Q.77 Match the organisms with the appropriate growth curves.
(P) Bacteria
(Q) Extracellular virus
(R) Intracellular virus
(A) P-iii, Q-i, R-ii (B) P-ii, Q-i, R-iii
(C) P-ii, Q-iii, R-i (D) P-i, Q-ii, R-iii

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Introduction

Different microorganisms exhibit distinct growth patterns depending on their mode of replication.

• Bacteria multiply independently by binary fission

• Extracellular viruses cannot replicate outside host cells

• Intracellular viruses show a characteristic one-step growth curve inside host cells

In competitive exams, questions often test the ability to match organisms with their correct growth curves. This article explains each curve and identifies the correct answer.

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Understanding the Growth Curves

Curve (ii): Sigmoid (S-shaped) Curve

• Shows lag, log, stationary, and decline phases

• Typical of bacterial population growth

• ✔ Matches Bacteria (P)

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Curve (i): Extracellular Virus Curve

• Viruses do not replicate outside host cells

• Viral count remains constant or slowly decreases

• No exponential increase

• ✔ Matches Extracellular virus (Q)

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Curve (iii): One-Step Growth Curve

• Shows latent period → burst → plateau

• Characteristic of intracellular viral replication

• Sudden increase due to host cell lysis

• ✔ Matches Intracellular virus (R)

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Correct Matching

• P (Bacteria) → (ii)

• Q (Extracellular virus) → (i)

• R (Intracellular virus) → (iii)

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Correct Answer

✅ Option (B)

P-ii, Q-i, R-iii

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Option-Wise Explanation

Option (A): P-iii, Q-i, R-ii

❌ Incorrect

• Bacteria do not show one-step growth

• Intracellular viruses do not show sigmoid growth

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Option (B): P-ii, Q-i, R-iii

✅ Correct

• All organisms are matched with their correct growth curves

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Option (C): P-ii, Q-iii, R-i

❌ Incorrect

• Extracellular viruses do not show one-step growth

• Intracellular viruses do not show flat curves

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Option (D): P-i, Q-ii, R-iii

❌ Incorrect

• Bacteria do not show flat growth

• Extracellular viruses do not show sigmoid growth

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Quick Revision Table

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Conclusion

Growth curves reflect the biological nature of organisms.

• Bacteria grow independently

• Extracellular viruses are metabolically inactive

• Intracellular viruses replicate only inside host cells

Among the given options, Option (B) correctly matches all organisms with their respective growth curves.

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Final Answer

✅ Option (B): P-ii, Q-i, R-iii