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Question
Read the assertion and reason carefully to mark the correct option in the question.
Assertion: C4 plants show tolerance to higher temperatures.
Reason: C4 plants have both RuBisCO and PEPcase enzymes.
Assertion: C4 plants show tolerance to higher temperatures.
Reason: C4 plants have both RuBisCO and PEPcase enzymes.
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Solution
Assertion-Reason relation
RuBisCO has dual functions since it can act as carboxylase in Calvin cycle and oxygenase during photorespiration.
The dual activity of RuBisCO depends on the CO2 and O2 ratio as well as the temperature. Low temperature and high CO2 and O2 ratio promotes the carboxylase activity which help in CO2 fixation. High temperature and low CO2 and O2 ratio promotes the oxygenase activity which results in photorespiration.
Assertion-Reason relation
Hence, RuBisCO enzyme can behave as oxygenase when in high temperature and high oxygen concentration.
On the other hand, bundle sheath cells containing RuBisCO are interiorly placed so that they are somewhat cooler and RuBisCO can thus behave as carboxylase.
Hence, the assertion statement is correct.
Assertion- Reason relation
In C4 plants, the synthesis of malic acid during carbon dioxide fixation occurs in the mesophyll cells.
Mesophyll cells lack the RuBisCO enzyme. The enzyme responsible for fixation is PEPcase. PEPcase has higher efficiency to take up CO2.
The malic acid formed is transported to bundle sheath cells for decarboxylation i.e., carbon dioxide is released. This carbon dioxide enters the Calvin cycle and with the help of RuBisCO enzyme, it is fixed.
Hence, the reason statement is correct.
Final answer
(B) If both assertion and reason are true but the reason is not the correct explanation of the assertion.
RuBisCO has dual functions since it can act as carboxylase in Calvin cycle and oxygenase during photorespiration.
The dual activity of RuBisCO depends on the CO2 and O2 ratio as well as the temperature. Low temperature and high CO2 and O2 ratio promotes the carboxylase activity which help in CO2 fixation. High temperature and low CO2 and O2 ratio promotes the oxygenase activity which results in photorespiration.
Assertion-Reason relation
Hence, RuBisCO enzyme can behave as oxygenase when in high temperature and high oxygen concentration.
On the other hand, bundle sheath cells containing RuBisCO are interiorly placed so that they are somewhat cooler and RuBisCO can thus behave as carboxylase.
Hence, the assertion statement is correct.
Assertion- Reason relation
In C4 plants, the synthesis of malic acid during carbon dioxide fixation occurs in the mesophyll cells.
Mesophyll cells lack the RuBisCO enzyme. The enzyme responsible for fixation is PEPcase. PEPcase has higher efficiency to take up CO2.
The malic acid formed is transported to bundle sheath cells for decarboxylation i.e., carbon dioxide is released. This carbon dioxide enters the Calvin cycle and with the help of RuBisCO enzyme, it is fixed.
Hence, the reason statement is correct.
Final answer
(B) If both assertion and reason are true but the reason is not the correct explanation of the assertion.
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