Presentation on theme: "V.C.E. Biology Unit 2 Life Cycles and Reproductive Strategies."— Presentation transcript:
V.C.E. Biology Unit 2 Life Cycles and Reproductive Strategies
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
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.
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.
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.
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.
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.
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
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
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.
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.