Exercise Solutions Available
Step-by-step answers for all textbook questions in this chapter
Why Do Living Organisms Need Control and Coordination?
Living organisms must constantly respond to their environment and regulate internal processes. This requires two systems working together: 1. Nervous system — fast, electrical signals (milliseconds) 2. Endocrine system — slow, chemical signals via hormones (minutes to hours)
The Nervous System
Neurons — The Basic Unit of the Nervous System
A neuron (nerve cell) is the structural and functional unit of the nervous system.
Parts of a neuron:
- Cell body (cyton) — contains nucleus and organelles
- Dendrites — short branched projections that receive signals from other neurons
- Axon — long fibre that carries impulses away from cell body
- Myelin sheath — insulating cover on some axons that speeds up impulse transmission
- Axon terminals — release neurotransmitters at the synapse
Types of neurons:
- Sensory neurons — carry signals FROM sense organs TO spinal cord/brain
- Motor neurons — carry signals FROM brain/spinal cord TO muscles/glands
- Relay neurons (interneurons) — connect sensory and motor neurons within spinal cord/brain
How Nerve Impulses Travel
1. A stimulus causes a change in electrical charge across the neuron membrane 2. This electrical impulse travels along the dendrite → cell body → axon 3. At the synapse (gap between neurons), the impulse triggers release of neurotransmitter chemicals 4. Neurotransmitters cross the synapse and trigger an impulse in the next neuron
Reflex Action and Reflex Arc
A reflex action is a rapid, automatic, involuntary response to a stimulus that does NOT involve the brain.
Reflex arc path: Stimulus → Receptor (sense organ) → Sensory neuron → Spinal cord → Motor neuron → Effector (muscle/gland) → Response
Examples of reflex actions:
- Pulling hand away from a hot/sharp object
- Blinking when an object comes near the eye
- Sneezing, coughing, hiccuping
- Knee-jerk reflex
Why reflex actions bypass the brain: Speed is critical in emergency responses. Waiting for brain processing would take too long and could cause harm.
The Human Brain
The brain is protected by the skull and three membranes called meninges. Cerebrospinal fluid cushions the brain.
Three Main Parts
Spinal Cord
- Extends from the base of the brain through the vertebral column
- Controls spinal reflexes
- Acts as a relay between brain and peripheral nerves
Endocrine System — Chemical Coordination
The endocrine system uses hormones (chemical messengers) secreted by ductless glands directly into the bloodstream.
Key Endocrine Glands and Their Hormones
| Gland | Hormone | Function |
|---|---|---|
| Hypothalamus | Releasing hormones | Controls pituitary gland |
| Pituitary (master gland) | Growth hormone (GH), TSH, gonadotropins | Controls growth and other glands |
| Thyroid | Thyroxine | Regulates metabolism; requires iodine |
| Parathyroid | Parathormone (PTH) | Regulates calcium levels in blood |
| Adrenal | Adrenaline | "Fight or flight" response; raises heart rate, blood glucose |
| Pancreas (islets of Langerhans) | Insulin, Glucagon | Insulin: lowers blood glucose; Glucagon: raises blood glucose |
| Testes | Testosterone | Male secondary sexual characters |
| Ovaries | Oestrogen, Progesterone | Female secondary sexual characters, menstrual cycle |
Feedback Mechanism
Hormone levels are regulated by negative feedback:
- When thyroxine level rises → it inhibits pituitary from secreting more TSH
- When blood glucose falls → glucagon is released (raises it back up)
- This maintains homeostasis (stable internal environment)
Adrenaline — The Emergency Hormone
Released by adrenal glands in response to fear, stress, or excitement.
- Increases heart rate and breathing rate
- Dilates pupils
- Redirects blood to muscles and brain
- Releases glucose from glycogen stores (raises blood glucose)
- "Fight or flight" response
Diabetes Mellitus
Insufficient insulin production (Type 1) or ineffective response to insulin (Type 2) leads to high blood glucose. Treatment: insulin injections or medication.
Coordination in Plants
Plants do not have a nervous system. They respond to stimuli using: 1. Plant hormones (phytohormones) 2. Tropic movements (growth movements toward/away from stimulus) 3. Nastic movements (non-directional responses)
Plant Hormones
| Hormone | Effect |
|---|---|
| Auxin | Promotes cell elongation; responsible for phototropism and geotropism |
| Gibberellin | Promotes stem elongation; breaks seed dormancy; promotes germination |
| Cytokinin | Promotes cell division; delays ageing in leaves |
| Abscisic acid (ABA) | Inhibits growth; promotes dormancy; closes stomata during drought |
| Ethylene | Promotes fruit ripening; causes leaf fall |
Tropic Movements
Tropic movements are growth movements in plants in response to directional stimuli.
| Tropism | Stimulus | Direction | Example |
|---|---|---|---|
| Phototropism | Light | Toward light (+) | Shoot bends toward light |
| Geotropism | Gravity | Toward gravity (+) | Roots grow downward |
| Hydrotropism | Water | Toward water (+) | Roots grow toward water |
| Thigmotropism | Touch/contact | Toward support | Tendril coiling |
| Chemotropism | Chemicals | Toward chemicals | Pollen tube grows toward ovule |
How phototropism works (auxin redistribution): 1. Light hits one side of the stem 2. Auxin migrates to the shaded side 3. Higher auxin concentration on shaded side → faster cell elongation there 4. Stem bends toward the light
Nastic Movements
Non-directional movements — same response regardless of direction of stimulus.
