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Cell Division and Diversity
The cell cycle is the process in which one parent cell divides in order to
produce two new daughter cells which then grow to full size
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The cell cycle is divided into four stages:
1
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Mitosis – The nucleus divides and the chromatids separate
 Prophase: Replicated chromosomes supercoil (the nuclear
envelope breaks down and the centriole divides into two
moving to opposite poles of the cell forming the spindle)
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 Anaphase: The replicas of each chromosome are pulled
apart from each other towards different poles of the cell
when the centromere splits
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Cytokinesis – The cytoplasm divides (This is splitting into two)
4
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Chromosomes hold the instructions for making a
new cell
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In humans there are 46 chromosomes in each cell
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Before a cell can divide the DNA of each chromosome needs to be
replicated and remain together at the centromere
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Although
before this happens the chromatin must
be supercoiled to make it shorter and
more sturdy to be able to move
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As the chromosomes are being replicated, proof reading enzymes move
along them and look for mutations which may7 mean that the cell will
not be able to function
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All bacteria are clones and are
produced from one cell using binary fission
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Bacteria are prokaryotes and
have a single strand of DNA
that is in the cytoplasm (not
the nucleus)
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Sexual reproduction involves fusing two
cell nuclei
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Cells such as
ovum cells and sperm cells are called
gametes two of these fused together are
called a zygote
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Normal adult
cells contain two sets of chromosomes and are called diploid
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During meiosis
one member of each homologous pair goes into each daughter cell
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Differentiation refers to the changes occurring in cells of a multicellular
organism so that each different type of cell becomes specialised to
perform a specific function
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Some cells will become different to others and so in
order for the body to function efficiently they need to be specialised in
their role
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Erythrocytes (red blood cells) are specialised for their function because
when they are produced from their undifferentiated stem cells in the
bone marrow, they contain no organelles to leave space for

haemoglobin (protein) and are biconcave
to increase surface area and allow more
space for the haemoglobin
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A sperm cell is specialised in that it contains lots of mitochondria to fluel
the tail with energy and lysomsomes that are used to digest the egg
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An organism consists of tissues, organs and organ systems
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For
example xylem and epithelial
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For example leaves or liver
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For example the reproductive system
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Squamous epithelial tissue is made of flattened cells so that it is ideal for
lining small tubes such as the walls of alveoli and aids diffusion
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The part that is exposed to the
cell surface (lumen) is covered with cilia
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Nicotine paralyses cilia so that
mucus is unable to be waved to the throat
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Stomata have two guard cells
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