Science — CBSE Class 10 board question

(i) Most bacteria would die due to the sudden rise in temperature. However, a few heat-resistant variants would survive and reproduce, gradually forming a new population adapted to warmer temperatures. This shows how variation helps species survive environmental changes.

(ii) The sperm fertilises the egg in the fallopian tube (oviduct), forming a zygote. The zygote divides and moves to the uterus, where it implants and develops into an embryo, eventually leading to pregnancy.

(iii) Since only pistil is present (no stamen/anther), self-pollination cannot occur. Cross-pollination by external agents (wind, insects) becomes necessary for fertilisation to take place.

(iv) If the egg is not fertilised, the uterine lining (which had thickened to receive the embryo) breaks down and sheds along with blood vessels. This is called menstruation.

(v) The seed germinates under appropriate conditions of water and air. The embryo inside the seed grows, breaking open the seed coat, and develops into a new seedling — this process is called germination.

Source: Chapter 7 — Reproduction, Sections 7.1.1, 7.3, What You Have Learnt

---

• Each sub-part targets a different concept: variation/survival, fertilisation, cross-pollination, menstruation, and germination.
• For (i), the key phrase from the text is "the few variants resistant to heat would survive and grow further."
• For (ii) and (iv), remember fertilisation occurs in the fallopian tube, not the uterus.
• For (iv), menstruation is directly caused by the egg not being fertilised — examiners specifically look for this reasoning.
• Keep each point concise; one to two sentences per situation is enough for the marks allotted.