v.c.e. biology unit 2

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


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.


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


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.


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.


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.


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 Technologies

In vitro Fertilisation Amniocentesis Chorionic villus sampling Ultrasound Artificial Insemination Contraception

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


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.


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.

v.c.e. biology unit 2

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