Comprehensive Solved Examples for Chapter 6
Board-focused examples covering all topics — from neurons to hormonal disorders.
Example 1: NCERT — What is Control and Coordination?
Define control and coordination. Why is it essential for living organisms?
Solution:
'Control and coordination' = the life process by which an organism senses changes in its environment (stimuli) and produces appropriate responses.
Why Essential: 1. Survival — detect predators, find food, escape danger. 2. Movement — coordinated muscle action. 3. Internal balance (homeostasis) — temperature, blood sugar regulation. 4. Growth & development — hormones control proper growth. 5. Reproduction — coordinate reproductive cycle.
Two systems work together: 1. Nervous system (fast, electrical, brief). 2. Endocrine system (slow, chemical, long-lasting).
[NCERT — fundamental]
Example 2: NCERT — Neuron Structure
Draw a labelled diagram of a neuron and explain its parts.
Solution:
4 Main Parts of a Neuron
Dendrites (input)
|
Cell Body (cyton)
|
━━━ Axon (with myelin sheath)
|
Axon Terminals (output)
1. Cell Body (Cyton): contains nucleus, cytoplasm. Maintains cell life. 2. Dendrites: short branches, receive signals from other neurons. 3. Axon: long fibre, carries signals away from cell body. Often covered with myelin sheath (speeds up signal). 4. Axon Terminals: end branches, transmit signal to next cell via synapse.
Signal direction: Dendrites → Cell body → Axon → Axon terminals.
3 Types of Neurons: 1. Sensory — receptor → CNS. 2. Motor — CNS → effector. 3. Relay/Interneurons — within CNS.
[NCERT — must-know diagram]
Example 3: NCERT — Reflex Arc
Describe reflex action with example. Draw a reflex arc.
Solution:
'Reflex action' = immediate, involuntary, automatic response to a stimulus. Speed: ~0.1 seconds. Bypasses brain (uses spinal cord).
Example: Withdrawing Hand from Hot Pan
Stimulus (hot pan)
↓
Receptor (skin)
↓
Sensory neuron ──→ Spinal cord (Relay neuron)
↓
Motor neuron
↓ ↓
Effector (arm muscle)
↓
Response (hand pulls back)
5 Components of Reflex Arc
1. Receptor — detects stimulus. 2. Sensory neuron — carries signal to CNS. 3. Spinal cord (relay neuron) — processes signal. 4. Motor neuron — carries response from CNS. 5. Effector — muscle/gland performs action.
Why through Spinal Cord? Faster than involving brain (~0.1 sec vs ~0.5 sec). Brain informed AFTER reflex.
Examples: knee-jerk, pupillary reflex, blinking, sneezing, salivation.
[NCERT — Board favourite]
Example 4: NCERT — Parts of Human Brain
Describe the 3 main parts of human brain with their functions.
Solution:
3 Main Parts of Brain
1. Forebrain (Largest): Cerebrum + Thalamus + Hypothalamus. Functions:
- Voluntary movements.
- Sensory processing.
- Thinking, reasoning, memory.
- Emotions, language.
2. Midbrain (Small): Functions:
- Visual reflexes.
- Auditory reflexes.
- Connects forebrain & hindbrain.
3. Hindbrain (3 Parts): a) Cerebellum — balance, coordination, fine motor skills. b) Pons — bridge, regulates breathing. c) Medulla Oblongata — heart rate, breathing, BP, vital reflexes.
Brain Protection
1. Skull (cranium) — bony case. 2. Meninges — 3 membranes. 3. Cerebrospinal fluid (CSF) — shock absorber.
Damage Effects:
- Cerebrum → cognitive problems.
- Cerebellum → balance issues, clumsy movements.
- Medulla → often fatal (heart/breathing stops).
[NCERT — important]
Example 5: NCERT — Tropic Movements
What are tropic movements? Give 3 examples with mechanism.
Solution:
'Tropic movements' = directional growth movements in plants in response to environmental stimuli. Direction depends on stimulus.
3 Examples
1. Phototropism (Light): Stems: positively phototropic (bend toward light). Roots: negatively phototropic. Mechanism: light moves auxin to shaded side → cells there elongate more → stem bends toward light.
