📚 CBSE Grade-10 Study Guide
Home › Science (086) (AI practice)

Science (086) — AI-generated practice question

AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.

Q1. [1] medium thorough-understanding
A sudden rise in environmental temperature kills most individuals in a species, but a small number survive and reproduce. Which of the following best explains why only some individuals survived? (i) The survivors had acquired heat tolerance by living in warm conditions. (ii) Pre-existing variations in the population gave some individuals better heat tolerance. (iii) All individuals tried to adapt, but only the strongest succeeded. (iv) The survivors belonged to a different species.
  1. A (i) only
  2. B (ii) only
  3. C (i) and (iii)
  4. D (iii) and (iv)
Generated by claude-sonnet-4-6 · 2026-06-26 01:03 · grounding rag
Model Answer

Answer: B — (ii) only

Pre-existing genetic variations in the population gave some individuals better heat tolerance, allowing them to survive and reproduce when environmental temperature rose suddenly.

Explanation

The passage (Ch. 7, Sec. 7.1.1) explicitly states that if some variations were present in a few individuals, those variants would survive a drastic niche change — e.g., bacteria resistant to heat survive a heat wave. This is natural selection acting on pre-existing variation, not acquired adaptation (i) or effort-based survival (iii). Option (iv) is wrong because all individuals belong to the same species. Examiners look for the key phrase "pre-existing variation."

Previous-year CBSE Grade 10 board exam questions, organised by subject and chapter, each with a model answer — free to read and print.