Describe the levels of organisation found in a multicellular organism, starting from the least complex level and ending with the most complex level.

Pearson Edexcel International GCSE Biology (4BI1) — 2.1 Levels of organisation · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Multicellular organisms are made up of many different components that are arranged in a hierarchy from the simplest to the most complex.

Model answer (4 marks)

1. Cell – the basic building block of living organisms.
2. Tissue – a group of similar cells that perform a specific function.
3. Organ – an aggregation of tissues that work together to carry out a particular function.
4. Organ system – a group of organs that cooperate to perform complex functions within the organism.

Examiner tips

Use the exact terms (cell, tissue, organ, organ system).
Show the hierarchy by numbering or bullet points.
Keep each description brief – one sentence per level.
Use the word ‘basic’ for cell and ‘most complex’ for organ system to match the scheme.

Common mistakes

Mixing up the order – e.g., putting organ before tissue.
Using vague phrases like ‘group of cells’ without specifying function.
Omitting the word ‘organ system’ or describing it as just a group of organs without noting its complexity.

Mark scheme (4 marks)

Cell is the least complex / basic level of organisation; described as the basic building block of living organisms
Tissue is a group of cells with a similar structure and function
Organ is an aggregation of tissues performing a specific function
Organ system is the most complex level; groups of organs that work together to form / within organisms

Key terms in this question

cell · organ