Transcript Celloedd a Phrosesau mewn Celloedd

Cells and Cell Processes
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BIOLOGY 2
Cells
All organisms (apart from viruses) are
made up of one or more cells.
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You contain billions of different cells. Here are some
cells in living organisms:
How many not how big!
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The cells in an ant and an elephant are about the
same size but the elephant is a much larger animal
because it has a lot more cells.
Important structures
Nucleus
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This is the centre that controls all the cell’s activities. It contains
chromosomes which are important in cell division. The nucleus
is usually circular in shape
nucleus
Cytoplasm
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This structure is outside the nucleus. It
is a clear jelly-like substance
containing dissolved materials needed
by the cell.
Cytoplasm
Cell Membrane
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This is the outer most layer of the cell which keeps the
cytoplasm in and separates the cell from its environment.
Substances can move through the cell membrane in a controlled
way.
Cell membrane
Plant Cell
Plant cells contain some parts that are
not present in animal cells. These are:
cell wall
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vacuole
chloroplast
Cell wall
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Cell wall
This is a thick and rigid layer made
of cellulose. The cell wall
surrounds the cytoplasm. Without
this, a cell would not be able to
maintain its shape.
Vacuole
Vacuole
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This is a fluid filled space. It is
surrounded by a plasma
membrane. The fluid is called cell
sap and it consists mainly of water,
containing soluble substances
such as minerals.
Chloroplasts
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Chloroplasts
These are green discs containing
the pigment chlorophyll. This is
what allows a plant to absorb
sunlight and is therefore needed
for photosynthesis.
Onion Cell
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Why aren’t there any
chloroplasts in an onion cell?
Clue: Where does the onion cell
grow? Does it see the sun?
Patterns of Growth
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When two cells divide we call this cell division. The type of cell
division that allows an organism to grow is called mitosis.
This happens in different places in plants compared to animals.
A cell dividing in two by
mitosis to create two
identical daughter cells.
Growth pattern in plants
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We only see mitosis
in the area where
growth occurs in a
plant – this is in the
tips of the roots and
the stem. These
areas are called the
meristem.
Growth pattern in plants
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This cross section
of a tree trunk
shows obvious
cycles of growth.
Growth pattern in animals
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Mitosis can take place in animal tissue at any stage in its
development. Even though plants have the ability to grow new
parts throughout their life cycle, on the whole animals are
unable to do this.
Specialised cells
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Cells adapt to perform different functions during their
development.
e.g. red blood cells haven’t got a nucleus. This allows them to pack
in the red pigment haemoglobin and can therefore they can carry a
lot more oxygen around the body.
Undifferentiated Cells
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Some cells are not specialised and can grow
to form a range of potential tissues. We call
these undifferentiated cells and they are
referred to as stem cells.
Stem cells – why all the controversy?
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Some scientists claim that stem cell
research holds the key to curing many
diseases.
Because these cells are taken from
embryos, some believe that destroying
them is immoral.
Use of Stem Cells
Stem cells can develop • Creating insulin-producing
cells in the pancreas. This
to become different
avoids the need to inject
tissues.
insulin.
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Here are two
examples of their
possible use in
medicine:
• Replacing nerves destroyed
after a spinal cord injury.
The Future
Scientists are now looking into using stem cells from adults so
that embryos will not be involved.
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In the year 2000, successful trials were held in Italy using adult
stem cells to cure leukaemia in children.