A cell is the basic unit of life. Some living
organisms such as animals and plants are made
of hundreds of trillions of these basic units
of life called cells.
Animal Cells -- A typical animal cell will
include the nucleus, a cell membrane and a
cell cytoplasm. The nucleus is the structure
that contains the genetic information, otherwise
known as DNA and it controls the actions and
the reactions of the cell. The cell membrane,
which is the border of the cell, acts as the
gatekeeper and its controls what enters and
exits the cell. As well as enabling neighbouring
cells to stick to one another. The cell cytoplasm
is the site of the cell's chemical reactions.
Lots of chemical reactions occur here such
as respiration. Respiration takes place in
specialised structures called mitochondria.
Plant Cells -- Plant cells contain the structures
that animal cells contain, that we've just
discussed, the nucleus, the cytoplasm and
the cell membrane, but they also include lots
of extra structures. For example, they contain
a cell wall. A cell wall is made of cellulose
and this structure provides support for shape
of the cell. Plant cells also contain chloroplasts
which are filled with a chemical called chlorophyll.
Chlorophyll enables plant cells to absorb
light so it can be used in photosynthesis.
Chlorophyll is also the substance that gives
plants its green colour. Finally, plant cells
also contain structures known as vacuoles;
these are filled with a watery substance which
contains dissolved sugars called cell sap.
The role of the vacuole is to provide support
for the cell shape and to store sugars.
Specialised Cells -- Some cells are specialised;
they are able to carry out particular jobs.
The specialised cells we will look at are
red blood cells, nerve cells and white blood
cells. Red blood cells do not possess a nucleus.
This is so that they have got enough space
to be able to absorb and transport as much
oxygen as possible. Nerve cells are specialised
in that they have branched endings called
dendrites. This is so they can communicate
with lots of other nerve cells. You will also
notice they have long axons along which the
electrical message can travel. Finally, white
blood cells enable us to fight infections.
They can be identified by the characteristic
lobed nucleus. White blood cells have a flexible
cytoplasm so that they can engulf pathogens
in a process called phagocytosis. Some other
white blood cells are specialised to produce
antibodies and it's these antibodies that
fight pathogens.
