Plant Kingdom Algae

8 MCQs9-step worked example
Source: NCERT Diversity in Living WorldPYQ coverage: NEET 2020, 2022, 2024Official key: NTA-verifiedLast updated: 25 Sep 2026

Plant Kingdom Algae, explained for NEET

The trap that repeatedly costs marks on algae is swapping the pigment and the stored food across the three classes — NCERT's Table 3.1 pairs Chlorophyceae with chlorophyll a, b and starch; Phaeophyceae with chlorophyll a, c, fucoxanthin and mannitol/laminarin; Rhodophyceae with chlorophyll a, d, phycoerythrin and floridean starch (NCERT Class 11 Biology, Chapter 3, page 27). Options shuffle these three pairs so a half-remembered fact still looks plausible.

Algae are chlorophyll-bearing, thalloid, autotrophic and largely aquatic organisms (page 24). They reproduce vegetatively by fragmentation, asexually by flagellated zoospores, and sexually in three distinct patterns based on gamete size and motility: isogamous (similar-sized gametes, flagellated or not, as in Ulothrix and Spirogyra), anisogamous (dissimilar-sized gametes, as in Eudorina) and oogamous (one large non-motile female gamete fuses with a smaller motile male gamete, as in Volvox and Fucus) (page 24).

A second, quieter trap sits right next to this: knowing "Phaeophyceae is brown and marine" is not the same as knowing which of Volvox or Fucus is oogamous versus which pattern belongs to Ulothrix. NEET distractors exploit exactly that gap — correctly naming the class, then guessing the reproduction mode, or vice versa.

Chlorophyceae members are grass green from chlorophyll a and b, store starch as their reserve (often in pyrenoids), and have a cellulose-inner/pectose-outer wall (page 26). Phaeophyceae range from olive-green to brown depending on fucoxanthin content, store mannitol or laminarin, and carry a cellulose wall coated with algin (pages 26–27). Rhodophyceae are marine, red from phycoerythrin, occur from well-lit surface waters to ocean depths, and store floridean starch (page 27).

Watch out: don't default to "if it's marine and brown, it must store floridean starch" — floridean starch belongs only to Rhodophyceae. Pin each fact to its class using the table, not by association with "marine."

Can you answer these Plant Kingdom Algae MCQs?

Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.

MCQ 1Easy RecallPractice

Which pigment combination is responsible for the grass-green colour of Chlorophyceae members?

Show answer and why every option is right or wrong

Answer: A. NCERT states Chlorophyceae members are usually grass green due to the dominance of chlorophyll a and b (NCERT Class 11 Biology, Chapter 3, page 26).

Why B is wrong: B is wrong because chlorophyll a and c is the Phaeophyceae (brown algae) pigment pair, not Chlorophyceae's.

Why C is wrong: C is wrong because chlorophyll a and d is the Rhodophyceae (red algae) pigment pair, not Chlorophyceae's.

Why D is wrong: D is wrong because fucoxanthin is the xanthophyll that colours Phaeophyceae brown; it is not a chlorophyll and is not present in Chlorophyceae.

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MCQ 2Easy RecallPractice

Which algal class stores its reserve food as floridean starch?

Show answer and why every option is right or wrong

Answer: C. Table 3.1 lists floridean starch as the stored food unique to Rhodophyceae, similar in structure to amylopectin and glycogen (NCERT Class 11 Biology, Chapter 3, page 27).

Why A is wrong: A is wrong because Chlorophyceae stores starch, not floridean starch.

Why B is wrong: B is wrong because Phaeophyceae stores mannitol and laminarin, not floridean starch.

Why D is wrong: D is wrong for the same reason as A and B individually — neither class stores floridean starch; it is exclusive to Rhodophyceae per Table 3.1.

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MCQ 3Easy RecallPractice

The pigment fucoxanthin, which gives brown algae their colour, occurs together with which chlorophyll combination?

Show answer and why every option is right or wrong

Answer: B. NCERT lists Phaeophyceae's major pigments as chlorophyll a, c, carotenoids and xanthophylls including fucoxanthin (NCERT Class 11 Biology, Chapter 3, page 26).

Why A is wrong: A is wrong because chlorophyll a and b is the Chlorophyceae pair; fucoxanthin is not one of its pigments.

Why C is wrong: C is wrong because chlorophyll a and d is the Rhodophyceae pair, and Rhodophyceae's colour pigment is phycoerythrin, not fucoxanthin.

Why D is wrong: D is wrong because no algal class in Table 3.1 is listed as chlorophyll b and c; this combination does not appear in NCERT's classification.

