Exercise 11.8
A human zygote has just formed. How many chromosomes does it have? Mother’s health during pregnancy A woman’s health during pregnancy plays a vital role in the baby’s growth and safety. She should eat a balanced diet rich in proteins, vitamins and minerals, attend regular medical check-ups, and follow her doctor’s advice regarding light exercise and rest. Her emotional well-being is also important, and support from family members helps her remain healthy and stress-free. Exploration|Grade
NCERT’s answer
$\displaystyle 46$ Chromosomes
$\displaystyle 46$ chromosomes — that is \(\displaystyle 23\) pairs.
A human body cell has \(\displaystyle 46\) chromosomes, but gametes are made by meiosis, which halves the number, so each sperm and each egg carries only \(\displaystyle 23\).
At fertilisation the two haploid gametes fuse: \(\displaystyle 23 + 23 = 46\).
This is exactly why meiosis is needed — it keeps the chromosome number of the species constant instead of doubling it every generation.