V.C.E. Biology Unit 2

1. V.C.E. Biology Unit 2 Life Cycles and Reproductive Strategies

2. Reproductive Strategies in Animals • Life cycle – the sequence of stages in the growth and development of sexually reproducing organisms from generation to the next. • Alternation of generations – alternation between diploid (2n) and haploid (n) generations. In animals this occurs in the gametes

3. Reproductive Strategies in Animals • Fertilisation can be external or internal • External fertilisation occurs in aquatic animals where large numbers of egg and sperm are released into the water and sperm seek out the eggs.

4. Reproductive Strategies in Animals • Internal fertilisation occurs in terrestrial animals. Two individuals must meet and the male deposits his sperm in the vagina of the female.

5. Reproductive Strategies in Animals • Indirect development refers to the influence of parents over the offspring of external fertilisation. • Little nutrient has been deposited with the egg • Larvae tend to hatch quickly after fertilisation. • Larvae tend to develop into adult form quickly • Many individuals do not make it to adult life stages.

6. Reproductive Strategies in Animals • Direct development refers to the management of offspring by parents following internal fertilisation. • Eggs contain more nutrient material. • Young hatch from egg or a born live after a period of gestation. • Parents are involved to some degree in teaching the young. • Fewer young are produced, but more are likely to survive.

7. Reproductive Strategies in Animals • Timing • Most sexual activity in most species is controlled by hormones that respond to seasonal changes in temperature and therefore food availability and/or water availability.

8. Reproductive Strategies in Animals • Mating Displays • Many animals need to perform elaborate mating rituals to attract and win a mate – these usually say look at me, my genes at the most fit

9. Reproductive Technologies • In vitro Fertilisation • Amniocentesis • Chorionic villus sampling • Ultrasound • Artificial Insemination • Contraception

10. Reproductive Strategies in Plants • Some plants use asexual means to reproduce • The alternation of generations in plants is different to animals with the haploid structures existing for longer periods of time. • Sporophyte – diploid life stage • Gametophyte – haploid life stage

11. Reproductive Strategies in Plants • Self fertilisation – while male and female gametes are made by the plant the pollen is used to fertilise the ova and therefore guarantee successful seed production. • Cross fertilisation – various techniques are used to ensure that the pollen and ova of a single plant do not meet. • No fertilisation – a rare case where no pollen is produced and the ova does not undergo meiosis.

12. Reproductive Strategies in Plants • Some plants give little nutrient to their ova to use for the next stage and so they must germinate quickly and produce their own energy – seeds of orchids and many Australian natives are like dust. • Some plants give their seed a great deal of energy – like the avocado. It can succeed wherever it lands. • Many seeds are able to lie dormant in the soil waiting for reasonable conditions for germination.