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MCQ 4Direct ApplicationPractice

In Volvox and Fucus, sexual reproduction occurs by fusion of one large, non-motile female gamete with a smaller, motile male gamete. NCERT terms this mode:

Show answer and why every option is right or wrong

Answer: D. NCERT names fusion of a large non-motile female gamete with a smaller motile male gamete as oogamous, citing Volvox and Fucus as examples (NCERT Class 11 Biology, Chapter 3, page 24).

Why A is wrong: A is wrong because isogamous fusion requires the two gametes to be similar in size, as in Ulothrix, not one non-motile and one motile gamete of different sizes.

Why B is wrong: B is wrong because anisogamous fusion involves two gametes that are merely dissimilar in size (as in Eudorina), without one of them being static; here one gamete is specifically non-motile.

Why C is wrong: C is wrong because vegetative reproduction in algae happens by fragmentation, not by gamete fusion at all.

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MCQ 5Direct ApplicationPractice

In Ulothrix, the fusing gametes are flagellated and similar in size. NCERT classifies this sexual reproduction mode as:

Show answer and why every option is right or wrong

Answer: A. NCERT defines isogamous reproduction as fusion of two gametes similar in size, flagellated or not, giving Ulothrix as an example (NCERT Class 11 Biology, Chapter 3, page 24).

Why B is wrong: B is wrong because anisogamous fusion needs the two gametes to be dissimilar in size, as in Eudorina — Ulothrix's gametes are described as similar in size.

Why C is wrong: C is wrong because oogamous fusion needs one large non-motile female gamete, as in Volvox — Ulothrix's gametes are both flagellated and motile.

Why D is wrong: D is wrong because zoospores are the asexual (not sexual) reproductive stage in algae; the question describes gamete fusion, which is sexual reproduction.

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MCQ 6Direct ApplicationPractice

An alga is marine, olive-green to brown, has a cellulose wall coated with a gelatinous layer of algin, and stores food as mannitol and laminarin. Which class and pigment set match all these features?

Show answer and why every option is right or wrong

Answer: B. NCERT describes Phaeophyceae as brown, with a cellulosic wall covered by a gelatinous coating of algin and food stored as mannitol or laminarin (NCERT Class 11 Biology, Chapter 3, pages 26–27).

Why A is wrong: A is wrong because Chlorophyceae stores starch (not mannitol/laminarin) and has a cellulose-inner/pectose-outer wall with no algin coating.

Why C is wrong: C is wrong because Rhodophyceae is red, not brown, stores floridean starch, and its wall is cellulose plus pectin and polysulphate esters, not algin.

Why D is wrong: D is wrong because NCERT states the algin coating belongs to Phaeophyceae's vegetative cells, not Chlorophyceae's.

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MCQ 7Concept TrapPractice

Which of the following statements about Rhodophyceae is correct per NCERT?

Show answer and why every option is right or wrong

Answer: C. NCERT states red algae occur in well-lighted regions near the surface and also at great depths where little light penetrates, and that they store floridean starch (NCERT Class 11 Biology, Chapter 3, page 27).

Why A is wrong: A is wrong because Chlorophyceae stores starch, not floridean starch — floridean starch is unique to Rhodophyceae per Table 3.1.

Why B is wrong: B is wrong on both counts: Table 3.1 lists an 'absent' flagellar number for Rhodophyceae, not Phaeophyceae, and Phaeophyceae occur primarily in marine habitats, with fresh water being rare for them.

Why D is wrong: D is wrong because Rhodophyceae's cell wall is cellulose plus pectin and polysulphate esters, not cellulose alone, per Table 3.1.

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MCQ 8CalculationPractice

Which row correctly pairs a genus with both its sexual reproduction mode and its stored food, per NCERT?

Show answer and why every option is right or wrong

Answer: D. Volvox is NCERT's example of oogamous reproduction, and as a Chlorophyceae genus (grouped with Chlamydomonas, Ulothrix, Spirogyra and Chara) it stores food as starch (NCERT Class 11 Biology, Chapter 3, pages 24 and 26).

Why A is wrong: A is wrong twice over: Ulothrix's gametes are similar in size, so it is isogamous, not oogamous, and as Chlorophyceae it stores starch, not mannitol.

Why B is wrong: B is wrong because Eudorina's gametes are dissimilar in size, so it is anisogamous, not isogamous; its stored food is not specified as starch in this text.

Why C is wrong: C is wrong twice over: Fucus is NCERT's oogamous example, not isogamous, and as Phaeophyceae it stores mannitol/laminarin, not floridean starch.

