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Cell Division – Revision Pack (B3)
Multicellular:
Advantages of being multicellular:
• allows organism to be larger
• allows for cell differentiation
• allows organism to be more complex.
Becoming multi-cellular requires the development of specialised organ systems,
limited to:
• communication between cells (nervous system)
• supplying the cells with nutrients (digestive system)
• controlling exchanges with the environment (respiratory and excretory
system)
Mitosis
New cells for growth are produced by mitosis, new cells are genetically identical
because they contain the same genetic information – it is a copied cell. Body cells
are DIPLOID (contain two copies of each chromosome).
The first step, before cells can divide is to replicate the DNA. This is done by:
-
‘unzipping’ the chromosome to make it into single strands
New strands forming by complementary base pairing
The following steps happen in mitosis:
1) The chromosomes line up in the centre
of the cell
2) They then divide; or are divided by an
enzyme
3) The two copies move to two poles of
the cell
These cells are genetically identical.
Cell Division – Revision Pack (B3)
Meiosis:
Gametes are produced by meiosis.
Gametes are haploid (contain one
chromosome from each pair). In
meiosis, the chromosome number is
halved and each cell is genetically
different because:
• One chromosome from
each pair separate to
opposite poles of the cell in
the first division
• Chromosomes divide and
the copies move to opposite
poles of the cell in the
second division.
Fertilisation results in genetic
variation because:
Gametes and Fertilisation:
-
-
The two gametes (egg
and sperm cells) form a
diploid zygote
Genes from the two
chromosomes combine
to determine the
characteristics of that
zygote
The structure of a sperm cell allows it to
be adapted to its function because:
-
It has a lot of mitochondria which
supplies energy
It has an acrosome releases
enzymes that help digest (enter)
the egg membrane
Cell Division – Revision Pack (B3)
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