Q.111 Botany ⭐ 360° Option Elimination Active

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NEET 2021 Botany Question 111 Solution

Topic: Plant Kingdom · Official NTA Booklet Code M1

Question

Which of the following algae contains mannitol as reserve food material?

(1)Ectocarpus
(2)Gracilaria
(3)Volvox
(4)Ulothrix

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Verified Against NTA Final Answer Key

Option (1) : Ectocarpus

📚 Plant Kingdom Easy

📋 Given Parameters & Problem Setup

Storage Food Mannitol (complex carbohydrate / sugar alcohol)

Candidate Genera Ectocarpus, Gracilaria, Volvox, Ulothrix

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The 30-Second Exam Hall Shortcut: ⚡ "Brown Algae = Laminarin & Mannitol"

⏱️ Save ~20 seconds

Mannitol is the diagnostic reserve food material of Phaeophyceae (brown algae), which includes Ectocarpus, Dictyota, Laminaria, Sargassum, and Fucus! Gracilaria has floridean starch (red), while Volvox and Ulothrix store starch (green). Match Option (1)!

1 Recall algal reserve foods: Chlorophyceae store starch; Phaeophyceae store complex carbohydrates as laminarin or mannitol; Rhodophyceae store floridean starch.

2 Identify taxonomic classes: Ectocarpus is a brown alga (Phaeophyceae); Gracilaria is a red alga (Rhodophyceae); Volvox and Ulothrix are green algae (Chlorophyceae).

3 Brown algae uniquely store mannitol.

4 Match Option (1).

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Why You Can 100% Trust This Shortcut: Canonical NCERT Plant Kingdom taxonomy on Algae Classes and Food Reserves.

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Taxonomic Division and Storage Material in Algae

The major classes of algae are classified based on photosynthetic pigments and the chemical nature of stored food reserves:

\begin{aligned} \text{\textbf{Chlorophyceae (Green algae):}} & \quad \text{Starch (in pyrenoids)} \\[4pt] \text{\textbf{Phaeophyceae (Brown algae):}} & \quad \mathbf{\text{Laminarin and Mannitol}} \\[4pt] \text{\textbf{Rhodophyceae (Red algae):}} & \quad \text{Floridean starch (amylopectin/glycogen-like)} \end{aligned}

Step 2

Classification of Candidate Genera

Evaluating each genus provided in the choices: - *Ectocarpus*: Filamentous brown alga belonging to Phaeophyceae $\implies$ stores mannitol and laminarin. - *Gracilaria*: Red alga belonging to Rhodophyceae $\implies$ stores floridean starch. - *Volvox*: Colonial green alga belonging to Chlorophyceae $\implies$ stores standard starch. - *Ulothrix*: Filamentous green alga belonging to Chlorophyceae $\implies$ stores standard starch.

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1 1

✓ 100% Correct

Verdict & Scientific Reason:

Ectocarpus is a brown alga (Phaeophyceae) which stores reserve food as complex carbohydrates in the form of laminarin or mannitol.

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Why this is airtight: None. Canonical textbook fact.

2 2

✗ Incorrect

Verdict & Scientific Reason:

Gracilaria is a red alga (Rhodophyceae) which stores floridean starch (structurally similar to amylopectin and glycogen).

⚠️

Student Fallacy (Why candidates pick this trap): Confusing the food reserve of red algae with that of brown algae.

3 3

✗ Incorrect

Verdict & Scientific Reason:

Volvox is a green alga (Chlorophyceae) which stores carbohydrates as starch located in pyrenoids.

⚠️

Student Fallacy (Why candidates pick this trap): Mixing up green and brown algal reserves.

4 4

✗ Incorrect

Verdict & Scientific Reason:

Ulothrix is a green alga (Chlorophyceae) storing starch, not mannitol.

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Student Fallacy (Why candidates pick this trap): Failing to categorize Ulothrix into Chlorophyceae.

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NTA Trap Alert: Mannitol vs Floridean Starch Assignment Confusion

Students frequently mix up the storage polysaccharides of Rhodophyceae (Floridean starch) and Phaeophyceae (Laminarin and Mannitol).

🛡️ How to avoid the -1 mark: Remember: Brown Algae = "BLM" (Brown = Laminarin + Mannitol); Red Algae = "RF" (Red = Floridean starch).

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Core NEET Syllabus Standard

NEET / NCERT Biology · Plant Kingdom Standard Benchmark

Core Scientific Principle Tested:

"Food in Phaeophyceae is stored as complex carbohydrates, which may be in the form of laminarin or mannitol."

Syllabus Focus: Algae: Phaeophyceae (Brown Algae)

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NEET 2021 Botany Question 111 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ "Brown Algae = Laminarin & Mannitol"

Step-by-Step Rigorous Workflow & Mathematical Proof

Taxonomic Division and Storage Material in Algae

Classification of Candidate Genera

360° Option Elimination Engine Key Feature

NTA Trap Alert: Mannitol vs Floridean Starch Assignment Confusion

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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