The Cell
The Cell
The Cell
The basic unit of structure and function in living organisms is the cell. Because cells are very minute,
they can only be seen under high magnification with the microscope.
While some organisms are very simple, containing a single cell (unicellular), there are some organisms
that are more complex (multi-cellular). In eukaryotes, cells often combine to make tissue and tissues
combine to form organs. These organs may then combine (work together) to form systems.
There are 2 types of cells: prokaryotic and eukaryotic cells.
Prokaryotic cells are much simpler, and hence smaller than eukaryotic cells. They do not have an
organized nucleus or the organelles found in eukaryotic cells. Examples of prokaryotes are bacteria.
Since eukaryotic cells are more complex, it means that they have an organized nucleus as well as several
organelles that are not found in prokaryotic cells. Examples of eukaryotes are plants, animals, fungi and
protists.
The diagram below shows the differences between a prokaryotic and eukaryotic cell.
Vacuoles
These are small sacs bounded by a single membrane called the vacuolar membrane. Vacuoles contain
cell sap, which is made up of variable amounts of water, mineral salts, sugars, pigments and enzymes
depending on the cell. Vacuoles are present in both the plant and animal cell, but they are much smaller
in the animal cell and are not permanent. The presence of a large vacuole increases the osmotic pressure
of the cell. It is the presence of a large vacuole in a plant cell that causes it to become turgid
(swollen). Plants need turgid cells to aid in support as it does not have a bone structure.
Cell wall
This structure is only found in plant cells. This rigid cell structure gives the cell a regular shape and
prevents it from bursting when the plant cells become swollen. The cell wall is made of cellulose,
which is a polysaccharide. The cell wall encloses/ covers the cell membrane and its contents
(protoplasm). Due to its structural make up its primary function is to provide protection and support to
the cell.
SUMMARY
Animal and
plant cells
Name of
part
cytoplasm
onlyPlant cells
cell
membrane
nucleus
cell wall
vacuole
chloroplast
Description
Where found
enclosed by
the cell
around the
cytoplasm
inside the
cytoplasm
around the
outside of
inside the
cytoplasm of
inside the
cytoplasm of
Function
(supplemen
contains the cell organelles, e.g.
mitochondria, nucleus site of chemical
prevents cell contents from escaping
controls what substances enter and leave
controls cell
division controls
cell development
prevents plant cells from bursting
allows water and salts to pass through
contains salts and
sugars helps to keep
traps light energy for photosynthesis
There are many other organelles present in both the animal and plant cells which we have not discussed.
However, at this stage in your studies only these will really be asked for. It would not hurt however to
familiarize yourself with other organelles.
These include:
-Golgi body/apparatus
-Ribosomes
-Lysosome
Specialization of Cells
In living organisms there are millions of cells present. If all the cells in a body were the same and
performed the same functions, there would be some functions that an organism would be unable to
perform. As a result, some of these cells are specialized and grouped together to form tissues which may
form organs. Since each of these tissues and organs perform a specific function, there is a division of
labour and increased efficiency.
Cells are able to perform different functions because of their structure, the proteins they produce and the
organelles present. Since different cells perform different functions a nerve cell, for example, cannot
have the same structure as a white blood cell. This specialization is the same for the organelles within
the cells. In the cell, each organelle has its own role involving its own specialized structure and
chemistry. All the cells and organelles within a cell do their own thing but they all come together for one
purpose and thats to allow proper body function.
Specialized cells differ in size, shape and function. These modifications of the cell enable it to perform
its task properly. Both plant and animal cells may be specialized for different tasks.
Examples of Specialized cells are:
-Nerve cell
-White blood cell
-Red blood cell
-Fat cells
-Root hair cell
-Palisade cell
NERVE CELL
Cells that perform the same specific functions are grouped together in the body to
form tissues. Some of the main tissues in Man are:
-Muscle
-Nerve
-Connective
-Epithelium
The main tissues in plants are:
-Xylem
-Phloem
Tissues are grouped together to form organs.
Examples of organs in animals are: kidney, liver and stomach.
Examples of organs in plants are: stem, root, leaf.
Organs are then grouped together to form systems.
An example of a system is the excretory system which we will be examining shortly.
From the flow chart above, it can be seen that cells group together to form tissues and tissues form
organs. Organs are grouped together to form systems which collectively form an organism.