Exchange of Materials

Question 1

Dissolved Substances move by which two processes?

Answer 1

Diffusion and Active Transport

Question 2

Water moves across partially permeable membranes by which process?

Answer 2

Osmosis

Question 3

What is Osmosis?

Answer 3

Osmosis is the diffusion of water from a high water concentration (dilute solution) to an area of low water concentration (concentrated solution) across a partially permeable membrane.

Question 4

What is Active transport?

When may cells use active transport?

Answer 4

Active transport is the process used by cells to absorb substances across a partially permeable membrane, from a low concentration to a high concentration, against the concentration gradient. This requires the use of energy released in respiration.
Cells use active transport when they need to absorb substances that are in short supply, i.e. agains the concentration gradient.

Question 5

The efficiency of an exchange surface is increased by what 3 factors?

Answer 5

1) Having a large surface area
2) Having thin walls, to provide a short diffusion path.
3) Having an efficient transport system (in animals) having an efficient blood supply.

Question 6

What do the lungs contain?
In humans the surface area of the lungs is increased by which structure?
What features of alveoli make them efficient exchange surfaces?
Why are the lungs ventilated?

Answer 6

The lungs contain the gaseous exchange surface.
The alveoli, which are efficient exchange surfaces because they have thin walls, a large surface area and a good blood supply.
The lungs are ventilated to maintain a steep diffusion gradient.

Question 7

What are villi?

Give two features of villi which make them efficient exchange surfaces.

Answer 7

Villi are finger like projections which line the inner surface of the small intestine, they greatly increase the surface area for absorption to take place.
The walls of the villi are very thin and there are many capillaries close to the wall.

Question 8

What two properties of osmosis are similar to diffusion?

Answer 8

1) The movement of water molecules is random.

2) Osmosis requires no energy from the cell.

Question 9

What type of membrane is the cell membrane?

Answer 9

The cell membrane is a partially permeable membrane.

Question 10

Give two examples of when cells use active transport?

Answer 10

1) Root cells absorb mineral ions from the dilute solutions in the soil by active transport.
2) Glucose can be reabsorbed in the kidney tubules by active transport.

Question 11

Describe the gaseous exchange that occurs in the alveoli.

Answer 11

Oxygen diffuses into the many capillaries surrounding the alveoli and carbon dioxide diffuses back out into the lungs to be breathed out.

Question 12

Explain how the food we eat is digested.

Answer 12

The food we eat is digest in the gut into small, soluble molecules. In the small intestine these solutes are absorbed into the blood. The villi line the inner surface of the small intestine and are the exchange surface for food molecules.

Question 13

How can the soluble products of digestion be absorbed into the villi?

Answer 13

The soluble products of digestion can be absorbed into the villi either by diffusion or active transport.

Question 14

How do gases diffuse in and out of leaves and what are the size of these controlled by?
What gases diffuse in and out? (2)
What does the movement of these gases depend on?

Answer 14

Gases diffuse in and out of leaves through tiny holes called ‘stomata’. The size of the stomata is controlled by guard cells which control them.
1) Oxygen: needed for respiration and is a waste product of photosynthesis.
2) Carbon dioxide: needed for photosynthesis and is a waste product of respiration.
The movement of these gases depends upon which process is taking place the most quickly.

Question 15

How do plants lose water vapour?

Answer 15

Plants lose water vapour through the stomata due to evaporation in the leaves.

Question 16

What features of plants means the gases do not need to diffuse very far? (3)

Answer 16

1) Leaves are flat
2) Leaves are very thin
3) There are internal air spaces

Question 17

What is the role of root hair cells?

What happens if plants lose water faster than it is replaced by the roots?

Answer 17

Root hair cells increase the surface are of roots for the absorption of water and mineral ions.
If plants loses water faster than it is replaced by the roots, the plant could become dehydrated and the stomata can close to prevent wilting.

Question 18

What is the transpiration stream?

Answer 18

The transpiration stream is the movement of water through plants. Plants take up water through the roots. The water passes through the plant to the leaves. In the leaves the water evaporates from the leaf cells and the water vapour diffuses out through the stomata.

