Control and Coordination Class 10 Notes (2026-27) — CBSE
Class 10 Science Chapter 6 notes: the neuron and nervous system, reflex action, the human brain, tropic movements and plant hormones, and animal hormones.
Control and Coordination — Class 10 Science Notes
Chapter Snapshot
Living things respond to changes around them (stimuli). In animals this is done by the nervous system and hormones; in plants by hormones alone (they have no nervous system). This chapter covers the neuron, reflex action, the human brain, the tropic movements and hormones of plants, and the endocrine hormones of animals.
Board relevance: commonly gives a neuron or reflex-arc diagram question and a hormones question (plant or animal). Learn the neuron parts and the gland–hormone–function table.
Key Concepts & Definitions
Stimulus — a change in the environment that produces a response.
Neuron (nerve cell) — the structural and functional unit of the nervous system. Parts:
- Dendrites — receive the impulse (information).
- Cell body (cyton) — contains the nucleus; processes the signal.
- Axon — a long fibre that carries the impulse away.
- Synapse — the tiny gap between two neurons; the impulse crosses it as a chemical signal (neurotransmitter).
A nerve impulse travels: dendrite → cell body → axon → synapse → next neuron.
Types of neurons: sensory (carry impulse from receptor to CNS), motor (CNS to muscle/effector), and relay/interneuron (within the CNS).
Reflex Action and the Reflex Arc
Reflex action — a sudden, automatic response to a stimulus, without conscious thought (e.g. withdrawing the hand from a hot object, blinking, sneezing). It is fast because it does not wait for the brain to decide.
Reflex arc — the pathway a reflex takes: receptor → sensory neuron → spinal cord → motor neuron → effector (muscle). The spinal cord processes reflexes, though the information also reaches the brain afterwards. Reflex arcs let animals respond quickly and protect the body from harm.
The Human Brain and Spinal Cord
The brain and spinal cord form the central nervous system (CNS); nerves outside them form the peripheral nervous system. The brain has three main regions:
Region Part Function
Forebrain Cerebrum Thinking, memory, reasoning, voluntary actions; receives sensory impulses
Midbrain — Reflex movements of the head, neck, and eyes
Hindbrain Cerebellum Balance, posture, precision of voluntary movement
Hindbrain Medulla oblongata Involuntary actions — heartbeat, breathing, blood pressure, vomiting
Hindbrain Pons Regulates breathing
The brain is protected by the skull and a fluid-filled cushion; the spinal cord runs inside the vertebral column and connects the brain to body nerves.
Coordination in Plants
Plants have no nervous system; they coordinate using hormones and show two kinds of movement:
1. Tropic (directional) movements — growth towards or away from a stimulus:
Tropism Stimulus Example
Phototropism Light Shoots grow towards light (positive), roots away (negative)
Geotropism Gravity Roots grow downward (positive), shoots upward (negative)
Hydrotropism Water Roots grow towards water
Chemotropism Chemicals Pollen tube grows towards the ovule
Thigmotropism Touch Tendrils coil around a support
2. Nastic (non-directional) movements — independent of the direction of the stimulus, e.g. the leaves of the touch-me-not (Mimosa) folding when touched (caused by water movement in cells, not growth).
Plant hormones (phytohormones):
Hormone Function
Auxin Promotes cell elongation; responsible for phototropism (accumulates on the shaded side)
Gibberellin Promotes stem growth
Cytokinin Promotes cell division (rich in fruits and seeds)
Abscisic acid (ABA) Inhibits growth; causes wilting and closing of stomata (a stress hormone)
Hormones in Animals (Endocrine System)
Hormones are chemical messengers secreted by endocrine glands directly into the blood, acting on specific target organs. They act more slowly than nerves but have longer-lasting effects.
Gland Hormone Function / deficiency
Adrenal Adrenaline "Fight-or-flight" — raises heartbeat, breathing, blood sugar in emergencies
Thyroid Thyroxine Regulates metabolism; needs iodine; deficiency → goitre
Pancreas Insulin Lowers blood sugar; deficiency → diabetes
Pituitary Growth hormone Controls body growth; deficiency → dwarfism, excess → gigantism
Testis Testosterone Male secondary sexual characters
Ovary Oestrogen Female secondary sexual characters
Feedback mechanism: hormone levels are self-regulated. For example, when blood sugar rises, the pancreas releases more insulin; when sugar falls, insulin release decreases. This keeps levels within a healthy range.
Key Facts
Quick facts boards ask directly:
Topic Fact to remember
Unit of the nervous system Neuron
Gap between two neurons Synapse
Reflex processed by Spinal cord
Thinking, memory Cerebrum
Balance and posture Cerebellum
Heartbeat, breathing Medulla oblongata
Bends shoot towards light Auxin (phototropism)
Promotes cell division Cytokinin
Closes stomata (stress) Abscisic acid
Fight-or-flight hormone Adrenaline (adrenal gland)
Needs iodine; deficiency → goitre Thyroxine (thyroid)
Controls blood sugar; deficiency → diabetes Insulin (pancreas)
Growth hormone gland Pituitary
Male / female sex hormone Testosterone / oestrogen
Two definitions to quote: Reflex arc — the nerve pathway (receptor → sensory neuron → spinal cord → motor neuron → effector) followed during a reflex action. Tropism — a directional growth movement of a plant in response to a stimulus.
Important Question Patterns
1. Neuron/nerve impulse (2–3 marks): label a neuron; describe how an impulse travels; what a synapse does.
2. Reflex action (3 marks): define reflex action; draw and label the reflex arc; why reflexes are faster than conscious responses.
3. Human brain (2–3 marks): functions of cerebrum, cerebellum, and medulla; which part controls a given activity.
4. Plant coordination (2–3 marks): tropic vs nastic movement; match tropism to stimulus; functions of auxin/gibberellin/cytokinin/ABA; the auxin explanation of phototropism.
5. Animal hormones (2–3 marks): match gland–hormone–function; deficiency diseases (goitre, diabetes); role of adrenaline; feedback control.
⚡ Quick Revision
- Neuron: dendrite (receive) → cell body → axon (carry away) → synapse (chemical gap). Types: sensory, motor, relay.
- Reflex arc: receptor → sensory neuron → spinal cord → motor neuron → effector. Fast, automatic, protective.
- Brain: cerebrum (thinking, voluntary), cerebellum (balance/posture), medulla (involuntary — heartbeat, breathing).
- Plant tropisms: photo (light), geo (gravity), hydro (water), chemo (chemicals), thigmo (touch). Nastic = non-directional (Mimosa).
- Plant hormones: auxin (elongation, phototropism), gibberellin (stem growth), cytokinin (cell division), abscisic acid (inhibitor, closes stomata).
- Animal hormones: adrenaline (adrenal, fight-or-flight), thyroxine (thyroid, needs iodine, deficiency → goitre), insulin (pancreas, deficiency → diabetes), growth hormone (pituitary), testosterone/oestrogen.
- Hormones = chemical messengers via blood; regulated by feedback.
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