Bio Paper 1 GCSE edexcel pmt

• Sexual reproduction


  Type of reproduction involving the production of gametes by meiosis, where a gamete from each parent fuses to form a zygote, mixing genetic information
• Gametes


  Sex cells (sperm cells, egg cells), haploid (half the number of chromosomes)
• Meiosis


  1. Form of cell division involved in the formation of gametes

  2. Chromosome number is halved

  3. Involves two divisions
• Interphase must occur prior to meiosis
• First stage of meiosis

  1. Chromosome pairs line up along the cell equator

  2. The pair of chromosomes are separated and move to opposite poles of the cell (the side to which each chromosome is pulled is random, creating variation)

  3. Chromosome number is halved
• Second stage of meiosis

  1. Chromosomes line up along the cell equator

  2. The chromatids are separated and move to opposite poles of the cell

  3. Four unique haploid gametes are produced
• Importance of meiosis for sexual reproduction

  • It increases genetic variation
  • It ensures that the resultant zygote is diploid
• Advantage of sexual reproduction

  It creates genetic variation, increasing the probability of a species adapting to and surviving environmental changes
• Disadvantages of sexual reproduction

  • Two parents are required, making reproduction difficult in endangered populations or in species which exhibit solitary lifestyles
  • More time and energy is required so fewer offspring are produced
• Asexual reproduction


  Type of reproduction involving mitosis, producing genetically identical offspring known as daughter cells
• Advantages of asexual reproduction

  • Only one parent is required
  • Lots of offspring can be produced in a short period of time, enabling the rapid colonisation of an area and reducing competition from other species
  • Requires less energy
• Disadvantage of asexual reproduction

  No genetic variation (except from spontaneous mutations) reducing the probability of a species being able to adapt to environmental change