fertilisation cannot be external in land animals.why?
Answers
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• Fertilisation: The fusion of a sperm with an egg is called fertilisation. During fertilisation, the nuclei of the sperm and the egg fuse to form a single nucleus. This results in the formation of a fertilised egg called Zygote.
Fertilisation may be:
Internal Fertilisation: Fertilisation which takes place inside the body of the female is called internal fertilisation. For example: as in humans, dogs, cows, birds etc.
External Fertilisation: Fertilisation which takes place outside the body of the female is called external fertilisation. It is very common in aquatic animals, such as fish, starfish and amphibians (animals who live in water as well as on land such as frog).
IVF or in vitro Fertilisation: The fertilisation of an egg that takes place outside the body in a test tine or in any other, apparatus is known IVF or in vitro fertilisation.
Test Tube Babies: In this technique freshly released egg and sperms are put together for a few hours for IMF. In case fertilisation occurs, the zygote is allowed to develop for about a week and then placed in the uterus of the mother. Complete development takes place in the uterus and the baby is born like any other normal baby. The term test tube babies is misleading, because babies cannot grow in test tubes.
• Embryo: The stage, when cells produced hp the division of the zygote begin to form groups that develop into different tissues and organs of the .body is termed as an embryo.
• Foetus: The stage of embryo in which al the body parts can be identified is known as foetus.
• Viviparous: The animals such as dog, lion, elephant, cat etc., which give birth to young ones are called viviparous.
• Oviparous: The animals, such as lizards, butterfly, crow and hen, which lay eggs that hatch and give rise. to young ones are called oviparous.
• Life-cycle of Animals: Sexually reproducing animals start their life from a zygote which develops into an embryo that grows into mature adult. The adult produces sex cells (egg and sperm). The fusion of sperm and egg leads to zygote. This whole cyclic order is known as life-cycle.
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Fertilization can't be external in land animals because land provides a harsh and dry condition which is not suitable for the sperm and egg cells. As we know that sperm have tail to swim in watery condition.
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