C3.1Theme C — Interaction and interdependence
Integration of body systems — IB Biology SL Revision Notes & Topical Questions
10 min read 13 parts Lesson 6 of 9 3 quizzes
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Lesson summary
C3.1 Integration of body systems — IB BIOLOGY SL notes: Explain how the nervous and endocrine systems integrate organ systems, including reflexes, hormones and feedback control.Organisation — cells form tissues, tissues form organs and organs form organ systemsEpithelial cells fo…
- Emergent properties
- Cerebral cortex
- Cerebellum
- Medulla (brainstem)
- Hypothalamus
- Pituitary gland
Part 1 of 11Hierarchy and emergent properties
Organisation
- Organisation cells form tissues, tissues form organs and organs form organ systems
- Epithelial cells form epithelial tissue that absorbs food in the small intestine.
- Muscle cells form muscle tissue that contracts.
- The heart is made of cardiac muscle, blood vessel and connective tissues.
Emergent properties
Emergent properties properties that arise when cells and systems organise and interact
- Multicellular organisms can move over long distances and digest large macromolecules, which single cells cannot.
- The whole is greater than the sum of its parts, so a systems approach is argued alongside the reductionist one.
Integration
- Integration nerves and hormones coordinate systems so they act in step
Transport
- Transport blood carries materials and heat between distant organs
- Oxygen and glucose go to all cells for respiration.
- Urea made in the liver goes to the kidneys for excretion.
- FSH and LH go from the pituitary to the ovaries in the menstrual cycle.
Part 2 of 11Nervous and endocrine signalling
| Feature | Nervous system | Endocrine system | Plant hormones |
|---|---|---|---|
| Signal type | Electrical impulses plus neurotransmitters | Chemical hormones | Chemical hormones |
| Route | Along neurones | In blood plasma | Cell to cell, phloem or diffusion |
| Speed | Very fast | Slower, seconds to hours | Slow, hours to days |
| Duration | Short-lived | Often longer lasting | Long lasting |
| Target | A specific muscle or gland | Any cell with matching receptors | Cells with receptors, such as the shoot tip |
| Example | Pain withdrawal reflex | Epinephrine in exercise | Auxin in phototropism |
- Hormone = a chemical messenger made by an endocrine gland and carried by the blood
- Endocrine glands are ductless and secrete hormones directly into the blood.
- A hormone acts only on cells with complementary receptors, on the surface or inside.
- Hormones control functions that do not need instant responses.
Part 3 of 11Brain and receptors
Cerebral cortex
- Cerebral cortex the highly folded outer layer in two hemispheres, for intelligence, memory, consciousness, personality and voluntary movement
Cerebellum
- Cerebellum balance, posture, and the timing and force of muscle contractions
Medulla (brainstem)
- Medulla (brainstem) relays messages and controls unconscious activities such as heart rate, breathing and swallowing
Hypothalamus
- Hypothalamus monitors the blood, regulates temperature and water balance and controls the pituitary gland
Pituitary gland
- Pituitary gland produces hormones such as FSH and LH, and the posterior part stores and releases ADH and oxytocin
Conscious input
- Photoreceptors in the retina.
- Chemoreceptors on the tongue.
- Thermoreceptors in the skin.
- Mechanoreceptors in the inner ear.
Unconscious input
- Osmoreceptors detect the water content of blood.
- Baroreceptors detect blood pressure.
- Proprioceptors in muscles and joints report balance and movement.
Part 4 of 11Receptors and sensory input
Receptor
Receptor a specialised cell that detects a stimulus and acts as a transducer, converting the energy to an electrical impulse
- A stimulus depolarises the receptor.
- A weak stimulus fails to depolarise it enough, so no impulse is triggered.
- A strong enough stimulus starts an action potential in the sensory neurone.
Taste example
1
Dissolved Na+ diffuses through channel proteins into a salt chemoreceptor cell in a taste bud.
2
The membrane depolarises, giving a receptor potential.
3
Voltage-gated Ca2+ channels open and Ca2+ enters.
4
Vesicles release neurotransmitter by exocytosis from the basal membrane.
5
The neurotransmitter starts an action potential in the sensory neurone, which carries it to the brain.
Part 5 of 11Spinal cord and reflex arc
Spinal cord
- Spinal cord a pathway between body and brain that also integrates unconscious processes
- White matter holds the axons that carry information to and from the brain.
- Grey matter holds the neurones and synapses of spinal integration.
Reflex
Reflex an automatic, rapid response without conscious thought
- Examples are blinking, coughing, the pupil reflex and the knee reflex.
- We become aware of the response only after it has happened.
Reflex arc
Reflex arc the pathway from a receptor to an effector that does not involve conscious regions of the brain
1
A pain receptor (nocireceptor) in the skin detects a harmful stimulus.
2
A sensory neurone carries the impulse to the spinal cord.
3
A relay neurone in the grey matter passes the impulse on.
4
The relay neurone synapses with a motor neurone.
5
The motor neurone carries the impulse out of the cord.
6
The effector muscle contracts and pulls the limb away.
Part 6 of 11Motor output and nerves
Motor cortex
- Motor cortex the part of the cerebrum that initiates voluntary movement
Neuromuscular junction
- Neuromuscular junction the synapse between a motor neurone and a muscle fibre
1
An impulse arrives and Ca2+ enters the neurone.
2
Vesicles release acetylcholine, which diffuses across and binds receptors on the sarcolemma.
3
Na+ channels open and the sarcolemma depolarises.
