2(h)

Question 1

Why can unicellular organisms rely on diffusion for movement of substances in and out of their cell?

Answer 1

Unicellular organisms have a high surface area to volume ratio and therefore can obtain nutrients and excrete waste by diffusion.

Question 2

Why do multicellular organisms need transport systems?

Answer 2

Direct diffusion from the outer surface would be too slow because substances would have to travel large distances to reach every single cell.

Question 3

What is the role of the xylem in plants?(3)

Answer 3

The xylem transports water and minerals from the roots up the shoot to the leaves in the transpiration stream. The xylem is made up of dead cells and can only transport upwards.

Question 4

What is the role of the phloem in plants?(4)

Answer 4

The phloem tubes transport sugars like sucrose and amino acids from where they’re made in leaves to other parts of plant.
This movement is called translocation.
Transport in the phloem can go up or down and the phloem is made of living cells.

Question 5

CHANGE

Answer 5

CARD

Question 6

Where is the phloem and xylem in micrographs of stem cell?(3)

Answer 6

The xylem is on the inside and the phloem is on the outside. Meanwhile the procambium is the line in-between them.

Question 7

How are root hair cells adapted to absorb water?(3)

Answer 7

They have a large surface area, thin cell wall, and lots of salts in their vacuoles so that the water potential of the cell is very low for osmosis.

Question 8

Describe and explain the process of transpiration?(4)

Answer 8

Transpiration is caused by the evaporation and diffusion of water from a plant’s surface. Most but not all at the leaves.
The evaporation causes a shortage of water in the leaf so more water is drawn up from the rest of the plant through the xylem vessels.
Cohesion in water molecules pull up the water molecules as one chain.
This in turn creates a constant stream of transpiration.

Question 9

State how and why increasing humidity affects rate of transpiration?(2)

Answer 9

Increasing humidity decreases the rate of transpiration because there is a higher concentration of water molecules outside the plant therefore the concentration gradient is shallow so less diffusion.

Question 10

State how and why increasing light intensity affects rate of transpiration?(2)

Answer 10

Increasing light intensity increases the rate of transpiration because the stomata don’t open at night because they don’t need to let out CO2 to photosynthesise therefore very little water can escape.

Question 11

State how and why increasing wind speed affects rate of transpiration?(3)

Answer 11

Increasing wind speed increases the rate of transpiration. If the wind speed around a leaf is low, water vapour just surrounds the leaf and doesn’t move away. Diffusion happens quickly from an area of high concentration to an area of low concentration.

Question 12

State how and why increasing temperature affects rate of transpiration?(2)

Answer 12

Increasing the temperature increases the rate of transpiration. When its warm particles have more energy to evaporate and diffuse out of the stomata.

Question 13

Explain how you can estimate transpiration rate using a Potometer.(6)

Answer 13

Cut a shoot underwater to prevent air from entering the xylem. Cut it at a slant to increase the surface area available for water uptake.
Assemble the potometer in water and insert the shoot underwater so no air can enter.
Remove the apparatus from the water but keep the end of the capillary tube submerged in a beaker of water.
Dry the leaves, allow time for the shoot to acclimatise and then shut the tap.
Remove the end of the capillary tub from the beaker of water until one air bubble has formed and then put it back.
Measure the start and final position of the air bubble.

Question 14

State the important things that plasma carries in the blood?(5)

Answer 14

Red and white blood cells and platelets.
Digested food products from the gut to all the body cells.
Carbon dioxide from the body cells to the lungs.
Urea from the liver to the kidneys.
Hormones.
Heat energy.

Question 15

What are platelets?(3)

Answer 15

Platelets clump together to plug damaged areas when you damage a blood vessel. This is called a blood clot.
In a blood clot platelets are held together by a mesh of protein called fibrin.
This stops bleeding and microorganisms from entering your body.

Question 16

How are red blood cells adapted for their job of carrying oxygen?(4)

Answer 16

Have a biconcave shape to give a large surface area for absorbing and releasing oxygen.
Small to fit into capillaries.
Contains haemoglobin which reacts with oxygen in the lungs to become oxyhemoglobin.
Don’t have a nucleus which frees up space for more haemoglobin.

