Free Introduction to Communication Systems revision notes for OCR A Level Biology – covering specification points 5.1.1 (a) and 5.1.1 (b)
Cell signalling
Cell signalling is the process by which cells detect, process, and respond to signals.
Cell signalling can be chemical (e.g. hormones, neurotransmitters) or electrical (e.g. action potentials).
- Intercellular (between cells) signalling is almost always chemical.
- Intracellular (within a cell) signalling can be chemical or electrical.
The table below outlines intercellular and intracellular cell signalling, with examples you will encounter at A level:
| Type | Chemical signalling | Chemical Examples | Electrical signalling | Electrical Examples |
|---|---|---|---|---|
| Intracellular | Signalling molecules or ions are inside the cell to transmit information from a receptor to a response pathway. |
|
Changes in membrane potential or ions within a cell signal a stimulus. |
|
| Intercellular | One cell releases signalling molecules that bind to receptors on another cell, triggering a response. |
|
Electrical impulses do not directly pass between cells. Electrical impulses are converted to chemical signals. |
|
The Importance of Cell Signalling
Cell signalling allows organisms to respond to changing external and internal conditions by detecting stimuli with receptors and producing a behavioural or physiological response.
- A behavioural response is a movement (towards or away from a stimulus).
- A physiological response is a change in cellular function.
Responding to changes in internal conditions allows for the maintenance of optimal conditions for cellular processes.
Responding to external conditions allows organisms to avoid, or minimise the effect of, unfavourable abiotic factors (e.g. extreme temperature, low pH, water stress) and hazardous biotic factors (e.g. predators, competition for food).
Communication Systems
Communication systems are how multicellular organisms coordinate the responses of their tissues and organs.
Communication systems can be electrical (neuronal) or hormonal (endocrine).
- Neuronal system: Neurones conduct electrical impulses rapidly, enabling fast responses to stimuli. At synapses, neurotransmitters act as the cell signalling molecules.
- Endocrine system: Hormones are secreted into the blood and transported throughout the body, acting only on target cells with complementary receptors.
