The respiration/transpiration also applies to plants where oxygen is required by cell respiration and carbon dioxide is released into the air

Opened Stoma

Closed Stoma

- During the day, photosynthesis

- Water enters the control cell through the process of osmosis causing the control cell to become fresh and curved

- Oxygen permeates into the cells through the stoma

- High carbon dioxide released by body cells diffuses out through the stoma

- At night, photosynthesis does not apply

- Water exits the control cell via osmosis

- The guard cells become wrinkled and the stoma closes

Contaminants

Effect

- Smoke

- Dust

- Haze

- The smoke particles clog the stoma pores and the rate of photosynthesis is reduced

- The haze prevents the penetration of sunlight and the rate of photosynthesis is reduced

Toxic gases such as nitrogen and sulfur dioxide

- The gases dissolve in rainwater into acid rain

- Acid rain makes acidic soils unsuitable for cultivation

The table shows two different situations faced by climbers when climbing two different mountains.

Sample answers:

- Mount X is higher than Mount Y. The air pressure on Mount X is lower than on Mount Y. 

- The quantity of oxygen is very low on Mount X.

- Small air pressure differences between the thoraic cavity and the atmosphere make breathing difficult.

- The volume of air entering the lungs is reduced so the climber needs an oxygen tank.