A cell is the basic structure of all life. Every living organism is made up of at least one cell..
Some organisms (eg amoeba) have only one cell (these are called single cellular organisms) but most have many cells (eg human) and these are called multicellular organisms.
[remember an organism is the name given to ANY living thing, animal or plant, whatever]
HUMANS and other mammals:
The body is made up of ORGANS.
Each organ has a particular job to do (eg the HEART pumps blood).
The organs are made up of groups of similar cells called TISSUE. eg a piece of liver, made up of liver cells, is called liver tissue.
In order of size: CELLS ——> TISSUE —–> ORGAN ——–> ORGANISM
[Of course some organisms, like the amoeba, do not have organs as they are only a single cell to start with]
A single cell multiplies by dividing in two
This is called binary fission and is a type of asexual reproduction.
Definitions:
Present in ALL cells
Cell membrane: The living outer layer to the cell. The membrane is selective about which substances enter and leave the cell.
Nucleus: Controls the function and behaviour of the cell. Contains the genetic information (genes). The genes are grouped into packages called chromosomes.
Mitochondria: The mitochondria supply the cell with the energy it needs.
Glucose is converted to energy during respiration
Present in PLANT CELLS ONLY
Chloroplasts: Where photosynthesis is carried out. Chlorosplasts contain a green chemical called chlorophyll which is needed for photosynthesis to take place.
Chloroplasts are only found above grouind in green parts of the plant. Mainly in the leaves.
Large vacuole: A cavity in the cytoplasm of a plant cell. It contains cell sap. It helps keep the cell rigid. Some cells ( animal and plant) also contain a smaller vacuole that helps regulate the water content of the cell.
Cell wall: A structure made df cellulose that surrounds a plant cell and helps it keep its shape.
Specialized cells:
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Examples of some cells in a human A: Sperm cell B: Nerve cell C: Muscle cells |
Cells have many shapes and are often adapted to help them perform their task
Example: A ciliated epithelial cell
Cilia are tiny hairs on a cell.
An epithelial cell makes up the outer covering of some structure or organ
(The most well known epithelial cells are on the surface of the skn, but these dont have cilia)
Epithelial cells that do have cilia line the wind pipe to the lungs (the trachea).
They are kept moist with slimey liquid to trap dust. They sway and waft the dust away from the lungs.
Cilia
