Problem 91 - Objective Biology for NEET

Question

How much percentage of water is used for photosynthesis? (a) \(1 \%\) (b) \(2 \%\) (c) \(3 \%\) (d) \(4 \%\)

Step-by-Step Solution

Answer

The percentage of water used for photosynthesis is (a) 1%.

Step 1: Recall Process of Photosynthesis

Photosynthesis is a process where plants convert sunlight, carbon dioxide and water into glucose and oxygen. Although water is a crucial component in this process, the majority of it is not used in photosynthesis but is used in other plant survival processes such as transpiration.

Step 2: Identify The Correct Percentage

The actual amount of water plants use specifically for photosynthesis is surprisingly low – only about 1%. Most of the absorbed water is lost during transpiration.

Key Concepts

Understanding Photosynthesis

Photosynthesis is a fascinating biological process in which green plants, algae, and certain bacteria transform light energy, typically from the sun, into chemical energy stored in glucose, a type of sugar. During this process, the organisms absorb carbon dioxide (CO₂) from the air and water (H₂O) from the soil, creating glucose (C₆H₁₂O₆) and releasing oxygen (O₂) as a byproduct.

This is fundamentally important for life on Earth as it forms the basis of the food chain and produces the oxygen necessary for aerobic organisms to survive. The simple chemical equation representing photosynthesis is:
\r\[\[\begin{align*} 6\mathrm{CO}_{2} + 6\mathrm{H}_{2}\mathrm{O} + \text{light energy} \rightarrow \mathrm{C}_{6}\mathrm{H}_{12}\mathrm{O}_{6} + 6\mathrm{O}_{2}. \end{align*}\]\]
Despite the significance of water in this equation, only a small percentage of the water taken up by plants is used for the synthesis of glucose. The rest supports other vital functions, such as regulating temperature through transpiration.

Plant Transpiration Explained

Plant transpiration is like the sweating process in humans – it's a way for plants to regulate temperature and maintain internal water balance. It occurs when water is absorbed by plant roots, moves up through the vessels in the stem, and is eventually released as water vapor through tiny pores in leaves named stomata.

This evaporative process helps to cool the plant and enables the continuous upward flow of water and nutrients from the roots. But it's not all about temperature regulation; transpiration also creates a negative pressure that helps draw water up through the plant – a process known as capillary action.

• Transpiration rate can be affected by several factors, such as temperature, humidity, light intensity, and wind.
• Despite its benefits, excessive transpiration can lead to water stress, especially in environments where water is scarce.
• Plant adaptations, like waxy leaves and reduced leaf surface area, can help minimize water loss.

The high rate of water loss through transpiration accounts for the fact that the vast majority of water absorbed by plants is not used for photosynthesis but is essential for plant health and growth.

Percentage Calculation in Biology

Percentage calculations are prevalent in biology, often used to quantify relative amounts of substances, like the water usage in photosynthesis. The exercise at hand requires understanding of the percentage of water a plant uses specifically for photosynthesis.

To address such questions, biologists will typically take measurements or use known data to establish the proportions of different components in a biological process. In our case, scientists have determined that about 1% of the water absorbed by plants is used in the photosynthesis process.

Calculating this percentage involves dividing the part by the whole and multiplying by 100:\r
\r\[\[\begin{align*} \frac{\text{Water used for photosynthesis}}{\text{Total water absorbed}} \times 100 = \text{Percentage of water used for photosynthesis}. \end{align*}\]\]
For students tackling such problems, it's crucial to understand not just the calculation itself, but the biological significance of the resulting percentage. Knowing that only 1% of the water absorbed by a plant is used for photosynthesis underscores the incredible efficiency of plants and the importance of transpiration in their overall water usage.