Biology · Lesson 16

Reproduction in animals & humans

JAMBWAECNECO

What the syllabus asks

JAMB: reproductive systems, reproduction in vertebrates and insects, metamorphosis, fertilisation and development, placenta, menstrual cycle

WAEC: asexual and sexual reproduction in animals, reproductive systems of mammals (male and female), gametogenesis, the menstrual cycle, fertilisation, implantation, development of the embryo, placenta, birth and parental care, reproduction in fish, amphibians, birds and insects (metamorphosis), birth control, sexually transmitted infections

NECO: asexual and sexual reproduction in animals, reproductive systems of mammals (male and female), gametogenesis, the menstrual cycle, fertilisation, implantation, development of the embryo, placenta, birth and parental care, reproduction in fish, amphibians, birds and insects (metamorphosis), birth control, sexually transmitted infections

What you will learn

Distinguish asexual from sexual reproduction with examples and state advantages of each.
Label and give functions of the parts of the male and female reproductive systems.
Describe the menstrual cycle and the roles of FSH, LH, oestrogen and progesterone.
Describe fertilisation, implantation, development, the placenta and birth.
Compare reproduction in fish, amphibians, birds and mammals.
Describe complete and incomplete metamorphosis in insects.
Describe methods of birth control and common STIs and their prevention.

Key points

Asexual reproduction: one parent, identical offspring (fission, budding); sexual: gametes fuse, variation.
Male: testes make sperm and testosterone; epididymis stores; glands add fluid to make semen.
Female: ovaries make eggs, oestrogen, progesterone; fertilisation in oviduct; implantation in uterus.
Gametes are haploid (23) so the zygote is diploid (46).
Cycle: FSH → follicle; oestrogen builds lining; LH → ovulation ~day 14; progesterone maintains lining.
Placenta: villi, thin barrier, no mixing of bloods; food and O₂ in, CO₂ and urea out; alcohol, nicotine and HIV can cross.
Birth: oxytocin causes contractions; colostrum protects the newborn.
Fish and amphibians: external fertilisation in water; reptiles, birds, mammals: internal.
Insects: complete (egg, larva, pupa, adult) or incomplete (egg, nymph, adult) metamorphosis.
Birth control: barrier, hormonal, IUD, surgical; condoms also prevent STIs.

Start here: Asexual and sexual reproduction

All living things must reproduce or their kind dies out. Animals do it in two basic ways.

Asexual reproduction

One parent produces offspring without gametes. The offspring are genetically identical to the parent (clones). Forms in animals:

Binary fission: one cell splits into two: Amoeba, Paramecium.
Budding: an outgrowth develops and breaks off: Hydra.
Fragmentation and regeneration: a piece grows into a whole new animal: planarian flatworms, some starfish.
Parthenogenesis: development from an unfertilised egg: aphids, drone honeybees.

Sexual reproduction

Two parents each produce gametes (sperm and egg). The gametes fuse in fertilisation to form a zygote, which grows into a new individual. Offspring receive a mix of genes from both parents, so they vary.

Asexual	Sexual
One parent	Usually two parents
No gametes, no fertilisation	Gametes fuse
Offspring identical	Offspring vary
Fast, many offspring, no need to find a mate	Slower, needs a mate
Whole population may be wiped out by one disease	Variation helps a species adapt and survive change

Worked example 16.1

A disease kills almost all members of a species that reproduces only asexually, but a related species that reproduces sexually survives. Explain.

Asexual offspring are identical, so if one is susceptible, all are.
Sexual reproduction produces variation; some individuals may happen to be resistant and survive to breed.

Variation from sexual reproduction allowed some to survive.

Try it yourself. Name the type of asexual reproduction in Hydra.

Show solution

Budding.

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Practice questions

1. Fertilisation in humans normally occurs in the

oviduct (fallopian tube)
uterus
vagina
ovary

Show answer

A: oviduct (fallopian tube)
The zygote then moves to the uterus to implant.

2. Fertilisation in humans normally takes place in the

uterus
vagina
ovary
oviduct (fallopian tube)

Show answer

D: oviduct (fallopian tube)
The sperm meets the ovum there.

3. The embryo implants in the

ovary
cervix
uterus
oviduct

Show answer

C: uterus
Into the thickened lining.

4. Sperm are produced in the

penis
testes
prostate gland
urethra

Show answer

B: testes
In the seminiferous tubules.

5. The placenta allows

exchange of materials between mother and foetus
direct mixing of maternal and foetal blood
production of sperm
digestion of food

Show answer

A: exchange of materials between mother and foetus
Diffusion across a thin barrier.

Key words

Gamete: A sex cell (sperm or ovum) with half the chromosome number (haploid).
Zygote: The diploid cell formed when two gametes fuse.
Fertilisation: Fusion of the nuclei of a male and a female gamete.
Ovulation: Release of a mature egg from the ovary.
Implantation: Embedding of the early embryo (blastocyst) in the uterus lining.
Placenta: Organ joining fetus to uterus wall for exchange of materials.
Umbilical cord: Cord with blood vessels linking the fetus to the placenta.
Amnion: Membrane enclosing the fetus in protective amniotic fluid.
Gestation: The period of development in the uterus (about 40 weeks in humans).
Menstruation: Monthly shedding of the uterus lining with blood.
Metamorphosis: Change in form from young to adult, as in insects and frogs.
Viviparous: Giving birth to live young.

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