2. Geotropism (Gravity): Roots: positively geotropic (grow downward). Stems: negatively geotropic (grow upward). Mechanism: gravity affects auxin distribution; in stems, more auxin → more growth (lower side); in roots, more auxin → less growth.
3. Hydrotropism (Water): Roots: positively hydrotropic (grow toward water). Important in dry conditions for survival.
Other Tropisms
4. Chemotropism — pollen tubes toward chemicals from ovary. 5. Thigmotropism — tendrils wrap around supports.
All driven by hormone auxin.
[NCERT — important]
Example 6: NCERT — Plant Hormones
Name the 5 main plant hormones and state their functions.
Solution:
| Hormone | Main Function | Example/Use |
|---|---|---|
| Auxin | Cell elongation, phototropism | Rooting in cuttings |
| Gibberellin | Stem elongation, germination | Bigger grapes |
| Cytokinin | Cell division, fruit growth | Tissue culture |
| Abscisic Acid | Inhibitor, closes stomata | Drought response |
| Ethylene | Fruit ripening (gas) | Banana ripening |
Detailed Functions
Auxin: Made in stem tips. Causes phototropism (bending toward light), apical dominance, root formation.
Gibberellin: Promotes stem elongation, seed germination, fruit growth.
Cytokinin: Made in roots. Promotes cell division, growth in fruits, delays leaf ageing.
Abscisic Acid (ABA) — 'stress hormone': Inhibits growth, closes stomata in drought, maintains seed dormancy.
Ethylene (gas): Promotes fruit ripening. Why fruits ripen faster when stored together!
All hormones are produced in TINY amounts but have BIG effects.
[NCERT — important]
Example 7: NCERT — Hormones vs Nervous System
Differentiate between nervous and hormonal coordination.
Solution:
Comparison Table
| Feature | Nervous | Hormonal |
|---|---|---|
| Signal | Electrical | Chemical (hormones) |
| Path | Neurons (nerves) | Blood |
| Speed | Very fast (ms) | Slow (min-days) |
| Duration | Brief | Long-lasting |
| Targets | Specific muscles | Target cells (with receptors) |
| Examples | Reflexes, voluntary movement | Growth, metabolism |
When Each is Used
Nervous System: 1. Quick reflexes (touch, pain). 2. Voluntary movements. 3. Senses.
Hormonal System: 1. Growth (over years). 2. Metabolism. 3. Reproduction. 4. Stress response (cortisol).
Both Work Together
Example: Stress response (fight or flight): 1. Nervous: brain detects danger → fast reaction. 2. Hormonal: adrenaline release → sustained body changes.
Together: comprehensive coordination.
Plants only have hormonal system — no nervous system.
[NCERT — comparison important]
Example 8: NCERT — Pituitary Gland
Why is pituitary called the 'master gland'? Name 3 hormones it produces.
Solution:
Why 'Master Gland'?
Pituitary controls many other endocrine glands: 1. Tells thyroid → produce thyroxine (via TSH). 2. Tells adrenal → produce cortisol (via ACTH). 3. Tells gonads → produce sex hormones (via FSH, LH). 4. Controls growth (via GH). 5. Controls water balance (via ADH).
Hence 'master gland'.
Note: pituitary itself controlled by hypothalamus (in brain).
3 Important Hormones
1. Growth Hormone (GH): Regulates body growth. Acts on bones, muscles. Disorders: dwarfism (low) / gigantism (excess).
2. Thyroid Stimulating Hormone (TSH): Tells thyroid to make thyroxine. Indirectly controls metabolism.
3. Anti-Diuretic Hormone (ADH): Acts on kidneys. Regulates water reabsorption. Low ADH → diabetes insipidus.
Other Hormones
4. FSH, LH — reproduction. 5. Prolactin — milk production. 6. Oxytocin — childbirth, milk ejection.
[NCERT — Board favourite]
Example 9: Application — Iodine and Goitre
Why is iodine important? What is goitre and how can it be prevented?
