Problem 145 - Objective Biology for NEET

Question

Which factor is not limited to normal conditions for photosynthesis? (a) Air (b) \(\mathrm{CO}_{2}\) (c) Water (d) Chlorophyll

Step-by-Step Solution

Answer

The factor not limited to normal conditions for photosynthesis is (d) Chlorophyll.

Step 1: Identifying external factors

Air (which contains CO2), and water are resources absorbed from the environment by the plant. Their amounts can vary depending on external conditions.

Step 2: Identifying internal factors

Chlorophyll, which is responsible for transferring light energy in the process, is an intrinsic factor, as it is inherently produced by the plant.

Step 3: Determine the non-limiting factor

In normal conditions, the factor not limited for photosynthesis is chlorophyll, because its quantity doesn't rely on external conditions but on the plant's own metabolic processes.

Key Concepts

External factors of photosynthesis

Plants depend on several essential resources from their environment to perform photosynthesis effectively. These are referred to as external factors and mainly include air, water, and sunlight. Each of these components plays a critical role in the photosynthetic process.

• Air: Air provides carbon dioxide (\( ext{CO}_2 \)) which is crucial for the synthesis of glucose. Plants absorb carbon dioxide through tiny openings in their leaves known as stomata.
• Water: Water is absorbed through the plant's roots and travels upwards to the leaves. It is important not just as a hydrogen source necessary for sugar formation but also for maintaining cell structure and transport of nutrients.
• Sunlight: Although not absorbed like other factors, sunlight is vital as it provides the energy required to drive photosynthesis.

These factors are impacted by the plant's external environment, such as the amount of light available, the concentration of carbon dioxide in the air, and water availability. Variations in any of these can influence the rate of photosynthesis.

Chlorophyll in photosynthesis

Chlorophyll is a green pigment found in the chloroplasts of plant cells, and it is crucial in capturing the light energy that drives photosynthesis. One important thing to remember is that chlorophyll itself is an internal factor, as it is produced by the plant.

Chlorophyll absorbs light most efficiently in the blue-violet and red parts of the electromagnetic spectrum, while it poorly absorbs green light—it reflects it, which is why plants appear green to our eyes. This absorption of light is fundamental as it converts light energy into chemical energy, which eventually gets used to transform carbon dioxide and water into glucose and oxygen.

Under normal conditions, the production of chlorophyll by a plant isn't limited by the external environment like air, water, or light. Instead, its production depends more on the plant's internal conditions and health, such as nutrient availability (e.g., magnesium and nitrogen are crucial elements) and overall metabolic processes. Therefore, in normal situations, the amount of chlorophyll present is usually adequate for photosynthesis.

Limiting factors in photosynthesis

Limiting factors are conditions that directly influence the rate of photosynthesis if they are below a certain threshold or concentration. In other words, they are the factors which, when in limited supply, can slow down the process. Let's explore some key limiting factors:

• Light intensity: Photosynthesis depends on light, and its intensity affects the rate at which photosynthesis occurs. Low light conditions can slow down or stop photosynthesis; however, too much light can cause damage.
• Carbon dioxide concentration: As carbon dioxide is a substrate of photosynthesis, its low levels can reduce the photosynthetic rate. In naturally higher concentrations, plants can usually photosynthesize more rapidly.
• Water availability: Water stress can lead to the closing of stomata, directly affecting carbon dioxide uptake, thus reducing photosynthesis efficiency.

While chlorophyll can regulate its levels internally, these limiting factors are generally tied to external conditions and can greatly affect the efficiency and productivity of photosynthesis when altered.