1. The uptake into a plant of water, solutes, or other substances by either active or passive means. Entry invariably involves movement across cellular membranes. Active absorption, for example the uptake of a solute against an osmotic gradient, involves expenditure of energy. An example of passive absorption is the intake of water by plantroots, which is controlled by the rate of transpiration.
2. The retention of radiant energy by the pigments of a plant. About 80% of the incident visible light and about 10% of the infrared radiation falling on a leaf is absorbed. Generally, less than 2% of this is used in photosynthesis.