Ravi suddenly notices that he is growing taller rapidly, his shoulders are broadening. Class 9

Ravi suddenly notices that he is growing taller rapidly, his shoulders are broadening. Class 9

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Question 1.

Ravi suddenly notices that he is growing taller rapidly, his shoulders are broadening, and his voice cracks. What stage of life is he entering? Class 9

Answer:

Ravi is entering the stage of adolescence (puberty). The changes he is experiencing - rapid increase in height, broadening of shoulders and voice cracking - are secondary sexual characteristics that appear due to the production of male sex hormones (testosterone) by the testes. These are signs of sexual maturation, which marks the transition from childhood to adulthood.

Question 2.

Rina’s period occurs every 28 days. Her last period was on the 5th of March. On which day is she most likely to get her next period? Class 9

Answer:

Rina's last period was on the 5th of March. Since her cycle is 28 days, her next period will most likely begin on 5th March + 28 days = 2nd April.

Question 3.

A human zygote has just formed. How many chromosomes does it have? Class 9

Answer:

A human zygote has 46 chromosomes (23 from the sperm and 23 from the egg). When the sperm (with 23 chromosomes) fuses with the egg (with 23 chromosomes) during fertilisation, the resulting zygote has the complete set of 46 chromosomes, restoring the diploid number characteristic of the human species.