| 2.5 | The Gas Exchange In Plants |
| Definition |
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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 |
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- 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 |
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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:
| Question | Answer | ||||
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The table shows two different situations faced by climbers when climbing two different mountains.
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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. |
