An amoeba.
Why do multicellular organisms need a transport system?
They have multiple cell layers, so the distance from the surface to the centre is too long for diffusion alone.
Diffusion to every cell would be too slow to meet the organism's needs.
Which transport system do animals have, and what does it carry?
The circulatory system, which carries substances in the blood — for example oxygen, glucose, carbon dioxide, water and urea.
Which transport system do plants have?
The vascular system:
Xylem — moves water and mineral ions from roots to shoots
Phloem — distributes sugars and amino acids through the plant
Unicellular organisms have a large ＿＿＿＿＿＿＿＿ relative to their volume, so diffusion is sufficient.
Unicellular organisms have a large surface area relative to their volume, so diffusion is sufficient.
In animals, substances are carried around the body by the ＿＿＿＿＿＿＿＿ system.
In animals, substances are carried around the body by the circulatory system.
True or False?
An amoeba needs a specialised exchange surface.
False.
Its surface area to volume ratio is large enough that the cell membrane alone can meet its exchange needs.
True or False?
Diffusion alone would be too slow to supply every cell in a human.
True.
This is exactly why larger, multicellular organisms need a transport system.
Why must all organisms exchange substances with their environment?
To take in food molecules and remove waste, so that they can function properly.
Name four substances carried in human blood.
Oxygen
Glucose
Carbon dioxide
Urea
Water is also transported.
What does the xylem transport, and in which direction?
Water and mineral ions, from the roots to other parts of the plant.
What does the phloem transport?
Sucrose and amino acids, from where they are produced or stored to where they are needed.
Describe the structure of a xylem vessel.
A hollow tube of dead cells with the end walls broken down, reinforced by lignin.
This gives an unbroken channel for water to travel from the roots to the rest of the plant.
Describe the structure of the phloem.
A tube formed from living cells, with small holes through which substances can move.
Why does the phloem carry sucrose away from the leaves?
Because sucrose and amino acids are produced in the leaves during photosynthesis, and must be moved to other parts of the plant that need them.
Which two tissues make up the transport system of a plant?
Xylem
Phloem
Xylem vessels are reinforced by ＿＿＿＿＿＿＿＿, which strengthens the hollow tube.
Xylem vessels are reinforced by lignin, which strengthens the hollow tube.
The phloem transports ＿＿＿＿＿＿＿＿ and amino acids around the plant.
The phloem transports sucrose and amino acids around the plant.
True or False?
Xylem vessels are made of living cells.
False.
Xylem is a hollow tube of dead cells reinforced by lignin. It is the phloem that is made of living cells.
True or False?
The xylem carries water only upwards from the roots.
True.
Water and mineral ions travel in one direction only — from the roots to other parts of the plant.
Why does a multicellular plant need a transport system?
Most of its cells are too far from the surface for diffusion alone to supply them quickly enough, because it has a small surface area to volume ratio.
Give one structural difference between xylem and phloem.
Xylem is made of dead cells with the walls between them broken down; phloem is made of living cells with small holes between them.
Name the four components of blood.
Red blood cells
White blood cells
Platelets
Plasma
Which component makes up over half the volume of blood?
Plasma.
Most of the other half is red blood cells, with white blood cells and platelets making up the small remaining fraction.
Describe the structure of a red blood cell.
A biconcave disc with no nucleus, containing haemoglobin.
Describe the structure of a white blood cell.
A large cell containing a large nucleus.
Different types have slightly different structures and functions.
What are platelets?
Fragments of cells.
Describe the appearance of plasma.
A clear, straw-coloured aqueous solution, in which the other blood components are suspended.
Name five things plasma transports.
Carbon dioxide, from respiring cells to the lungs
Digested food and mineral ions, from the small intestine to cells
Urea, to the kidneys
Hormones, from glands to target organs
Heat energy, to cooler parts of the body or to the skin
Where does plasma carry carbon dioxide from and to?
From respiring cells to the lungs, dissolved in the plasma.
Where does plasma transport urea to?
The kidneys.
Give the three adaptations of red blood cells for carrying oxygen.
Packed with haemoglobin, a protein that binds oxygen to form oxyhaemoglobin
No nucleus, leaving more space for haemoglobin
A biconcave disc shape, giving a larger surface area to volume ratio for fast diffusion
What does haemoglobin form when it binds to oxygen?
Oxyhaemoglobin.
Why is the biconcave disc shape useful?
