# Explain how the nervous system and endocrine system work together to bring about the 'fight or flight' response when an organism perceives a threat.

> OCR A-Level Biology A (H420) — 5.5 Plant and animal responses · Explain · 4 marks

> When an organism detects a threat, a rapid series of coordinated changes occur in the body that prepare it for either confronting or escaping the danger. These changes involve both electrical signalling and chemical signalling, and the two systems must act in a precise sequence to produce the full response.

## Mark scheme (4 marks)

1. The nervous system rapidly transmits a signal to the adrenal gland
2. The adrenal medulla releases adrenaline into the blood
3. Adrenaline binds to receptors on target cells, producing physiological changes
4. The two systems are complementary because the nervous system provides speed whereas the endocrine system provides a sustained, widespread response

## Key terms

- [nervous system](https://www.gradenine.co.uk/glossary/nervous-system)
- [endocrine system](https://www.gradenine.co.uk/glossary/endocrine-system)

## Related

- [Revision notes for OCR A-Level Biology A (H420)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-nervous-system-and-92bb59d2) · Published by Druglandscape Ltd.