OCR · A-Level · Biology
Course version: H420 · Version from Sept 2025
(a) the need for communication systems in multicellular organisms
Full specification wording
Communication and homeostasis: (a) the need for communication systems in multicellular organisms
Multicellular organisms are large and complex, so their cells are far apart and specialised for different tasks.
Checked against the OCR H420 specification (opens in a new tab) on .
- Point 1 of 4
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Multicellular organisms are large and complex, so their cells are far apart and specialised for different tasks. Diffusion alone is too slow to coordinate these cells, because the distance is great and the surface area to volume ratio is small. A communication system carries signals quickly from one part of the body to another so that responses are coordinated. In animals the nervous system provides rapid electrical signalling and the endocrine system provides slower hormonal signalling. These systems allow the body to detect changes, coordinate organs and maintain a stable internal environment (homeostasis). The need therefore arises from size, cell specialisation and the requirement for fast, coordinated responses.
What earns the marks
- Multicellular organisms have a small surface area to volume ratio and large distances between cells, so diffusion alone is too slow.
- Cells are specialised for different functions, so coordination between distant tissues is required.
- Communication systems carry signals rapidly so that responses can be coordinated.
- The nervous system provides rapid electrical coordination, while the endocrine system provides slower hormonal coordination.
- Coordinated communication allows homeostasis, maintaining a stable internal environment despite external change.
Common mistakes and how to put them right
Claiming diffusion is impossible in multicellular organisms.
Put it right: Diffusion still occurs, but it is too slow over large distances to coordinate the whole organism.
Treating the nervous and endocrine systems as identical.
Put it right: The nervous system is rapid and electrical, whereas the endocrine system is slower and hormonal.
Ignoring cell specialisation; correction: because cells perform different roles, they must communicate to coordinate their activities.
Exam tips
- State the reason for the need (size, distance, surface area to volume ratio, specialisation) before naming the systems.
- Name both the nervous and endocrine systems and contrast their speed and mode of signalling.
- Link communication explicitly to homeostasis as the outcome it enables.
Try the lesson
The start of the Communication and homeostasis: (a) the need for communication systems in multicellular organisms lesson, made from checked teaching notes for this specification point.
Have a go first
Which of the following is an example of cell communication in a multicellular organism?
Listen
Multicellular organisms are large and complex, so their cells are far apart and specialised for different tasks. Diffusion alone is too slow to coordinate these cells, because the distance is great and the surface area to volume ratio is small. A communication system carries signals quickly from one part of the body to another so that responses are coordinated. In animals the nervous system provides rapid electrical signalling and the endocrine system provides slower hormonal signalling. These systems allow the body to detect changes, coordinate organs and maintain a stable internal environment (homeostasis). The need therefore arises from size, cell specialisation and the requirement for fast, coordinated responses. A strong answer earns marks for these points. Multicellular organisms have a small surface area to volume ratio and large distances between cells, so diffusion alone is too slow. Cells are specialised for different functions, so coordination between distant tissues is required. Communication systems carry signals rapidly so that responses can be coordinated. The nervous system provides rapid electrical coordination, while the endocrine system provides slower hormonal coordination. A common slip: Claiming diffusion is impossible in multicellular organisms. Instead, diffusion still occurs, but it is too slow over large distances to coordinate the whole organism. Exam tip: State the reason for the need (size, distance, surface area to volume ratio, specialisation) before naming the systems.
Key words
Say what each word means before you turn the card.
Surface area to volume ratio and diffusion limits
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Cell specialisation
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Nervous and endocrine coordination
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Homeostasis
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See every definition
- Surface area to volume ratio and diffusion limits
- Multicellular organisms have a small surface area to volume ratio and large distances between cells, so diffusion alone is too slow to coordinate the whole organism.
- Cell specialisation
- Cells are specialised for different functions, so coordination between distant tissues is required.
- Nervous and endocrine coordination
- The nervous system provides rapid electrical coordination, while the endocrine system provides slower hormonal coordination.
- Homeostasis
- Coordinated communication allows the maintenance of a stable internal environment despite external change.
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