Mechanisms for Australian Organisms to survive, asexual reproduction, reasons for evolution, + 1 female and male Australian scientists

Essay by elurpHigh School, 11th gradeA+, June 2008

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Biology: Research Task and Oral PresentationResearch Task:1.Describe some mechanisms found in Australian fauna to ensure:•Fertilisation•Survival of the embryo and of the young after birthFertilisation is the fusion of haploid sex cells in the action of sexual reproduction. It is often a difficult process as:• careful timing is required: both female and male gametes need to be produced and released at the same time• arrangements need to be made to bring the gametes together• A watery medium is always needed to carry the sperm to the ovum and prevent the gametes drying out.

Fertilisation can be internal or external:•Internal: fertilisation occurs inside the female's body•External: fertilisation occurs outside the organisms bodyMany Australian organisms have produced certain mechanisms to assist in the process of fertilisation.

•Sexually mature, gamete production and release may be stimulated by environmental factors¹. For example coral polyps off the Ningaloo Reef in West Australia, have cyclical breeding seasons so the female and male gametes are released simultaneously , increasing the chance of fertilisation.

Most aquatic organisms have external fertilisation, so a watery medium is already present.

•Organisms using external fertilisation, may produce large numbers of gametes to increase the chance of fertilisation, however this results in much gamete wastage². For example the Sydney Rock Oyster (Crassostrea commercialia) produces 500 million eggs in one season. A high concentration of gametes increases the probability of the eggs and sperm colliding and fertilisation occurring.

•In some cases, the shredding of gametes by one individual releases a chemical which stimulates the release of ripe gametes by other individuals near by. ¹ For example Sydney Rock Oyster (Crassostrea commercialia)•Some organisms have developed courtship rituals and recognition displays, so that members of the opposite sex (same species) can recognise each other, and know that the other is ready for mating¹. For Example the...