Class 10 : Science (In English) – Lesson 6. Control and Coordination

EXPLANATION & SUMMARY

🔵 Detailed Explanation
Introduction: The Need for Control and Coordination
Living organisms continuously respond to changes around them—light, sound, touch, smell, taste, and internal stimuli like hunger or pain. To survive, they require systems that control activities and coordinate responses efficiently.
In plants, coordination is mainly chemical, through hormones.
In animals, it is through the nervous system and endocrine system.

💡 Concept: Control ensures order, coordination ensures integration—together they make responses accurate.

🔵 Nervous System in Animals
The nervous system is the fastest way of control in animals. It works via specialised cells called neurons.
Structure of Neuron

Cell body: Contains nucleus and cytoplasm.
Dendrites: Receive impulses from surroundings.
Axon: Transmits impulses away from cell body.
Synapse: Junction between two neurons; impulses travel chemically here.
➡️ Function: Neurons transmit impulses as electrochemical signals, measured in milliseconds.

🟢 Transmission of Nerve Impulse
Stimulus received by dendrites.
Electrical signal generated in cell body.
Travels through axon → synapse.
Chemical neurotransmitters carry impulse to next neuron or effector organ.
✔️ Effector: A muscle (contracts) or a gland (secretes).

🟡 Human Nervous System
Divided into:
Central Nervous System (CNS): Brain and spinal cord.
Peripheral Nervous System (PNS): Nerves branching from CNS.
Autonomic Nervous System (ANS): Involuntary activities (heartbeat, digestion).
Brain

Forebrain: Controls thinking, reasoning, memory, voluntary actions, sensory interpretation.
Midbrain: Controls reflexes related to vision and hearing.

Hindbrain:
🔵 Cerebellum – balance and posture.
🟢 Medulla oblongata – involuntary functions (breathing, heartbeat).
🟡 Pons – relay centre.
✏️ Note: Brain is protected by skull, cushioned by cerebrospinal fluid (CSF).

🔴 Reflex Action
Reflex: Quick, automatic response to a stimulus without conscious thought.
Pathway: Stimulus → receptor → sensory neuron → spinal cord → motor neuron → effector.
Example: Withdrawing hand from hot object.
💡 Concept: Reflexes protect the body from sudden danger.

🟢 Coordination by Hormones in Animals
Hormones are chemical messengers secreted by endocrine glands, released into blood, and act on target organs.
Major Human Hormones

Pituitary gland: Master gland; growth hormone; controls other glands.
Thyroid: Produces thyroxine; regulates metabolism.
Adrenal glands: Adrenaline; increases heartbeat, blood pressure in emergencies.
Pancreas: Insulin regulates blood sugar.
Testes/Ovaries: Sex hormones (testosterone, estrogen, progesterone).
✔️ Endocrine system provides slower but longer-lasting control compared to nervous system.

🟡 Coordination in Plants
Plants lack nervous system but show responses using chemical messengers and growth regulators.

Tropic Movements 🌿
Directional responses of plants to stimuli:
Phototropism: Stem bends towards light.
Geotropism: Roots grow downward due to gravity.
Hydrotropism: Roots grow towards water.
Thigmotropism: Tendrils coil around support.

✔️ Controlled by plant hormones (auxins).
Nastic Movements
Non-directional responses:
Example: Folding of leaves in Mimosa pudica when touched.
Caused by changes in turgor pressure in specialized cells.

🔴 Plant Hormones
Auxins: Promote cell elongation, root initiation, phototropism.
Gibberellins: Stimulate stem elongation, seed germination.
Cytokinins: Promote cell division, delay aging of leaves.
Abscisic Acid (ABA): Inhibits growth, induces dormancy, closes stomata during stress.
✏️ Note: Hormones work in coordination to maintain plant growth and responses.

Importance of Control and Coordination
Maintains internal balance (homeostasis).
Enables organisms to respond and adapt to environment.
Helps in growth, reproduction, defense, and survival.

