Year 7 Science — Biology

Reproduction

Explore how living things reproduce — comparing asexual and sexual reproduction, and discovering the fascinating strategies used by Australian plants and animals.

Why Do Living Things Reproduce?

Reproduction is one of the key characteristics of living things. It is the process by which organisms produce offspring, ensuring the continuation of their species. Without reproduction, a species would become extinct.

There are two main types of reproduction: asexual reproduction (involving one parent) and sexual reproduction (involving two parents and the fusion of sex cells).

Australian Curriculum Connection

This lesson aligns with AC9S7U01: "Multicellular organisms contain systems of organs that carry out specialised functions that contribute to the survival of the organism; reproduction ensures the survival of the species."

Asexual vs Sexual Reproduction

Asexual Reproduction

Involves one parent only. Offspring are genetically identical to the parent (clones). Fast and efficient, but produces no genetic variation.

Types:

Binary fission — bacteria split in two (e.g. E. coli divides every 20 minutes)

Budding — a new organism grows from the parent (e.g. hydra, yeast)

Vegetative propagation — plants grow new individuals from roots, stems, or leaves (e.g. strawberry runners, potato eyes)

Spore formation — fungi and ferns release spores that grow into new organisms

Sexual Reproduction

Involves two parents. A male sex cell (sperm/pollen) fuses with a female sex cell (egg/ovule) in a process called fertilisation. Offspring have genetic variation.

Key terms:

Gametes — sex cells (sperm and egg)

Fertilisation — fusion of male and female gametes to form a zygote

Internal fertilisation — occurs inside the body (most mammals, birds, reptiles)

External fertilisation — occurs outside the body in water (most fish, amphibians)

Advantage of genetic variation: Sexual reproduction produces variation in offspring, which helps populations survive when environments change (natural selection).

Plant Reproduction

Flowering plants (angiosperms) reproduce sexually through flowers. The process involves pollination, fertilisation, seed formation, and seed dispersal.

Stages of Sexual Reproduction in Flowering Plants

Pollination: Pollen (containing male gametes) is transferred from the anther to the stigma of a flower. Agents include bees, birds, wind, and water. Australian bees are crucial pollinators of eucalyptus and wattles.

Fertilisation: A pollen tube grows from the pollen grain down to the ovule. The male gamete fuses with the female gamete (ovule) to form a zygote.

Seed and fruit formation: The zygote develops into a seed; the surrounding ovary becomes the fruit (e.g. an Australian mango or banksia cone).

Seed dispersal: Seeds are spread by wind (grass seeds), animals (burrs on fur), water, or fire (Australian banksias open seeds after fire).

Asexual Plant Reproduction

Stolons (runners) — strawberries
Tubers — potatoes, yams
Bulbs — onions, tulips
Cuttings — many garden plants
Rhizomes — couch grass, ginger

Australian Plant Examples

Banksia — seeds opened by bushfire (serotiny)
Wattle — wind and insect pollinated
Eucalyptus — adapted for fire-prone environments
Grass trees — can reshoot from underground bulb after fire

Key Vocabulary

Fertilisation

The fusion of a male gamete (sperm/pollen) with a female gamete (egg/ovule) to form a zygote.

Gamete

A sex cell — sperm or egg in animals; pollen or ovule in plants. Gametes contain half the normal number of chromosomes.

Pollination

The transfer of pollen from the anther of one flower to the stigma of another (cross-pollination) or the same flower (self-pollination).

Genetic Variation

Differences in genetic information between offspring; produced by sexual reproduction and important for species survival.

Worked Examples

A gardener takes cuttings from a rose bush to grow new plants. Is this asexual or sexual reproduction?

Type: Asexual reproduction (vegetative propagation).

Reason: Only one parent plant is involved. No gametes (pollen or eggs) are produced or fused.

Result: The new rose plants will be genetically identical clones of the parent plant.

Compare the advantages of asexual and sexual reproduction for a species.

Asexual advantages: Rapid reproduction (many offspring quickly), only one parent needed, successful in stable environments, all offspring can reproduce.

Sexual advantages: Produces genetic variation in offspring, which allows the species to adapt to changing environments and resist disease. Better for long-term survival of the species.

Conclusion: Sexual reproduction is better for long-term survival; asexual is better for rapid population growth in stable conditions.

A kangaroo gives birth to a tiny, undeveloped joey that develops in a pouch. What type of reproduction is this?

Type: Sexual reproduction with internal fertilisation.

Reason: Two parents are involved (male and female kangaroo). The sperm fertilises the egg internally.

Note: Kangaroos are marsupials — a unique group of Australian mammals where the young (joey) is born at an early stage of development and completes its development in the mother's pouch. This is very different from placental mammals.

Knowledge Check

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Key Concepts Summary

✓ Reproduction ensures species survival; there are two types: asexual (one parent) and sexual (two parents).
✓ Asexual reproduction produces genetically identical offspring (clones); methods include binary fission, budding, and vegetative propagation.
✓ Sexual reproduction involves fertilisation — the fusion of male and female gametes to form a zygote.
✓ In flowering plants: pollination → fertilisation → seed formation → seed dispersal.
✓ Sexual reproduction produces genetic variation, which is important for adaptation and species survival.