Control and Coordination – Detailed Exam Notes

Concept of Movement, Life & the Need for Coordination

• We instinctively label “moving things” as living; ex:
  • Seedling pushes soil, cat runs, children swing, buffaloes chew cud.
• Two broad categories of movement:
  • Growth-related (mostly in plants) ⇒ movement stops if growth stops.
  • Non-growth (muscle-driven) movement in animals & some plants.
• Movement usually represents a response to environmental change aimed at advantage or protection.
• Correct, situation-specific response implies the organism must:
  • Detect the event (stimulus).
  • Select & execute an appropriate movement.
  • Therefore requires integrated systems of control & coordination.

Animal Coordination: The Nervous System

• Multicellular animals evolved specialised tissues for:
  • Control (nervous tissue)
  • Action (muscular tissue)
• Example scenario: touching a hot object – dangerously high temperature → rapid withdrawal.

Receptors & Neurons

• Receptors = specialised dendritic tips located mainly in sense organs:
  • Gustatory (taste)
  • Olfactory (smell)
  • Photoreceptors (sight), phono-receptors (hearing), etc.
• Neuron pathway [Fig. 6.1(a)]:
  • Information acquisition at dendritic tip.
  • Electrical impulse travels: dendrite → cell body → axon.
  • At axon terminal, impulse triggers neurotransmitter release across \text{synapse}.
  • Neurotransmitter starts a new impulse in next neuron or muscle cell [Fig. 6.1(b)].

Activity 6.1 (Sugar-Nose Block)

• Demonstrates taste-smell interdependence.
• Blocking nose dulls sugar/flavour perception; similar effect during common cold.

Reflex Actions

• Definition: rapid, automatic responses executed without conscious thought.
• Examples: withdrawing hand from flame, jumping away from bus, salivating when hungry.
• Reflex Arc [Fig. 6.2]:
  1. Receptor detects stimulus.
  2. Sensory neuron → spinal cord.
  3. Interneuron forms immediate synapse with motor neuron.
  4. Motor neuron → effector muscle/gland produces response.
• Arc usually formed inside spinal cord – saves time versus routing to brain.

Human Brain – Central Control Hub

• Central Nervous System (CNS) = brain + spinal cord; communicates via Peripheral Nervous System (cranial & spinal nerves).
• Three major brain regions & their roles [Fig. 6.3]:
  • Fore-brain (cerebrum): thinking, memory, interpretation, voluntary action; hunger centre.
  • Mid-brain: bridges fore- & hind-brain; some involuntary actions.
  • Hind-brain:
    • Cerebellum – precision, posture, balance (e.g.
    walking, cycling).
    • Medulla oblongata – autonomic functions (heartbeat, blood pressure, vomiting, salivation, breathing rhythm).
• Voluntary vs Involuntary:
  • Writing/clapping = fore-brain mediated.
  • Breathing/heartbeat = hind-brain & medulla, outside conscious control.

Protection of Nervous Tissue

• Brain: encased in bony cranium + cushioned by cerebro-spinal fluid (CSF) filled membranes.
• Spinal Cord: runs inside vertebral column (back-bone).

From Nerve Impulse to Action – Muscular Level

• Arrival of impulse at neuromuscular junction → release of neurotransmitter → triggers sliding of contractile proteins inside muscle fibre.
• Proteins change shape/arrangement ⇒ fibre shortens ⇒ movement.
• Voluntary muscles (skeletal) vs involuntary (smooth, cardiac) correspond to whether brain control is conscious.

Plant Coordination – With No Nerves or Muscles

• Plants still perceive & respond to stimuli; two movement classes:
  1. Nastic/Immediate (independent of growth).
  2. Tropic/Growth-dependent.

Immediate Response (Nastic) – Mimosa pudica Example

• Touch leaves ⇒ rapid folding & drooping.
• Mechanism:
  • Electrical-chemical message travels cell-to-cell (no specialised nerves).
  • Motor cells at pulvinus lose water (turgor) → shrinkage → leaflet closure.