Solution:
Why Iodine is Important
Iodine is required for thyroxine production. Thyroxine = hormone from thyroid gland. Functions: 1. Regulates body metabolism. 2. Body heat production. 3. Brain development (children). 4. Heart rate. 5. Growth.
Without iodine → no thyroxine → many problems!
Goitre
'Goitre' = enlarged thyroid gland.
Mechanism: 1. Diet has insufficient iodine. 2. Thyroid can't make thyroxine. 3. Pituitary detects low thyroxine. 4. Releases more TSH. 5. TSH stimulates thyroid → tries harder. 6. Thyroid grows larger (still can't make thyroxine without iodine). 7. Result: visible neck swelling = goitre.
Prevention: Iodised Salt
Indian government adds iodine to common salt. Mandatory in all packaged salt. Successful public health intervention.
Other sources: seafood, eggs, dairy.
Children's Risk
Severe iodine deficiency in children = cretinism (stunted growth, mental retardation, permanent damage).
Hence iodised salt critical for child health.
[Application — Real life]
Example 10: NCERT — Diabetes
What is diabetes mellitus? Distinguish between Type 1 and Type 2.
Solution:
Diabetes Mellitus
'Diabetes mellitus' = condition of high blood sugar due to insulin problems.
Symptoms: 1. Frequent urination (polyuria). 2. Excessive thirst (polydipsia). 3. Excessive hunger (polyphagia). 4. Weight loss. 5. Fatigue. 6. Glucose in urine.
Type 1 vs Type 2
| Feature | Type 1 | Type 2 |
|---|---|---|
| Cause | Pancreas can't make insulin | Cells don't respond to insulin |
| Onset | Usually children | Usually adults |
| Treatment | Insulin injections (lifelong) | Diet, exercise, medications |
| Frequency | Less common (~5-10%) | Most common (~90%) |
Long-term Complications
1. Heart disease. 2. Kidney damage. 3. Eye damage (blindness). 4. Nerve damage. 5. Foot problems.
Prevention (Type 2)
1. Healthy diet (less sugar). 2. Regular exercise. 3. Maintain healthy weight. 4. Don't smoke. 5. Manage stress. 6. Regular check-ups.
India's Crisis
~10 crore Indians have diabetes (rising). India = 'diabetes capital of the world'.
[NCERT — Real life]
Example 11: NCERT — Adrenaline
What is adrenaline? Describe its effects.
Solution:
Adrenaline
'Adrenaline' (or epinephrine) = hormone from adrenal medulla. Released during stress, danger, exercise, excitement. 'Fight or flight' hormone.
Effects on Body
1. Heart rate increases — pumps more blood. 2. Blood pressure rises. 3. Pupils dilate — better vision. 4. Breathing speeds up — more O₂. 5. Liver releases glucose — energy for muscles. 6. Blood diverts to muscles (away from gut). 7. Sweating — body cools. 8. Slows digestion. 9. Goosebumps.
Why Useful
Evolutionary survival tool. Helps respond to danger:
- Fight (defend self).
- Flight (run away).
- Freeze (sometimes).
Modern Problem: Chronic Stress
Constant adrenaline = harmful. Effects: 1. High BP. 2. Heart disease. 3. Anxiety. 4. Sleep problems.
Solution: stress management (yoga, meditation, exercise).
Medical Use
Synthetic adrenaline (EpiPen) — saves lives in: 1. Anaphylactic shock (severe allergy). 2. Cardiac arrest.
[Application — JEE/NEET]
Example 12: NCERT — Insulin
What is insulin? Why is it important?
Solution:
Insulin
'Insulin' = hormone produced by beta cells of pancreas. Function: lowers blood glucose.
How It Works
After eating: 1. Food digested → glucose enters blood. 2. Blood sugar rises. 3. Pancreas detects high sugar. 4. Releases insulin. 5. Insulin acts on:
- Liver: stores glucose as glycogen.
- Muscles: take up glucose.
- Fat cells: store glucose as fat. 6. Blood sugar normalises.
Why Important
Without insulin: 1. Glucose stays in blood (high blood sugar). 2. Cells can't get energy. 3. Body breaks down fats/proteins instead. 4. Result: diabetes.