🟢 Summary
Nervous System: Neurons transmit impulses; CNS (brain, spinal cord), PNS, ANS; brain functions in forebrain, midbrain, hindbrain. Reflex action provides quick response.
Hormonal Control in Animals: Endocrine glands secrete hormones—pituitary, thyroid, adrenal, pancreas, testes/ovaries. Provide slow but lasting regulation.
Coordination in Plants: Tropic movements (photo, geo, hydro, thigmo), nastic movements. Plant hormones—auxins, gibberellins, cytokinins, abscisic acid.
Significance: Ensures survival, adaptation, and smooth functioning of organisms.

📝 Quick Recap
🧠 Nervous system: Neurons, brain parts, reflex action.
🌿 Plant coordination: Tropic and nastic movements.
⚡ Hormones: Chemical messengers in animals and plants.
✔️ Control + coordination = balance, adaptation, survival.

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QUESTIONS FROM TEXTBOOK

Question 1
Which of the following is a plant hormone?
(a) Insulin
(b) Thyroxin
(c) Oestrogen
(d) Cytokinin
Answer
✔️ Cytokinin is a plant hormone.
It promotes cell division, growth of shoots, and delays aging of leaves.
Other options are animal hormones: Insulin (pancreas), Thyroxin (thyroid), Oestrogen (ovary).
Correct option: (d) Cytokinin

Question 2
The gap between two neurons is called a
(a) dendrite
(b) synapse
(c) axon
(d) impulse
Answer
✔️ The gap between the axon terminal of one neuron and the dendrite of the next neuron is a synapse.
It allows transmission of impulses via chemical neurotransmitters.
Correct option: (b) synapse

Question 3
The brain is responsible for
(a) thinking
(b) regulating the heart beat
(c) balancing the body
(d) all of the above
Answer
✔️ The brain performs all these functions:
Forebrain: Thinking, reasoning.
Medulla: Regulates heartbeat, breathing.
Cerebellum: Controls posture and balance.
Correct option: (d) all of the above

Question 4
What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?
Answer
✔️ Functions of receptors:
Detect external and internal stimuli (light, sound, touch, temperature, chemicals).
Convert stimuli into electrical signals for transmission by nerves.
➡️ If receptors fail:
Eye receptors (retina) damaged → blindness.
Ear receptors (cochlea) damaged → deafness.
Skin receptors damaged → inability to sense pain, touch, temperature.
Overall, loss of sensation leads to poor survival and coordination.

Question 5
Draw the structure of a neuron and explain its function.
Answer
✔️ Structure of neuron:

Cell body (cyton): Contains nucleus, cytoplasm.
Dendrites: Receive impulses.
Axon: Long extension conducting impulse away.
Myelin sheath: Insulates axon, speeds impulse.
Synaptic knobs: Release neurotransmitters to next neuron.
✔️ Function: Neuron is the functional unit of nervous system, transmitting impulses rapidly to and from brain, spinal cord, and effectors.

Question 6
How does phototropism occur in plants?
Answer
✔️ Phototropism = Growth of plant parts in response to light.
Shoots show positive phototropism (bend towards light).
Roots show negative phototropism (grow away from light).
Mechanism: Auxin hormone accumulates on the shaded side → cells elongate more → bending towards light.

Question 7
Which signals will get disrupted in case of a spinal cord injury?
Answer
✔️ Spinal cord controls reflex actions and transmission of impulses between brain and body.
➡️ Injury disrupts:
Reflex actions like knee-jerk, withdrawal from pain.
Voluntary movements (legs, hands).
Coordination between brain and effectors below the injury site.

Question 8
How does chemical coordination occur in plants?
Answer
✔️ Chemical coordination occurs through plant hormones (phytohormones).
Auxins: Promote elongation, phototropism.
Gibberellins: Stem elongation, seed germination.
Cytokinins: Cell division, delay aging.
Abscisic Acid: Inhibits growth, induces dormancy, closes stomata in stress.
💡 Concept: Hormones move through diffusion or transport in vascular tissues to target cells.

