Problem 170 - Objective Biology for NEET

Question

Assertion: Dark reaction is controlled by temperature. Reason: Dark reaction is enzymatic reaction.

Step-by-Step Solution

Answer

Yes, the assertion 'Dark reaction is controlled by temperature' is indeed correct, because 'Dark reaction is an enzymatic reaction', and enzymatic reactions are known to be influenced by temperature changes.

Step 1: Understand Dark Reaction

Dark reaction, also known as the Calvin Cycle, is part of the photosynthesis process that occurs in plants. It is named 'dark reaction' because unlike the 'light reaction', it does not require light directly but uses the ATP and NADPH produced in the light reactions to convert carbon dioxide to glucose. This step is crucial to grasp, as it provides the context for the assertion.

Step 2: Connect Dark Reaction and Enzymes

The dark reaction is an enzymatic reaction - it is facilitated by enzymes; proteins that speed up chemical reactions. Enzymes act as catalysts to reduce the amount of energy needed for the reactions to proceed.

Step 3: Understand Effect of Temperature on Enzymes

Enzymes have an optimal temperature range in which they work most efficiently. If the temperature is too low, the enzyme activity slows down. If the temperature becomes too high, the enzyme's structure can be altered (denatured), making it unable to perform its function. This concept correlates the assertion and the reason provided.

Step 4: Conclude

Given that the dark reaction is an enzymatic process and that enzymatic processes are influenced by temperature, it can be concluded that the dark reaction is controlled by temperature. The reason logically supports the assertion.

Key Concepts

Photosynthesis

Photosynthesis is a fundamental process that plants and some other organisms use to convert light energy into chemical energy. This process takes place in the chloroplasts using chlorophyll, the green pigment in plants. Photosynthesis consists of two main stages: the light reactions and the dark reactions, also known as the Calvin Cycle.
The light reactions occur in the thylakoid membranes and require sunlight to produce ATP and NADPH, which are energy carriers. These reactions capture and convert sunlight into chemical energy.

• Light Reactions: Transform solar energy into chemical energy.
• Calvin Cycle (Dark Reactions): Use the ATP and NADPH from the light reactions to fix carbon dioxide into glucose.

The Calvin Cycle does not directly require light, but it relies on the products of the light reactions to synthesize glucose. This cycle is crucial for building sugars that serve as food for the plant and energy storage for later use.

Enzymatic Reactions

Enzymatic reactions are chemical reactions that are facilitated by enzymes, which are protein molecules that act as biological catalysts. Enzymes speed up reactions by lowering the activation energy required for the reaction to proceed. This enables metabolic processes to occur at a rate fast enough to sustain life.

• Function of Enzymes: Catalyze biochemical reactions, increasing reaction rates.
• Specificity: Enzymes are highly specific, meaning they will only catalyze one particular reaction or type of reaction.
• Active Site: Each enzyme has an active site, which is the specific region where substrate molecules bind and undergo a chemical reaction.

The Calvin Cycle is an excellent example of an enzymatic reaction, where several enzymes work together to fix carbon dioxide and produce glucose. For instance, one of the primary enzymes involved is RuBisCO, which catalyzes the first major step of carbon fixation.

Effect of Temperature on Enzymes

The activity of enzymes is significantly influenced by temperature. Each enzyme has an optimal temperature range in which it functions best. Above or below this range, the enzyme activity diminishes.

• Optimal Temperature: The temperature at which an enzyme's activity is at its highest.
• High Temperatures: Can lead to denaturation, a process where enzymes lose their structure and, consequently, their functionality.
• Low Temperatures: Slow down enzyme activity, reducing the rate of reaction.

In the context of the Calvin Cycle, if the temperature is too high, enzymes may denature, and the cycle's efficiency drops as crucial reactions slow down or halt. Conversely, if it is too cold, the enzymes do not operate optimally, also inhibiting the process. Thus, maintaining a suitable temperature is vital for the efficient progression of the Calvin Cycle.