Biology · Plant Kingdom · NEET
The main difference is the dominant pigment, which sets the colour. Chlorophyceae (green algae) are grass-green because chlorophyll a and b dominate. Phaeophyceae (brown algae) look brown because the xanthophyll fucoxanthin masks the green. Rhodophyceae (red algae) look red because the pigment r-phycoerythrin dominates. Once you fix the colour and pigment, the stored food and cell wall follow. NEET loves to swap these three rows in match-the-column questions, so learn them as a set.
Green algae (Chlorophyceae) store starch (sometimes oil droplets). Brown algae (Phaeophyceae) store mannitol or laminarin. Red algae (Rhodophyceae) store floridean starch, which NCERT says is very similar to amylopectin and glycogen. A common trap: students write mannitol for green algae. Mannitol is BROWN algae only. This exact swap was tested in NEET (Ulothrix–Mannitol was the wrong match).
Fucoxanthin (a xanthophyll) gives brown algae (Phaeophyceae) their brown colour. r-Phycoerythrin gives red algae (Rhodophyceae) their red colour. NEET 2023 asked exactly this: fucoxanthin and phycoerythrin belong to Phaeophyceae and Rhodophyceae respectively. Do not mix them up — fucoxanthin is never in red algae.
Chlorophyceae: an inner layer of cellulose and an outer layer of pectose. Phaeophyceae: cellulose covered on the outside by a gelatinous coating of algin. Rhodophyceae: cellulose, pectin and polysulphate esters. Notice cellulose is the common inner base in all three; only the outer material changes (pectose vs algin vs pectin/polysulphate). NEET 2024 confirmed the algin coating for brown algae as a correct statement.
Only Chlorophyceae (green algae) have pyrenoids — storage bodies inside the chloroplast that contain protein plus starch. Some green algae also store food as oil droplets. Brown and red algae do NOT have pyrenoids in NCERT. So if a question links pyrenoids to any algae, the answer is green algae.
Green algae (Chlorophyceae) reproduce sexually by isogamous, anisogamous or oogamous gametes, and asexually by flagellated zoospores. Brown algae (Phaeophyceae) also show isogamy, anisogamy or oogamy, with biflagellate zoospores. Red algae (Rhodophyceae) are special: they reproduce sexually by NON-MOTILE (non-flagellated) gametes and asexually by non-motile spores. NEET 2018 trapped students with 'uniflagellate gametes – Polysiphonia' (a red alga) — this is wrong because red algae gametes are non-motile.
Which classes of algae possess pigment fucoxanthin and pigment phycoerythrin, respectively?
Which of the following is incorrectly matched?
In the members of Phaeophyceae: A. Asexual reproduction usually by biflagellate zoospores. B. Sexual reproduction is oogamous only. C. Stored food is mannitol or laminarin. D. Major pigments are chlorophyll a, c, carotenoids and xanthophyll. E. Vegetative cells have a cellulosic wall covered outside by a gelatinous coating of algin. Choose the correct set.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Phaeophyceae (brown algae). NCERT says kelps may reach a height of 100 metres, making them the largest algae. Examples: Ectocarpus, Laminaria, Sargassum, Fucus.
Yes. Cellulose is the common inner cell-wall material in Chlorophyceae, Phaeophyceae and Rhodophyceae. Only the outer coating differs: pectose (green), algin (brown), pectin/polysulphate esters (red).
r-Phycoerythrin absorbs the blue-green light that penetrates deep into oceans. This lets red algae photosynthesise even at great depths where little light reaches, which NCERT notes is where many red algae grow.
Green (Chlorophyceae): Chlamydomonas, Volvox, Ulothrix, Spirogyra, Chara. Brown (Phaeophyceae): Ectocarpus, Dictyota, Laminaria, Sargassum, Fucus. Red (Rhodophyceae): Polysiphonia, Porphyra, Gracilaria, Gelidium. NEET often uses these genera to test which class they belong to.