Question 9
What is the need for a system of control and coordination in an organism?
Answer
✔️ Reasons:
Organisms face changes in environment; need to respond properly.
Internal processes like heartbeat, digestion, excretion must be regulated.
Ensures survival, growth, reproduction, and adaptation.
Maintains homeostasis (internal balance).

Question 10
How are involuntary actions and reflex actions different from each other?
Answer
✔️ Involuntary actions:
Controlled by brain (medulla/ANS).
Continuous, not consciously controlled.
Examples: Breathing, heartbeat, peristalsis.
✔️ Reflex actions:
Rapid, automatic responses through spinal cord.
Protective in nature.
Examples: Withdrawing hand from hot object, knee-jerk.

Question 11
Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
Answer
✔️ Nervous mechanism:
Fast, short-lived, transmitted by neurons.
Messages in form of electrochemical impulses.
Acts on specific organs (muscles, glands).
✔️ Hormonal mechanism:
Slow, long-lasting, transmitted by blood.
Messages in form of chemicals (hormones).
Acts on distant organs (target tissues).
➡️ Both ensure survival and proper functioning of organism.

Question 12
What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?
Answer
✔️ Movement in sensitive plant (Mimosa pudica):
Nastic movement (non-directional).
Due to changes in turgor pressure of cells.
No specialised tissues like nerves or muscles.
✔️ Movement in human legs:
Voluntary movement.
Controlled by nervous system and skeletal muscles.
Depends on contraction and relaxation of muscle fibres under nerve impulses.

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OTHER IMPORTANT QUESTIONS FOR EXAMS

🔵 Section A (Q1–20: MCQs, 1 mark each; Q11–Q20 Assertion–Reason)
Question 1
Which part of the brain controls voluntary actions like writing?
Cerebellum
Medulla
Forebrain
Midbrain
Answer: 3

Question 2
Which plant hormone promotes cell division?
Auxin
Cytokinin
Gibberellin
Abscisic acid
Answer: 2

Question 3
Which of the following is not an involuntary action?
Heartbeat
Breathing
Blinking of eyes
Walking
Answer: 4

Question 4
In reflex action, the pathway is completed through
brain
spinal cord
cerebellum
forebrain
Answer: 2

Question 5
Which hormone regulates blood sugar levels in humans?
Insulin
Adrenaline
Thyroxine
Testosterone
Answer: 1

Question 6
The part of the neuron which carries impulse away from cell body is
Dendrite
Axon
Synapse
Cyton
Answer: 2

Question 7
Which movement in plants is non-directional?
Phototropism
Geotropism
Hydrotropism
Nastic movement
Answer: 4

Question 8
Which hormone prepares the body for emergency situations?
Adrenaline
Insulin
Thyroxine
Estrogen
Answer: 1

Question 9
Which of the following glands is called the “Master Gland”?
Pancreas
Thyroid
Pituitary
Adrenal
Answer: 3

Question 10
Auxins are responsible for
Closing of stomata
Growth of shoot tip towards light
Inhibition of growth
Aging of leaves
Answer: 2

Question 11
A: Cerebellum controls posture and balance.
R: Medulla regulates voluntary actions.
Both A and R true; R is the correct explanation of A
Both A and R true; R is NOT the correct explanation of A
A true; R false
A false; R true
Answer: 3

Question 12
A: Reflex actions are under the control of spinal cord.
R: They occur rapidly without involvement of brain.
Both A and R true; R is the correct explanation of A
Both A and R true; R is NOT the correct explanation of A
A true; R false
A false; R true
Answer: 1

Question 13
A: Gibberellins help in elongation of stems.
R: Cytokinins inhibit cell division.
Both A and R true; R is the correct explanation of A
Both A and R true; R is NOT the correct explanation of A
A true; R false
A false; R true
Answer: 3

