Plant Physiology - Lecture Notes - O. M. Tarnopilska 2019

4. Photosynthesis
4.12 The Significance of Photosynthetic Organisms for the Biosphere

Five main aspects of the planetary role of Photosynthetic organisms are distinguished.

Accumulation of organic matter. In The process of PHOTOSYNTHESIS, terrestrial plants produce up to 170 billion tons, and marine plants up to 70 billion tons of biomass per year in terms of dry matter, which is utilized by heterotrophic organisms.

Maintaining a constant level of CO₂ in the atmosphere. The fixation of CO₂ during photosynthesis largely compensates for its release through other processes (Respiration, Fermentation, volcanic activity, human industrial activity).

Prevention of the greenhouse effect. Part of the sunlight is reflected from the Earth's surface as thermal infrared rays. CO2 absorbs infrared radiation, thereby retaining heat on Earth. An increase in the content of CO₂ in the atmosphere can contribute to a rise in Temperature, thus creating a greenhouse effect. This would lead to the flooding of coastal areas due to rising sea levels caused by the melting of glaciers in the mountains and at the poles. However, a high concentration of CO₂ in the air stimulates photosynthesis, which subsequently reduces the atmospheric concentration of CO₂ back down.

Accumulation of oxygen in the atmosphere. Initially, there was very little oxygen in the Earth's atmosphere. Today, its content accounts for 21% by volume of air. This oxygen is predominantly a product of photosynthesis. Annually, plants and other photosynthetic organisms release approximately 120 billion tons of oxygen into the atmosphere.

Ozone layer. Ozone (O₃) is formed As a result of the photodissociation of oxygen molecules under METABOLISM/18.html">The Influence of solar radiation at an altitude of about 25 km. Ozone filters out a large portion of ultraviolet radiation, which is harmful to all living things.