Is it correct to say: Confusing reflex action with voluntary action?

Reflex is UNCONSCIOUS, mediated by the spinal cord — the brain registers pain AFTER the response has already happened.

Is it correct to say: Saying nerve impulses are only electrical?

Impulses are ELECTRICAL along the neuron but CHEMICAL (neurotransmitter) across the synapse.

Is it correct to say: Confusing tropic movements with nastic movements?

TROPIC: directional response to stimulus (phototropism, geotropism). NASTIC: non-directional (touch-me-not folding, Mimosa).

Is it correct to say: Placing 'heartbeat control' in the cerebrum?

Heartbeat, breathing and BP are controlled by the MEDULLA OBLONGATA in the hindbrain.

Is it correct to say: Writing that insulin is secreted by the thyroid?

Insulin is secreted by the PANCREAS (β-cells of the islets of Langerhans). Thyroid secretes THYROXINE.

Is it correct to say: Confusing endocrine and exocrine glands?

ENDOCRINE = ductless, secretes hormone into BLOOD (thyroid, adrenal). EXOCRINE = has ducts, secretes into cavity/surface (salivary, sweat, part of pancreas).

Is it correct to say: Saying plants have a nervous system?

Plants have NO nervous system. Coordination is via PHYTOHORMONES (chemical messengers) and slow growth movements.

Formula sheet (PDF) →

Biology · Chapter 6

Control and Coordination

Nervous system, reflex arc, human brain, animal hormones and phytohormones — NCERT Class 10 Science Ch 6

9 formulas · 3 solved examples · 6 practice questions · Board weight: 5 marks · CBSE Class 10 · 2025–26 syllabus

Board Exam Tips

→Reflex arc pathway with a labelled diagram is a guaranteed 3-mark question — trace ALL 7 stages.
→Structure of a neuron (dendrite → cell body → axon → synapse) is a 3-mark labelling question.
→Endocrine gland → hormone → effect table (any 4 pairs) — recurring 4-mark question.
→Phytohormones table (auxin, gibberellin, cytokinin, ABA, ethylene) with functions.
→Difference between tropic and nastic movements — favourite 2-mark distinction.

Formulas(9)

Reflex Arc PathwayBoard favourite

Stimulus \to Receptor \to Sensory neuron \to Spinal cord \to Motor neuron \to Effector \to Response

Neuron Structure Pathway

Dendrite \to Cell body \to Axon \to Axon terminal \to Synapse

Divisions of the Human Nervous System

Nervous System = CNS (Brain + Spinal Cord) + PNS (Nerves)

Three Parts of the BrainBoard favourite

Brain = Forebrain + Midbrain + Hindbrain

Adrenaline (Stress Hormone)Board favourite

Adrenaline (epinephrine): C_{9} H_{13} N O_{3}

Insulin (Blood-Sugar Regulator)

Insulin: peptide, 51 amino acids, \sim 5.8 kDa

Thyroxine (Metabolism Hormone)

Thyroxine (T_{4}): C_{15} H_{11} I_{4} N O_{4}

Auxin Redistribution (Phototropism)

Light \Rightarrow auxin migrates to shaded side \Rightarrow cells elongate \Rightarrow shoot bends towards light

Feedback Control of Hormones

↑ Hormone \to target effect \to↓ gland activity (negative feedback)

Solved Examples

1Solved Exampleeasy3 steps

Define reflex action. Draw a labelled reflex arc showing what happens when you touch a hot object.

Definition: reflex action is a quick, involuntary and automatic response of the body to a stimulus, coordinated by the SPINAL CORD (not the brain).

2Solved Exampleboard6 steps

Trace the reflex arc pathway when a doctor taps your knee with a rubber hammer (knee-jerk reflex). Name the neurons involved and explain why this is called a 'monosynaptic' reflex.

STIMULUS: sudden stretch of the quadriceps tendon by the hammer tap.

3Solved ExampleHOTS5 steps

Match each endocrine gland with its hormone and effect. State the disease caused by (a) deficiency of insulin and (b) deficiency of iodine.

PITUITARY → Growth Hormone → body growth. Excess in childhood → gigantism; deficiency → dwarfism.

