1. Introduction to Control and Coordination
All living organisms must detect and respond to changes in their surroundings to survive. Control and coordination help different parts of the body work together and produce an appropriate response to a stimulus.
Control means regulating different functions so they happen at the right time and in the right order.
Coordination is the working together of different organs of the body to carry out a particular activity smoothly.
Living beings respond to stimuli (changes in the environment). The body needs to maintain coordination between organs and respond appropriately to keep itself safe and functioning.
Stimulus, Receptor, Coordinator, Effector and Response
The basic pathway of response in an organism is:
Stimulus → Receptor → Coordinator → Effector → Response
- Stimulus: Any change in the environment that produces a response (e.g. heat, light, touch, sound).
- Receptor: A sense organ that detects the stimulus (e.g. skin detects heat, eyes detect light).
- Coordinator: Part that receives information from the receptor and decides the response (brain or spinal cord).
- Effector: Muscles or glands that carry out the response.
- Response: The action taken by the body (e.g. withdrawing hand from a hot object).
Animals use the nervous system and endocrine (hormonal) system for control and coordination. Plants mainly use chemical coordination through plant hormones.
2. Nervous System
The nervous system is a network of nerves that carries messages between different parts of the body and the brain/spinal cord. It helps us react quickly to changes in our surroundings.
Neuron – The Structural and Functional Unit of the Nervous System
A neuron (nerve cell) is the basic structural and functional unit of the nervous system. It carries nerve impulses (electrical signals) from one part of the body to another.
Structure of a Neuron
A typical neuron has three main parts: Cell body, Dendrites and Axon.
- Cell body (cyton): Contains the nucleus and cytoplasm. It controls the activities of the neuron.
- Dendrites: Short, branched extensions that receive nerve impulses from other neurons and carry them towards the cell body.
- Axon: A long, single extension that carries nerve impulses away from the cell body to other neurons, muscles or glands.
- Nerve endings: The branched ends of the axon where impulses are passed on to the next neuron (at a synapse).
- Myelin sheath (protective covering): Insulates the axon and helps in faster transmission of impulses (at Class 10 level, basic understanding is sufficient).
Direction of nerve impulse: Dendrites → Cell body → Axon → Nerve endings
Synapse
A synapse is the small gap between the nerve endings of one neuron and the dendrites of the next neuron, where nerve impulses are transmitted from one neuron to another.
At the synapse, the electrical impulse is converted into a chemical signal for transmission across the gap. This ensures impulses travel in one direction only.
Pathway of Nerve Impulse (General)
Receptor → Sensory Neuron → Central Nervous System (CNS) → Motor Neuron → Effector → Response
- Sensory neurons carry impulses from receptors (sense organs) to the CNS (brain and spinal cord).
- Motor neurons carry impulses from the CNS to effectors (muscles/glands).
- Relay/Interneurons (introduced at appropriate level) connect sensory and motor neurons inside the CNS.
3. Reflex Action
A reflex action is an automatic, sudden and involuntary response to a stimulus that occurs without the involvement of conscious thought (thinking).
Examples: Withdrawing hand immediately from a hot object, blinking when something comes near the eye, coughing, sneezing, knee-jerk reflex.
Reflex actions are very fast and help protect the body from danger by providing an immediate response, without waiting for the brain to think.
Reflex Arc
The path taken by the nerve impulse during a reflex action is called the reflex arc. It usually involves the spinal cord (not the brain) for quick response.
Pathway of a reflex arc:
Stimulus → Receptor → Sensory Neuron → Spinal Cord → Motor Neuron → Effector → Response
- Stimulus: Heat from a hot object.
- Receptor: Skin receptors detect heat.
- Sensory Neuron: Carries impulse from skin to spinal cord.
- Spinal Cord (Coordinator): Processes information and sends a response via motor neuron.
- Motor Neuron: Carries impulse from spinal cord to muscles.
- Effector: Muscles of the hand/arm.
- Response: Hand is withdrawn immediately.