Question 17

How does exercise increase heart rate?(3)

Answer 17

Exercise increases the amount of carbon dioxide in the blood.
High levels of blood CO2 are detected by receptors in the aorta and carotid artery.
These receptors send signals to the brain which sends signals to the heart causing it to contract more frequently and with more force.

Question 18

How does the hormonal system help to control heart rate?(3)

Answer 18

When an organism is threatened(e.g by a predator) the adrenal glands release adrenaline.
Adrenaline binds to specific receptors in the heart. This causes the cardiac muscle to contract more frequently and with more force, so heart rate increases and the heart pumps more blood.
This increases oxygen supply to the tissues getting the body ready for action.

Question 19

How are the arteries adapted for their function?(5)

Answer 19

Very thick walls to withstand high pressure of oxygenated blood pumped from the heart.
Large amount of elastic tissue in the walls to allow the wall to stretch and recoil.
Lots of smooth muscles to allow vasoconstriction or vasodilation.
Small diameter of lumen to maintain high pressure.
No valves except for start of pulmonary artory and aorta.

Question 20

How are the veins adapted for their function?(5)

Answer 20

Thin walls because low pressure.
Small amount of elastic tissue as blood is low pressure.
Few smooth muscles as blood is returning to heart
Lumen has large diameter so blood moves easily.
Valves to prevent back flow of blood in veins.

Question 21

How are the capillaries adapted for their function?(3)

Answer 21

Only one cell thick to allow rapid exchange of substances between blood and tissues.
Tiny lumen diameter.
No elastic tissue, smooth muscles or valves.

Question 22

What are the main factors that can cause coronary heart disease?(3)

Answer 22

Having a diet high in saturated fat can lead to fatty deposits forming inside arteries.
Smoking increases blood pressure which can cause damage to the inside of the coronary arteries. Chemicals in the cigarette smoke can also cause damage. From this fatty deposits become more likely.
Being inactive can lead to high blood pressure which can damage the lining of arteries. This damage makes it more likely that fatty deposits will form.

Question 23

What is coronary heart disease?(2)

Answer 23

Coronary heart disease is when the coronary arteries that supply the blood to the muscle of the heart get blocked by layers of fatty material building up.
This causes the arteries to become narrow, so blood flow is restricted - this can lead to heart attack.

Question 24

What are phagocytes?(3)

Answer 24

70% of white blood cells are phagocytes, and they ingest microorganisms(such as bacteria) by producing extensions of their cytoplasm called pseudopodia.
The pseudopodia surrounds and encloses the microorganism into a vacuole, after which the phagocyte secretes enzymes to break the organism down.
This whole process is called phagocytosis.

Question 25

What are lymphocytes?(4)

Answer 25

25% of white blood cells are lymphocytes, they make chemicals called antibodies. Antibodies are soluble proteins that pass into plasma.
Pathogens such as viruses have chemical ‘markers’ on their surfaces which are recognised by the antibodies. These markers are called antigens.
The antibodies stick to the surface of the antigens and could do various things: cause bacteria to stick together so it is easier ingested by phagocytes; act as a label on pathogens so it is easier recognised by phagocytes; cause bacterial cells to burst open; neutralise toxins produced by pathogens.

Question 26

Explain immunity?(2)

Answer 26

Upon infection, some lymphocyte cells may not get involved in killing microorganisms and instead develop into memory cells. These remain in the blood for up to a lifetime.
If the same microorganism re-infects a person, the memory lymphocytes start to reproduce and produce antibodies rapidly. This is a secondary immune response and is much faster, greater scale and more effective than a primary response.

Question 27

How can vaccination induce artificial immunity?(2)

Answer 27

A person is injected with an ‘agent’ that carries the same antigens as a specific pathogen. The immunity process then occurs.
Some agents used as vaccines may be; a weakened strain of the actual microorganism; dead microorganisms; modified toxins of the bacteria.