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प्रश्न
When there is plenty of light and a higher concentration of O2, what kind of pathway does the plant undergo? Analyse the reasons.
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उत्तर
The rate of photosynthesis decreases when there is an increase in oxygen concentration. This inhibitory effect of oxygen was first discovered by Warburg (1920) using green algae, chlorella.
Analysis and Reasons:
- Photorespiration Pathway: In conditions where there is abundant light and high oxygen concentration, the enzyme RuBisCO, which normally fixes carbon dioxide (CO2) during the Calvin cycle in photosynthesis, has a higher affinity for oxygen. Instead of binding to CO2, RuBisCO binds to O2, initiating photorespiration.
- Mechanism: During photorespiration, RuBisCO reacts with oxygen, leading to the formation of a two-carbon compound called phosphoglycolate, which is then converted into CO2 and energy in a series of reactions. However, unlike photosynthesis, photorespiration does not produce glucose or ATP and is considered an energy-wasting process.
- Reasons for Photorespiration:
- High O2 Concentration: When the concentration of oxygen is higher than that of carbon dioxide, RuBisCO is more likely to bind with oxygen.
- High Light Intensity: Increased light intensity boosts the production of oxygen through photosynthesis, further raising the O2 concentration in the leaf.
- Closed Stomata: In hot or dry conditions, plants often close their stomata to reduce water loss, limiting CO2 entry and increasing the relative concentration of O2 within the leaf.
संबंधित प्रश्न
Look at leaves of the same plant on the shady side and compare it with the leaves on the sunny side. Or, compare the potted plants kept in the sunlight with those in the shade. Which of them has leaves that are darker green? Why?
Short answer question.
Why do leaves generally look green?
Suppose we compare the leaf with a factory, match the items in Column A with those in Column B.
| Column A | Column B | ||
| Left | Factory | ||
| 1 | Cells in the leaf | a | Raw materials |
| 2 | Chloroplast | b | Power |
| 3 | Sunlight | c | Machinery |
| 4 | Oxygen and water | d | End product |
| 5 | Carbon dioxide and water | e | By product |
| 6 | Glucose | f | Workroom |
State whether the following statement is True or False:
The chlorophyll enables the plants to use light energy.
State whether the following statement is True or False:
The free oxygen in the atmospheric air is the result of photosynthesis.
Long answer question.
In order to carry out photosynthesis, what are the substances that a plant must take in? Also mention their sources.
Answer the following in one word.
Which organ is called the voice box?
Identify the false statement and rewrite it correctly by changing the first or last word only.
Photosynthesis requires enzymes.
Identify the false statement and rewrite it correctly by changing the first or last word only.
Photosynthesis stops at a temperature of about 35°C.
Two groups (A & B) of bean plants of similar size and same leaf area were placed in identical conditions. Group A was exposed to the light of wavelength 400-450 nm & Group B to light of wavelength of 500-550 nm. Compare the photosynthetic rate of the 2 groups giving reasons.
Draw and label the structure of oxysomes.
Process of photosynthesis is ______.
Photorespiration is favoured by :
According to Blackman, respiration of carbohydrates and fats is ______.
The figure shows the effect of light on the rate of photosynthesis. Based on the graph, answer the following question:
- At which point/s (A, B or C) in the curve is light a limiting factor?
- What could be the limiting factor/s in Region A?
- What do C and D represent on the curve?
Graph of light intensity on the rate of photosynthesis