Reflex Action vs Voluntary Action
| Reflex Action | Voluntary Action |
|---|---|
| Automatic, involuntary, sudden | Conscious, intentional, under our control |
| No involvement of thinking/brain (mainly spinal cord) | Involves brain (thinking and decision-making) |
| Very fast response | Slower response compared to reflex |
| Examples: Hand withdrawn from hot object, sneezing, blinking | Examples: Walking, writing, reading, eating |
4. Human Brain
The brain is the main coordinating centre of the body. It receives information from sense organs, processes it, and sends instructions to muscles/glands for appropriate response. It also controls thinking, memory, reasoning, emotions and balance.
The CNS consists of the brain and spinal cord. It receives, processes and coordinates information.
The PNS consists of all nerves that arise from the brain and spinal cord and connect the CNS to all parts of the body.
Major Parts of the Human Brain
The human brain is divided into three main regions: Forebrain, Midbrain and Hindbrain.
- Forebrain: Largest part of the brain. Includes cerebrum, thalamus and hypothalamus.
- Midbrain: Small region connecting forebrain and hindbrain. Controls reflexes related to vision and hearing.
- Hindbrain: Lower part of the brain. Includes cerebellum, pons and medulla oblongata.
Important Parts and Their Functions
| Part of Brain | Region | Main Functions |
|---|---|---|
| Cerebrum | Forebrain | Controls thinking, memory, reasoning, intelligence, speech, learning, voluntary actions and interpretation of sensory information. It is the largest part. |
| Hypothalamus | Forebrain | Controls hunger, thirst, body temperature, sleep, emotions and maintains homeostasis (internal balance). |
| Midbrain | Midbrain | Acts as a relay centre and controls reflex movements of head, neck and eyes in response to visual/auditory stimuli. |
| Cerebellum | Hindbrain | Maintains balance, posture, coordination of body movements (especially walking, running, writing). Helps make movements smooth and precise. |
| Pons | Hindbrain | Connects cerebellum and medulla. Helps regulate breathing rate and relays signals between different parts of the brain. |
| Medulla (Medulla Oblongata) | Hindbrain | Controls involuntary actions like breathing, heartbeat, blood pressure, swallowing, coughing, sneezing. Connects brain to spinal cord. |
Key Functions at a Glance
- Thinking, Memory, Reasoning: Cerebrum
- Balance and Posture: Cerebellum
- Voluntary Actions: Cerebrum
- Involuntary Actions: Medulla Oblongata (e.g. heartbeat, breathing)
- Coordination of Movements: Cerebellum (with cerebrum)
- Body Temperature & Hunger: Hypothalamus
5. Protection of the Brain
The brain is a very delicate and vital organ. It is protected by:
- Skull (Cranium): A hard bony box that encloses and protects the brain from mechanical injury.
- Meninges: Three protective membranes that cover the brain and spinal cord (Class 10 level: they provide cushioning and protection).
- Cerebrospinal Fluid (CSF): A fluid present between the meninges and inside the brain cavities. It acts as a shock absorber, cushions the brain from jolts, and also provides nourishment.
6. Coordination in Plants
Unlike animals, plants do not have a nervous system or nerves. They still respond to changes in their environment (stimuli) through chemical coordination using plant hormones.
Plants respond to stimuli by showing growth movements or non-growth movements. These responses are usually slower than animal responses.
Types of Plant Movements
- Growth-based movements: Movements caused by unequal growth of plant parts (e.g. bending of shoot towards light).
- Non-growth movements: Movements not caused by growth (e.g. folding of leaves in touch-me-not plant) – mainly nastic movements (brief mention at Class 10 level).
Tropisms
A tropism is a directional growth movement of a plant part in response to an external stimulus. The movement can be towards (positive) or away from (negative) the stimulus.
Growth of a plant part towards the stimulus.
Growth of a plant part away from the stimulus.
