Write notes about the follwing.
1. Photosynthesis
Answers
photosynthesis is the process in which plants make their own food by the help of sun water and carbon dioxide or soil and a green pigment On The Leaves called chlorophyll
FOR CLASS 5
Photosynthesis, the process by which green plants and certain other organisms transform light energy into chemical energy. During photosynthesis in green plants, light energy is captured and used to convert water, carbon dioxide, and minerals into oxygen and energy-rich organic compounds.
FOR CLASS 6-7
The process by which plants make their own food in the presence of sunlight, carbon-dioxide present in air, water, minerals and chlorophyll present in leaves is termed as photosynthesis.
FOR CLASS 8
Photosynthesis is the physico-chemical process by which plants can convert light energy into chemical energy, in the form of carbohydrate from simple inorganic substances like atmospheric carbon dioxide and water. Photosynthesis requires carbon dioxide, sunlight, water and chlorophyll as its basic raw materials.
FOR CLASS 9
Photosynthesis is a physiological process by which plant cells containing chlorophyll produce food in the form of carbohydrates by using carbon dioxide, water and light energy. Oxygen is released as a by-product.
FOR CLASS 10
6CO2 + 12H2O −−−−−−−−−> C6H12O6 + 6O2 + 6H2O
6CO2 + 12H2O −−−−−−−−−> C6H12O6 + 6O2 + 6H2O
Photosynthesis involves two types of reactions namely, light reactions and dark reactions.
a) Light reactions: Light reactions are light dependent reactions. These reactions happen only in the presence of sunlight. The photosynthetic pigments trap the energy from the sunlight. PS-I and PS-II collectively bring in the cyclic photophosphorylation and non-cyclic photophosphorylation reactions. As a result of these reactions energy rich molecules like ATP and NADPH2 are synthesised. Photolysis of water molecules results in the release of oxygen as a by-product.
H2O → 2H+ + 2e- + ½O2
b) Dark reactions: Dark reactions are independent of light. Energy rich molecules like ATP andNADPH2 are utilised in these reactions. Dark reactions involve Calvin cycle during which carbon dioxide is reduced to carbohydrate.
C3 pathway is also known as Calvin cycle.C3 pathway involves set of carbon reactions which are catalysed by the enzyme Rubisco to synthesise 3 carbon compound, 3-phosphoglycerate from 5-carbon compound, Ribulose bisphosphate.
- Ribulose bisphosphate is the primary acceptor of CO2.
- Chloroplasts present are only of one type.
- Anatomy of leaves does not resemble Kranz anatomy.
- Phosphoglyceric acid is synthesised as the product.
- Mesophyll cells exhibit Calvin cycle.
Photorespiration is observed.
- Optimum temperature required for photosynthesis is between 20 degree celsius to 25 degree celsius.
- This cycle is less efficient in utilising CO2.