Chapter Overview & Weightage
Control and Coordination is one of the most important chapters in CBSE Class 10 Science (Biology). It covers how plants and animals detect environmental stimuli and coordinate responses — from the nervous system in animals to hormones and tropisms in plants.
This chapter carries 8–10 marks in CBSE Class 10 board exams. Typically: 1 MCQ + 1 assertion-reason + 1 short answer (difference between reflex and voluntary action) + 1 diagram question (neuron or reflex arc) + 1 long answer on hormones or plant movements. Board toppers always prepare diagrams well — they earn 2–3 marks reliably.
| Year | Marks | Common Questions |
|---|---|---|
| 2024 | 9 | Reflex arc diagram, difference between hormones and nerves |
| 2023 | 10 | Neuron diagram, tropic movements, endocrine glands |
| 2022 | 8 | Brain structure, plant hormones, iodine deficiency |
| 2021 | 9 | Reflex arc, auxin, feedback mechanism |
Key Concepts You Must Know
1. Nervous System in Animals:
- Neurons are structural and functional units of the nervous system
- Reflex arc: Receptor → Sensory neuron → Spinal cord → Motor neuron → Effector
- Reflex action: Involuntary, rapid, controlled by spinal cord
- Voluntary action: Controlled by brain (cerebrum)
- Brain regions: Cerebrum (thinking), Cerebellum (balance), Medulla (autonomic functions)
2. Chemical Coordination — Hormones:
- Secreted by endocrine glands, travel through blood
- Slower but longer-lasting than nerve impulses
- Key hormones: Insulin (glucose regulation), Thyroxine (metabolism), Adrenaline (emergency), Growth hormone, Testosterone, Oestrogen
3. Plant Movements (Tropic Movements):
- Phototropism: Growth response to light (shoots = positive, roots = negative)
- Geotropism: Growth response to gravity (roots = positive, shoots = negative)
- Chemotropism: Growth response to chemicals (pollen tube towards ovule)
- Hydrotropism: Growth response to water
- Thigmotropism: Response to touch (tendrils)
4. Plant Hormones:
- Auxin: Produced at shoot tip, causes cell elongation, explains phototropism
- Gibberellin: Promotes stem elongation and seed germination
- Cytokinin: Promotes cell division and delays ageing
- Abscisic acid (ABA): Inhibits growth, promotes dormancy (“stress hormone”)
- Ethylene: Promotes fruit ripening
Important Formulas
Tropic movements (growth-based, directional):
- Phototropism, Geotropism, Chemotropism, Hydrotropism, Thigmotropism
Nastic movements (not directional, independent of stimulus direction):
- Thermonasty, Seismonasty (Mimosa pudica — touch-me-not)
| Feature | Nervous System | Hormones |
|---|---|---|
| Medium | Electrical impulses | Chemical (blood) |
| Speed | Fast (100–150 m/s) | Slow |
| Duration | Short-lived | Longer-lasting |
| Target | Specific (nerve connects) | Broad (reaches via blood) |
Solved Previous Year Questions
PYQ 1 — Draw and Label a Neuron (CBSE 2023, 3 marks)
Key parts to label:
- Cell body (Soma): Contains nucleus, cytoplasm
- Dendrites: Short branched projections; receive impulses
- Axon: Long fibre; transmits impulse away from cell body
- Myelin sheath: Insulating layer (absent in some neurons)
- Nodes of Ranvier: Gaps in myelin sheath
- Axon terminals (Synaptic knobs): Release neurotransmitters
Always draw dendrites as branched (multiple short branches) and axon as a single long straight fibre. CBSE deducts marks for swapping these.
PYQ 2 — How does auxin explain phototropism? (2 marks)
Answer: Auxin is produced at the shoot tip. When light falls on one side, auxin migrates to the shaded side (away from light). Higher auxin concentration on the shaded side causes more cell elongation there, making the shoot bend toward the light.
This is why shoots are positively phototropic — they grow toward the light source.
PYQ 3 — What is a reflex action? Explain with an example (3 marks)
Answer: A reflex action is an involuntary, rapid, automatic response to a stimulus, controlled by the spinal cord without involvement of the brain.
Example: Withdrawing hand from a hot object.
- Heat receptor in skin (receptor) detects stimulus
- Sensory neuron carries impulse to spinal cord
- Relay neuron in spinal cord processes it
- Motor neuron carries impulse to muscles
- Arm muscles (effector) contract, withdrawing the hand
This entire sequence takes milliseconds — the brain only becomes aware of the pain after the hand has already been withdrawn.
Difficulty Distribution
| Difficulty | Topics | Approximate % |
|---|---|---|
| Easy | Plant tropisms, hormone names and functions | 35% |
| Medium | Neuron diagram, reflex arc, differences | 45% |
| Hard | Mechanism of nerve impulse, feedback loops | 20% |
Expert Strategy
Master the diagrams. Three diagrams are exam staples: neuron, reflex arc, and human brain. Practice drawing these until you can reproduce them in under 3 minutes with all labels.
Use tables for differences. “Difference between nervous and hormonal coordination” is a perennial 3-mark question. A neat 3-row table earns full marks faster than paragraph prose.
Plant hormones: use a mnemonic. “AGCEt” — Auxin, Gibberellin, Cytokinin, Ethylene, abscisic acid (t). Associate each with its primary function.
“Adrenaline — the emergency hormone” is a phrase that appears verbatim in NCERT. Write it exactly: “Adrenaline is secreted by the adrenal glands and prepares the body for ‘fight or flight’ response.” Board papers use this language.
Common Traps
Trap 1: Saying the brain controls all actions. Reflex actions are controlled by the spinal cord, not the brain. Many students write “brain controls reflex actions” — this is incorrect and costs marks. The brain is informed of the reflex after it occurs.
Trap 2: Confusing auxin’s effect on shoots vs roots. Auxin at the same concentration promotes elongation in shoot cells but inhibits elongation in root cells. This concentration sensitivity explains geotropism: more auxin on the lower side promotes shoot growth (bending upward) but inhibits root growth (bending downward toward gravity).
Trap 3: Saying hormones travel through nerves. Hormones travel through blood (circulatory system), not through nerves. Nerve impulses travel through neurons. These are two completely separate systems.
Trap 4: Seismonasty vs Thigmotropism for Mimosa. The folding of Mimosa pudica (touch-me-not) leaves is seismonasty (nastic movement), NOT thigmotropism. Thigmotropism is the growth of tendrils around a support — a permanent directional growth response.