One Mark Questions
Q: What are the requirements for photosynthesis?
A: Carbondioxide, water, sunlight and chlorophyll are the requirements for photosynthesis.
Q: Which wavelength of light is more suitable for photosynthesis? Why?
A: In visible light, wavelength of red rays and blue rays is more suitable for photosynthesis as they are absorbed maximum.
Q: What are the end products of light reactions?
A: Oxygen, NADPH and ATP are the end products of light reaction.
Two Mark Questions
Q: What is a reaction centre?
A: Chlorophyll and other accessory pigment molecules are situated in the thylakoid membranes and organized to form reaction centres called photosystem I and photosystem II.
Highly reactive special forms of chlorophyll-a called p700 and p680 are present in PS I and PS II respectively.
P700 and p680 constitute the reaction centres.
Q: What is the difference between oxidation and reduction?
A: Oxidation : 1. Oxygen atoms are added.
2. Hydrogen atoms are removed.
3. Electrons are removed from atoms.
Reduction : 1. Oxygen atoms are removed.
2. Hydrogen atoms are added.
3. Electrons are added to the atoms.
Q: What is an electron acceptor? Give some examples.
A: The acceptors which accept electrons are called electron acceptors.
e.g.: NAD, NADP, Cytochromes, ferredoxins.
Four Mark Questions
Q: How do you prove that carbon dioxide is essential for photosynthesis?
A: Aim: To prove that carbon dioxide is essential for photosynthesis by Moll’s half leaf experiment.
Apparatus: A wide mouthed bottle, KOH solution, potted plant, vertically split cork, iodine solution.
Procedure: A healthy potted plant with narrow and long leaves is
taken. It has to be kept in dark for 2 or 3 days in order to make all
leaves free from starch.
On the day of the experiment take 5-10 ml of potassium hydroxide in a wide mouthed glass bottle with a vertically split cork. Insert one leaf of the potted plant into the bottle through split cork in such a way that half of the leaf is inside and the remaining half outside. Now keep the entire unit in the sun for 3 to 4 hours. Detach the leaf after 3,4 hours from the bottle and test it for starch.
The part of the leaf outside the bottle turns blue because starch is formed in that part due to photosynthesis. The part of the leaf inside the bottle does not turn blue.
Observation: The part of the leaf inside the bottle is provided with
water. Chlorophyll and sunlight but not carbondioxide, since it is absorbed by KOH solution. So starch is not formed because of non-occurrence of photosynthesis.
Result: This experiment proves that CO2 is necessary for photosynthesis.
Precautions: The part of the leaf kept inside should not touch KOH solution. The apparatus should be kept, air tight, by applying grease or Vaseline.
Q: How do you prove that oxygen is evolved during photosynthesis?
A: Aim: To prove that oxygen is released during photosynthesis.
Apparatus: Hydrilla twigs, test tube, beaker with water
Experiment: Small pieces of Hydrilla twigs are placed in a funnel which kept in a beaker of water. A test tube is filled with water. Carefully it is inverted over the funnel. The entire set-up is kept in sunlight.
Observation: After sometime small gas bubbles come out of the leaves of hydrilla. These bubbles collect at the end of the test tube. When more gas is collected the test tube is taken out by closing its mouth with the thumb. When the gas is tested with a burning splinter it glows indicating that the gas released is oxygen.
Inference: By this experiment we can prove that oxygen is released during photosynthesis.