2.10Structures and Functions in Living Organisms
Co-ordination and response — Edexcel Modular - OL Revision Notes & Topical Questions
15 min read 23 parts Lesson 10 of 12 1 quiz
Co-ordination and response Edexcel O Level Modular Biology notes: understand how organisms are able to respond to changes in their environmentMyelin sheath speeds up impulses.Adrenaline prepares the body for fight or flight.Auxin moves to the shaded side of a shoot.understand how…
- Co-ordination and response Edexcel O Level Modular Biology: what to do next
- Sensory neuron
- Motor neuron
- Reflex arc
- Endocrine gland
- Give / State / Name
Section 1 of 23Process & sequence
- Stimulus
- Receptor
- Sensory neuron
- Relay neuron (spinal cord)
- Motor neuron
- Effector
- Response
Section 2 of 23Keep going
Co-ordination and response Edexcel O Level Modular Biology: what to do next
These Co-ordination and response Edexcel O Level Modular Biology notes covered the key ideas, worked examples and exam technique for this topic. Check your Co-ordination and response Edexcel O Level Modular Biology understanding with the practice questions below, then reread any Co-ordination and response Edexcel O Level Modular Biology point you were unsure about before moving on.
Section 3 of 23Two control systems
Humans use two systems that work together. Changes in the external or internal environment act as stimuli. The nervous system sends electrical impulses along neurones, making responses fast and short-lived. The hormonal (endocrine) system sends chemical messages in the blood, with slower and longer-lasting effects.
| Nervous system | Endocrine system | |
|---|---|---|
| Made up of | Nerves (bundles of neurones) | Glands |
| Information | Electrical impulses | Hormones |
| Carried by | Neurones | Blood |
| Speed | Very fast | Slower |
| Duration | Short | Long |
Hormones alter the activity of specific target organs and provide a signal that triggers a response. The endocrine glands that produce them are collectively the endocrine system.
Section 4 of 23The nervous system and reflexes
The central nervous system (CNS) comprises the brain and spinal cord; the peripheral nervous system (PNS) comprises the nerves that branch out from the CNS to the rest of the body.
- where the impulse triggers the release of a chemical that diffuses across the gap and stimulates the next neurone.
A reflex response is automatic and rapid and does not involve the conscious part of the brain; awareness occurs after the response. Examples: pain withdrawal, blinking and coughing. The pathway is stimulus, receptor, sensory neurone, relay neurone (spinal cord), motor neurone, effector, response.
Section 5 of 23The eye as a sense organ
The retina of the eye contains receptor cells sensitive to light.
- giving the sharpest colour vision; the optic nerve carries impulses between the eye and the brain.
| Cell type | Light level | Colour |
|---|---|---|
| Rods | Work in dim light | No colour |
| Cones | Need bright light | Colour vision |
Section 6 of 23The nervous system in detail and common questions
Types of neurone and their structure
- a sensory neurone has its cell body to the side of the long axon;
- a motor neurone has its cell body at one end, in the CNS, and a long axon to the muscle;
- a relay neurone is short and lies wholly within the CNS.
- because the transmitter is released only from the end of the presynaptic neurone and receptors lie only on the postsynaptic side.
| Part of brain | Function |
|---|---|
| Cerebral hemispheres | Conscious thought, memory, language and voluntary actions |
| Cerebellum | Balance and coordinated muscle movement |
| Medulla oblongata | Control of heart rate and breathing |
| Hypothalamus | Body temperature and water balance |
| Pituitary gland | Releases hormones |
Voluntary actions start in the cerebral cortex, pass along motor neurones and need conscious decisions. Eye defects: short sight (myopia) means that distant objects are blurred because the lens is too strong or the eyeball too long; long sight is the opposite. They can be corrected with concave or convex lenses respectively.
Section 7 of 23Compare
| Feature | Nervous system | Endocrine system | Signal | Speed | Example |
|---|---|---|---|---|---|
| Signal type | Electrical impulses | Hormones | — | — | — |
| Transmission | Neurons | Blood | — | — | — |
| Speed | Very fast | Slower | — | — | — |
| Duration | Short | Long-lasting | — | — | — |
| Target | Specific muscles/glands | Target organs with receptors | — | — | — |
| Example | Withdrawal reflex | Insulin, adrenaline, thyroxine | — | — | — |
Section 8 of 23Worked examples
Give two differences between nervous and hormonal communication. [2]2 marks
Nerve: electrical impulses, fast, short-lived; hormones: chemicals in blood, slower, longer-lasting.
Describe what happens at a synapse. [3]3 marks
The impulse triggers the release of a chemical, which diffuses across the gap and triggers an impulse in the next neurone.
Why are reflexes useful? [2]2 marks
Rapid and automatic, so they protect the body from injury.
Section 9 of 23Accommodation: focusing near and distant
The lens is elastic and its shape changes when the suspensory ligaments are loosened or tightened by the ciliary muscles. This fine focusing is called accommodation.
| Near object | Distant object | |
|---|---|---|
| Ciliary muscles | Contract | Relax |
| Suspensory ligaments | Loose / slack | Tight / taut |
| Lens shape | Thick, more curved | Thin, less curved |
| Light refraction | More | Less |
Section 10 of 23The pupil reflex
| Stimulus | Radial muscles | Circular muscles | Pupil | Light entering |
|---|---|---|---|---|
| Bright light | Relax | Contract | Constricts (smaller) | Less - protects retina |
| Dim light | Contract | Relax | Dilates (larger) | More - helps vision |
This is a reflex response controlled by the iris.
