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💡 The reset button
If no sperm arrives, the thickened lining is no longer needed. The body clears it away and quietly prepares for the next chance.
What is menstruation?
- If the egg is not fertilised, it degenerates in about a day, and the thick, blood-rich uterine lining is no longer needed.
- The lining, along with some blood, leaves the body through the vagina — this is menstruation (a period), lasting about 3 to 7 days .
- The cycle of ovulation, uterus preparation and menstruation repeats every 21–35 days (often about 28), from puberty until menopause (Fig. 11.21).
| Days | What happens |
|---|---|
| Day 1–5 | Menstruation — shedding of the uterine lining. |
| Day 6–14 | Uterine lining gradually rebuilds; an egg matures in the ovary. |
| Day 14 | Ovulation — the ovary releases a mature egg. |
| Day 15–28 | Uterine lining becomes thicker and rich with blood vessels; if no fertilisation happens it breaks down around day 28 and the cycle repeats. |
NCERT Question 5 — Explain why the menstrual cycle
Explain why the menstrual cycle stops during pregnancy.
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NCERT Question 13 — A student claims, “In humans
A student claims, “In humans, ovulation always happens on day 14 of the menstrual cycle”. Critically examine this claim and state whether the claim is correct or not. Give at least two reasons for your answer.
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🧵 Threads of Curiosity
- What determines a baby’s biological sex?
- Everyone has two sex chromosomes: females XX, males XY.
- The mother always contributes an X chromosome.
- The father contributes either an X or a Y.
- An X gives a female (XX); a Y gives a male (XY).
- So the father’s contribution decides the biological sex.
🌎 Bridging Science and Society
- Use clean menstrual products — pads, tampons or cups.
- Wash regularly with water during menstruation.
- Wash hands with soap before and after changing a pad.
- Dispose of used products responsibly, wrapped in a bin.
- Never flush used menstrual products.
- Keep reusable products clean and fully dry.
- Change products every 4–6 hours, or more if needed.
