Gas and solute exchange

Question 1

What do life processes need before they can happen?

Answer 1

Gases, or other dissolved substances.

Question 2

What does photosynthesis need in plant cells to happen?

Answer 2

Carbon dioxide and water.

Question 3

What does respiration need in cells to take place?

Answer 3

Glucose and oxygen.

Question 4

How do substances get where they need to be?

Answer 4

By diffusion, osmosis and active transport.

Question 5

What is diffusion?

Answer 5

Diffusion is the movement of particles from an area of high concentration to an area of low concentration.

Question 6

Examples of diffusion?

Answer 6

Gases diffusing through one another (like a smell spreading through a room), or dissolved particles diffusing in and out of cells through cell membranes.

Question 7

In life processes what do gases and dissolved substances have to move through?

Answer 7

Some sort of exchange surface.

Question 8

What do exchange surfaces have to do?

Answer 8

They have to allow enough of the necessary substances to pass through.

Question 9

How are exchange surfaces adapted to maximise effectiveness?

Answer 9

• They are thin, so substances only have a short distance to diffuse.
• They have a large surface area so lots of a substance can diffuse at once.
• Exchange surfaces in animals contain lots of blood vessels, to get stuff into and out of the blood quickly.
• Gas exchange surfaces In animals are often ventilated too (air moves in and out).

Question 10

What does the structure of leaves do?

Answer 10

They allow gases to diffuse in and out of cells.

Question 11

Where does carbon dioxide diffuse to in a leaf?

Answer 11

It diffuses into the air spaces within the leaf, and then it diffuses into the cells where photosynthesis takes place.

Question 12

How is a leafs structure adapted so that carbon dioxide can diffuse through?

Answer 12

The underneath of the leaf is an exchange surface. Its covered with little holes called stomata, which allow carbon dioxide to diffuse through.

Question 13

What else diffuses out of the stomata?

Answer 13

• Oxygen

- Water vapour

Question 14

What controls the size of the stomata?

Answer 14

Guard cells

Question 15

What do guard cells do?

Answer 15

They close the stomata if the plant is loosing water faster than it is being replaced by the roots (without guard cells the plant would soon wilt).

Question 16

How is a leafs exchange surface adapted to maximise effectiveness?

Answer 16

• The flattened shape of the leaf increases the area of the exchange surface
• The walls of the cells inside the leaf form another exchange surface, the air spaces inside the leaf increase the area of this surface so there is more chance for carbon dioxide to get into the cells.

Question 17

Where does the water vapour evaporate from?

Answer 17

From the cells inside the leaf.

Question 18

How does the water vapour escape the leaf?

Answer 18

By diffusion because there is a lot of it inside the leaf and less of it in the air outside.

Question 19

What conditions make evaporation quicker?

Answer 19

• Hot
• Dry
• Windy