Reproduction in Human Beings: Quick Revision

A brief note on Reproduction in Human Beings. Read it before a test. Try each question at the end before you open its answer.

The reproductive systems

• Puberty: the reproductive organs become active, usually between about ten and fifteen years.
• Male: the testes in the scrotum make sperm and testosterone.
• The vas deferens carries sperm to the urethra, the shared path for sperm and urine.
• The seminal vesicles and the prostate add fluid that helps the sperm travel and feeds them.
• Female: the ovaries release one egg a month.
• The oviduct carries it to the uterus, which opens through the cervix into the vagina.

From zygote to baby

• Fertilisation happens in the oviduct: sperm and egg fuse into a zygote.
• The zygote divides as it moves to the uterus, and settles in its thick lining.
• The placenta passes glucose and oxygen to the embryo and takes away its wastes.
• About nine months later, the uterus contracts and the baby is born.
• No fertilisation: the lining breaks down as menstruation, about once a month, for two to eight days.

Reproductive health

• Infections: gonorrhoea and syphilis (bacteria), warts and HIV-AIDS (viruses).
• Contraception: condom or covering (barrier), hormone pills, loop or copper-T, or surgery.
• Surgery blocks the vas deferens or the fallopian tubes.
• Only a condom also lowers the risk of infections.
• Sex ratio: $\dfrac{1000 \times \text{girls}}{\text{boys}}$.
• Finding a child's sex before birth is banned by law.

A worked example

A zygote divides every day for the first few days. Each division doubles the cells. How many cells are there after $5$ divisions, and where does fertilisation take place?

1. Double each time. $1 \to 2 \to 4 \to 8 \to 16 \to 32$.
2. Count. After $5$ divisions there are $32$ cells, that is $2^5$.
3. Where. Fertilisation took place earlier, in the oviduct.

Practice with new numbers

A program to try

The program turns the length of a pregnancy into weeks and months.

Mistakes to avoid

• Fertilisation is not in the uterus. It happens in the oviduct.
• Both ovaries do not release an egg every month. Usually one egg is released.
• The two bloods do not mix. Substances cross the placenta.
• Hormone pills do not stop infections. A condom lowers that risk.
• The ratio is girls for every 1000 boys, so girls go on top.

Check yourself

1. Name the organ that makes testosterone.

2. In which part of the female body does a sperm meet the egg?

3. What leaves the body during menstruation, and why?

4. A village has $490$ girls and $500$ boys. Find the sex ratio.

5. Name one method of contraception that uses surgery in males.