PLANT PROCESSES

Besides producing organic substances, one of the most important things plants do is create oxygen, in fact, without plants, there could be no life on Earth. Since they are the only organism that can make their own food, they are the primary producers that sustain all other life forms. The basic plant processes are photosynthesis and respiration, which occur at the same time during the day.

Photosynthesis

Plants take in the carbon dioxide (CO2) that humans and animals breathe out and release the oxygen that humans and animals breathe in. This process is called photosynthesis1; it is also referred to as the carbon-fixation process, since it produces carbon compounds which store chemical energy to be used in cell life. The basic requirements for the photosynthesis process are light, water, mineral salts, chlorophyll and carbon dioxide.
This process consists of different steps:

  • carbon dioxide in the atmosphere enters the plant leaf through the stomata, which are minute epidermal pores in the leaves and stem of the plant which facilitate the transfer of various gases and water vapour;
  • water enters the leaves, primarily through the roots which absorb groundwater, and transport it to the leaves through the stem;
  • light energy is captured in the chloroplasts by chlorophyll. This is a pigment found in the cells of leaves which is formed only in the presence of light and is the substance that colours plants green;
  • carbon dioxide absorbed from the air and water absorbed from the soil react with the sun’s energy to form carbohydrates (glucose, starches and cellulose). Oxygen is let out by the plant through the stomata.

DO

1 Do you know if all plants photosynthesise?


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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1 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.