4
An action potential passes down the T-tubules.
5
Ca2+ is released from the sarcoplasmic reticulum and binds troponin.
6
Myosin-binding sites on actin are exposed and the sliding filament process starts.
- Nerve
- a bundle of sensory or motor neurones, often both, wrapped in connective tissue
- Schwann cells form a myelin sheath about 1 mm long around each segment of axon.
Part 7 of 11Cerebellum and melatonin
Cerebellum
- Cerebellum coordinates balance, posture, walking, hand movements and speech
- It does not start movement, as the motor cortex does.
- It receives feedback from the moving body and sense organs and then sends signals to control the movement.
Circadian rhythm
Circadian rhythm a daily cycle of physiology and behaviour
Melatonin
- Melatonin secreted by the pineal gland, rising in the evening in response to darkness and falling at dawn
- It promotes sleepiness and falls to prepare waking.
- Its targets include the hypothalamus, pituitary, immune cells, kidney and gut.
- It reduces urine production at night.
- The cycle continues at about 24 h in constant darkness, so light resets it each day.
Part 8 of 11Epinephrine
Epinephrine (adrenaline)
- Epinephrine (adrenaline) secreted by the adrenal medulla when sympathetic neurones are stimulated in stress, fear or excitement
- It prepares the body for fight or flight.
- It raises the heart rate by acting on the SAN and the cardiovascular centre in the medulla.
- More blood brings more oxygen and glucose to muscles, so aerobic respiration releases more energy.
- Blood vessels to the gut and skin constrict to divert blood to active organs.
- Blood flow to the brain stays constant.
Combined control
- Combined control the response is both nervous and hormonal
Part 9 of 11Feedback control of heart rate and ventilation
- Heart rate
- receptors send impulses to the medulla
- Baroreceptors in the aorta and carotid arteries detect pressure.
- Chemoreceptors there detect CO2 and pH.
- The acceleratory centre sends sympathetic impulses, with noradrenaline, so the SAN fires more often.
- The inhibitory centre sends parasympathetic impulses, with acetylcholine, so the SAN fires less often.
1
Blood pressure drops.
2
Baroreceptors detect less stretch.
3
Impulses reach the cardiovascular centre in the medulla.
4
Sympathetic impulses reach the SA node.
5
The SA node fires more often and the heart rate rises.
6
Blood pressure returns towards normal, which is negative feedback.
Ventilation rate
- Ventilation rate respiratory centres in the medulla control the diaphragm and intercostal muscles
- CO2 travels as hydrogencarbonate ions (about 85%), dissolved in plasma (about 5%) and bound to haemoglobin (about 10%).
- Carbonic anhydrase in red cells catalyses CO2 + H2O ⇌ H2CO3.
- The acid dissociates into H+ and HCO3-, lowering the pH.
- Chemoreceptors detect the lower pH and the medulla sends more impulses, raising ventilation.
- Blood pH returns to normal, which is negative feedback.
Peristalsis
- Peristalsis waves of contraction of smooth muscle controlled by the enteric nervous system
- Stretch receptors detect the bolus of food.
- One motor neurone makes muscle behind the bolus contract, and another makes muscle ahead relax.
Part 10 of 11Plant coordination
Tropism
Tropism a directional growth response, such as positive phototropism in shoots
Phototropism
- Efflux carriers move auxin to the shaded side.
- Auxin stimulates proton pumping, which loosens cell walls so cells elongate.
- The shaded side grows faster, so the shoot bends towards light.
Hormone interaction
- Hormone interaction auxin and cytokinin together balance root and shoot growth
Ethylene
- Ethylene triggers ripening, and ripe fruit releases more ethylene, so ripening spreads by positive feedback
Part 11 of 11More from the specification
More from the specification
Autonomic nervous regulation
- Involuntary neural pathways coordinating organ systems without conscious control in living organisms.
Brainstem cardiovascular center
- The medulla oblongata, located in the lower brainstem, monitors blood pH and carbon dioxide concentrations to regulate heart rate.
Alimentary canal peristalsis
- Waves of coordinated smooth muscle contraction along the gut wall ensure mechanical transport and digestion of food.
Chemoreceptor feedback loop
- Elevated CO2 lowers blood pH, triggering medullary chemoreceptors to accelerate ventilation and restore homeostasis.
Alimentary canal
- The tube from mouth to anus through which food passes.
Key terms
| Term | Meaning |
|---|---|
| Emergent property | A property that arises from the interaction of cells and systems and is not found in the parts alone. |
| Hormone | A chemical messenger made by an endocrine gland and carried by the blood to target cells. |
| Reflex arc | The pathway from receptor to effector that gives an automatic response without the conscious brain. |
| Receptor | A specialised cell or neurone ending that detects a stimulus and converts it to an electrical impulse. |
| Melatonin | A hormone from the pineal gland that sets circadian rhythms. |
| Epinephrine | A hormone from the adrenal medulla that prepares the body for fight or flight. |
| Negative feedback | A control process that reverses a change and returns a variable to its set value. |
| Neuromuscular junction | The synapse between a motor neurone and a muscle fibre. |
Avoid these mistakes
1
Saying the brain controls every response — reflexes are processed by the spinal cord without the brain
2
Saying hormones act on every cell — only cells with matching receptors respond
3
Saying a stronger stimulus gives a bigger impulse — it gives a higher frequency of impulses
4
Saying negative feedback amplifies a change — it reverses the change and returns the value to normal
Marked practiceQuizzes for this lesson
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