Reproduction in Humans
ICSE Class 8 · Biology · Chapter 3
What this chapter covers
- Sexual reproduction in humans
- The male reproductive system
- The sperm
- The female reproductive system
- The ovum
- Fertilisation
- Development of the baby (in brief)
Key points
- Humans reproduce only sexually; two parents each give one gamete.
- The sperm is the male gamete and the ovum is the female gamete.
- The testes, held in the scrotum, make sperm and testosterone.
- Sperm mature in the epididymis and travel through the sperm ducts to the urethra.
- Glands add fluid to sperm to form semen, which leaves through the urethra and penis.
- The ovaries release usually one ovum a month and make oestrogen and progesterone.
- Fertilisation normally happens in the oviduct, not in the uterus; the oviduct then carries the zygote to the uterus.
- The uterus shelters and feeds the growing baby; the vagina is the birth canal.
- Fertilisation is the fusion of sperm and ovum nuclei to form a zygote, inside the body.
- The zygote divides to form an embryo, which implants in the lining of the uterus.
- The placenta and umbilical cord supply the baby with food and oxygen and remove wastes.
- The baby is called a foetus once its main body parts form; birth comes after about nine months.
Questions answered
Name the male and female gametes in humans.
The male gamete is the sperm and the female gamete is the ovum (egg cell).
Why are the testes held outside the abdomen in the scrotum?
Sperm develop properly only at a temperature about 2 to 3 °C lower than body temperature. The scrotum keeps the testes slightly cooler than the inside of the body.
What is semen, and why are the glands of the male system important?
Semen is sperm mixed with fluids from the seminal vesicles, the prostate and other glands. The fluids nourish the sperm, give them energy and let them swim.
Give the function of each part of a sperm.
The head carries the nucleus and helps the sperm enter the ovum; the middle piece releases energy; the tail lashes to make the sperm swim.
Name the organ in which each of the following happens: (a) ova are produced, (b) fertilisation takes place, (c) the baby grows.
(a) Ovary, (b) oviduct (fallopian tube), (c) uterus (womb).
State two differences between a sperm and an ovum.
A sperm is tiny and swims with a tail, while an ovum is much larger and cannot move. Millions of sperm are made every day, but usually only one ovum is released each month.
Why is fertilisation in humans called internal fertilisation?
Because the sperm and ovum fuse inside the mother's body, in the oviduct.
What is a zygote? How many cells will there be after it has divided 4 times?
A zygote is the single cell formed when the nucleus of a sperm fuses with the nucleus of an ovum. After 4 divisions there will be 2 × 2 × 2 × 2 = 16 cells.