Accessory Pigments and Their Role in Photosynthesis
Biology · Photosynthesis in Higher Plants · NEET
Accessory pigments are the thylakoid pigments other than chlorophyll a — namely chlorophyll b, xanthophylls and carotenoids. They absorb light at wavelengths chlorophyll a cannot, then hand this energy over to chlorophyll a, and they also protect chlorophyll a from damage by light (photo-oxidation). Memory hook: "b, xantho, caro = the helpers who CATCH light and GUARD chlorophyll a."
Accessory pigments (chlorophyll b, xanthophylls, carotenoids) absorb light at extra wavelengths and transfer the energy to chlorophyll a, the chief pigment that drives the light reaction. They also shield chlorophyll a from photo-oxidation.
Your doubts, answered
Which pigments are the accessory pigments?
NCERT lists four leaf pigments: chlorophyll a, chlorophyll b, xanthophylls and carotenoids. Of these, chlorophyll b, xanthophylls and carotenoids are the accessory pigments. Chlorophyll a is NOT an accessory pigment — it is the chief (main) pigment and the reaction-centre pigment.
What exactly do accessory pigments do?
They do two jobs. First, they absorb light at wavelengths that chlorophyll a absorbs poorly, so they widen the range of light usable for photosynthesis. Second, they transfer this trapped energy to chlorophyll a, which then drives the light reaction. They do not carry out the reaction themselves.
Do accessory pigments only broaden the absorption range?
No. NCERT adds a second, protective role: accessory pigments (especially carotenoids) protect chlorophyll a from photo-oxidation, i.e. from being destroyed by excess light. This protection point is often skipped by students and is a common NEET trap.
Can a plant photosynthesise with only accessory pigments (no chlorophyll a)?
No. Accessory pigments cannot run the light reaction alone. They always pass energy to chlorophyll a, which is the pigment at the reaction centre (P680 and P700). Without chlorophyll a, the collected energy has nowhere to go, so photosynthesis stops. This is why chlorophyll a is called the chief pigment.
Are carotenoids just colouring pigments?
They give yellow/orange colour, but that is not their main job in the leaf. Inside the thylakoid they act as accessory pigments — absorbing light, passing energy to chlorophyll a, and protecting chlorophyll a. Xanthophylls and carotenoids together are the carotenoid group; both are accessory pigments.
⚠️ The NEET trap ✗ Chlorophyll a is an accessory pigment because it also absorbs light. ✓ Chlorophyll a is the chief (main) reaction-centre pigment. Accessory pigments are only chlorophyll b, xanthophylls and carotenoids — they feed energy TO chlorophyll a. 🧠 NEET loves to slip chlorophyll a into the accessory list. Rule: the pigment that RECEIVES the energy (chlorophyll a) is never accessory; the ones that GIVE energy are accessory.
Real NEET questions
2023
Match List I (Pigment) with List II (Colour in chromatogram): A. Chlorophyll a B. Chlorophyll b C. Xanthophyll D. Carotenoid | I. Yellow to yellow orange II. Yellow green III. Blue green IV. Yellow
A · A-II, B-III, C-I, D-IV
B · A-IV, B-III, C-II, D-I
C · A-III, B-II, C-IV, D-I ✓
D · A-III, B-I, C-IV, D-II
Solution: Paper chromatography separates leaf pigments by colour: chlorophyll a = blue green (III), chlorophyll b = yellow green (II), xanthophylls = yellow (IV), carotenoids = yellow to yellow-orange (I). So A-III, B-II, C-IV, D-I, which is option C. Note that chlorophyll b, xanthophyll and carotenoid here are the accessory pigments.
2025
Match List I (Pigment) with List II (Colour): A. Chlorophyll a B. Chlorophyll b C. Xanthophylls D. Carotenoids | I. Yellow-green II. Yellow III. Blue-green IV. Yellow to Yellow-orange
A · A-I, B-II, C-IV, D-III
B · A-I, B-IV, C-III, D-II
C · A-III, B-IV, C-II, D-I
D · A-III, B-I, C-II, D-IV ✓
Solution: Chlorophyll a = blue-green (III), chlorophyll b = yellow-green (I), xanthophylls = yellow (II), carotenoids = yellow to yellow-orange (IV). So A-III, B-I, C-II, D-IV, which is option D. The three accessory pigments (chlorophyll b, xanthophylls, carotenoids) all show non-blue-green colours in the chromatogram.
Solved Photosynthesis in Higher Plants NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Thylakoid pigments other than chlorophyll a — chlorophyll b, xanthophylls and carotenoids — that absorb light and pass the energy to chlorophyll a.
Is chlorophyll a an accessory pigment?
No. Chlorophyll a is the chief pigment and sits at the reaction centre. Accessory pigments feed energy to it.
What are the two roles of accessory pigments?
(1) They absorb wavelengths chlorophyll a cannot and transfer that energy to chlorophyll a, widening the absorption range. (2) They protect chlorophyll a from photo-oxidation (light damage).
Why can't accessory pigments do photosynthesis alone?
They only collect and pass on energy. The actual light reaction happens at chlorophyll a in the reaction centre, so chlorophyll a is essential.
Which accessory pigment protects chlorophyll a the most?
Carotenoids (carotenes and xanthophylls) are mainly credited with protecting chlorophyll a from photo-oxidation.
