Science (086) — AI-generated practice question

(a) In asexually reproducing organisms, variations arise due to small inaccuracies (errors) in DNA copying during reproduction. For example, when one bacterium divides to produce four individuals, the resultant bacteria are very similar with only minor differences. Variations are limited because only one parent is involved — there is no mixing of genetic material from two individuals. In sexual reproduction, genetic material from two parents combines, generating far greater diversity.

(b) If bacteria living in temperate water face a rise in temperature due to global warming, most will die. However, variants that are heat-resistant will survive and reproduce. This environmental selection of variants is crucial for long-term survival because it ensures that at least some individuals can adapt when conditions change, preventing the species from being wiped out.

(c) Equal genetic contribution is ensured because each parent contributes one set of chromosomes through their gametes (sperm and egg). Since gametes are formed by meiosis (having half the chromosomes), when they fuse at fertilisation, the offspring receives practically equal amounts of DNA from each parent.

Source: Chapter 8, Section 8.1 — Accumulation of Variation During Reproduction; Chapter 7, Section 7.1.1 — The Importance of Variation

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• (a) The key phrase examiners look for is "inaccuracies in DNA copying" as the source of variation, and the point that only one parent means no mixing — hence limited variation.
• (b) Always use a specific example (bacteria + heat/global warming is directly from the textbook). Link selection → survival of species for full marks.
• (c) This is a 1-mark question — one crisp mechanistic point is enough: meiosis halves the chromosome number, fertilisation restores it, ensuring equal contribution. You don't need to write more than 2 lines.