Reproduction

The One Thing

Reproduction produces new individuals and ensures the continuation of a species. Asexual reproduction uses one parent and produces genetically identical offspring, whereas sexual reproduction involves gametes and produces genetically varied offspring.

Reactions, Processes and Experiments

Key Terms

• Reproduction: The biological process by which organisms produce new individuals of the same species.
• Asexual reproduction: Reproduction involving one parent and no fusion of gametes; offspring are usually genetically identical to the parent.
• Sexual reproduction: Reproduction involving the fusion of male and female gametes, producing offspring with genetic variation.
• Clone: An organism genetically identical to another organism, usually produced by asexual reproduction.
• Gamete: A haploid reproductive cell, such as a sperm cell or egg cell, containing half the normal chromosome number.
• Fertilisation: The fusion of the nuclei of male and female gametes to form a diploid zygote.
• Zygote: The diploid cell formed when two gamete nuclei fuse during fertilisation.
• Genetic variation: Differences in genetic information between individuals of the same species.
• Pollination: The transfer of pollen grains from anther to stigma.
• Self-pollination: The transfer of pollen from the anther to the stigma of the same flower or another flower on the same plant.
• Cross-pollination: The transfer of pollen from a flower on one plant to a flower on another plant of the same species.
• Anther: The part of the stamen that produces and releases pollen grains.
• Stamen: The male reproductive structure of a flower, consisting of the anther and filament.
• Stigma: The sticky surface at the top of the carpel that receives pollen.
• Carpel: The female reproductive structure of a flower, consisting of the stigma, style and ovary.
• Ovary: The swollen base of the carpel containing ovules; after fertilisation it usually develops into a fruit.
• Ovule: A structure inside the ovary containing the female gamete; after fertilisation it develops into a seed.
• Pollen tube: A tube that grows from a pollen grain through the style to an ovule, allowing the male nucleus to reach the egg cell.
• Seed dispersal: The movement of seeds away from the parent plant, reducing competition and helping plants colonise new areas.
• Germination: The beginning of growth of a seed when suitable conditions are present.
• Wind pollination: Pollination in which pollen is carried by air; wind-pollinated flowers commonly have exposed anthers, large feathery stigmas and produce much pollen.
• Insect pollination: Pollination in which insects transfer pollen; insect-pollinated flowers commonly have attractive petals, scent, nectar and sticky or spiky pollen.
• Testis: The male reproductive organ that produces sperm cells and testosterone.
• Sperm cell: The small, motile male gamete adapted to swim toward and fuse with an egg cell.
• Ovary in humans: The female reproductive organ that produces ova and releases hormones such as oestrogen and progesterone.
• Ovum: The female gamete; it is larger than a sperm cell and contains nutrient-rich cytoplasm.
• Oviduct: The tube through which an ovum travels; fertilisation usually occurs here.
• Uterus: The muscular organ where an embryo implants and develops during pregnancy.
• Endometrium: The lining of the uterus, which thickens during the menstrual cycle and is maintained during pregnancy.
• Cervix: The muscular ring at the lower end of the uterus leading to the vagina.
• Vagina: The muscular canal leading from the cervix to the outside of the body.
• Placenta: An organ that allows exchange of substances between the mother's blood and the fetus without their blood directly mixing.
• Umbilical cord: The structure connecting the fetus to the placenta and carrying blood vessels.
• Embryo: The developing organism during the early stages after fertilisation.
• Fetus: The developing human from about eight weeks after fertilisation until birth.
• Puberty: The period when hormonal changes make the body sexually mature and capable of reproduction.
• Menstrual cycle: The recurring sequence of changes in the ovaries and uterus that prepares the body for possible pregnancy.
• Oestrogen: A hormone produced mainly by the ovaries that helps rebuild the uterine lining and contributes to female secondary sexual characteristics.
• Progesterone: A hormone produced by the corpus luteum that maintains the uterine lining after ovulation.
• Testosterone: A hormone produced mainly by the testes that stimulates sperm production and male secondary sexual characteristics.
• FSH: Follicle-stimulating hormone, which promotes development of an ovarian follicle and stimulates oestrogen production.
• LH: Luteinising hormone, which triggers ovulation and formation of the corpus luteum.
• Contraception: Methods used to reduce the chance of fertilisation or implantation, including barrier, hormonal, intrauterine and surgical methods.
• Sexually transmitted infection: An infection transmitted mainly through sexual contact, such as HIV or chlamydia.

