CIE Categories Archives: 2. Organisation of the organism

2.2) Levels of organisation

2.2) Levels of organisation

Most cells, when they have finished dividing and growing, become specialised.

  • They do one particular job
  • They develop a distinct shape
  • Special kinds of chemical change take place in their cytoplasm.

‘Division of labour’- the specialisation of cells to carry out particular functions in an organism.


Palisade mesophyll cells – photosynthesis

Nerve cells – conduction of impulses

Sperm and egg cells – reproduction


Tissue is a group of cells with similar structures, working together to perform a shared function.

Eg. Bone, nerve, muscle, epidermis, xylem

Organ is a structure made up of a group of tissues, working together to perform a specific function.

Eg. Stomach, heart, lungs, intestines, brain, eyes

Organ system is a group of organs with related functions, working together to perform a body function.

Eg. Nervous and circulatory system

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2.1) Cell structure and organisation

2.1) Cell structure and organisation

Cytoplasm contains ribosomes on rough endoplasmic reticulum and vesicles.

Almost all cells, except prokaryotes, have mitochondria and  rough endoplasmic reticulum.

Mitochondria are responsible for producing energy from food substances through the process of aerobic respiration.

Cells with high rates of metabolism require large numbers of mitochondria to provide sufficient energy

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