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This topic takes on average 45 minutes to read.

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Topic last updated: 27 Jan 2022
    • Biology Biology
    • Ico Chemistry Chemistry
    • Ico Human Biology Human biology
    • 16+
    • 45

Cell division

10  of  10

Sexual reproduction 2 - fertilisation

The final stage of meiosis in the ovum doesn’t take place until the sperm starts to penetrate the surface cell membranemembrane
 A thin, flexible sheet-like structure that acts as a lining or a boundary in an organism. . Then it is mitosis all the way to produce the billions of cells needed to make a new individual – until the first meiotic divisions take place to form the oocytes in the ovaries if the fetus is a girl.

Fertilisation

It takes many sperm to fertilise an egg, although only one will penetrate the ovum. The enzymes from many acrosomes are needed to digest away the protective zona pellucida. When the head of a single sperm touches the membrane of the ovum it triggers a number of changes

S R 2 Fertilisation

Sperm entering the ovum

  • The chromosomechromosome
     A chromosome is like a packet of coiled up DNA. Humans have 23 pairs of chromosomes. They are in the nucleus of every human cell.     s of the secondary oocyte move into their second meiotic division to give a haploidhaploid
     Have a single set of chromosomes.     ovum nucleus
  • Ion channels in the membranemembrane
     A thin, flexible sheet-like structure that acts as a lining or a boundary in an organism.     change so the inside of the ovum becomes positive with respect to the outside instead of negative. The charge difference temporarily blocks the entry of any more sperm
  • A fertilisation membrane forms around the membrane, blocking the entry of any more sperm and allowing the ion balance to return to normal.
  • The head of the sperm moves into the ovum leaving the tail outside
  • It absorbs water and swells, releasing the chromosomes. They combine with the chromosomes of the ovum at the end of their second meiotic division to form a diploiddiploid
     Have two sets of paired chromosomes.     zygotezygote
     A fertilised cell produced as the result of the combination of an ovum and a sperm.     .
  • The zygote undergoes mitosis to form an embryoembryo
     The name for a group of cells that are developing into a fetus. In humans this is from implantation to the 8th week of development.     , a fetus and eventually a baby.

Activity:

Produce an infographic on meiosis and mitosis in human beings – find out as many useful and interesting facts as possible about length of divisions, number of divisions, number of cells made etc and display as effectively as possible.

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Sexual reproduction 1 - gametogenesis