An organism is a collection of cells, tissues,
organs and systems that is capable of
independent existence and reproduction.
All cells produced from the zygote by mitosis
have identical DNA
Cells with identical genetic information
differentiate to become different cells with their
own structure and function
Cells can be identical or different according to
the specific genes that are either active or
inactive in the cell
Cell differentiation is the term used to name the
process in which cells with identical cells with
identical nuclear composition, i.e. same number
and type of genes, become different and
specialized in both their structure and function.
How many cells can you name?
Muscle cells: elongated and consisting of
filaments allowing for contraction.
Red blood cell: biconcave shaped cells
containing haemoglobin to transport oxygen.
Palisade cells: rectangular shaped plant cells
containing chloroplasts for photosynthesis
Guard cells: specialised shape controlling
opening and closing of stomatal pores
Cells of the same type are usually found
together in a tissue, held together by
extracellular fluid or fibres.
In human bodies there are four basic types.
1. Epithelial tissues – consist of tightly packed
cells that cover and protect the inside and
outside surfaces of the body. They are named
according to their shape
- cuboidal epithelium
- columnar epithelium
- squamous epithelium
2. Connective Tissues – support or bind other cells
and tissues together
- fat (adipose tissue)
3. Muscle tissue – cells which are able to contract.
Contain contractile protein myosin and actin
- skeletal (voluntary)
- smooth (involuntary)
- cardiac (heart)
4. Nervous tissue- able to detect and transmit
electro chemical messages
Organs consist of a collection of tissues and
perform important specific tasks in the body.
For example the stomach is one organ found within
the digestive system consisting of tissues which are
responsible for the storage and digestion of food.
Epithelial cells secrete digestive juices
Blood cells carry blood to and from the small
intestine allowing transport of nutrients
Muscle cells allow for peristalsis, a process which
allows food to move via waves of muscular