Class 10 Science Notes — Chapter 6: Control and Coordination
Nervous and hormonal control in animals; plant movements and hormones.
Detailed NCERT notes
- Control and coordination in animals: nervous system + endocrine system.
- Neuron structure: dendrites → cell body → axon → axon terminals. Impulse travels dendrite→axon; passes to next neuron via synapse (chemical/neurotransmitter).
- Types of neurons: sensory (receptor→CNS), motor (CNS→effector), interneurons (within CNS).
- Reflex action: quick, automatic response — path: receptor → sensory neuron → spinal cord → motor neuron → effector (this is the reflex arc). No conscious thought needed → faster than voluntary action.
- Central Nervous System: brain + spinal cord. Brain regions: forebrain (thinking, memory, voluntary actions, hunger, sensory perception), midbrain (involuntary — pupil, reflexes to sound), hindbrain (cerebellum for balance, medulla for involuntary — heartbeat, breathing, pons).
- Peripheral Nervous System: cranial + spinal nerves; autonomic nervous system (sympathetic — fight/flight; parasympathetic — rest).
- Voluntary actions controlled by forebrain; involuntary by midbrain/hindbrain; reflex by spinal cord.
- Endocrine system: ductless glands secreting hormones directly into blood.
- Pituitary — 'master gland' — growth hormone (deficiency: dwarfism, excess: gigantism).
- Thyroid — thyroxine — regulates metabolism; needs iodine (deficiency: goitre).
- Adrenal — adrenaline — fight/flight response.
- Pancreas — insulin — controls blood sugar (deficiency: diabetes).
- Testes — testosterone; Ovaries — oestrogen; secondary sexual characters.
- Feedback mechanism: high blood sugar → pancreas releases insulin → glucose stored → sugar falls → insulin release stops.
- Plant control: no nervous system; controlled by chemical (hormones) and by growth movement (tropisms).
- Tropic movements (growth-dependent, directional): phototropism (toward light), geotropism (toward/against gravity), hydrotropism (toward water), chemotropism (toward chemicals, e.g., pollen tube to ovule), thigmotropism (touch, e.g., tendrils).
- Nastic movements (non-directional, quick): folding of Mimosa leaves on touch — due to change in turgor pressure.
- Plant hormones:
- Auxin — cell elongation, phototropism (moves to shaded side).
- Gibberellin — stem elongation.
- Cytokinin — cell division, delays ageing (found in fruits, seeds).
- Abscisic acid (ABA) — inhibitor; causes wilting, closes stomata (stress hormone).
- Ethylene — gaseous hormone; ripens fruits.
Formulas & key results
- Reflex arc: receptor → sensory neuron → spinal cord → motor neuron → effector
- Feedback: hormone → target effect → feedback stops secretion
Mind map
- Nervous (CNS + PNS + ANS) + Endocrine
- Reflex vs voluntary vs involuntary
- Plant: tropic vs nastic; hormones auxin, gibberellin, cytokinin, ABA, ethylene
Tricks & shortcuts
- Auxin bends plant toward light — moves to shaded side.
- Cerebellum = balance; medulla = involuntary essentials.
- Iodine deficiency → goitre.
Common mistakes to avoid
- Confusing tropism types (phototropism vs geotropism).
- Placing adrenaline in the thyroid — it's from adrenal glands.
Competency-based questions & answers
- Q. Why do we not touch a hot object even after realising?A. Reflex action via spinal cord is quicker than conscious control via brain — hand is pulled back before pain is registered.
- Q. How does auxin cause a shoot to bend toward light?A. Auxin migrates to the shaded side, causing cells there to elongate more → shoot bends toward light.
- Q. A person's iodine intake is low. Predict a possible disorder.A. Goitre — thyroid enlarges because it cannot produce enough thyroxine without iodine.