Types of Tropisms
| Tropism | Stimulus | Direction | Example | Biological Significance |
|---|---|---|---|---|
| Phototropism | Light | Shoot: towards light (+ve), Roots: away from light (–ve) | Shoot of a plant bends towards sunlight | Helps plant get maximum light for photosynthesis |
| Geotropism (Gravitropism) | Gravity | Roots: towards gravity (+ve), Shoot: away from gravity (–ve) | Roots grow downward into soil; shoot grows upward | Roots get water/minerals; shoot reaches light |
| Hydrotropism | Water | Roots: towards water (+ve) | Roots grow towards moist areas in soil | Helps roots absorb water for plant |
| Chemotropism | Chemicals | Towards/away from chemical | Pollen tube grows towards ovule (chemicals secreted by ovule) | Helps in fertilisation (growth of pollen tube) |
Diagrams of Tropisms (Simple)
7. Plant Hormones
Plants do not have nerves, so they coordinate through chemical messengers called plant hormones. These hormones are made in small quantities in one part of the plant and move to another part, where they regulate growth and responses.
A plant hormone is a chemical produced in one part of a plant that is transported to another part to bring about growth or a response to a stimulus.
Auxins
- Role in plant growth: Auxins promote growth by causing cell elongation in shoots and roots.
- Phototropism: Auxin moves towards the shaded side of the shoot, making cells there grow longer, so the shoot bends towards light (positive phototropism).
- Produced mainly at the tips of shoots and roots.
Gibberellins
- Stimulate stem elongation, seed germination, flowering and development of fruits.
Cytokinins
- Promote cell division in growing parts such as roots and shoots, and delay ageing of leaves.
Abscisic Acid
- Growth inhibition: Inhibits plant growth and promotes dormancy of seeds.
- Stress-related response: Helps the plant survive unfavourable conditions such as drought.
- Stomatal closure: Causes closing of stomata to reduce water loss when water is scarce.
Plant Hormones – Comparison Table
| Hormone | Effect on Growth | Main Role |
|---|---|---|
| Auxin | Promotes cell elongation | Phototropism, growth of shoot tip, root growth |
| Gibberellin | Promotes stem elongation | Seed germination, flowering, fruit development |
| Cytokinin | Promotes cell division | Growth of roots and shoots, delays leaf ageing |
| Abscisic acid | Inhibits growth | Seed dormancy, stomatal closure, stress response |
8. Movement in Plants
Plants show two broad types of movements: growth movements (tropic/turgor-based) and non-growth movements (e.g. folding of touch-me-not leaves on touching).
Growth Movements (Directional / Tropic)
Tropic movements are directional growth movements of a plant part in response to a stimulus. They can be towards the stimulus (positive tropism) or away from it (negative tropism).
- Shoot bending towards light – positive phototropism.
- Roots growing downward – positive geotropism (gravitropism).
- Roots growing towards water – positive hydrotropism.
- Pollen tube growing towards the ovule – chemotropism.
| Positive Tropism | Negative Tropism |
|---|---|
| Growth of a plant part towards the stimulus | Growth of a plant part away from the stimulus |
| Example: Shoot grows towards light (positive phototropism) | Example: Root grows away from light (negative phototropism) |
| Example: Root grows towards gravity (positive geotropism) | Example: Shoot grows away from gravity (negative geotropism) |
Non-Growth Movements
Some plants show quick movements that do not involve growth at all. For example, the leaves of the touch-me-not (mimosa) plant fold when touched. This happens due to loss of water pressure (turgor) in certain cells.
9. Hormonal Coordination in Animals
Animals control and coordinate their functions through two systems: the nervous system and the hormonal (endocrine) system.
A hormone is a chemical messenger produced by an endocrine gland and transported through the blood to a target organ, where it brings about a specific response.
An endocrine gland is a ductless gland whose secretion (hormone) is released directly into the blood.
Hormones are carried by blood from the gland to the target organ. Even tiny amounts of a hormone can produce a large effect.