Section 11 of 23Role of skin in temperature regulation
Skin contains receptors for touch, pressure, pain, heat and cold, and structures that help regulate body temperature. Temperature regulation is an example of homeostasis since core temperature (about 37 C) must be maintained within narrow limits. The brain (hypothalamus) detects blood temperature and coordinates a cooling or heating response.
| If body temperature is too high | If body temperature is too low |
|---|---|
| Vasodilation: arteriole muscles relax, arterioles widen and more blood flows through skin capillaries, so heat is lost by radiation | Vasoconstriction: arteriole muscles contract, arterioles narrow, less blood flows near the skin, reducing heat loss |
| Sweating: sweat evaporates, taking heat from the body | Sweating decreases, so less heat is lost |
| Hair erector muscles relax, hairs lie flat, no insulating air layer, so heat escapes | Shivering: muscles contract, releasing heat from respiration |
When asked how the skin responds in a cold environment, focus on vasoconstriction and reduced sweating. Note that arterioles do not move closer to the surface; the blood flow through them changes.
Section 12 of 23Practical and exam applications for the eye and skin
Pupil reflex practical
- in a dim room, shine a torch into a partner's eye (briefly) and observe the pupil get smaller;
- turn the light away and watch it enlarge.
Why is it that we feel cold even though we are shivering?
- and effectors restore the temperature.
- (sweat glands, muscles in arteriole walls, skeletal muscles)
Section 13 of 23Worked examples
Describe the changes in the eye when focusing on a distant object. [3]3 marks
Ciliary muscles relax, suspensory ligaments tighten, and the lens becomes thinner.
Describe the response of the skin to a hot environment. [3]3 marks
Vasodilation, more sweating, and hairs lying flat.
Explain why the pupil constricts in bright light. [2]2 marks
To reduce the light reaching the retina and prevent damage.
Section 14 of 23Control of blood glucose
Blood glucose must be kept in a narrow range.
Section 15 of 23Hormones of the menstrual cycle
| Hormone | Made in | Effects |
|---|---|---|
| FSH | Pituitary | Stimulates development of an egg in a follicle; stimulates oestrogen release |
| LH | Pituitary | Stimulates release of the egg (ovulation) |
| Oestrogen | Ovaries | Repairs and thickens the uterus lining after menstruation; secondary sexual characteristics in females |
| Progesterone | Corpus luteum in ovary | Maintains the uterus lining; prevents further ovulation during pregnancy |
Oestrogen and progesterone both control events of the menstrual cycle by preparing and maintaining the uterus, and they influence FSH and LH.
Section 16 of 23Other hormones and ADH
| Hormone | Gland | Effect |
|---|---|---|
| Adrenaline | Adrenal gland | Prepares body for fight or flight |
| Testosterone | Testes | Male secondary sexual characteristics, sperm production |
| ADH | Pituitary | Increases permeability of collecting ducts, so more water is reabsorbed |
If the water potential of the blood is too low (high solute concentration), more ADH is released and less water is lost in the urine. Hormones are produced by a gland, carried in the blood, and alter the activity of target organs.
Section 17 of 23Putting the hormone systems together: exam tips
Questions on the menstrual cycle often show a graph of hormone levels over 28 days.
- which triggers ovulation.
| Question type | What to include |
|---|---|
| Explain how insulin controls glucose | Source (pancreas), target (liver), conversion to glycogen, negative feedback |
| Explain how ADH works | Pituitary, blood too concentrated, collecting ducts, water reabsorbed |
| Describe the cycle graph | Quote data from the graph for each hormone |
Diabetes control and the glucose tolerance test also appear: blood glucose is measured every half hour after drinking glucose. In a healthy person it rises to a peak then falls within two hours; in a diabetic person it stays high.
Section 18 of 23Insulin treatment and the liver
The liver stores glycogen as an energy reserve, about 100 g in an adult, and releases glucose between meals.
- so sugar must be taken quickly.
Section 19 of 23Worked examples
Explain how insulin lowers blood glucose. [3]3 marks
It makes liver cells take up glucose and convert it to glycogen for storage.
State the roles of FSH and LH. [2]2 marks
FSH stimulates egg development; LH stimulates ovulation.
Which hormone maintains the uterus lining? [1]1 mark
Progesterone.
Section 20 of 23Key terms
| Term | Meaning |
|---|---|
| CNS | Brain and spinal cord. |
| Receptor | Cell that detects a stimulus. |
| Synapse | Gap between neurones. |
| Fovea | Region of retina with most cones. |
| Conjunctiva | Membrane covering the front of the eye. |
| Term | Meaning |
|---|---|
| Accommodation | Change in lens shape to focus. |
| Vasodilation | Widening of skin arterioles. |
| Vasoconstriction | Narrowing of skin arterioles. |
| Hypothalamus | Part of the brain monitoring temperature. |
| Iris | Muscle controlling pupil size. |
| Term | Meaning |
|---|---|
| Insulin | Hormone that lowers blood glucose. |
| Glucagon | Hormone that raises blood glucose. |
| Glycogen | Storage carbohydrate in liver and muscles. |
| Ovulation | Release of an egg. |
| Corpus luteum | Empty follicle that makes progesterone. |
Section 21 of 23Syllabus checklist
- adrenaline
- insulin
- testosterone
- progesterone and oestrogen
Section 22 of 23Command terms
Section 23 of 23Exam technique
Marked practiceQuizzes for this lesson
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