3.6.1Inquiry Process
Integration in Living Organisms — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 141 of 160
Section 1 of 5What Integration Means
Body systems
- Groups of organs, such as the circulatory, respiratory and digestive systems, each perform a main function for the whole organism.
Emergent function
- Systems working together achieve results that no single system could, for example supplying oxygen to muscles during running.
Communication
- Coordination requires information to pass between systems, so the nervous and endocrine systems act as the main communication networks.
Control centres
- The brain, and especially the hypothalamus, receives input from receptors throughout the body and issues instructions to effectors.
Section 2 of 5Nervous and Endocrine Coordination
Nervous and Endocrine Coordination
Nervous system
- Uses electrical impulses along neurones and chemical transmitters at synapses, giving fast, short-lived and highly localised responses.
Endocrine system
- Uses hormones carried in the blood to distant target cells, giving slower, longer-lasting and more widespread effects.
Working together
- The hypothalamus links the two systems, because nerve cells there control the pituitary gland, which releases hormones.
Feedback
- Information about the result of a response is fed back so that the response can be reduced or increased as required.
| Feature | Nervous | Endocrine |
|---|---|---|
| Signal | Electrical impulses and neurotransmitters | Hormones in blood |
| Speed | Very fast | Slower |
| Duration | Short | Longer lasting |
| Target | Specific cells | Any cell with receptor |
Section 3 of 5Example: Running a Race
1
Muscles use more ATP, so carbon dioxide concentration in the blood rises and is detected by receptors.
2
The brain increases the breathing rate and heart rate through the autonomic nervous system.
3
Epinephrine from the adrenal glands raises heart rate further and releases glucose from liver glycogen.
4
Blood flow is redirected to the working muscles, and sweating is increased to lose the extra heat produced.
5
After exercise the systems return to resting levels as feedback signals reduce the stimulus.
Section 4 of 5Worked Example
Question Give two reasons why a runner’s heart rate increases within seconds of starting a sprint but takes minutes to return to normal.
- The rapid rise is due to nerve impulses from the brain to the heart, because nervous coordination is fast.
- Epinephrine reaches the heart in the blood and keeps stimulating it for as long as it is present.
- Hormones are removed slowly from the blood, so the effect lasts longer than the nerve impulse that began it.
Answer
- Nerves cause the fast onset;
- hormones prolong the response so recovery is slow.
Section 5 of 5Exam Checklist & Tips
3.6.1 – Key Points for the Exam
- Integration Coordination of body systems so they work together as a single organism.
- Hypothalamus Part of the brain that links the nervous and endocrine systems.
- Effector A muscle or gland that carries out a response.
- Hormone A chemical messenger carried in the blood to target cells.
Common Mistakes
- Treating each organ system as independent when answering integration questions.
- Saying hormones are faster than nerve impulses; nerves act in milliseconds.
- Forgetting that the brain also controls the endocrine system via the pituitary.
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