Year 9science Notes
Half yearly studies
Chapter 2: Reproduction
What is Sexual Reproduction?
Sexual reproduction occurs when offspring result from the fusion of a male reproductive cell and a female reproductive cell. These special reproductive cells are called gametes and they are produced in the reproductive organs of the organism.
External Fertilisation * Gametes are tiny and are dehydrated extremely easily, so they only survive in specific conditions. * Some animals, specifically those that live in the water, like fish and amphibians perform external fertilisation were fertilisation occurs outside of the female body. * The female releases her unfertilised eggs to be fertilised * Male sperm is also released into the water. * Very inefficient often wasting a lot of the gametes as most of them do not fuse. * Predators and other dangerous situations such as hardship in obtaining resources such as food and shelter also hinder the survival of these developing zygotes.
Internal Fertilisation * Animals that live or breed on land fertilise internally. * This keeps gametes inside the body so there is no chance of dehydration occurring * This occurs doing copulation or sexual intercourse. * The fertilised egg can be retained within the female and develop within or it may be enclosed in a shell such as the eggs of reptiles and birds.
Methods of development * After fertilisation, a zygote can be expelled from the body as an egg or remain inside the body for development * Fish, reptiles, birds and amphibians all lay eggs where the offspring develops over time * The eggs of amphibians and fish are laid in water without any risk of dehydration so they do not have a shell and feature jelly like coatings * Eggs laid on land however require hard shells to lock in moisture * The egg must also contain a supply of nutrients for the aid in development * Some animals leave their eggs unsupervised until hatching while other
Chapter 2: Reproduction
What is Sexual Reproduction?
Sexual reproduction occurs when offspring result from the fusion of a male reproductive cell and a female reproductive cell. These special reproductive cells are called gametes and they are produced in the reproductive organs of the organism.
External Fertilisation * Gametes are tiny and are dehydrated extremely easily, so they only survive in specific conditions. * Some animals, specifically those that live in the water, like fish and amphibians perform external fertilisation were fertilisation occurs outside of the female body. * The female releases her unfertilised eggs to be fertilised * Male sperm is also released into the water. * Very inefficient often wasting a lot of the gametes as most of them do not fuse. * Predators and other dangerous situations such as hardship in obtaining resources such as food and shelter also hinder the survival of these developing zygotes.
Internal Fertilisation * Animals that live or breed on land fertilise internally. * This keeps gametes inside the body so there is no chance of dehydration occurring * This occurs doing copulation or sexual intercourse. * The fertilised egg can be retained within the female and develop within or it may be enclosed in a shell such as the eggs of reptiles and birds.
Methods of development * After fertilisation, a zygote can be expelled from the body as an egg or remain inside the body for development * Fish, reptiles, birds and amphibians all lay eggs where the offspring develops over time * The eggs of amphibians and fish are laid in water without any risk of dehydration so they do not have a shell and feature jelly like coatings * Eggs laid on land however require hard shells to lock in moisture * The egg must also contain a supply of nutrients for the aid in development * Some animals leave their eggs unsupervised until hatching while other