Which of the following best defines respiration in plants?

Respiration in plants is best defined as the conversion of stored food into usable energy. During this process, plants break down glucose and other organic molecules, which they have stored from photosynthesis, to release energy. This energy is crucial for various physiological functions, including growth, development, and maintenance of cells.

Respiration occurs in the mitochondria of plant cells and involves a series of biochemical reactions that require oxygen and result in the production of carbon dioxide and water as byproducts. This definition highlights the fundamental role respiration plays in providing the energy that all living cells, including plant cells, need to carry out their functions.

The other options, while related to plant processes, do not accurately capture the essence of respiration. For instance, the absorption of carbon dioxide, the release of oxygen, and the absorption of water through roots pertain to different processes such as photosynthesis and nutrient uptake. These processes are integral to a plant's life cycle but do not define respiration itself.