Gas Exchange in Flowering Plants Edexcel IGCSE

Hydrogen Carbonate indicator indicates what

how much carbon dioxide is present

Colour of Hydrogen Carbonate indicator in no change of concentration of carbon dioxide

orange

colour of Hydrogen Carbonate indicator in a decrease of carbon dioxide concentrations

purple

colour of Hydrogen Carbonate indicator in an increase in carbon dioxide concentrations

yellow

Role of Diffusion in gas exchange

• Oxygen diffuses into cells for respiration.

• Carbon dioxide diffuses out as a waste product.

• In plants, gases move through stomata and air spaces in the leaf.

Gas exchange in relation to respiration and photosynthesis

• Respiration: Oxygen is taken in, and carbon dioxide is released.

• Photosynthesis: Carbon dioxide is absorbed, and oxygen is released.

• During the day, photosynthesis occurs alongside respiration, leading to a net oxygen release. At night, only respiration happens, so carbon dioxide is released.

Leaf Structure Adaptations for Gas Exchange

• Large surface area for maximum diffusion.

• Thin structure for short diffusion distance.

• Air spaces in the spongy mesophyll to allow gas movement.

• Stomata to regulate gas entry and exit.

Role of Stomata in Gas Exchange

Stomata are tiny pores on the leaf surface controlled by guard cells:

• Open during the day to allow carbon dioxide in for photosynthesis.

• Close at night or in dry conditions to prevent water loss.

• Facilitate oxygen release and carbon dioxide uptake.

Respiration and Light Intensity

• Daytime: Photosynthesis exceeds respiration, leading to a net oxygen release.

• Nighttime: Only respiration occurs, causing a net carbon dioxide release.

• Low light intensity: Photosynthesis slows, and respiration dominates.