Photosynthesis

Photosynthesis Process

• Photosynthesis is a complex cellular process that occurs in green plants, algae, and some bacteria.
• This process involves the conversion of light energy into chemical energy, the latter stored in glucose and other organic molecules.
• Photosynthesis occurs primarily in the chloroplasts in the cells of green plants, more specifically in the grana and stroma.
• The process has two distinct stages: the light-dependent reactions and the light-independent reactions or Calvin cycle.
• The light-dependent reactions take place in the thylakoid membranes in the chloroplasts. Here, light energy is trapped by chlorophyll and other pigments, and is used to split water molecules - a process called photolysis. This produces oxygen and converts ADP and NADP+ into the energy carriers ATP and NADPH.
• The light-independent reactions or Calvin cycle happens in the stroma. ATP and NADPH produced in the light-dependent reactions convert CO2 into glucose through a series of reactions in this cycle.

Importance of Photosynthesis

• Photosynthesis is crucial for the sustenance of life on Earth as it is the principal source of all oxygen in the atmosphere which is vital for most living organisms.
• It is a major source of energy for most ecosystems. Plants provide food and hence chemical potential energy for consumers in the food chain.
• Photosynthesis is also responsible for the carbon fixation in the carbon cycle, reducing the amount of carbon dioxide in the atmosphere and hence mitigating some impacts of global warming.

Factors Affecting Photosynthesis

• Light intensity, temperature, and carbon dioxide concentration are the three primary factors affecting the rate of photosynthesis, which can be investigated experimentally via the limiting factor principle.
• Photosynthesis is most efficient at a light intensity that is not too high or too low, as too much light can damage plant tissues while too little light would limit the energy supply for photosynthesis.
• There is an optimal temperature range for photosynthesis, as enzymes involved in the process can be denatured by high temperatures and have low activities at low temperatures.
• High carbon dioxide concentration generally results in a higher rate of photosynthesis, until other factors become limiting.

Regulation of Photosynthesis

• Photosynthesis is regulated by enzyme activity, especially that of RuBisCO, the enzyme that catalyses the first major step of carbon fixation in the Calvin cycle.
• The activity of RuBisCO is governed by various factors, including temperature, carbon dioxide and oxygen concentrations, pH level and the concentration of its substrate RuBP.
• Stomata in leaves control gas exchange for photosynthesis. They open to allow intake of carbon dioxide and release of oxygen, but also account for most water loss in plants. Factors including light, carbon dioxide concentration, and relative humidity can affect the opening and closing of stomata.