Question

Transpiration ratio is the ratio of moles of H$_2$O transpired / moles of CO$_2$ fixed. This ratio is measure of
a) The efficiency of guard cells on stomatal movement.
b) Effectiveness of stomata is maximizing photosynthesis, while minimizing water loss
c) Distinguishing a xerophyte from a glycophyte
d) Stomatal pore size of the leaves.

Answer 1

Hint: Transpiration is the loss of water by evaporation in actively growing plants from the surface of its leaf cells. From the soil, Water is absorbed by roots and transported as a liquid to the leaves via xylem.

Complete answer:
In order to generate the reducing power, Water is required which is used to reduce carbon dioxide during photosynthesis. These water molecules break apart and release oxygen as a by-product.
The protons are utilized to synthesize reducing power. Water enters the root and passes through the cortex and endodermal layers of cells to reach the xylem. Of all the water absorbed by plants, less than 5% is used and remains in the plant for growth.
Loss of water is reduced in plants by closing their stomata, developing thick cuticles, or by possessing leaf hairs to increase the boundary layer. In fact, all the water that is absorbed is never used up and the water that is actually utilized is just a small fraction of water that is absorbed.
Stomata are small pores found in the leaves that allow carbon dioxide to enter and water to escape as a vapor. Stomata involved in the process of exchange of water and carbon dioxide between plants and atmosphere. In order to find out the effectiveness of stomata in maximizing photosynthesis and minimizing loss of water, transpiration ratio is calculated. Its role is to protect the plant from losing too much water and allows enough carbon dioxide to drive photosynthesis.
Thus, the right option is B.

Note: Transpiration rates are increased when stomata are open and the closure of stomata leads to decrease in transpiration rates. Rates of transpiration are highest in C$_3$ plants which possess greater CO$_2$ responsiveness due to opening of stomata and transpiration rate will be low during certain environmental factors like high humidity in the atmosphere.