Which one of the following is not a function of chlorophyll?
- (a)Splitting of water
- (b)Absorption of photon
- (c)Oxidation of carbohydrate
- (d)Conversion of light energy into chemical energy
Correct — C, Oxidation of carbohydrate. Chlorophyll is the pigment of photosynthesis, and photosynthesis builds carbohydrate rather than breaking it down. Oxidising carbohydrate to release energy is respiration, which runs in the mitochondria of every living cell, plants included, and needs no pigment at all. The two processes are opposites: one stores energy in a sugar, the other spends it.
- (a)Splitting of water — The splitting of water is one of the events NCERT lists under photosynthesis, and it is driven by the energy chlorophyll has absorbed. The oxygen released into the air comes from that water, not from carbon dioxide.
- (b)Absorption of photon — Absorbing photons is what chlorophyll is for. The molecule absorbs strongly in the blue and the red and reflects in the green, which is why leaves look green.
- (d)Conversion of light energy into chemical energy — Converting light energy into chemical energy is the central function of the pigment; the captured energy is passed on to build ATP and NADPH and then sugar.
Photosynthesis begins when chlorophyll in the chloroplast absorbs light. The energy is used to split water into hydrogen and oxygen, oxygen is released, and the hydrogen is used to reduce carbon dioxide to carbohydrate. Respiration runs the balance sheet the other way — carbohydrate is oxidised in the mitochondrion to carbon dioxide and water, releasing energy as ATP. Plants do both; only the first needs chlorophyll and light.
Three of the four options come straight from the NCERT list of photosynthetic events, so a candidate who has that list can eliminate them at a glance. The fourth belongs to a different chapter altogether. The wording is the trap — 'oxidation of carbohydrate' sounds close enough to the sugar-making of photosynthesis to slip past a hurried reading, but photosynthesis reduces carbon dioxide, it does not oxidise sugar.
- Chlorophyll absorbs light most strongly in the blue and red parts of the spectrum and reflects green.
- The oxygen released in photosynthesis comes from the splitting of water, not from carbon dioxide.
- Photosynthesis converts light energy into chemical energy stored in carbohydrate.
- Respiration oxidises carbohydrate in the mitochondrion and does not involve chlorophyll.
- Photosynthesis takes place in the chloroplast, whose grana hold the pigment.
Three printed options are steps of the first process; the fourth belongs to the second.
- Reading 'oxidation of carbohydrate' as sugar-making rather than sugar-breaking.
- Believing the oxygen released comes from carbon dioxide.
- Assuming plants do not respire because they photosynthesise.
A negative item built on the NCERT list of photosynthetic events; the sibling papers ask the same list positively, most often through the source of the oxygen released.
Which one of the following is the process involved in photosynthesis?
- (a) Potential energy is released to form free energy
- (b) Free energy is converted into potential energy and stored
- (c) Food is oxidized to release carbon dioxide and water
- (d) Oxygen is taken in, and carbon dioxide and water vapour are given out
Answer(b) Free energy is converted into potential energy and stored
Its two rejected options describe respiration in the same words this CAPF distractor uses, which makes the direction of energy flow the deciding test in both.
The oxygen evolved during photosynthesis comes from splitting of
- (a) water
- (b) carbon dioxide
- (c) oxygen
- (d) light
Answer(a) water
Confirms that the splitting of water belongs to photosynthesis, which removes the first of the printed options here.
Which one of the following statements about the process of photosynthesis is correct?
- (a) Light energy is directly converted to kinetic energy which oxidizes carbon dioxide.
- (b) Light energy is directly converted to chemical energy which causes reduction of water.
- (c) Chlorophyll absorbs the chemical energy of light which causes oxidation of carbon dioxide.
- (d) Chlorophyll absorbs light energy which causes splitting of water molecules and reduction of carbon dioxide.
Answer(d) Chlorophyll absorbs light energy which causes splitting of water molecules and reduction of carbon dioxide.
Its keyed option names three of the four functions listed here in a single sentence, and its wrong options all turn on the same oxidation-versus-reduction slip.
- practice — not a real PYQ
The oxygen released during photosynthesis comes from
- (a)carbon dioxide
- (b)water
- (c)glucose
- (d)chlorophyll
Answer(b) water — photolysis splits water and the oxygen escapes to the air.
- practice — not a real PYQ
Chlorophyll appears green because it
- (a)absorbs green light strongly
- (b)reflects green light
- (c)emits green light
- (d)converts blue light to green
Answer(b) reflects green light — it absorbs mainly in the blue and the red.