Question

Increased humidity in the atmosphere decreases the rate of:
a. Transpiration
b. Photosynthesis
c. Glycolysis
d. Growth

Answer 1

Hint: Growth and glycolysis are processes which do not require humidity as a factor. They are not dependent on humidity. Further for photosynthesis, sunlight, water and carbon dioxide are required. Therefore, the process of photosynthesis majorly depends on these factors.

Complete answer:
Transpiration is the loss of water in the form of water vapour from the aerial parts of the plant. Transpiration is of three types:
• Stomatal transpiration- The transpiration which takes place from the stomata is known as the stomatal transpiration
• Lenticular transpiration- The transpiration that takes place from the lenticels is known as the lenticular transpiration. Lenticels are small openings on the bark of the woody stem.
• Cuticular transpiration- The transpiration which takes place from the cuticle. Cuticle is the outer covering of the parts of non-woody plants

There are various factors which affect the rate of transpiration:
• Light- The maximum opening of stomata takes place in red light then blue and no opening of the stomata occurs in green light. Therefore, the maximum transpiration also occurs in red light.
• Temperature- Stomata opens with the increase in the temperature. But at temperature higher than a particular limit, the closing of stomata takes place, thereby affecting the rate of transpiration.
• Atmospheric pressure- The rate of transpiration increases with the decrease in the atmospheric pressure and vice-versa.
• Humidity- The amount of water vapour present in the air is called humidity. If the air already has too much water vapour, then the transpiration will be decreased. Similarly, if there is less humidity, the rate of transpiration will increase.

Hence, the correct answer is option (A).

Note:
Here it must be noted that there are several internal factors also which affect the transpiration rate. These are:
• Root- shoot Ratio- Higher this ratio, more will be the transpiration
• Leaf Area- More the leaf area, more will be the number of stomata present on its surface and in turn more will be the transpiration.
• Leaf structure- Plants which grow in deserts (xerophytes) develop cuticles on their leaf surface which helps in the reduction of water loss through transpiration.