It makes the cell thinner in the middle than at the edges, giving a larger surface area to volume ratio so oxygen diffuses in and out quickly.
Red blood cells have no ＿＿＿＿＿＿＿＿, which leaves more room for haemoglobin.
Red blood cells have no nucleus, which leaves more room for haemoglobin.
Hormones are chemical messengers transported around the body in the ＿＿＿＿＿＿＿＿.
Hormones are chemical messengers transported around the body in the plasma.
True or False?
Plasma helps distribute heat around the body.
True.
Heat energy created in respiration is transferred in the plasma to cooler parts of the body, or to the skin where it can be lost.
True or False?
Platelets are complete cells.
False.
Platelets are fragments of cells.
Name the two main types of white blood cell.
Phagocytes
Lymphocytes
How does a phagocyte destroy a pathogen?
Its sensitive cell surface membrane detects chemicals produced by the pathogen.
It then engulfs the pathogen and releases digestive enzymes to digest it.
Why is phagocytosis described as a non-specific response?
Because a phagocyte will engulf and digest any pathogen it encounters, not just one particular type.
Define antigen.
A marker on the surface of a cell or pathogen that the body recognises as foreign, causing the immune system to respond.
Define antibody.
A protein made by lymphocytes whose shape is complementary to an antigen.
When attached, it clumps pathogens together and marks them for destruction.
Why is the lymphocyte response described as specific?
Because the antibodies produced will only fit one type of antigen.
Describe the immune response to an infection.
The pathogen enters the bloodstream and multiplies, releasing toxins and infecting body cells, which causes symptoms.
Phagocytes engulf and digest pathogens they encounter.
Lymphocytes recognise the pathogen and release antibodies specific to it.
Antibodies bind to the pathogens and mark them for destruction, and phagocytes engulf them.
How does a white blood cell differ from a red blood cell?
A white blood cell has a nucleus; a red blood cell does not
White blood cells defend against pathogens; red blood cells transport oxygen
Why can a pathogen still make you ill before the immune response works?
Lymphocytes take time to produce enough specific antibodies.
In the meantime the pathogen multiplies and releases toxins, causing symptoms.
How do the roles of phagocytes and lymphocytes differ?
Phagocytes engulf and digest pathogens — this works against any pathogen
Lymphocytes release antibodies that are specific to one pathogen
What is the role of the immune system once a pathogen enters?
To prevent the infectious organism from reproducing and to destroy it.
Antibodies are produced by ＿＿＿＿＿＿＿＿, a type of white blood cell.
Antibodies are produced by lymphocytes, a type of white blood cell.
Phagocytes engulf pathogens and release digestive ＿＿＿＿＿＿＿＿ to break them down.
Phagocytes engulf pathogens and release digestive enzymes to break them down.
True or False?
One antibody can bind to any antigen.
False.
Each antibody's shape is complementary to one specific antigen, so it fits only that one.
True or False?
Antibodies destroy pathogens by digesting them.
False.
Antibodies bind to the pathogen and mark it for destruction — the digesting is done by phagocytes.
Why is the heart described as a double pump?
The left side pumps oxygenated blood from the lungs to the rest of the body (the systemic circuit).
The right side pumps deoxygenated blood from the body to the lungs (the pulmonary circuit).
Why is the left ventricle wall thicker than the right?
Because it must pump blood at high pressure around the entire body, while the right ventricle only pumps at lower pressure to the lungs.
Define septum.
The muscle wall that separates the two sides of the heart.
What is the function of the coronary arteries?
They supply the heart's own cardiac muscle tissue with oxygenated blood, so it can respire aerobically and keep contracting.
What is the function of the valves in the heart?
To prevent blood flowing backwards.
Trace deoxygenated blood from the body to the lungs.
It flows through the vena cava into the right atrium.
The atrium contracts, forcing blood through the tricuspid valve into the right ventricle.
The ventricle contracts, pushing blood through the semilunar valve into the pulmonary artery, and on to the lungs.
Trace oxygenated blood from the lungs to the body.
It returns via the pulmonary vein into the left atrium.
The atrium contracts, forcing blood through the bicuspid valve into the left ventricle.
The ventricle contracts, pushing blood through the semilunar valve and out of the aorta.
Why is blood pumped to the lungs at low pressure?
To prevent damage to the delicate capillaries in the lungs.
In which direction do arteries and veins carry blood?
Arteries carry blood away from the heart
Veins carry blood towards the heart
Which valve sits between the left atrium and left ventricle?
