Integrated body systems coordinate neural, hormonal and plant responses through receptors, control centres and effectors, maintaining function across organisms and changing environmental conditions.
Integration is the coordination of interacting parts so the whole biological system performs an overall function. An emergent property appears through those interactions and is not a property of any isolated part.
| If the claim describes… | Classify it as… |
|---|---|
| what one component can do by itself | a component property |
| what coordinated components achieve together | an emergent property |
| information or material passing between components | evidence of integration |
A smooth-muscle cell can contract, but one cell cannot propel a meal through an intestine. Peristalsis emerges when many cells, tissues and neural signals coordinate waves of contraction.
cells → tissues → organs → organ systems → organism
Each level contains interacting subsystems from the level below; moving upward adds organisation, not merely more material.
| Level | Contribution to the intestine |
|---|---|
| epithelial tissue | forms a selective surface for secretion and absorption |
| smooth-muscle tissue | contracts and relaxes repeatedly |
| nervous and connective tissues | coordinate movement and hold working tissues together |
| whole organ | combines movement, digestion, absorption and transport |
The organ's function depends on different tissue types interacting. Calling an organ ‘a group of similar cells’ misses the transition from tissue to organ.
| Region | Main integration role |
|---|---|
| cerebral hemispheres | conscious perception, memory, planning and voluntary motor commands |
| cerebellum | compares intended movement with sensory feedback to refine timing, force, posture and balance |
| hypothalamus | links nervous information and blood conditions to autonomic and endocrine control |
| medulla | adjusts involuntary functions including heart rate and ventilation |
The brain is an integration organ because it receives, compares, stores and redistributes information. A region's role is not an isolated behaviour; it contributes to coordinated networks.
receptor transduces a stimulus → sensory neuron carries impulses into the CNS → relay neurons in brain networks support conscious perception → an upper motor neuron carries a command downward → a lower motor neuron reaches skeletal muscle → neurotransmitter at the neuromuscular junction triggers muscle action potentials and contraction
| Fibre | Direction relative to CNS | Function |
|---|---|---|
| sensory (afferent) | receptor → CNS | delivers information for integration |
| motor (efferent) | CNS → skeletal muscle | delivers the coordinated response |
The cerebral hemispheres coordinate voluntary action, but they do not contract the muscle directly. The final output is carried by motor neurons to the neuromuscular junction.
| Structure | What it encloses |
|---|---|
| endoneurium | one nerve fibre |
| perineurium | one fascicle, or bundle of fibres |
| epineurium | several fascicles plus blood vessels, forming the whole nerve |
A neuron is one cell. A nerve fibre is a neuron's long conducting process, usually an axon. A nerve is a connective-tissue package containing many fibres.
A mixed nerve can carry sensory impulses toward the CNS and motor impulses away from it at the same time because those signals travel in different fibres.
| Route | Earliest outcome |
|---|---|
| spinal reflex arc | rapid involuntary withdrawal |
| ascending pathways to brain | conscious pain, awareness and memory |
| descending input from brain | may modify the response after integration |
The reflex trades deliberation for speed: a predictable protective response starts through a short spinal pathway while the brain receives and interprets the same event.
intended movement from cerebral cortex + sensory feedback about position and balance → cerebellum compares intention with performance → timing and force of motor output are adjusted → movement becomes smooth and posture remains stable
| Cerebellar contribution | Example |
|---|---|
| timing | activates muscles in the correct sequence |
| force | prevents contraction from overshooting or undershooting |
| balance and posture | uses receptor input to correct body position |
| learned precision | refines writing, speech and practiced hand movements |
The cerebellum coordinates and corrects skeletal-muscle contraction. Voluntary movement is initiated elsewhere, particularly in the cerebral cortex.
| Pituitary part | Hypothalamic route | What the pituitary does |
|---|---|---|
| anterior | releasing or inhibiting hormones travel through portal blood vessels | endocrine cells synthesize and release pituitary hormones |
| posterior | axons of hypothalamic neurosecretory cells end in the gland | stores and releases ADH and oxytocin made in the hypothalamus |
Anterior-pituitary hormones regulate processes including growth, reproduction and homeostasis and can control endocrine glands such as the thyroid, gonads and adrenal cortex.
Calling the pituitary the ‘master gland’ is incomplete: the hypothalamus largely controls its activity, linking neural and endocrine information.
| Observation | Best interpretation |
|---|---|
| CO₂ rises and pH falls | ventilation should increase |
| exercise stops and CO₂ falls | ventilation can decrease gradually |
| O₂ falls strongly | peripheral chemoreceptors add a weaker but important drive |
The principal routine stimulus is CO₂-linked H⁺, not a direct measurement of how hard the muscles are working. Voluntary control can temporarily override the automatic rhythm but does not replace it.
lateral light is detected at the shoot tip → auxin becomes more concentrated on the shaded side → auxin moves to the elongation zone below the tip → shaded-side cells elongate more → unequal length curves the shoot toward the light
The shaded side becomes the longer outside of the curve, so the tip bends toward the illuminated side. Auxin does not pull the shoot toward light; it changes relative growth rates.
| Light condition | Auxin/growth across shoot | Shape |
|---|---|---|
| light distributed equally | approximately equal elongation on both sides | grows straight |
| lateral light | more auxin-driven elongation on shaded side | curves toward light |
auxin activates plasma-membrane H⁺ pumps → H⁺ accumulates in the apoplast → lower wall pH activates expansins → cellulose–hemicellulose interactions loosen → wall resistance to stretching falls → ion uptake and water entry maintain turgor → the yielding wall extends and the cell elongates
| Necessary contribution | What it supplies |
|---|---|
| proton pumping | acidic wall conditions |
| expansins and loosened cross-links | wall extensibility |
| water entry and turgor | force that stretches the loosened wall |
Auxin does not enlarge a cell by adding wall material alone. It changes wall mechanics so existing turgor can produce elongation; sustained growth later requires new wall components.
fruit begins to ripen → ethylene production rises → gaseous ethylene diffuses within and between fruit → ethylene stimulates more ripening → ripening tissues produce still more ethylene
This is positive feedback because the response increases the original change. The loop drives rapid, synchronized ripening rather than restoring fruit to its unripe state.
| Storage action | Mechanistic prediction |
|---|---|
| remove ethylene from air or ventilate | slows propagation of the ripening signal |
| keep ripe fruit beside unripe fruit | accelerates ripening of neighbours |
| block ethylene perception | reduces the tissue response even if ethylene is present |