2.1.8 explain that cells in multicellular organisms differentiate to carry out the specialised functions by expressing some of their genes but not others.

Process of differentiation.

Cells specialised to perform their function.

This happens because some genes are expressed (switched on) and others are not.

After fertilisation

That’s when (in humans), a sperm cell and an egg cell (ovum) join to make a zygote.

The zygote undergoes mitosis. One cell divides to form two. Each with exactly the same genetic information. They are identical.

Mitosis continues

2 cells become 4.

4 cells become 8……….

Until a ‘ball’ of cells forms.

This is known as an embryo.

The embryo

At this stage, any one of these cells contains a complete set of genetic information to make a human.

These cells will specialise.

Some will become nerve cells

Some become blood cells

Others become muscle cells ……..

Going back to the embryo

These cells will go through a process called:

DIFFERENTIATION

SPECIALISED FUNCTIONS

Each of these cells has become specialised to carry out a particular function.

e.g.

Nerve cells to transmit electrical impulses

Blood cells to carry O2 and CO2

Muscle cells to contract.

Special functions require a change in cell shape.

How do these cells become specialised?

Interesting: because we know that all of these cells contain the genetic information to become a:

Nerve cell or

Muscle cell or

Red blood cell…..

‘Switching on’

Genes for the nerve cell pathway are ‘switched on’ or expressed and the others are not.

Genes for the muscle cell pathway are ‘switched on’ and the others are not.

Genes for the red blood cell pathway are ‘switched on’ and the others are not.

Cells differentiate.

Specialise.

and change shape.

typical of multicellular organisms.