Respiration
Respiration is the process of burning glucose (sugar produced during photosynthesis) combined with oxygen from the air to produce cellular energy used to fuel growth and all normal cellular functions. While photosynthesis takes place in the leaves and stems only, respiration occurs in the leaves, stems and roots1
of the plant.
Carbon dioxide and water are formed as by-products of respiration. Since respiration does not require light energy, it occurs both at night (dark respiration) and during the day (photorespiration).
Under water, photosynthesis takes place at a slower pace than normal photosynthesis; this is because energy from the sun is absorbed by the water layers and only a part of this energy actually reaches the plant.
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It is important that the growing medium has enough oxygen for plant roots to function properly. Roots which are overwatered or in soils with poor drainage, cannot take up oxygen and convert glucose to maintain cell metabolic processes. As a result, waterlogging and excessive irrigation can deprive roots of oxygen, kill root tissue, damage trees, and reduce yield.