Question 14
A: Thyroxine controls metabolism in body.
R: Its deficiency leads to goitre.
Both A and R true; R is the correct explanation of A
Both A and R true; R is NOT the correct explanation of A
A true; R false
A false; R true
Answer: 1

Question 15
A: Synapse is a junction between two neurons.
R: Transmission of impulse across synapse is electrical only.
Both A and R true; R is the correct explanation of A
Both A and R true; R is NOT the correct explanation of A
A true; R false
A false; R true
Answer: 3

Question 16
A: Mimosa plant folds its leaves on touch due to nastic movement.
R: It is caused by sudden loss of water from specialised cells.
Both A and R true; R is the correct explanation of A
Both A and R true; R is NOT the correct explanation of A
A true; R false
A false; R true
Answer: 1

Question 17
A: Pituitary gland secretes growth hormone.
R: Its deficiency in children causes dwarfism.
Both A and R true; R is the correct explanation of A
Both A and R true; R is NOT the correct explanation of A
A true; R false
A false; R true
Answer: 1

Question 18
A: Reflex actions are protective in nature.
R: They always require thinking by the forebrain.
Both A and R true; R is the correct explanation of A
Both A and R true; R is NOT the correct explanation of A
A true; R false
A false; R true
Answer: 3

Question 19
A: Abscisic acid promotes growth of plants.
R: It helps in closing of stomata during water stress.
Both A and R true; R is the correct explanation of A
Both A and R true; R is NOT the correct explanation of A
A true; R false
A false; R true
Answer: 4

Question 20
A: Pancreas is both endocrine and exocrine gland.
R: It secretes insulin into blood and digestive enzymes into intestine.
Both A and R true; R is the correct explanation of A
Both A and R true; R is NOT the correct explanation of A
A true; R false
A false; R true
Answer: 1

🟢 Section B (Q21–26: Very Short Answers, 2 marks each)
Question 21
What are plant hormones? Name two growth-promoting plant hormones.
Answer
Plant hormones = chemical messengers regulating growth and responses.
Examples: Auxins and Gibberellins (growth promoters).

Question 22
Why is brain protected by skull and cerebrospinal fluid?
Answer
Skull forms hard bony case to prevent injuries.
Cerebrospinal fluid cushions brain and prevents shocks.

Question 23
What is the function of adrenaline hormone?
Answer
Secreted by adrenal glands during emergency.
Increases heartbeat, blood pressure, breathing rate.
Prepares body for “fight or flight” response.

Question 24
What are dendrites? State their function.
Answer
Dendrites are short branched processes of neuron.
Function: Receive impulses from environment/other neurons and transmit to cell body.

Question 25
What is the difference between tropic and nastic movements?
Answer
Tropic movements: Directional, towards/away from stimulus (e.g. phototropism).
Nastic movements: Non-directional, independent of stimulus direction (e.g. touch in Mimosa).

Question 26
Why are reflex actions important?
Answer
Reflexes are quick, automatic responses without brain involvement.
Protect body from sudden harm (e.g. withdrawing hand from hot object).

🟡 Section C (Q27–33: Short Answers, 3 marks each)
Question 27
Explain the role of auxins in phototropism.
Answer
Auxins accumulate on shaded side of stem.
Promote cell elongation there.
Stem bends towards light → positive phototropism.

Question 28
Differentiate between central and peripheral nervous system.
Answer
CNS: Brain + spinal cord; controls processing and command.
PNS: Nerves arising from CNS; carry impulses to and from organs.
CNS = command centre; PNS = communication lines.

Question 29
What are the functions of forebrain?
Answer
Thinking, reasoning, memory.
Sensory interpretation (vision, smell, hearing, taste).
Controls voluntary actions like writing, walking.

Question 30
What is hydrotropism? Give one example.
Answer
Growth movement of plant parts in response to water.
Roots show positive hydrotropism (grow towards water).

