CIE IGCSE Biology

Revision Notes

16.1.1 Types of Reproduction

Asexual Reproduction

  • Asexual reproduction does not involve sex cells or fertilisation
  • Only one parent is required so there is no fusion of gametes and no mixing of genetic information
  • As a result, the offspring are genetically identical to the parent and to each other (clones)
  • Asexual reproduction is defined as a process resulting in genetically identical offspring from one parent

Bacteria produce exact genetic copies of themselves in a type of asexual reproduction called binary fission:

Binary fission in bacteria, IGCSE & GCSE Biology revision notesBacteria produce exact genetic copies of themselves in a type of asexual reproduction called binary fission

 

Plants can reproduce asexually using bulbs and tubers; these are food storage organs from which budding can occur, producing new plants which are genetically identical to the parent plant:

Bulbs and tubers, IGCSE & GCSE Biology revision notesSome plants develop underground food storage organs that will develop into next years plants – they can take different forms, such as bulbs or tubers

 

Some plants grow side shoots called runners that contain tiny plantlets on them (a good example of this are strawberry plants. These will grow roots and develop into separate plants, again being genetically identical to the parent plant:

Runners, IGCSE & GCSE Biology revision notesSome plants grow side shoots called runners that contain tiny plantlets on them. These will grow roots and develop into separate plants

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Advantages & Disadvantages of Asexual Reproduction

Advantages & Disadvantages of Asexual Reproduction table, IGCSE & GCSE Biology revision notes

  • Specifically in crop plants, asexual reproduction can be advantageous as it means that a plant that has good characteristics (high yield, disease-resistant, hardy) can be made to reproduce asexually and the entire crop will show the same characteristics

Sexual Reproduction

  • Sexual reproduction is a process involving the fusion of the nuclei of two gametes (sex cells) to form a zygote (fertilised egg cell) and the production of offspring that are genetically different from each other
  • Fertilisation is defined as the fusion of gamete nuclei, and as each gamete comes from a different parent, there is variation in the offspring
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Gametes & Zygotes

  • A gamete is a sex cell (in animals: sperm and ovum; in plants pollen nucleus and ovum)
  • Gametes differ from normal cells as they contain half the number of chromosomes found in other body cells – we say they have a haploid nucleus
  • This is because they only contain one copy of each chromosome, rather than the two copies found in other body cells
  • In human beings, a normal body cell contains 46 chromosomes but each gamete contains 23 chromosomes
  • When the male and female gametes fuse, they become a zygote (fertilised egg cell)
  • This contains the full 46 chromosomes, half of which came from the father and half from the mother – we say the zygote has a diploid nucleus
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Advantages & Disadvantages of Sexual Reproduction

Advantages & Disadvantages of Sexual Reproduction table, IGCSE & GCSE Biology revision notes

  • Most crop plants reproduce sexually and this is an advantage as it means variation is increased and a genetic variant may be produced which is better able to cope with weather changes, or produces significantly higher yield
  • The disadvantage is that the variation may lead to offspring that are less successful than the parent plant at growing well or producing a good harvest

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.
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