Question 1

The splitting of water (photolysis) that releases O₂, protons and electrons is associated with:

Accepted Answer

Photosystem II. Water splitting occurs on the inner thylakoid side associated with PS II, replenishing its electrons.

Question 2

The products of the light reaction that are used in the dark reaction are:

Accepted Answer

ATP and NADPH. The light reaction produces assimilatory power (ATP + NADPH) used to fix CO₂ in the Calvin cycle.

Question 3

In NON-cyclic photophosphorylation, electrons flow from ______ and both ATP and NADPH are produced:

Accepted Answer

PS II → PS I (Z-scheme), with water as the electron source. The Z-scheme: PS II → electron carriers → PS I → NADP⁺; water donates electrons and NADPH is formed.

Question 4

CYCLIC photophosphorylation involves only ______ and produces ______ (no NADPH, no O₂):

Accepted Answer

PS I; ATP only. In cyclic flow, electrons return to PS I; only ATP is made, with no water splitting or NADPH.

Question 5

The reaction-centre chlorophyll of PS I and PS II absorb maximally at, respectively:

Accepted Answer

P700 and P680. PS I peaks at 700 nm (P700) and PS II at 680 nm (P680) — hence their names.

Question 6

Cyclic photophosphorylation also occurs when only wavelengths beyond ______ are available (only PS I functional):

Accepted Answer

680 nm. Beyond 680 nm only PS I works, so electron flow is cyclic, producing only ATP (the "red drop"/enhancement context).

Question 7

In the Z-scheme of the light reaction, the correct sequence through which an electron passes after leaving the water-splitting complex is:

Accepted Answer

PS II → plastoquinone → cytochrome complex → plastocyanin → PS I → ferredoxin → NADP⁺. Electrons flow from PS II through plastoquinone, the cytochrome b6f complex and plastocyanin to PS I, then via ferredoxin to NADP⁺ reductase, giving the characteristic Z shape on a redox scale.

Question 8

The oxygen-evolving complex that carries out photolysis of water is physically associated with photosystem II and requires the ions:

Accepted Answer

manganese, chloride and calcium. Water splitting by the oxygen-evolving (water-splitting) complex on the inner thylakoid side needs Mn²⁺, Cl⁻ and Ca²⁺; it is linked to PS II, not PS I.

Question 9

When light of wavelength longer than 680 nm is supplied, only PS I operates and cyclic photophosphorylation dominates. The functional consequence is that the chloroplast then produces:

Accepted Answer

ATP only, with no NADPH and no oxygen. In cyclic photophosphorylation electrons cycle back to PS I; only ATP is made — there is no NADP⁺ reduction and no water splitting, hence no NADPH and no O₂.

Question 10

The "reaction centre" of a photosystem differs from the rest of its light-harvesting (antenna) complex in that the reaction centre:

Accepted Answer

is the specific chlorophyll a molecule that loses an excited electron to an acceptor. Hundreds of antenna pigments funnel absorbed energy to a single reaction-centre chlorophyll a (P700 or P680), which alone ejects the high-energy electron and becomes oxidised.

Question 11

Assertion (A): Non-cyclic photophosphorylation requires the cooperation of both photosystems. Reason (R): PS II re-supplies the electrons that PS I loses to ferredoxin.

Accepted Answer

Both A and R are true and R is the correct explanation of A. In the non-cyclic pathway PS I passes electrons to ferredoxin (and on to NADP⁺); those electrons are replaced from PS II (ultimately from water), so both photosystems must act in series.

Question 12

The mobile electron carrier that shuttles electrons from the cytochrome b6f complex to photosystem I is:

Accepted Answer

plastocyanin. Plastocyanin, a copper-containing protein on the lumen side, transfers electrons from the cytochrome complex to P700 of PS I; plastoquinone works upstream (PS II to cytochrome).

Question 13

The reaction-centre chlorophylls P700 and P680 are named after the wavelength each absorbs maximally; they belong, respectively, to:

Accepted Answer

photosystem I and photosystem II. P700 (700 nm) is the PS I reaction centre and P680 (680 nm) is the PS II reaction centre — the numbers simply denote their absorption maxima.

Question 14

The very last electron acceptor before NADP⁺ in the non-cyclic pathway, which passes electrons to NADP⁺ reductase, is:

Accepted Answer

ferredoxin. On the stroma side of PS I, ferredoxin receives the electron and, with NADP⁺ reductase, reduces NADP⁺ to NADPH; plastocyanin and plastoquinone act earlier in the chain.

Question 15

In non-cyclic photophosphorylation the electrons that reduce NADP⁺ originate ultimately from:

Accepted Answer

the photolysis of water at photosystem II. Splitting of water at PS II supplies the electrons that travel through the chain to replace those lost by PS I, ultimately reducing NADP⁺ and releasing O₂.

Question 16

Light Reaction is also known as

Accepted Answer

photochemical phase. The light reaction is the photochemical phase where light is absorbed and light energy is converted; the biosynthetic (dark) phase is the Calvin cycle.

Question 17

Choose the correct order of events in light reaction:
I. ATP & NADPH formation
II. Water Splitting
III. Oxygen release
IV. Light absorption

Accepted Answer

IV II III I. Light is first absorbed (IV), then water is split (II), oxygen is released (III), and finally ATP and NADPH are formed (I).

Question 18

LHC stands for

Accepted Answer

Light Harvesting Complex. LHC is the Light Harvesting Complex, made of hundreds of pigment molecules bound to proteins that funnel absorbed light energy to the reaction centre.

Question 19

The naming of PS I & PS II was based on

Accepted Answer

The sequence of their discovery. Photosystem I and II are named in the sequence of their discovery, not in the order in which they function (PS II actually acts before PS I).

Question 20

Which of the following is correct?

Accepted Answer

PS II is called P680. PS I has its reaction centre absorbing at 700 nm (P700) and PS II at 680 nm (P680); hence 'PS II is called P680' is correct.

Light Reaction & Photophosphorylation — NEET Biology MCQs with Solutions

Questions with solutions