- Touch-me-not plant (Mimosa pudica): leaves fold when touched (due to loss of water from cells — turgor change)
- Flowers opening/closing in response to light/dark
Nervous System vs Endocrine System
| Feature | Nervous System | Endocrine System |
|---|---|---|
| Messenger | Electrical impulse | Chemical hormone |
| Speed | Very fast (milliseconds) | Slow (minutes to hours) |
| Duration of effect | Short (stops when stimulus stops) | Long-lasting |
| Pathway | Along nerves | Through bloodstream |
| Target | Specific organs | Can be widespread |
Board Exam Tips
- 6–8 marks from this chapter
- Reflex arc diagram — draw and label all 5 parts: receptor, sensory neuron, spinal cord (relay neuron), motor neuron, effector. Very commonly asked.
- Human brain diagram — label cerebrum, cerebellum, medulla oblongata. Describe functions of each (3+3 = 6 marks type)
- All 5 plant hormones: auxin, gibberellin, cytokinin, abscisic acid, ethylene — know one function each
- Adrenaline — roles in emergency responses (2-mark question)
- Iodine and thyroid — deficiency of iodine causes goitre (swelling of thyroid)
- Difference between nervous and endocrine control in a table is a common 3-mark question
📚 Lakhmir Singh Science Class 10 — Control and Coordination Chapter
📝 Oswaal CBSE Question Bank — Board Exam Practice Papers
NCERT Exercise Solutions
Intext Questions
Page 119, Q1: What is the difference between a reflex action and walking?
| Feature | Reflex action | Walking |
|---|---|---|
| Type of response | Involuntary (automatic) | Voluntary (consciously controlled) |
| Controlled by | Spinal cord | Brain (cerebrum + cerebellum) |
| Speed | Extremely fast (no brain delay) | Slower, deliberate |
| Example | Withdrawing hand from hot object | Choosing to walk to a destination |
| Purpose | Immediate protection from harm | Goal-directed movement |
Page 122, Q1: What happens at the synapse between two neurons?
Page 125, Q1: Which signals will get disrupted if the cerebellum gets damaged?
- Coordination of voluntary movements — smooth, precise movements
- Balance and posture — maintaining equilibrium
- Motor learning — ability to learn and remember motor skills (like cycling, writing)
If the cerebellum is damaged:
- Movements become jerky and uncoordinated (ataxia)
- Balance is lost — difficulty standing or walking straight
- Fine motor skills are impaired
Chapter-End Exercise
Q1. How do auxins promote the growth of a tendril around a support?
- The cells on the touching side receive a contact stimulus
- Auxin (plant hormone) moves away from the contact side to the non-contact side
- Higher auxin concentration causes faster cell elongation on the non-contact side
- The non-contact side grows faster → the tendril bends toward the support and wraps around it
This is a thigmotropism (response to touch). Auxins cause differential growth that enables coiling.
Q2. Design an experiment to demonstrate hydrotropism.
Expected result: In the damp soil container, roots grow toward the water source (wet sponge). In dry soil, roots grow randomly or downward.
Conclusion: Roots show hydrotropism — they grow in the direction of water (positive hydrotropism). This demonstrates that water acts as a stimulus for root growth direction.
Q3. How does chemical coordination take place in animals?
1. Endocrine glands (ductless glands) produce hormones — chemical messengers. 2. Hormones are secreted directly into the bloodstream (no ducts). 3. Blood carries hormones to target organs — only cells with specific receptors respond. 4. The hormone binds to the receptor and triggers a response (which may take seconds to days).
Examples:
- Adrenaline (from adrenal gland) → increases heart rate, dilates pupils during emergencies
- Insulin (from pancreas) → lowers blood glucose after meals
- Thyroxine (from thyroid) → regulates body's metabolic rate
Unlike nervous coordination (very fast, short-lived), hormonal coordination is slower but longer-lasting.
Q4. Why are some patients of diabetes treated by giving injections of insulin?
- Blood glucose level rises dangerously (hyperglycemia)
- Cells cannot use glucose → they use fat and protein for energy instead
- Glucose is excreted in urine
Since insulin is a protein, it would be digested and destroyed in the stomach if taken orally. Therefore, it must be given as injections directly into the bloodstream so it can reach target cells intact.
Q5. What is the function of the following hormones: (a) Thyroxine (b) Growth hormone (c) Adrenaline?
- Regulates the body's metabolic rate — how fast cells use energy
- Controls carbohydrate, fat, and protein metabolism
- Deficiency → hypothyroidism (low energy, weight gain), goitre (enlarged thyroid due to iodine deficiency)
(b) Growth hormone (pituitary gland):
- Stimulates growth of bones and muscles during childhood and adolescence
- Excess → gigantism (excessive growth); deficiency → dwarfism
(c) Adrenaline (adrenal gland, secreted in emergencies — 'fight or flight' hormone):
- Increases heart rate and blood pressure
- Dilates pupils
- Increases breathing rate
- Redirects blood from digestive system to muscles
- Releases glucose from glycogen stores → provides immediate energy