Question 31
Explain the pathway of a reflex action with example.
Answer
Receptor detects stimulus → sensory neuron → spinal cord → motor neuron → effector.
Example: Touching hot object → withdrawal of hand.

Question 32
Why is thyroxine called a metabolism hormone?
Answer
Secreted by thyroid gland.
Regulates metabolism of carbohydrates, proteins, fats.
Controls energy release in body.

Question 33
How does gibberellin hormone help farmers?
Answer
Induces stem elongation → increases yield.
Breaks seed dormancy → ensures germination.
Promotes flowering and fruit development.

🔴 Section D (Q34–36: Long Answers, 5 marks each)

Question 34
Describe the structure and functions of human brain.
Answer
Brain: Soft, delicate organ enclosed in skull, protected by meninges and cerebrospinal fluid.
Forebrain:
Cerebrum controls intelligence, memory, emotions, voluntary actions.
Sensory interpretation (vision, hearing, smell, taste).
Midbrain:
Controls reflexes related to sight and hearing.
Hindbrain:
Cerebellum: Maintains posture and balance.
Pons: Relay centre.
Medulla oblongata: Controls involuntary actions (heartbeat, breathing).
✔️ Brain integrates all body functions, coordinating both voluntary and involuntary actions.

Question 35
Explain the mechanism of reflex action with a labelled flow sequence.
Answer
Reflex action: Sudden, automatic response to a stimulus without conscious thought.
Pathway:
🔵 Receptor → detects stimulus (e.g. pain).
🟢 Sensory neuron → carries message to spinal cord.
🟡 Spinal cord → processes and sends command.
🔴 Motor neuron → carries message to effector.
🟠 Effector → muscle/gland performs action.
✔️ Example: Hand withdrawal on touching a hot object.
Advantage: Saves time, protects body from harm.

Question 36
Discuss the role of hormones in maintaining control and coordination in animals.
Answer
Hormones: Chemical messengers secreted by endocrine glands, transported in blood.
Pituitary gland: Master gland, secretes growth hormone, controls other glands.
Thyroid gland: Secretes thyroxine, regulates metabolism.
Adrenal gland: Adrenaline prepares body for stress (“fight or flight”).
Pancreas: Insulin maintains blood sugar.
Sex glands: Testes (testosterone), ovaries (oestrogen, progesterone).
✔️ Together, hormones regulate growth, reproduction, stress response, metabolism, and homeostasis.

🟣 Section E (Q37–Q39: Case/Source Based, 4 marks each)

Question 37
Case: A student touches a hot pan accidentally and immediately withdraws his hand.
Questions:
(a) Which type of action is this?
(b) Name the pathway involved.
(c) Why is this action advantageous?
(d) Which part of CNS controls it?
Answer
(a) Reflex action.
(b) Reflex arc: Receptor → sensory neuron → spinal cord → motor neuron → effector.
(c) Quick response prevents injury.
(d) Controlled by spinal cord.

Question 38
Case: A patient shows symptoms of restlessness, weight loss and excessive sweating. The doctor suspects a problem in endocrine system.
Questions:
(a) Which gland is most likely affected?
(b) Which hormone is secreted by this gland?
(c) What disorder may be caused?
(d) How can it be treated?
Answer
(a) Thyroid gland.
(b) Thyroxine.
(c) Hyperthyroidism (over-secretion of thyroxine).
(d) Controlled by medicines or surgery.

Question 39
Case: A gardener notices that a plant’s shoot bends towards sunlight while roots grow deeper into soil.
Questions:
(a) Which types of movements are these?
(b) Which hormone is mainly responsible for bending of shoot?
(c) Why do roots show positive geotropism?
(d) Name one more type of tropism.
Answer
(a) Phototropism (shoot) and geotropism (root).
(b) Auxin.
(c) Roots grow downward to absorb water and minerals efficiently.
(d) Hydrotropism or thigmotropism.

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MIND MAPS

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