Photosynthesis is the process by which green plants convert carbon dioxide and water into glucose and oxygen using sunlight. It is the fundamental process that sustains almost all life on Earth by producing food and oxygen. The CBSE Class 10 Life Processes chapter covers this in detail.
Photosynthesis is the process by which autotrophic organisms (mainly green plants) convert light energy into chemical energy stored in glucose. The overall balanced equation is: 6CO₂ + 6H₂O + sunlight energy → C₆H₁₂O₆ + 6O₂. The process occurs primarily in the chloroplasts of leaf cells.
Chlorophyll is the green pigment found in chloroplasts that absorbs sunlight (mainly red and blue wavelengths) and reflects green light, giving plants their colour. Chloroplasts contain an internal membrane system (thylakoids stacked into grana) and a fluid-filled space (stroma). The light reactions occur on thylakoid membranes, while the dark reactions occur in the stroma.
Light reactions occur in the thylakoid membranes and require direct sunlight. During these reactions: (1) Chlorophyll absorbs light energy. (2) Water molecules are split (photolysis of water): 2H₂O → 4H⁺ + 4e⁻ + O₂. This is the source of the oxygen released during photosynthesis. (3) ATP is generated from ADP. (4) NADPH is produced by reducing NADP⁺ with the hydrogen from water.
Dark reactions (light-independent reactions) occur in the stroma and do not require direct light, though they use products of light reactions. The Calvin cycle: (1) CO₂ is fixed by combining with a 5-carbon compound (RuBP). (2) The resulting 6-carbon compound splits into two 3-carbon molecules (G3P). (3) ATP and NADPH from light reactions are used to convert G3P into glucose. (4) RuBP is regenerated to continue the cycle.
Stomata are tiny pores on the surface of leaves (mainly on the lower epidermis). They are surrounded by guard cells that control their opening and closing. Stomata allow CO₂ to enter the leaf for photosynthesis and O₂ to exit. They also regulate water loss through transpiration.
Several factors influence the rate of photosynthesis: (1) Light intensity — rate increases with light up to a saturation point. (2) Carbon dioxide concentration — higher CO₂ increases rate up to a limit. (3) Temperature — optimal around 25–35°C; too high or too low reduces enzyme activity. (4) Water availability — insufficient water limits the reaction. The concept of the limiting factor (Blackman's law) states that the rate is determined by the factor in shortest supply.
No. Dark reactions are called "dark" because they do not directly require light, not because they only occur at night. They happen continuously as long as ATP and NADPH from light reactions are available.
The oxygen released during photosynthesis comes from the splitting (photolysis) of water molecules during the light reactions, not from CO₂.
Yes. Photosynthesis can occur under artificial light as long as the light contains the wavelengths (primarily red and blue) absorbed by chlorophyll.
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