The bicuspid (atrioventricular) valve.
Which valve sits between the right atrium and right ventricle?
The tricuspid (atrioventricular) valve.
Deoxygenated blood from the body enters the heart through the ＿＿＿＿＿＿＿＿.
Deoxygenated blood from the body enters the heart through the vena cava.
Oxygenated blood leaves the left ventricle through the ＿＿＿＿＿＿＿＿.
Oxygenated blood leaves the left ventricle through the aorta.
True or False?
Both atria contract at the same time.
True.
Both atria contract together, and both ventricles contract together — even though the pathway is usually described one chamber at a time.
True or False?
The left side of a heart diagram shows the heart's left side.
False.
The heart is labelled as if it were in the chest, so the left of the diagram is the patient's right side, and vice versa.
How is heart rate measured?
By counting the number of times the heart beats in a minute (bpm).
Define adrenaline.
A hormone released by the adrenal glands that prepares the body for action.
Where is adrenaline produced?
In the adrenal glands, which sit just above the kidneys.
Why does the heart rate increase during exercise?
Muscle cells respire faster to release more energy for contraction, increasing the demand for oxygen and glucose and for the removal of carbon dioxide.
What two changes does the nervous system make during exercise?
Increases heart rate, so oxygen and glucose arrive faster and carbon dioxide is removed faster
Increases the volume of blood pumped per beat, so more blood reaches the muscles each minute
Why does the heart rate stay high after exercise ends?
To keep supplying the oxygen needed to break down the lactic acid that built up during anaerobic respiration.
How does adrenaline affect the heart rate?
It increases heart rate as part of the 'fight or flight' response, preparing the body for action.
Why does the heart pump blood to respiring cells?
To supply oxygen and glucose for respiration and to remove carbon dioxide.
When does anaerobic respiration occur during exercise?
During intense exercise, when the oxygen supply is insufficient to meet the muscle cells' energy needs.
Aerobic respiration still continues at the same time.
During exercise the heart rate ＿＿＿＿＿＿＿＿, so oxygen reaches the muscles faster.
During exercise the heart rate increases, so oxygen reaches the muscles faster.
The hormone ＿＿＿＿＿＿＿＿ increases heart rate as part of the fight or flight response.
The hormone adrenaline increases heart rate as part of the fight or flight response.
True or False?
Heart rate returns to normal the moment exercise stops.
False.
It remains high for a period, to supply the oxygen needed to break down the lactic acid built up during anaerobic respiration.
True or False?
Exercise increases the volume of blood pumped per heartbeat.
True.
Both the rate and the volume per beat increase, so much more blood reaches the muscles each minute.
What happens to the coronary arteries in coronary heart disease?
Layers of fatty material (plaque) build up inside them, narrowing the lumen and reducing blood flow to the cardiac muscle.
What are the fatty deposits in the coronary arteries mainly made of?
Cholesterol.
What are the two sources of cholesterol in the body?
Dietary cholesterol, from animal products eaten
Cholesterol synthesised by the liver
What does a partial blockage of a coronary artery cause?
Restricted blood flow to the cardiac muscle cells, causing severe chest pains called angina.
What does a complete blockage of a coronary artery cause?
A heart attack — cells in that area of the heart can no longer respire aerobically.
Name four risk factors for coronary heart disease.
Obesity
High blood pressure
High cholesterol
Smoking
Why does obesity increase the risk of coronary heart disease?
Carrying extra weight puts a strain on the heart, and can lead to Type 2 diabetes, which further damages the blood vessels.
Why does high blood pressure increase the risk?
It increases the force of the blood against the artery walls, which damages the vessels.
Why does high cholesterol increase the risk?
It speeds up the build-up of fatty plaques in the arteries, leading to blockages.
Give three ways smoking increases the risk of heart disease.
Chemicals in smoke increase plaque build-up
They also increase blood pressure
Carbon monoxide reduces the oxygen-carrying capacity of red blood cells
What do the coronary arteries supply the heart muscle with?
Oxygen and glucose.
The fatty plaques that build up in the coronary arteries are formed mainly from ＿＿＿＿＿＿＿＿.
The fatty plaques that build up in the coronary arteries are formed mainly from cholesterol.
Severe chest pain caused by restricted blood flow to the heart muscle is called ＿＿＿＿＿＿＿＿.
Severe chest pain caused by restricted blood flow to the heart muscle is called angina.
True or False?