Question 19

In what conditions is evaporation more rapid? (4)

What can be done to prevent excessive water loss?

Answer 19

Evaporation is more rapid in hot, dry, windy or bright conditions.
The guard cells can close to prevent excessive water loss, wilting of the whole plant can also reduce water loss. The leaves collapse and hang down, which reduces the surface area.

Question 20

What can a potometer be used for?

Answer 20

A potometer can be used to show how the uptake of water by plants changes with different conditions, which gives a good idea of the amount of water lost by transpiration.

Question 21

What do the lungs contain?

Where are the lungs situated?

Answer 21

The lungs contain the exchange surface of the breathing system.
The lungs are situated in the thorax, inside the ribcage and above the diaphragm which separates the lungs from the abdomen.

Question 22

What happens when we breathe in? (4)

Answer 22

When we breathe in:

1) The intercostal muscles between the ribs and the diaphragm contract.
2) The ribcage moves up and out and the diaphragm flattens.
3) The volume of the thorax increases.
4) The pressure in the thorax decreases and air is drawn in.

Question 23

What happens when we breathe out? (4)

What is the movement of air in and out of the lungs known as?

Answer 23

When we breathe out:
1) The intercostal muscles of the ribcage and diaphragm relax.
2) The ribcage moves down and in and the diaphragm becomes domed.
3) The volume of the thorax decreases.
4) The pressure in the thorax increases and air is forced out.
The movement of air into and out of the lungs is known as ventilation.

Question 24

Give three reasons why someone may not be able to get enough oxygen into their bloodstream.

Answer 24

1) If the alveoli are damage the surface area for gas exchange is reduced.
2) If the tubes leading to the lungs are narrowed, less air can be moved through them.
3) If the person is paralysed, their muscles will not work to pull the ribcage up and out.

Question 25

What was the ‘iron lung ventilator’ used for?
How did the ‘iron lung’ work to draw air into a persons lungs?
What kind of pressure did the vacuum that was formed inside the cylinder create?
How was air pumped out of the persons lungs?

Answer 25

The ‘iron lung’ was used for people with polio who were paralysed. The person lay with their chest sealed in a large metal cylinder. When air was drawn out the cylinder the person’s chest moved out and they breathed in.
The vacuum formed inside the cylinder created negative pressure.
When air was pumped back into the cylinder it created pressure on the person’s chest and forced air out of the person’s lungs.

Question 26

What sort of pressure do modern breathing aids use? How can air be transferred to the trachea?
What are the benefits of positive pressure aids? (3)

Answer 26

Modern breathing aids use positive pressure to force measured amounts of air into the lungs. Bags of air connected to masks can force air into the trachea.
Positive pressure aids are often smaller, easier to mange in the home and can be linked to computers for control.

Question 27

When you exercise, what do your muscles do and why?

What is used in the process?

Answer 27

When you exercise, your muscles respire to release energy. Glucose, a sugar is used in respiration.

Question 28

Why does your body sweat during exercise?
What does sweat contain?
What can happen if you sweat too much?
What may it be necessary to do if you exercise for a long time?

Answer 28

During exercise, the body sweats to cool down, sweat contains water and mineral ions. If you sweat too much the cells of the body may become dehydrated.
If you exercise for a long time it may be necessary to replace the sugar, mineral ions and water which have been lost or used.

Question 29

What are sports drinks?
What does the water in sports drinks help to do?
What are sports drinks designed to do?
What is an isotonic sports drink?

Answer 29

Sports drinks are solutions of sugar and mineral ions.
The water in the drinks helps to rehydrate body cells
Sports drinks are designed to help balance the concentration of body fluids and the concentrations inside cells.
Isotonic drinks are where the drink concentration matches the body fluids.

Question 30

What do some sports scientists say is just as good as a sports drinks for short periods of exercise?
Who may sports drinks be helpful to?

Answer 30

Some sports scientists say a drink of water is just as good for short periods of exercise.
The drinks may help athletes who need to replace mineral ions and sugar as well as water.