Q.Which chlorophyll molecule does not have a phytol tail?
a. Chl- a b. Chl-b c. Chl- c d. Chl -d

Chlorophyll a, b, and d all carry a long hydrophobic phytol chain that anchors them in the thylakoid membrane, but chlorophyll c lacks this phytol tail, making it structurally distinct.

All chlorophyll molecules share a porphyrin "head" (a magnesium-centred tetrapyrrole ring) that absorbs light, but most of them additionally carry a long hydrophobic side chain called the phytol tail, esterified to the porphyrin ring. This phytol tail is what embeds and anchors the chlorophyll molecule within the lipid environment of the thylakoid membrane.

Chlorophyll a, chlorophyll b, and chlorophyll d all possess this phytol tail. Chlorophyll c, found mainly in certain algal groups (e.g., diatoms, brown algae, dinoflagellates), is structurally different: it retains the porphyrin ring but does NOT have the phytol chain esterified to it, making it a smaller, more polar molecule compared to the other chlorophylls.

Quantasomes, the particulate units that carry out the light reactions of photosynthesis, are located in the thylakoid membranes inside the chloroplast.

The chloroplast is the site of photosynthesis in plant cells. Internally, it consists of a matrix called the stroma, within which lie flattened, membrane-bound sacs called thylakoids, often stacked into structures called grana and interconnected by stroma lamellae.

When the thylakoid membrane was examined under the electron microscope, it appeared studded with small, regularly arranged particles. These particles — named quantasomes by Park and Biggins (1964) — were proposed to be the basic structural and functional units of photosynthesis, each containing an assembly of several hundred chlorophyll and accessory pigment molecules along with the electron-transport components needed to capture light energy (quanta) and drive the light reactions. (The concept has since been refined into today's understanding of discrete photosystems, PS I and PS II, but the term 'quantasome' specifically denotes this thylakoid-membrane photosynthetic unit.)

Since quantasomes are, by definition, the photosynthetic unit of the thylakoid membrane, they are found in the chloroplast and not in the Golgi bodies, mitochondria, or endoplasmic reticulum, which are unrelated to photosynthesis.

Chlorophyll a is the only pigment that directly converts light energy into chemical energy; all other pigments (chlorophyll b, xanthophylls, carotenoids) are accessory pigments that merely absorb light and transfer that energy to chlorophyll a.

In the thylakoid membrane, pigments are organised into light-harvesting complexes surrounding a special pair of chlorophyll a molecules at the reaction centre (P680 in Photosystem II, P700 in Photosystem I). Chlorophyll b, xanthophylls, and carotenoids absorb light of wavelengths chlorophyll a does not absorb efficiently, and funnel that captured energy, by resonance transfer, to the chlorophyll a molecules at the reaction centre.

Only the reaction-centre chlorophyll a undergoes the actual photochemical act: it becomes excited, loses an electron, and that electron is passed into the electron transport chain — this is the step where light energy is genuinely converted into chemical energy (ultimately stored as ATP and NADPH). The accessory pigments never lose an electron themselves; they only harvest and relay light energy.

As a fruit ripens, its green chlorophyll degrades, unmasking the underlying carotenoid pigments, which is why ripening fruit changes colour towards yellow, orange, or red.

Let us check each pair:

1. Change of Fruit colour in Tomato - Lutein — INCORRECT. The red colour of ripe tomato is due to lycopene (a red carotenoid), not lutein (which is a yellow xanthophyll pigment found mainly in leaves and some flowers, not the main tomato pigment).
2. Fruit ripening - Carotenoids — CORRECT. During ripening, chlorophyll breaks down and the carotenoid pigments (carotenes and xanthophylls, including lycopene in tomato) already present in the chromoplasts become visible, giving ripe fruits their yellow/orange/red colours.
3. Yellowing in Leaf - Chlorophyll — INCORRECT/MISLEADING as stated. Leaf yellowing (as in autumn or senescence) is caused by the breakdown/loss of chlorophyll, which then unmasks the carotenoids already present — chlorophyll itself is the pigment that is lost, not the cause of yellow colour.
4. Change in Leaf colour - Lycopene — INCORRECT. Lycopene is specifically the red pigment of tomato fruit; autumn leaf colour changes are due to carotenoids (yellow/orange) and anthocyanins (red/purple), not lycopene.

Chlorophyll's molecular structure contains a magnesium (Mg) atom at the centre of its porphyrin head.

Chlorophyll molecules consist of a porphyrin 'head' — a ring made of four pyrrole units — with a magnesium ion coordinated at its centre, plus a long hydrocarbon 'tail' (phytol) that anchors the molecule in the thylakoid membrane. This Mg-porphyrin structure is what allows chlorophyll to absorb light energy efficiently in the red and blue regions of the visible spectrum, driving the light reactions of photosynthesis.

Quantasomes are the small spherical particles studding the inner surface of the thylakoid (lamellar) membrane, representing the photosynthetic functional units.

Inside the chloroplast, the internal membrane system is organised into flattened sacs called thylakoids, which are stacked into grana and interconnected by stroma lamellae. When the thylakoid membrane is examined closely, tiny spherical particles are seen studding its inner surface — these particles were named quantasomes, and were originally thought to represent the basic structural/functional unit of photosynthesis (containing the pigment molecules and electron-transport components needed to carry out the light reactions).

The other options are related but distinct structures: Stroma is the fluid matrix surrounding the thylakoids (site of the Calvin cycle/dark reactions), Granum is a stack of thylakoid discs, and Thylakoid is the membrane-bound sac itself — not the small spherical particles on its inner surface.

Correct answer: (d) Anthocyanin

Carotene, xanthophyll and phycobilins are accessory photosynthetic pigments; anthocyanin is a non-photosynthetic vacuolar pigment.

Carotene, xanthophyll (both carotenoids) and phycobilins (found in algae/cyanobacteria) are accessory pigments that absorb light energy and pass it on to chlorophyll during photosynthesis, broadening the range of wavelengths that can be used. Anthocyanin, on the other hand, is a water-soluble flavonoid pigment located in the cell vacuole (not in chloroplasts), responsible for red, purple and blue colours in flowers, fruits and autumn leaves. It plays no role in light absorption for photosynthesis, so it is not a photosynthetic pigment.