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How do you solve a Plant Kingdom Algae question? A worked example

  1. 1

    Given

    A NEET-style identification question describes an alga: marine habitat, olive-brown colour, cell wall of cellulose coated with a gelatinous layer of algin, food reserve stored as mannitol and laminarin, and sexual reproduction by fusion of one large non-motile female gamete with a smaller motile male gamete (its example genus is Fucus).

  2. 2

    Required

    Name the algal class this description matches, and the sexual reproduction mode it illustrates.

  3. 3

    Concept

    NCERT sorts algae into Chlorophyceae, Phaeophyceae and Rhodophyceae by pigment, stored food and cell-wall composition (Table 3.1), and separately classes sexual reproduction as isogamous, anisogamous or oogamous by gamete size and motility.

  4. 4

    Formula

    No numerical formula applies. The diagnostic pairing to use: Phaeophyceae → chlorophyll a, c, fucoxanthin; cellulose wall with algin coating; mannitol/laminarin storage. Oogamous → one large non-motile gamete fused with one small motile gamete.

  5. 5

    Substitution

    Match each stated feature against the table: brown colour + algin-coated wall + mannitol/laminarin storage → Phaeophyceae (page 26–27). One large non-motile female gamete fusing with a smaller motile male gamete, with Fucus named as the example → oogamous (page 24).

  6. 6

    Calculation

    No arithmetic is required here — this is a feature-to-class identification match, not a computed value.

  7. 7

    Final answer

    The alga belongs to Phaeophyceae, and its sexual reproduction is oogamous.

  8. 8

    Common trap

    A student who correctly identifies "brown, marine, algin-coated" as Phaeophyceae often still guesses the reproduction mode wrong, defaulting to isogamous or anisogamous because they remember the class but not that Fucus specifically is NCERT's oogamous example (the class ID and the reproduction mode are tested and mis-recalled independently). A second, separate slip swaps in floridean starch for mannitol/laminarin because "marine" gets over-associated with Rhodophyceae.

  9. 9

    Similar NEET-style question

    A red, marine alga is found both in well-lit surface waters and at great ocean depths, stores food as floridean starch, and reproduces asexually by non-motile spores. Which class is it, and by which pigment is it recognised? (Answer: Rhodophyceae — recognised by the red pigment r-phycoerythrin, occurring alongside chlorophyll a and d; the combination of greater depth tolerance, floridean starch storage and phycoerythrin dominance matches NCERT's Rhodophyceae description on page 27, distinct from Phaeophyceae's mannitol/laminarin storage and fucoxanthin pigment.)

What to remember before solving Plant Kingdom Algae questions

Key Fact

Algae

Algae are chlorophyll-bearing, simple, thalloid, autotrophic and largely aquatic organisms (fresh water and marine), also found on moist stones, soils, wood, and in association with fungi (lichen) and animals (e.g., sloth bear). Form and size vary from colonial forms like Volvox and filamentous forms like Ulothrix and Spirogyra to massive marine forms such as kelps. Algae reproduce vegetatively by fragmentation; asexually by flagellated zoospores; and sexually by fusion of two gametes. Isogamous reproduction fuses flagellated, similar-sized gametes (Ulothrix) or non-flagellated similar-sized gametes (Spirogyra). Anisogamous reproduction fuses dissimilar-sized gametes (Eudorina). Oogamous reproduction fuses a large, non-motile female gamete with a smaller, motile male gamete (Volvox, Fucus).

-- NCERT Class 11 Biology, Ch. 3, p. 24
Key Fact

Chlorophyceae

Members of Chlorophyceae are commonly called green algae. The plant body may be unicellular, colonial or filamentous. They are usually grass green due to the dominance of chlorophyll a and b, localised in definite chloroplasts that may be discoid, plate-like, reticulate, cup-shaped, spiral or ribbon-shaped. Most members have storage bodies called pyrenoids in the chloroplasts, containing protein besides starch; some algae store food as oil droplets. The rigid cell wall has an inner cellulose layer and an outer pectose layer. Vegetative reproduction is by fragmentation; asexual reproduction by flagellated zoospores in zoosporangia; sexual reproduction may be isogamous, anisogamous or oogamous. Common green algae: Chlamydomonas, Volvox, Ulothrix, Spirogyra and Chara.

