1. 7 Reproduction

2. Reproduction: making offspring Reproduction according to embedded genetic instructions is a characteristic of living organisms. Two types of reproduction can occur: asexual and sexual. Offspring produced through asexual reproduction are clones of the single parent and of each other. Offspring produced through sexual reproduction show variation.

3. Reproduction without sex Asexual reproduction produces clones of a single parent or cell. In prokaryotes (bacteria), asexual reproduction occurs through binary fission. Asexual reproduction in eukaryotes involves the process of mitosis. Asexual reproduction in some eukaryotes, such as protists and simple animals, involves splitting and budding.

4. Reproduction without sex Asexual reproduction in plants involves structures such as runners, rhizomes and bulbs. Plant clones can be produced through tissue culture. Artificial cloning of mammals has been achieved through separating embryo cells and through somatic cell cloning.

5. Sexual reproduction Male gametes involved in sexual reproduction are sperm (and pollen) and female gametes are eggs. Plant life cycles have an alternation of generations, with a diploid spore producing stage alternating with a gamete-producing stage.

6. Sexual reproduction In some animals, egg and sperm production occur in separate female and male organisms. An hermaphrodite animal can produce both male and female gametes. Flowering plants show a variety of conditions regarding egg and pollen formation.

7. Getting gametes together Sexual reproduction involves fusion of an egg and a sperm at fertilisation. In animals, fertilisation may be internal or external. Some species that use external fertilisation have developed strategies to increase the chance of fertilisation occurring.

8. Getting gametes together With internal fertilisation, there is a greater chance of gametes meeting and hence the chance of fertilisation is increased. Cross-pollination in plants is more common than self-pollination. Various natural agents assist the transfer of pollen between different plant species. Natural breeding can be altered by various technologies.

9. Meiosis: making gametes

12. Meiosis is involved in gamete production. Starting from a diploid cell (2n), meiosis results in four haploid (n) cells. Meiosis involves a reshuffling of genetic material. Fertilisation restores the diploid number of chromosomes. In flowering plants, fertilisation involves the fusion of an egg produced in the ovule with a sperm nucleus formed in the pollen grain.

13. Meiosis: making gametes Double fertilisation occurs only in flowering plants. In flowering plants, the developing embryo is enclosed within a seed formed from the ovule. In flowering plants, one or more seeds are enclosed within fruit formed from the ovary.

14. Human reproduction Human eggs and sperm are produced in ovaries and testes respectively. From one starting cell undergoing meiosis, only one egg is produced by a human female but four sperm result. A human egg completes meiosis only after fertilisation.