Nervous System vs Hormonal System – Comparison
| Feature | Nervous Coordination | Hormonal Coordination |
|---|---|---|
| Message carrier | Electric nerve impulses | Chemical hormones |
| Path | Along nerves, directly | Through blood, circulates |
| Speed | Very fast | Slow |
| Effect duration | Short-lived | Long-lasting |
| Action area | Specific organ/muscle | Can affect many organs |
| Example | Pulling hand away from a hot object | Insulin controlling blood sugar level |
10. Endocrine Glands and Important Hormones
The table below summarises the major endocrine glands, the hormones they secrete, their functions and an important point for each.
| Gland | Hormone | Main Function | Important Point |
|---|---|---|---|
| Pituitary | Growth hormone | Controls growth of the body; regulates other endocrine glands | Often called the “master gland” |
| Thyroid | Thyroxine | Regulates metabolism, growth and development of the body | Needs iodine; deficiency causes goitre |
| Adrenal glands | Adrenaline | Prepares the body for emergency; increases heartbeat, breathing rate and blood supply to muscles | Fight-or-flight response |
| Pancreas | Insulin | Regulates blood sugar level; helps cells take up glucose | Deficiency causes diabetes |
| Testes | Testosterone | Controls development of male reproductive organs and male secondary sexual characteristics | Present in males |
| Ovaries | Oestrogen | Controls development of female reproductive organs and female secondary sexual characteristics | Present in females |
Important Hormones and Their Functions
- Growth hormone: Promotes growth of the body; secreted by the pituitary.
- Thyroxine: Regulates metabolism and growth; secreted by the thyroid.
- Adrenaline: Prepares the body for emergencies; secreted by the adrenal glands.
- Insulin: Lowers blood sugar level; secreted by the pancreas.
- Testosterone: Controls male secondary sexual characteristics; secreted by the testes.
- Oestrogen: Controls female secondary sexual characteristics; secreted by the ovaries.
11. Important Definitions
A change in the environment of an organism that produces a response (e.g. heat, light, touch).
The reaction of the body to a stimulus (e.g. withdrawing the hand on touching a hot object).
A sense organ (or cell) that detects a stimulus, e.g. skin detects heat, eye detects light.
A muscle or gland that carries out the response to an impulse from the nervous system.
The structural and functional unit of the nervous system that carries nerve impulses.
The small gap between the nerve ending of one neuron and the dendrite of the next, across which the impulse passes chemically.
A quick, automatic and involuntary response to a stimulus without conscious thought, e.g. blinking.
The pathway of a nerve impulse during a reflex action, generally through the spinal cord.
The brain and spinal cord, which receive, process and coordinate information.
All the nerves that connect the CNS to different parts of the body.
A chemical messenger secreted by endocrine glands, carried by blood to a target organ to produce a specific effect.
A ductless gland that releases its secretion (hormone) directly into the blood.
A directional growth movement of a plant part in response to a stimulus.
Directional growth movement in response to light (shoot positive, root negative).
Directional growth movement in response to gravity (root positive, shoot negative).
Directional growth movement in response to water (root grows towards water).
Directional growth movement in response to chemicals (e.g. pollen tube towards ovule).
12. Solved Examples
Note: All questions below are original CBSE exam-style questions. None are claimed to be past board (PYQ) questions.
Basic Concept Questions (5)
Example 1
Question: Name the basic structural and functional unit of the nervous system.
Concept: Recall the unit cell of the nervous system.
Answer: The neuron (nerve cell) is the structural and functional unit of the nervous system.
Final Answer: Neuron.
Example 2
Question: What is the message-carrying signal in a neuron called?
Concept: Recall how information travels in nerves.
Answer: The signal is a nerve impulse (an electrical impulse).
Final Answer: Nerve impulse.
Example 3
Question: Name the gap between two neurons.
Concept: Recall the junction between neurons.
Answer: The synapse is the small gap between the ending of one neuron and the dendrite of the next.
Final Answer: Synapse.
Example 4
Question: Which plant hormone promotes growth?
Concept: Recall the growth-related plant hormone.
Answer: Auxin promotes growth by causing cell elongation.
Final Answer: Auxin.
Example 5
Question: Which hormone regulates blood sugar level and which gland produces it?
Concept: Recall the hormone that controls glucose level.
Answer: Insulin, produced by the pancreas, regulates blood sugar level.
Final Answer: Insulin; pancreas.
Moderate Questions (7)
Example 6
Question: What is a reflex action? Name two involuntary reflex actions.
Concept: Reflex actions are sudden, involuntary and automatic.