Traps & Common Mistakes

Common Mistakes7

1
Confusing reflex action with voluntary action
✓Reflex is UNCONSCIOUS, mediated by the spinal cord — the brain registers pain AFTER the response has already happened.
2
Saying nerve impulses are only electrical
✓Impulses are ELECTRICAL along the neuron but CHEMICAL (neurotransmitter) across the synapse.
3
Confusing tropic movements with nastic movements
✓TROPIC: directional response to stimulus (phototropism, geotropism). NASTIC: non-directional (touch-me-not folding, Mimosa).
4
Placing 'heartbeat control' in the cerebrum
✓Heartbeat, breathing and BP are controlled by the MEDULLA OBLONGATA in the hindbrain.
5
Writing that insulin is secreted by the thyroid
✓Insulin is secreted by the PANCREAS (β-cells of the islets of Langerhans). Thyroid secretes THYROXINE.
6
Confusing endocrine and exocrine glands
✓ENDOCRINE = ductless, secretes hormone into BLOOD (thyroid, adrenal). EXOCRINE = has ducts, secretes into cavity/surface (salivary, sweat, part of pancreas).
7
Saying plants have a nervous system
✓Plants have NO nervous system. Coordination is via PHYTOHORMONES (chemical messengers) and slow growth movements.

Practice Yourself

Practice Yourself6 questions

Q1
Name the endocrine gland and hormone that regulates blood-sugar level. State the disease caused by its deficiency.
Q2
State two differences between the nervous and endocrine systems.
Q3
Which part of the brain maintains posture and balance? Give one symptom of its damage.
Q4
Name the plant hormone that (a) promotes cell division, (b) inhibits growth and closes stomata, (c) causes stem elongation, (d) ripens fruit.
Q5
Give one example each of chemotropism, hydrotropism and geotropism.
Q6
Which hormone is called the 'emergency hormone' and what changes does it produce in the body?

Notes

Control and Coordination

Multicellular animals need to coordinate their body parts. They use two overlapping systems:

Nervous system — fast, electrochemical, short-lived, precisely targeted.
Endocrine (hormonal) system — slow, chemical (via blood), long-lasting.

Plants have NO nervous system — they rely only on chemical messengers called phytohormones and slow growth movements.

Nervous system — components

CNS = Brain + Spinal cord (integrates and decides).
PNS = Cranial + spinal nerves (carries signals in and out).
Neuron = dendrite → cell body → axon → synapse. Signal is electrical along the axon and chemical across the synapse (via neurotransmitter such as acetylcholine).

Reflex arc

Fast, automatic, does NOT need the brain.
Path: Stimulus → Receptor → Sensory neuron → Spinal cord → Motor neuron → Effector → Response.
Evolutionary advantage: cuts reaction time by ~0.2 s — critical for survival.

Human brain

Region	Key jobs
Forebrain (cerebrum)	Thinking, memory, senses, voluntary action
Midbrain	Visual + auditory reflexes
Cerebellum (hindbrain)	Balance and posture
Medulla oblongata (hindbrain)	Heartbeat, breathing, BP, vomiting
Pons (hindbrain)	Bridge; coordinates breathing depth

Endocrine glands, hormones and effects

Gland	Hormone	Chemical class	Effect
Pituitary	Growth hormone (GH)	Peptide	Body growth
Thyroid	Thyroxine (T₄)	Iodine-containing	Metabolism
Pancreas (β-cells)	Insulin	Peptide (51 aa)	Lowers blood sugar
Adrenal medulla	Adrenaline	C₉H₁₃NO₃	Fight-or-flight
Testis	Testosterone	Steroid	Male secondary characters
Ovary	Oestrogen, progesterone	Steroid	Female secondary characters, pregnancy

Plant hormones — the big five

Auxin (IAA) — cell elongation, phototropism (shoot tip).
Gibberellin — stem elongation, seed germination.
Cytokinin — cell division, delays senescence.
Abscisic acid (ABA) — stress hormone; closes stomata; inhibits growth.
Ethylene (C₂H₄) — fruit ripening.

Tropic vs nastic movements

Tropic — directional growth response to a stimulus (phototropism, geotropism, hydrotropism, chemotropism, thigmotropism).
Nastic — non-directional response (Mimosa 'touch-me-not' folding, sunflower opening at dawn).

Quick sanity checks

Reflex saves ~0.1-0.3 s of reaction time — brain does NOT process it.
Negative feedback keeps hormone levels balanced: high thyroxine → low TSH → thyroid slows.
Phototropism → auxin shifts to shaded side of the shoot tip.