All the cholesterol in the body comes from the diet.
False.
Some is dietary, from animal products, but cholesterol is also synthesised by the liver.
True or False?
Obesity can lead to Type 2 diabetes, which damages blood vessels.
True.
This is one of the ways obesity raises the risk of coronary heart disease, alongside the extra strain on the heart.
Name the three main types of blood vessel.
Arteries
Veins
Capillaries
What are arterioles and venules?
Arterioles — the smaller vessels that branch off arteries
Venules — the small vessels that join to form veins
Give the key features of an artery.
Carries blood at high pressure away from the heart
Carries oxygenated blood, except the pulmonary artery
Thick muscular walls containing elastic fibres
A narrow lumen
Blood flows fast
How is an artery adapted to its function?
The thick muscular walls with elastic fibres withstand the high pressure and maintain it by recoiling after blood has passed.
The narrow lumen also helps maintain the high pressure.
Give the key features of a vein.
Carries blood at low pressure towards the heart
Carries deoxygenated blood, except the pulmonary vein
Thin walls and a large lumen
Contains valves
Blood flows slowly
How is a vein adapted to its function?
Its large lumen reduces resistance to blood flowing under low pressure.
Its valves prevent the backflow of blood.
Give the key features of a capillary.
Carries blood at low pressure within tissues
Carries both oxygenated and deoxygenated blood
Walls are one cell thick and 'leaky'
Blood flows slowly
How is a capillary adapted to its function?
Walls one cell thick give a short diffusion distance, so substances diffuse in and out easily.
'Leaky' walls let blood plasma leak out and form tissue fluid around the cells.
Why do veins need valves but arteries do not?
Blood in veins is under low pressure, so it could flow backwards. Blood in arteries is under high pressure, which keeps it moving forwards.
Arteries have a narrow lumen and thick muscular walls to withstand ＿＿＿＿＿＿＿＿ blood pressure.
Arteries have a narrow lumen and thick muscular walls to withstand high blood pressure.
Plasma leaking out of capillaries forms ＿＿＿＿＿＿＿＿, which surrounds the cells.
Plasma leaking out of capillaries forms tissue fluid, which surrounds the cells.
True or False?
All arteries carry oxygenated blood.
False.
The pulmonary artery is the exception — it carries deoxygenated blood from the heart to the lungs.
True or False?
Capillary walls are one cell thick.
True.
This gives a short diffusion distance, so substances can pass in and out easily.
Which vessel carries blood most slowly, and why does that help?
The capillaries. Slow flow at low pressure gives more time for diffusion of substances into and out of the surrounding tissues.
Describe the general structure of the circulatory system.
A closed network of blood vessels connected to the heart, with blood flowing in one direction.
Trace the vessels from an artery to a vein within an organ.
Artery ➔ arteriole ➔ capillary ➔ venule ➔ vein
Respiring cells in the organ use up the oxygen from the blood in the capillaries.
Which artery and vein are exceptions to the usual rule?
The pulmonary artery carries deoxygenated blood away from the heart
The pulmonary vein carries oxygenated blood to the heart
Name the vessels carrying blood to and from the heart.
Towards — vena cava and pulmonary vein
Away — aorta and pulmonary artery
Name the vessels carrying blood to and from the lungs.
Towards — pulmonary artery
Away — pulmonary vein
Name the vessels carrying blood to and from the liver.
Towards — hepatic artery and hepatic portal vein
Away — hepatic vein
Name the vessels carrying blood to and from the kidneys.
Towards — renal artery
Away — renal vein
Why does the liver receive blood from two vessels?
The hepatic artery brings oxygenated blood
The hepatic portal vein brings blood carrying the products of digestion from the small intestine
Why does blood leaving an organ usually carry less oxygen?
Because the respiring cells in the organ have used up the oxygen from the blood.
The liver is unusual because it receives blood from both the hepatic artery and the hepatic ＿＿＿＿＿＿＿＿ vein.
The liver is unusual because it receives blood from both the hepatic artery and the hepatic portal vein.
Blood is carried away from the kidney in the ＿＿＿＿＿＿＿＿ vein.
Blood is carried away from the kidney in the renal vein.
True or False?
Blood in the circulatory system can flow in either direction.
False.
The circulatory system is a closed network in which blood flows in one direction only.
True or False?
The pulmonary vein carries oxygenated blood.
True.
It is the exception among veins, carrying oxygenated blood from the lungs back to the heart.
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