Directional Growth Movements (Tropism)

• Thigmotropism: tendrils coil around support; contact side grows slower → curvature.
• Phototropism: shoots bend toward light (+ve); roots bend away (–ve).
• Geotropism: roots grow downward (+ve), shoots upward (–ve) [Fig. 6.6].
• Hydrotropism: roots grow toward water.
• Chemotropism: pollen tube growth toward ovule.

Activity 6.2 (Phototropism Demonstration)

• Germinated bean seeds on mesh over water inside box with one open side.
• Shoots curve toward light; roots away.
• Rotating flask reverses direction in new growth only ⇒ stimulus affects zones of active growth.

Why Chemical Communication is Favoured in Plants

• Electrical impulse approach is limited to few cells & cannot be continuous.
• Hormonal diffusion reaches all growing cells, though slower.

Major Plant Hormones

• Auxins: synthesised at shoot tip; diffuse to shady side → cell elongation → bending toward light; also mediate tendril coiling.
• Gibberellins: stem elongation.
• Cytokinins: promote cell division; high in fruits & seeds.
• Abscisic Acid (ABA): inhibits growth, induces dormancy, leaf wilting.

Hormonal Coordination in Animals – The Endocrine System

• Complements nervous system, especially for wide-spread, longer-lasting effects.
• Hormones secreted by ductless glands → directly into blood.

Adrenaline & the ‘Fight-or-Flight’ Response

• Secreted by adrenal medulla during stress/fear.
• Effects:
  • ↑ heart rate ⇒ more \text{O}_2 supply.
  • Vasoconstriction in gut/skin ⇒ blood diverted to skeletal muscles.
  • ↑ breathing rate via diaphragm & rib-muscle contractions.
  • Overall: prepares body for rapid action (fight/run).

Key Endocrine Glands, Hormones & Functions (Table 6.1 completed)

• Hypothalamus: releasing hormones; ex: Growth Hormone Releasing Factor stimulates pituitary.
• Pituitary (master gland):
  • Growth Hormone (GH) – overall growth; deficiency → dwarfism, excess → gigantism.
• Thyroid:
  • Thyroxin – regulates carbohydrate, protein & fat metabolism; needs iodine (iodised salt prevents goitre).
• Pancreas (Islets of Langerhans):
  • Insulin – lowers blood glucose; deficiency → diabetes mellitus (treated with insulin injections).
• Adrenal (above kidneys):
  • Adrenaline (see above).
• Testes (male):
  • Testosterone – secondary sexual characters, sperm production.
• Ovaries (female):
  • Oestrogen & Progesterone – development of female sex organs, menstrual cycle, secondary sexual traits.

Feedback Regulation Example

• Rising blood glucose → pancreatic \beta-cells secrete more insulin → glucose uptake/storage ↑ → glucose levels fall → insulin output reduced.

Comparative Themes & Implications

• Nervous impulses: very fast, short-lived, cell-to-cell, need synaptic resets.
• Hormones: slower, long-lasting, broadcast via blood/diffusion, reach almost all cells.
• Organisms integrate both systems for optimal survival.

Ethical & Practical Notes

• Public-health policy mandates iodised salt to prevent thyroid disorders.
• Insulin therapy for diabetes underscores equitable access to hormone replacement.
• Understanding plant hormones drives agricultural practices (e.g., rooting powders with auxin, gibberellin sprays for fruit size).

Sample Study/Exam Questions Mentioned in Text

• Define reflex action vs walking; mechanism of synapse; role of cerebellum.
• Plant hormones & demonstrations of tropisms (design a hydrotropism experiment).
• Explain adrenaline pathway; compare nervous vs hormonal control; movement in Mimosa vs human limb.
• Draw neuron; list endocrine glands.

Numerical & Sectional References

• Chapter 6, pages 100\text{–}112 (NCERT reprint 2025\text{–}26).
• Sections: 6.1 (Animals – Nervous System), 6.2 (Coordination in Plants), 6.3 (Hormones in Animals).