With a decrease in atmospheric pressure, the rate of transpiration will
A. Remain unaffected
B. Increase
C. Decrease slowly
D. Decrease rapidly

Hint: The term transpiration refers to the loss of water and other gaseous wastes through the lenticels of the stem and fruits and stomata of the leaf. The process of transpiration keeps the plant cool and allows the root tip to absorb more water and other important nutrients from the soil.

Complete answer: Absorption of water in plants takes place by two processes are active absorption and passive absorption. Passive absorption is also called inactive absorption. The absorption of water by root cells with the help of ATP, generated by the process of root respiration is called active absorption. In inactive or passive absorption metabolic energy is not required for the utilization of water. Transpiration pull is created at the end of the leaf and is responsible for the upward flow of water in plants. The process of transpiration is possible due to the fact of transpiration pull. Transpiration pull refers to the force of pulling which is produced inside the xylem tissue. The upward movement of water into the xylem is regulated by transpiration pull. Various factors affecting the rate of transpiration are humidity, temperature, light, wind, and the leaf surface. The rate of transpiration will increase with a decrease in atmospheric pressure. Air will move out of the plant easily as the atmospheric pressure decreases. Hence, the rate of transpiration increases, and plants lose more water easily.
So, option B is the correct option.

Note: The water molecules absorbed by the xylem is used for the process of photosynthesis. The excess amount of water is evaporated in the form of vapors from the stomata. Transpiration in plants regulates the function of maintaining the proper flow of water and protection from an embolism.