Chapter 29, Problem 1QC

Summary Introduction

To explain:

The reason why do plants transpire.

Introduction:

Plants transpire by the process of transpiration. Transpiration is a process by which water is carried through the roots of the plant to small openings in the leaves. The water at the opening of leaves change into vapor state and released to the surroundings. So the loss of water from the leaves is known as transpiration.

Explanation of Solution

The minor constituent of air is ${\text{CO}}_{\text{2}}$ present about 400 parts per million. The low concentration of ${\text{CO}}_{\text{2}}$ limits it rate of diffusion in the leaf. Therefore, the fast uptake of ${\text{CO}}_{\text{2}}$ depends on the degree of exposed cells to the surrounding air. If these spaces preset on a leaf for the exchange were sealed off, then the photosynthesis will soon run out of ${\text{CO}}_{\text{2}}$ and get halt.

The ability of the plant leaves to draw ${\text{CO}}_{\text{2}}$ comes with a price of loss of water. When the ${\text{CO}}_{\text{2}}$ diffuses into leaf, then the water vapors diffuses out of the leaf. Furthermore, the rate of diffusion of water is faster than the rate of diffusion of ${\text{CO}}_{\text{2}}$. The plants can completely seal off to prevent the water loss, but it will prevent them obtaining ${\text{CO}}_{\text{2}}$ which is required to perform photosynthesis. Thus, the process of transpiration is unavoidable.

Conclusion

Plants transpire to obtain ${\text{CO}}_{\text{2}}$ which results in loss of water vapors.