Easily Confused

• Asexual and sexual reproduction: Asexual reproduction uses one parent and no gamete fusion, producing genetically identical offspring; sexual reproduction involves gamete fusion and usually produces genetic variation.
• Self-pollination and cross-pollination: Self-pollination occurs within the same flower or plant; cross-pollination occurs between flowers on different plants of the same species.
• Pollination and fertilisation: Pollination transfers pollen to a stigma; fertilisation is the fusion of male and female gamete nuclei.
• Anther and stigma: The anther produces and releases pollen; the stigma receives pollen.
• Stamen and carpel: The stamen is the male reproductive structure; the carpel is the female reproductive structure.
• Ovary and ovule in flowering plants: The ovary contains ovules and usually develops into a fruit; each ovule usually develops into a seed after fertilisation.
• Ovary in humans and ovary in flowering plants: The human ovary produces ova and hormones; the plant ovary contains ovules and develops into a fruit after fertilisation.
• Embryo and fetus: An embryo is the developing organism during the early stages after fertilisation; a fetus is the developing human from about eight weeks after fertilisation until birth.
• Oviduct and uterus: Fertilisation usually occurs in the oviduct; implantation and fetal development occur in the uterus.
• FSH and LH: FSH promotes follicle development and oestrogen production; LH triggers ovulation and corpus luteum formation.
• Oestrogen and progesterone: Oestrogen helps rebuild the uterine lining and contributes to female secondary sexual characteristics; progesterone maintains the lining after ovulation.
• Placenta and umbilical cord: The placenta is the exchange organ; the umbilical cord connects the fetus to the placenta and carries blood vessels.
• Fertilisation and implantation: Fertilisation forms a zygote through gamete fusion; implantation is the attachment of the embryo in the uterus.
• HIV and AIDS: HIV is the virus that attacks helper T cells; AIDS is the condition that may result from advanced HIV infection.
• Wind and insect pollination: Wind-pollinated flowers are adapted for airborne pollen transfer; insect-pollinated flowers use features such as petals, scent and nectar to attract insects.

What Gets Asked

• Compare asexual and sexual reproduction: Marks depend on stating the number of parents, whether gametes fuse, the genetic similarity or variation of offspring, and the relevant advantages and disadvantages.
• Explain the stages of sexual reproduction in flowering plants: The required sequence is pollination, pollen tube growth, fertilisation, seed formation, fruit formation, seed dispersal and germination. A common error is confusing the ovule developing into a seed with the ovary developing into a fruit.
• Identify adaptations for wind and insect pollination: Wind-pollinated flowers have exposed anthers, feathery stigmas and abundant light pollen; insect-pollinated flowers commonly have colourful petals, scent, nectar and sticky pollen. The features must be matched to the correct pollination method.
• Describe the human reproductive pathways: The male pathway is testes, sperm ducts, urethra and penis; the female pathway is ovary, oviduct, uterus, cervix and vagina. Fertilisation usually occurs in the oviduct, not the uterus.
• Explain hormonal control of the menstrual cycle: The sequence must include FSH, follicle development, oestrogen, the LH surge, ovulation, the corpus luteum and progesterone. Omitting the link between high oestrogen and the LH surge loses the causal relationship.
• Explain placental exchange and pregnancy: Glucose, amino acids, oxygen and antibodies pass to the fetus, while carbon dioxide and urea pass to the mother; the blood supplies normally remain separate. A frequent error is stating that maternal and fetal blood directly mix.