Discovered
1921 — by Banting and Best. Saved millions of lives. Before insulin: type 1 diabetes was a death sentence.
Treatment of Type 1 Diabetes
Injections of synthetic insulin. Multiple times daily. Lifelong. Now also: insulin pumps.
Glucagon — The Opposite
Pancreas also produces glucagon. Raises blood sugar (when low). Together with insulin → maintains balance.
Example of negative feedback in action.
[NCERT — important]
Example 13: NCERT — Negative Feedback
What is negative feedback? Explain with blood sugar example.
Solution:
Negative Feedback
'Negative feedback' = a self-regulating mechanism where the output of a system reduces its own input. Maintains balance and stability.
Like a thermostat: room hot → AC on → cools → AC off.
Blood Sugar Regulation Example
When Blood Sugar Rises (after meal):
1. Eat → glucose enters blood. 2. Pancreas detects high sugar. 3. Pancreas releases insulin. 4. Insulin makes cells take up glucose. 5. Blood sugar drops to normal. 6. Negative feedback: pancreas detects normal sugar → stops insulin release.
When Blood Sugar Falls (between meals):
1. Pancreas detects low sugar. 2. Releases glucagon. 3. Glucagon → liver releases stored glucose. 4. Blood sugar rises to normal. 5. Negative feedback: pancreas stops glucagon release.
Insulin and Glucagon Together
| Stimulus | Hormone | Effect |
|---|---|---|
| High sugar | Insulin | Lowers sugar |
| Low sugar | Glucagon | Raises sugar |
Like two opposing forces maintaining balance.
Why Important
Without negative feedback: 1. Hormones would go too high or too low. 2. Body chemistry chaotic. 3. Diseases would result.
With it: stability + health.
Most body systems use negative feedback.
[NCERT — important concept]
Example 14: Application — Real-life Coordination
When you suddenly see a snake on the path, what happens in your body? Explain the coordination.
Solution:
Phase 1: Detection (Nervous - Milliseconds)
1. Eyes detect snake (photoreceptors). 2. Signal → brain. 3. Brain processes — recognises 'snake' as danger. 4. Brain activates muscles — ready to react.
Time: ~0.1 seconds.
Phase 2: Hormonal Response (Seconds-Minutes)
Brain signals adrenal glands → release adrenaline.
Effects: 1. Heart rate increases. 2. Pupils dilate. 3. Breathing speeds up. 4. Liver releases glucose for energy. 5. Blood diverts to muscles. 6. Sweating begins. 7. Digestion stops.
Time: starts in seconds, peaks at 1-2 minutes.
Phase 3: Action
Now ready to: 1. Run (flight) — most common. 2. Fight (if cornered). 3. Freeze (sometimes).
This is the famous 'fight or flight' response.
Phase 4: Recovery (After Danger)
1. Brain calms. 2. Adrenaline breaks down. 3. Heart rate normalises. 4. Body returns to baseline.
Time: 15-30 minutes.
Coordination Involved
Nervous System: 1. Detect danger. 2. Decide to act. 3. Activate muscles.
Hormonal System: 1. Release adrenaline. 2. Long-term effects.
Both Together: 1. Fast initial reaction (nervous). 2. Sustained body changes (hormonal). 3. Returning to normal (both).
Why Useful?
Evolution gave us this response for survival. Modern uses: sports, public speaking, emergencies. Modern problem: chronic stress (constant fight-flight) → harmful.
[Application — JEE/NEET]
Example 15: Synthesis — Comprehensive
(a) Why are reflex actions faster than conscious actions? (b) Compare nervous and endocrine systems. (c) Explain how plants respond to stimuli without nervous system.
Solution:
(a) Reflex vs Conscious — Speed Comparison
Reflex action: ~0.1 seconds. Conscious action: ~0.5-1 seconds.
Reflex (Hot Pan): Skin → sensory neuron → SPINAL CORD → motor neuron → muscle. Bypasses brain. Distance: short. Time: ~0.1 sec.
Conscious (Picking Cup): Eyes → sensory neuron → BRAIN → motor neuron → muscle. Brain decides — takes time. Distance: longer. Time: ~0.5 sec.
