g) gas exchange

What happens with gas exchange during photosynthesis with CO2?

When a plant photosynthesises it uses lots of CO2 leaving hardly any in the leaf. This makes more CO2 move into the leaf by diffusion.

How are leaves adapted for gas exchange?

1. They’re broad so have a large surface area for diffusion.

2. They’re thin so gases gave a short distance to travel.

3. Have air spaces inside the leaf which lets gases move easily between cells.

What is the role of the stomata in gas exchange?

Allow gases to diffuse in and out.

Allow water to escape(transpiration).

Close as it gets dark so water doesn’t escape meaning plant doesn’t dry out.

What happens during photosynthesis and respiration when light intensity is high?

Plants make more oxygen by photosynthesis than they use in respiration. So they release oxygen in daylight.

They use up more carbon dioxide than they produce so they take in CO2.

What happens during photosynthesis and respiration in plants when light intensity is low?

Plants only respire in night.

Take in oxygen and release CO2.

In a hydrogen-carbonate indicator what colour shows a normal, increased and decreased CO2 concentration?

Normal: orange

Increase: Yellow

Decrease: purple

How to investigate the effect of light on gas exchange from a. Leaf using hydrogen-carbonate indicator?

1. Add same volume of hydrogen-carbonate indicator to four boiling tubes.

2. Put leaves into 3 of the tubes and seal with rubber bung.

3. Wrap one in aluminium foil and one in gauze.

4. Place all tubes in bright light.

5. Leave tubes for hour and check colour.

What should the results be of the boiling tubes in the hydrogen-carbonate indicator practical?

Control- orange

Foil- yellow

Gauze- orange

Uncovered- purple