| 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
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The stoma structure:
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Opened Stoma
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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
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- At night, photosynthesis does not apply
- Water exits the control cell via osmosis
- The guard cells become wrinkled and the stoma closes
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Effects of pollution on plants and preventive measures:
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Contaminants
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Effect
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- Smoke
- Dust
- Haze
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- 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
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- The gases dissolve in rainwater into acid rain
- Acid rain makes acidic soils unsuitable for cultivation
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Example question:
| Question |
Answer |
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The table shows two different situations faced by climbers when climbing two different mountains.
| Mountain X |
Mountain Y |
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Elevation above sea level:
9 000 m
Use an oxygen tank
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Elevation above sea level:
4 000 m
Do not use an oxygen tank
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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.
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