Question

1. how is photosynthesis affected by the following environmental conditions?

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Explanation:

• Increased light intensity: Light is essential for the light - dependent reactions of photosynthesis. More light (up to a certain saturation point) provides more energy for the excitation of electrons in chlorophyll, which drives the production of ATP and NADPH. These are used in the light - independent reactions (Calvin cycle) to fix carbon dioxide. So, initially, the rate of photosynthesis increases.
• Increased \(CO_2\) concentration: \(CO_2\) is the raw material for the Calvin cycle. Rubisco (the enzyme that fixes \(CO_2\)) has a greater substrate availability when \(CO_2\) concentration is increased. This leads to an increase in the rate of the light - independent reactions, and thus an increase in the overall rate of photosynthesis (up to a point where other factors become limiting).
• Colder temperatures (below \(25^{\circ}C\)): Enzymes involved in photosynthesis (such as rubisco in the Calvin cycle) have an optimal temperature range. At colder temperatures, enzyme activity slows down. The kinetic energy of molecules (including reactants like \(CO_2\) and substrates for enzymatic reactions) is reduced. So, the rate of photosynthesis decreases.
• Warmer temperatures (above \(35^{\circ}C\)): At very high temperatures (above the optimal range for photosynthetic enzymes), enzymes can denature. Also, high temperatures can cause stomata to close (to reduce water loss), which limits the entry of \(CO_2\) into the leaf. Both these factors lead to a decrease in the rate of photosynthesis.

Answer:

• Increased light intensity: Increases
• Increased \(CO_2\) concentration: Increases
• Colder temperatures (below \(25^{\circ}C\)): Decreases
• Warmer temperatures (above \(35^{\circ}C\)): Decreases