Why Faster? 1. Spinal cord closer to body. 2. No 'thinking' required. 3. Pre-programmed responses. 4. Saves brain capacity.
Result: instant protection in emergencies.
(b) Nervous vs Endocrine Systems
| Feature | Nervous | Endocrine |
|---|---|---|
| Signal | Electrical (neurons) | Chemical (hormones) |
| Path | Through neurons | Via blood |
| Speed | Very fast (ms) | Slow (min-days) |
| Duration | Brief | Long-lasting |
| Components | Brain, spinal cord, neurons | Glands, hormones |
| Examples | Reflexes, movement | Growth, metabolism |
Both work together for complete coordination.
(c) Plant Response Without Nervous System
Plants don't have neurons but still respond. How?
Through Hormones: 1. Auxin — for tropisms (light, gravity). 2. Gibberellin — growth, germination. 3. Cytokinin — cell division. 4. Abscisic acid — stress response. 5. Ethylene — fruit ripening.
Mechanism Example: Phototropism 1. Tip senses light. 2. Auxin moves to shaded side. 3. Cells on shaded side elongate more. 4. Stem bends toward light.
Slower But Effective: Plant responses take hours-days (vs animal's milliseconds). But effective for plant lifestyle (stationary, no immediate danger).
Plants also have nastic movements (e.g., Mimosa folding) — fast but not directional.
Final Insight
Nature uses different strategies for different lifestyles: 1. Fast nervous + slow hormonal — animals (mobile). 2. Only hormonal — plants (stationary). 3. Both work — perfectly suited to organism's needs.
[Board: 5-mark synthesis]
Example 16: NCERT — Hormonal Disorders
List 5 hormonal disorders, their causes and symptoms.
Solution:
5 Major Hormonal Disorders
1. Diabetes Mellitus: Cause: Insulin deficiency or resistance. Type 1: Pancreas can't produce insulin. Type 2: Cells don't respond to insulin. Symptoms: high blood sugar, frequent urination, thirst, weight loss, fatigue. Treatment: insulin (Type 1), diet/exercise/medications (Type 2).
2. Goitre: Cause: Iodine deficiency. Mechanism: No iodine → no thyroxine → thyroid enlarges. Symptoms: visible neck swelling, fatigue, weight gain. Prevention: iodised salt.
3. Cretinism: Cause: Severe iodine/thyroxine deficiency in children. Symptoms: stunted growth, mental retardation, permanent damage. Prevention: iodine in pregnancy & childhood.
4. Dwarfism: Cause: Low growth hormone (GH) in childhood. Symptoms: very short stature. Treatment: GH injections during childhood.
5. Hyperthyroidism (Graves' disease): Cause: Excess thyroxine. Symptoms: weight loss, fast heart rate, anxiety, bulging eyes, heat intolerance. Treatment: medication, surgery, radioactive iodine.
Other Disorders
6. Hypothyroidism — low thyroxine: fatigue, weight gain. 7. Gigantism — excess GH (children): very tall. 8. Acromegaly — excess GH (adults): enlarged hands/feet. 9. Diabetes Insipidus — low ADH: excessive urine.
Common Causes Summary
| Cause | Disorders |
|---|---|
| Iodine deficiency | Goitre, cretinism |
| Insulin problem | Diabetes mellitus |
| GH problem | Dwarfism, gigantism, acromegaly |
| Thyroxine excess | Hyperthyroidism |
| Thyroxine low | Hypothyroidism |
| ADH problem | Diabetes insipidus |
Prevention Strategies
1. Iodised salt — prevents goitre, cretinism. 2. Healthy lifestyle — prevents type 2 diabetes. 3. Regular check-ups — early detection. 4. Balanced diet — provides essential nutrients. 5. Exercise — maintains hormone balance.
Why Hormonal Health Matters
Hormones control: 1. Growth. 2. Metabolism. 3. Reproduction. 4. Mood. 5. Stress response.
Imbalance affects everything — diagnosis + treatment critical.
Key takeaway: many hormonal disorders are preventable or treatable with awareness and lifestyle.
[NCERT — Real life]