-- NCERT Class 11 Biology, Ch. 3, p. 26
Key Fact

Phaeophyceae

Members of Phaeophyceae, or brown algae, are found primarily in marine habitats. They show great variation in size and form, ranging from simple branched filamentous forms (Ectocarpus) to profusely branched forms like kelps, which may reach 100 metres in height. They possess chlorophyll a, c, carotenoids and xanthophylls, and vary in colour from olive green to shades of brown depending on the amount of the xanthophyll pigment fucoxanthin present.

-- NCERT Class 11 Biology, Ch. 3, p. 26
Key Fact

Rhodophyceae

Members of Rhodophyceae are commonly called red algae because of the predominance of the red pigment r-phycoerythrin in their body. Most red algae are marine, with greater concentrations in warmer areas. They occur in both well-lighted regions close to the water surface and at great ocean depths where relatively little light penetrates. Red thalli of most red algae are multicellular, and some have complex body organisation. Food is stored as floridean starch, structurally very similar to amylopectin and glycogen. Red algae reproduce vegetatively by fragmentation, asexually by non-motile spores, and sexually by non-motile gametes (oogamous, with complex post-fertilisation development). Common members: Polysiphonia, Porphyra, Gracilaria and Gelidium.

-- NCERT Class 11 Biology, Ch. 3, p. 27
Key Fact

Table 3.1: Divisions of Algae and their Main Characteristics

Table 3.1 compares the three algal classes. Chlorophyceae (green algae): pigments chlorophyll a, b; stored food starch; cell wall cellulose; flagella 2-8, equal, apical insertion; habitat fresh water, brackish water, salt water. Phaeophyceae (brown algae): pigments chlorophyll a, c, fucoxanthin; stored food mannitol, laminarin and algin; cell wall cellulose; flagella 2, unequal, lateral insertion; habitat fresh water (rare), brackish water, salt water. Rhodophyceae (red algae): pigments chlorophyll a, d, phycoerythrin; stored food floridean starch; cell wall cellulose, pectin and polysulphate esters; flagella absent; habitat fresh water (some), brackish water, salt water (most).

-- NCERT Class 11 Biology, Ch. 3, p. 27

Where do students lose marks on Plant Kingdom Algae?

These are the exact patterns that cause wrong answers in NEET. Each trap includes when it triggers and how to avoid it.

Trap

Swapping pigment/storage food across the three algal classes

Category: Similar Terms

NEET options mix up which pigment and which storage carbohydrate belongs to Chlorophyceae, Phaeophyceae and Rhodophyceae.

When it triggers

A question lists a stored food (starch, mannitol/laminarin, or floridean starch) or a pigment (chlorophyll b, fucoxanthin, phycoerythrin) and asks which algal class it belongs to, with the classes shuffled as distractors.

How to avoid

Table 3.1: Chlorophyceae stores starch (chlorophyll a, b); Phaeophyceae stores mannitol/laminarin (chlorophyll a, c, fucoxanthin); Rhodophyceae stores floridean starch (chlorophyll a, d, phycoerythrin).

Trap

Isogamous vs anisogamous vs oogamous

Category: Similar Terms

Students confuse the three sexual reproduction modes in algae and misassign the example genus.

When it triggers

A question names a genus (Ulothrix, Eudorina, Volvox/Fucus) and asks whether its sexual reproduction is isogamous, anisogamous or oogamous.

How to avoid

Isogamous = similar-sized gametes (Ulothrix, Spirogyra); anisogamous = dissimilar-sized gametes (Eudorina); oogamous = large non-motile female + small motile male gamete (Volvox, Fucus).

More in Diversity in Living World: 12 exam traps and mistakes · 1 question pattern from its other lessons.

Plant Kingdom Algae questions from past NEET papers

4 questions from NEET 2020, 2022, 2024. Answers verified against NTA official keys.

NEET 2024Revised key

Read the following statements and choose the set of correct statements: In the members of Phaeophyceae, A. Asexual reproduction occurs usually by biflagellate zoospores. B. Sexual reproduction is by oogamous method only. C. Stored food is in the form of carbohydrates which is either mannitol or laminarin. D. The major pigments found are chlorophyll a, c and carotenoids and xanthophyll. E. Vegetative cells have a cellulosic wall, usually covered on the outside by gelatinous coating of algin. Choose the correct answer from the options given below:

1A, B, C and D only
2B, C, D and E only
3A, C, D and E only
4A, B, C and E only
NTA Answer: Option 3(revised_final)

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All 59 past-paper questions from Diversity in Living World →

Sources

NCERT refs: Class 11 Biology Chapter 3, p.27

Page numbers are the ones printed in the current NCERT textbook (2023 rationalised edition), unless marked pre-2023. The books are free at ncert.nic.in.

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