We are multicellular organisms - made of approx 10 trilion cells

each cell contain same genetic info/code

we have different cell types

all start life as single fertilised cell (zygote)  - genetic information is stored in nucleus of first cell

as zygote divides cell structures become different

during development cells all become defined part of organism - differentiation

differentiation occurs in developing foetus after sixteen-cell stage - each cell has chemical signals that cause certain genes to be switch on/off

in large organisms, similar cells are grouped into tissues which carry out a single function - the same genes inside the nucleus of each tissue are switched on/off

muscle cells form muscle tissues which contract and relax to eable movement

certain cells differentiate into cells which secrete enzymes and hormones - these form glandular tissue 

skin - epethelial tissue

collection of tissues which work togeher to carry out same fucntion - organ 

e.g. stomach: muscular tissue - to churn up food. Glandular tissues - secete pepsin (protease enzyme needed to start digestion of protein). Epethelial tissue - inside and outside of stomach.

organ system- collection of organs which carry out a function

if the wrong genes are switched on/off during diferentiation, problems can arise 

All living things…


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