Plant Nutrition:

How do you define the process of Photosynthesis?

Photosynthesis is the fundamental process by which plants manufacture food molecules (carbohydrates) from raw materials CO2 and H2O) using energy from sunlight.

What happens during the process of Photosynthesis?

  • Green plant cells absorb the light energy light by Chlorophyll – a green substance present in chloroplasts in green plant cells.
  • Then this absorbed light energy is used to convert carbon dioxide (from the air) and water (from the soil) into a sugar called glucose
  • Oxygen is released as a by-product.

Equation for the process of photosynthesis:


What is the Importance of Chlorophyll, carbon dioxide, and light?

  • Chlorophyll is required because it helps to absorb the light needed for the process of Photosynthesis.
  • With the help of light energy, a chemical reaction occurs that breaks down the molecules of carbon dioxide (taken from air) and water (taken from the soil) and reorganizes them to make the sugar (glucose).
  •  Light is an essential factor because it acts as the “fuel” or energy to drive the reaction.

How does the process of Photosynthesis occur?

  •  Firstly the water is absorbed from the soil by the roots through root hairs and carried it in the water vessels called Xylem by the process of osmosis.
  • Carbon dioxide present in the environment is absorbed from the air through stomata (pores present in the leaf) with diffusion.
  • In the leaf cells, Carbon dioxide and water are combined to make sugar (glucose).
  • A green pigment called Chlorophyll present in chloroplast absorbs the energy from the sun for chemical reaction to make sugar(glucose)
  • Energy absorbs by the Chlorophyll is used to break the water molecules into hydrogen and oxygen.
  • The oxygen escapes from the leaf, and the hydrogen molecules are added to carbon dioxide molecules to form sugar(glucose)
  • In this way, the light energy is converted into chemical energy as carbohydrates are synthesized.

What would happen to the products of Photosynthesis?

  • Glucose is an immediate sugar that forms after the process of Photosynthesis. Starch is stored food, while sucrose is a moving food in plants.
  • Transported food called sucrose is distributed throughout the plant body with the help of plant veins called Phloem.
  • These veins distribute sucrose to all parts of the plant, e.g., growing buds, the ripening fruits, the roots, and the underground storage organs.
  • The cells in these regions use sucrose (disaccharide, produce in plants naturally) in various ways.
  • The sugar can be used to provide energy.
  • It is also oxidized by respiration to Carbon dioxide and water and energy. This released energy is used to carry out other chemical reactions taking place in the cells, making the molecules of proteins (mega molecules of amino acids).
  • Sugar that is surplus and is not needed for respiration is turned into starch and stored. Sugar converts into starch for storage because glucose is not a very good storage molecule. Starch cannot dissolve in water, while glucose can easily dissolve in water.
  • Different substances are built up from the sugar molecules and other molecules produced in Photosynthesis, e.g., cellulose for its cell wall, lipids for its cell membrane, proteins for its cytoplasm, and pigments for its flower petals, etc.

What are the factors affecting the rate of Photosynthesis?

Factors affecting the rate of Photosynthesis are:

  • Light intensity
  • Carbon dioxide concentration
  • Temperature

These three factors are also limiting factors for the process of Photosynthesis.Limiting factors can be defined as something present in the environment in such a short supply that it restricts life processes.

What does happen when Light intensity is a limiting factor?

Without enough light, a plant cannot photosynthesize the food – even if there is plenty of water and carbon dioxide. Increasing the light intensity will increase the rate of Photosynthesis until some other factor – a limiting factor – becomes in short supply.When light is a limiting factor, the rate of Photosynthesis is directly proportional (as the amount of light increases, rate of Photosynthesis also increases) to light intensity (concentration). As light intensity is increased, the volume/amount of oxygen produced and carbon dioxide absorbed due to which rate of Photosynthesis will increase to a point where it is exactly balanced by the oxygen absorbed and the carbon dioxide produced by cellular respiration. At this point there will be no net exchange of gases in or out of the plant – compensation point (The compensation point is the light intensity at which the rate of Photosynthesis is equal to the rate of respiration.) And if there is a further increase in light intensity, then it will cause a direct proportional rise in the process of Photosynthesis, and eventually giving off oxygen and taking up carbon dioxide will also increase. A point will be reached at which further increases in light intensity will not affect Photosynthesis. At this point, some other factor is limiting the reaction.


What does happen when Carbon dioxide concentration is a limiting factor?

All the required factors for the process of Photosynthesis should be in a balanced amount because even if there is plenty of light, a plant cannot photosynthesize if there is insufficient carbon dioxide. In the same way, if the concentration of carbon dioxide is increased, the rate of Photosynthesis will also rise. And in the same way, at some point, a different factor may become a limiting factor. Beyond this concentration, further increases in the concentration of carbon dioxide will not result in the rate of Photosynthesis and would appear on a graph as a horizontal line.


What does happen when Temperature is a limiting factor?

Different enzymes are there to control the chemical reactions that combine carbon dioxide and water to produce glucose. As with any other enzyme-controlled reaction, the rate of Photosynthesis is affected by temperature. At low temperatures, the photosynthesis rate is limited by the number of molecular collisions between enzymes and substrates. At high temperatures, enzymes are denatured.