Friday, May 10, 2013

CBSE Class 10 - Science - CH6 Life Processes (Photosynthesis)

Photosynthesis Process
credits : original chloroplast image taken from Wikipedia

Q & A

Q1: What is photosynthesis?

Answer: The process by which green plants make their own food from carbon dioxide and water in the presence of sunlight and chlorophyll is called photosynthesis.

During this process, oxygen gas is released. This process can be represented as:

    6CO2   + 12H2O        C6H12O6   +    6H2O +    6O2

The green plants convert the energy of sunlight into chemical energy by making glucose.
The extra glucose formed changes into starch which is stored in leaves.
The Oxygen released comes from the water.

Q2: Define Translocation.

Answer: Transportation of food from photosynthetic parts of the plant to the non-green part of the plant through phloem is known as translocation.

Q3: What are the important events occur during photosynthesis process?

Answer: The following events occur during this process:

  1. Absorption of light energy by chlorophyll.
  2. Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen. (Light Reaction)
  3. Reduction of carbon dioxide to carbohydrates. (Dark Reaction by Calvin Cycle)

Q4: Mention the conditions for photosynthesis. Also, mention the process involved in each of these steps.

Chlorophyll of the leaves of the plant trap sunlight and converts them into chemical energy during photosynthesis. The plant utilizes visible light only which is made up of 7 colours and the green colour is least absorbed ( it reflects green the most - that's why the leaves appear green).

Chlorophyll is a green pigment mainly present in the leaves of the plant. There are many types of chlorophyll named a, b, c, d, e and bacterio-chlorophyll. Chlorophyll a and chlorophyll b are most abundantly present in nature.

Plants take carbon dioxide through stomata to make glucose(food for the plants).

Water is absorbed by the roots of the plants through osmosis. Through xylem, water is transported to all parts of the plant.

Q5: Name other two pigments which absorb sunlight ( other than chlorophyll ).

Answer: Carotenoids and Fucoxanthin

Q6: How do aquatic plants get oxygen for photosynthesis?

Answer: Aquatic plants obtain carbon dioxide through the process of diffusion.

Q7: Where does light reaction occur?

Answer: In the grana thylakoids of chloroplasts.

Q8: Where does dark reaction occur?

Answer: In the stroma of chloroplasts.

Q9: Which wavelength of light is best absorbed by chlorophyll?

Answer: Red colour wavelength

Q10: Why do most plants appear green in colour?

Answer: The green pigment of chlorophyll absorbs all light colours and reflect the green light.

Q11: Which products formed during light reaction in photosynthesis process are used by the dark reaction?

Answer: NADPH and ATP

Q12: What is the function of thylakoid membranes in the chloroplast?

Answer: Thylakoid membranes provide large surface area for light absorption.

Q13: Write down the full form of the following:
  • ADP 
  • ATP 
  • NADP

   ADP: Adenosine diphosphate
   ATP:  Adenosine triphosphate
NADP: Nicotinamide adenine dinucleotide phosphate

Q14: Why is photosynthesis important to the global world?


  • In photosynthesis solar energy (sunlight) is converted to chemical energy and is stored in plants as starch.
  • Plants also store excess sugar by synthesis of starch
  • Heterotrophs, including humans, may completely or partially consume plants for fuel and raw materials.
  • Photosynthesis is responsible for the presence of oxygen in our atmosphere.
  • Each year, photosynthesis synthesizes approx. 160 billion metric tons of carbohydrate

Q15: Deficiency of metal 'X' causes lack of formation of chlorophyll in a plant. Identify metal 'X.

Answer:  Magnesium (Mg)

Watch Khanacademy Photosynthesis video on Photosynthesis:


  1. What is the connecting substance between light reaction and dark reaction