Cells and Cell Processes

1
Cells and Cell Processes

• BIOLOGY 2

2
Cells

• All organisms (apart from viruses) are made up
  of one or more cells.
• You contain billions of different cells. Here
  are some cells in living organisms

3
How many not how big!

• 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.

4
Important structures

• Nucleus
• This is the centre that controls all the cells
  activities. It contains chromosomes which are
  important in cell division. The nucleus is
  usually circular in shape

nucleus
5

• Cytoplasm
• This structure is outside the nucleus. It is a
  clear jelly-like substance containing dissolved
  materials needed by the cell.

Cytoplasm
6

• Cell Membrane
• 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
7
Plant Cell

• Plant cells contain some parts that are not
  present in animal cells. These are

cell wall
vacuole
chloroplast
8
Cell wall

• 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.

9
Vacuole

• Vacuole
• 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.

10
Chloroplasts

• Chloroplasts
• These are green discs containing the pigment
  chlorophyll. This is what allows a plant to
  absorb sunlight and is therefore needed for
  photosynthesis.

11
Onion Cell

• Why arent there any chloroplasts in an onion
  cell?
• Clue Where does the onion cell grow? Does it
  see the sun?

12
Patterns of Growth

• 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.
13
Growth pattern in plants

• 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.

14
Growth pattern in plants

• This cross section of a tree trunk shows obvious
  cycles of growth.

15
Growth pattern in animals

• 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.

16
Specialised cells

• Cells adapt to perform different functions
  during their development.
• e.g. red blood cells havent 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.

17
Undifferentiated Cells

• 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.

18
Stem cells why all the controversy?

• 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.

19
Use of Stem Cells

• Creating insulin-producing cells in the pancreas.
  This avoids the need to inject insulin.
• Replacing nerves destroyed after a spinal cord
  injury.

• Stem cells can develop to become different
  tissues.
• Here are two examples of their possible use in
  medicine

20
The Future

• Scientists are now looking into using stem
  cells from adults so that embryos will not be
  involved.
• In the year 2000, successful trials were held in
  Italy using adult stem cells to cure leukaemia in
  children.