Factors Affecting Photosynthesis - NEET MCQ

Frederick Frost Blackman proposed the law of limiting factors. Blackman proposed this law in 1905 according to which, a chemical process depends on multiple factors the rate of the process will be limited by the pace of the slowest factor or limiting factor.

The rate of photosynthesis typically stops increasing at about 10% of full sunlight, a point known as light saturation, beyond which other factors become limiting.

Carbon dioxide is often the primary limiting factor in photosynthesis, as it is essential for the process and can limit the rate of photosynthesis when in low supply.

C4 plants typically reach saturation in photosynthesis at around 360 µlL-1 of CO2 concentration, beyond which their photosynthetic rates do not increase significantly.

- Statement i is incorrect because the dark reactions are not more sensitive to temperature changes; in fact, the light reactions are also temperature sensitive but to a lesser extent.

- Statement ii is correct; C4 plants perform better at higher temperatures compared to C3 plants.

- Statement iii is incorrect; tropical plants have a higher temperature optimum for photosynthesis than temperate plants.

- Statement iv is correct; water stress indeed leads to stomatal closure, thereby reducing CO2 availability.

Thus, the correct statements are ii and iv.

- Statement i is incorrect; while water is a reactant in the light reactions, its effect is more indirect through its role in plant health and stomatal function.

- Statement ii is correct; water stress leads to wilting, which reduces leaf surface area and consequently metabolic activity.

- Statement iii is incorrect; C3 plants generally have a lower temperature optimum compared to C4 plants.

- Statement iv is correct; different plants have different temperature optima based on their habitats.

Thus, the correct statements are ii and iv.

Both statements are true. Light saturation does occur at low levels of full sunlight, making light rarely a limiting factor. At higher intensities, other factors, such as CO2 and temperature, become the limiting factors.

The enrichment of carbon dioxide in the atmosphere of greenhouses leads to increased rates of photosynthesis in C3 plants, such as tomatoes and bell peppers. This increased photosynthesis boosts the productivity and yields of these crops, hence the beneficial use of CO₂ enrichment in greenhouse farming.

While increasing CO₂ concentration up to 0.05 percent can enhance CO2 fixation rates and stimulate photosynthesis, exceeding this level can become detrimental to plants over extended periods, potentially harming their physiological processes and overall health.

 The assertion is correct as high light intensities indeed increase the rate of photosynthesis in both C₃ and C₄ plants. However, the reason is incorrect. C₄ plants generally perform better at higher temperatures compared to C₃ plants, not at lower temperatures. Therefore, the Reason is false, making option c the correct answer.