automatic control systems always include three receptors, __________ and effectors. what one word completes the sentence?

The missing word is “co-ordination centres” (often written as the singular “control centre” or “coordination centre” in exam mark schemes).

Quick fill‑in answer

• Automatic control systems always include three things:
  • Receptors
  • Coordination centres / control centres
  • Effectors
• So the sentence completes as:

“Automatic control systems always include three receptors, coordination centres , and effectors.”

Why this is the right word

In GCSE biology and physiology:

• Automatic control systems in the body (like temperature or blood glucose regulation) are described as having receptors, coordination centres, and effectors.

• Coordination centres (such as the brain, spinal cord, or pancreas) receive information from receptors and send instructions to effectors.

So the one-word answer your question is looking for is “coordination” (as in coordination centres).

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