Biology- Reproductive Strategies

Asexual v sexual reproduction, internal and external fertilsation, insects and flowers

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  • Created by: ava.scott
  • Created on: 15-04-14 10:28

Asexual Reproduction

Reproduction: The ability to produce other individuals of the same species.

Asexual reproduction: the 'cloning' of parent organisms.


  • Genetically identical offspring
  • Diploid cells produced by mitosis
  • Binary Fission= CLONE.


  • Very quick, produces a lot of a beneficial gene in a very short amount of time.
  • only needs one parent
  • encourages adaptation, a mutations occur a lot.


  • Susceptible to disease and environmental change, as there is no genetic variation.
  • a lot of competition between offspiring
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Sexual Reproduction

Definition: The fusion of two haploid gametes to create a diploid zygote, producing genetically different offspring to the parent organisms.


  • genetically different offspring
  • gametes are formed by meiosis


  • genetic variation allows resistance to disease and environmental change.
  • allows a resistant stage in life cycle to form
  • Formation of spores/seeds etc allows intra-specific competition, and genetic variety.


  • time consuming
  • two parents needed
  • less offspring
  • open to mutation
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External Fertilisation

e.g. fish

Female 'lays' eggs in the water, and the male releases sperm all over them.


  • many offspring produced
  • little energy or time required


  • susceptible to predators
  • less developed at birth- limited by yolk
  • gametes are wasted
  • environmental conditions change easily
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Internal fertilisation

e.g. mammals, birds

Sperm is released inside the femal during intercourse, where it meets the egg.


  • more protection from predators, including the opportunity to develop a hard shell
  • less waste of gametes
  • independent of water as a medium for sperm to swim in
  • usually more parental care


  • less eggs, so less offspring
  • expensive energywise for the mother who carries the eggs
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The egg


The amniote is a fluid filled cavity surrounded by a membrane (shell). Yolk is the food source.

Why fluid filled?- to carry away waste products from the foetus. - gases can dissolve in it and reach foetus. -prevents the egg drying out.

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Internal development- live births

e.g. mammals

mammals tak the internal fertilisation method further, and grow fully inside the mothers womb, before being born live.


  • very well protected throughout initial development
  • well developed by birth, as their food source is not limited (they recieve nutrients through the placenta). this also means they are less susceptible to predators
  • often much more parental care e.g training to become adults, provision of foodshelter


  • less offspring produced
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Insects- Metamorphoses


e.g. grasshoppers

Zygote develops into intermediate forms before becoming an adult.

Larvae ----> Nymph x5 -------> adult

To grow, the insect has to shed its exoskeleton, leaving it very vulnerable.


e.g. butterflies, moths

Larvae are different from an adult; they go into a pupal phase, where all their consistuent ions and compounds are mixed up and reformed into the adult.

pros                                                                         cons

very specialised                                                       pupa/chrysallis is open to predation

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Flowering Plants

Simple plant (algae) are contained to aquatic conditions.

Mosses have to stay in damp area because the male gamete needs moisture to swim.

Flowering plants adaptions:

  • Pollen grains have a hard coat to prevent dessication. They contain the male gamete and travel by wind or insects.
  • Brightly coloured flowers attract insects to carry the gametes. 
  • The pollen grain easily reaches the female gamete through a pollen tube, so no water is needed.
  • The zygote develops into a seed.

KEY: Exploit animals for pollination and seed dispersal. Enclosure of eggs in ovary. Seeds and pollen grains have hard shells

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Flowering Plants- reasons for success?

Why are flowering plants so successful?

  • Interval between flower production and seed dispersal is short, so many offspring are produced.
  • Seed has a food source to allow the sapling to develop before photosynthesis.
  • Leaves are decidious and succelent, so they decay quickly. This encourages the production of 'humus' which recycles the ions for reuse.
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