The respiration/transpiration also applies to plants where oxygen is required by cell respiration and carbon dioxide is released into the air
The stoma structure:
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
Effects of pollution on plants and preventive measures:
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
Example question:
The table shows two different situations faced by climbers when climbing two different mountains.
Elevation above sea level:
9 000 m
Use an oxygen tank
4 000 m
Do not use an oxygen tank
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.
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