(a) Level of organisation
- Syllabus
- 2024
- Topic
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- Level
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Learning objectives
Build the levels of organisation
Organisation in a multicellular organism forms a hierarchy: specialised parts combine into progressively larger units that coordinate a shared function.
| Level | Meaning | Example in one animal hierarchy |
|---|---|---|
| organelle | a structure within a cell that performs a particular function | a mitochondrion in a muscle cell |
| cell | the living unit that contains organelles | a cardiac muscle cell |
| tissue | a group of similar cells working together for a function | cardiac muscle tissue |
| organ | different tissues working together for a particular function | the heart |
| organ system | several organs working together for a major body function | the circulatory system |
The direction is: organelle ightarrow cell ightarrow tissue ightarrow organ ightarrow organ system. At each step, the smaller level becomes a component of the next; the heart, for example, contains muscle tissue but also other tissues that let the organ work as a whole.
A tissue is not simply any collection of cells: its similar cells cooperate in a function. An organ contains more than one tissue type, whereas an organ system contains multiple organs. Do not include the whole organism as one of the five levels required by this objective.