The process by which plants loss water to the atmosphere is

1. Analyze the question The question asks for the process by which plants lose water to the atmosphere. Note that it says "to the atmosphere", meaning the water is lost as vapour.

2. Explain the concept

• Transpiration: the loss of water vapour from the aerial parts of a plant, mainly through the stomata on the leaves. Some also leaves through the cuticle and lenticels. It is the main way plants lose water to the air.
• Guttation: the loss of water as liquid droplets, not vapour, through hydathodes at leaf margins. It usually happens at night or in the early morning when humidity is high. Because it is liquid water, it does not fit "to the atmosphere" as well as transpiration.
• Translocation: the movement of manufactured food (sugars) through the phloem from the leaves to other parts of the plant. No water is lost to the atmosphere.
• Evaporation: a physical process in which liquid turns to vapour at a surface. It is a general physical process and not the specific biological process by which plants lose water. Evaporation from the leaf's moist cell surfaces is only one step within transpiration.

3. Step-by-step solution

1. Water is absorbed by the roots and travels up the xylem to the leaves.
2. In the leaves, water evaporates from the surfaces of the mesophyll cells into the air spaces.
3. The water vapour diffuses out through the open stomata into the atmosphere.
4. This whole process of water vapour loss from plants is called transpiration.

4. Answer The correct option is A. transpiration.

5. Exam tip Remember the three "T/G" pairs:

• Transpiration = water vapour lost through stomata.
• Guttation = liquid water drops lost through hydathodes.
• Translocation = food moved through the phloem.

If a question says "plants lose water to the atmosphere", think transpiration first.