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.