Asexual & Sexual Reproduction


Asexual & Sexual

  • rapid production of large numbers of individuals having an identical genetic composition
  • clones
  • binery fission, budding, bulbs runners tubers


  • two parents 
  • less rapid
  • offspring are genetically varied
  • diploid body cells produce haploid gametes, fusion of two haploids makes a zygote
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Advantages & Disadvantages


  • lack of variety to environmental change
  • however if an individual has genetic makeup suited ta particular set of conditons large numbers of this successful type may be built up


  • slower
  • increase in genetic variety for adaptation
  • development of resistant stage in life cycle for wthstanding adverse conditions
  • dispersal of offspring reduces competition enabling genetic variety
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Gamete Production

  • diploid body cells / haploid sex cells/gametes
  • body cells with full chromosome numbers produced by mitosis
  • haploid cells have half produced by meiosis
  • at fertilisation male gamete sperm fuses with female egg gamete producing a dipoid zygote which further divides by mitosis for growth
  • male gamete is very small and motile 
  • female gamete is large and sedentary due to presence of stored food
  • mammalian eggs contain very little stored food as materials used for growth are obtained from the mother via the placenta
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  • aquatic organisms discharge their gametes directly into the surrounding water, as gametes are quickly dispersed theres a likely chance many eggs will not be fertilised this is external fertilisation
    • large wastage so large numbers of gametes produced to increase chances 
  • in frogs the joining of sperm and egg is facillitated by sexual coupling
    • eggs laid by female and male immediately releases sperm directly over them
    • fertilisation is still external for amphibians
  • terrestial animals mainly use internal fertilisation inside the females body requiring the use of an intromittent organ to introduce the sperm
    • less waste as increased chance of fertilisation
    • male gamete is independant of water for movement
    • fertilised agg can be enclosed in protective covering before leaving female body (eggs) or can develop within the mother and recieve nourishment via a placenta like in mammals
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Adaptations to Life on Land

  • zygote usually undergoes development outside the body 
  • easy prey= many produced to increase chances of survival
  • internal fertilisation increases chance of fertilisation
  • evolution of eggs in reptiles and birds with a fluid filled cavity with a protective shell membrane enclosing the embryo within a yolk sac
  • birds incubate eggs 
  • in mammals the young are incubated inside the womb and nourished from the mothers blood via placenta and born highly developed
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Parental Care

  • laying fertilised eggs and leaving them unattended is little/ no parental care
  • male stickleback looks after the egss and defends his territory and fans them to give them oxygen until hatching
  • parental care is mst common with birds and mammals 
  • providing shelter, feeding, protection and training prepares the offspring for adult life
  • more parental care leads to less offspring being produced
  • fish spawn thousands while humans spawn one
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Insect Colonisation

  • the zygote develops into a nymph or larva juvinile
  • these insects have a hard exoskeleton that must be shed in order to grow, which is done several times 
  • this is incomplete metamorphis
  • the nymph simply grows to full size e.g. a locust
  • advanced insects go through complete metamorphis 
  • here the insect larva grows and eats 
  • then enters a pupa stage where it undergoes considerable change 
  • it emerges as a specialised adult for dispersal and reproduction e.g a butterfly
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Flowering Plants Colonisation

  • pollen grains have a hard coat and contain the male gamete to be transferred to the female part by wind or insects
  • male gamete travels down the pollen tube to the egg, gametes no longer need to travel through water
  • the ovule develops into a seed with a food store
  • key aspet of their success is their link with animals
  • plant flowers attract insects and exploit their mobility for pollenation and seed dispersal
  • enclosure of the eggs in an ovary and evolution of a seed containing food reserves and a resistant coat allowing withstance against adverse conditions
  • why so successful?
    • time between flower production and seed setting is a couple of weeks
    • seed with a food store allows embryo to develop until leaves can reach above ground to photosynthesise and also protects the seed from harm
    • leaves decaying on the ground rapidly allows rapid recycling of ions
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