Answer: A reflex action is a quick, involuntary response to a stimulus. Examples: blinking, withdrawing the hand from a hot object, sneezing.
Final Answer: Reflex action is an automatic involuntary response; e.g. blinking and sneezing.
Example 7
Question: What is the reflex arc? Write its path.
Concept: Trace the path of impulse in a reflex.
Answer: The reflex arc is the pathway of impulses during a reflex action: Receptor → Sensory neuron → Spinal cord → Motor neuron → Effector.
Final Answer: Reflex arc path: Receptor → Sensory neuron → Spinal cord → Motor neuron → Effector.
Example 8
Question: Distinguish between reflex action and voluntary action.
Concept: Compare on the basis of control, thought and speed.
Answer: Reflex actions are automatic, involuntary, not under conscious control and are fast. Voluntary actions are done with thinking, under conscious control and are slower. See the comparison table in section 3.
Final Answer: See reflex vs voluntary table (section 3).
Example 9
Question: What are the main parts of the human brain?
Concept: Recall the three regions of the brain.
Answer: The brain has three main parts: forebrain, midbrain and hindbrain. The forebrain contains the cerebrum and hypothalamus; the hindbrain contains the cerebellum, pons and medulla.
Final Answer: Forebrain, midbrain and hindbrain.
Example 10
Question: Which plant hormone is responsible for seed dormancy and closing of stomata?
Concept: Recall the inhibitory plant hormone.
Answer: Abscisic acid inhibits growth, helps in seed dormancy and closes stomata during water stress.
Final Answer: Abscisic acid.
Example 11
Question: Why do roots of a plant grow downwards and shoots grow upwards?
Concept: Relate to geotropism.
Answer: Roots respond positively to gravity (positive geotropism) and grow downwards into the soil. Shoots grow away from gravity (negative geotropism) and upwards.
Final Answer: Positive geotropism in roots; negative geotropism in shoots.
Example 12
Question: What are the functions of thyroxine and adrenaline?
Concept: Link each hormone to its gland and effect.
Answer: Thyroxine (thyroid) regulates metabolism and growth. Adrenaline (adrenal glands) prepares the body for emergencies by increasing heartbeat and breathing rate.
Final Answer: Thyroxine regulates metabolism; adrenaline prepares for emergencies.
Application-Based Questions (5)
Example 13 (Application)
Question: We withdraw our hand immediately when we touch a hot object, even before thinking. Why?
Concept: A reflex action is involved.
Answer: Sensory neurons carry the impulse from skin to the spinal cord, which directly sends a response via motor neurons to muscles, without going to the brain. This makes the response immediate and protects us from injury.
Final Answer: It is a reflex action controlled by the spinal cord.
Example 14 (Application)
Question: A person cannot maintain balance while walking after an accident. Which part of the brain is likely affected?
Concept: Balance is controlled by the cerebellum.
Answer: The cerebellum controls balance and posture. If someone cannot balance, the cerebellum is likely damaged.
Final Answer: Cerebellum.
Example 15 (Application)
Question: A potted plant kept near a window bends towards sunlight. Explain this with the role of a plant hormone.
Concept: Phototropism and auxin.
Answer: Auxin collects more on the shaded side of the shoot, causing the shaded side to grow faster. The shoot therefore bends towards light (positive phototropism).
Final Answer: Unequal auxin distribution causes the shoot to bend towards light.
Example 16 (Application)
Question: Why is insulin important for a person with diabetes?
Concept: Insulin controls blood sugar.
Answer: Insulin enables cells to take up glucose from blood, lowering blood sugar. Diabetic patients cannot produce enough insulin, so they need insulin injections to control sugar level.
Final Answer: Insulin lowers blood sugar by helping cells take up glucose.
Example 17 (Application)
Question: A patient shows a swollen neck (goitre). Which mineral deficiency and which gland is related?
Concept: Iodine is needed for thyroxine.
Answer: Iodine deficiency prevents the thyroid from producing thyroxine, causing the gland to enlarge, leading to goitre.
Final Answer: Iodine deficiency; thyroid gland.
Competency / Reasoning Questions (4)
Example 18 (Competency)
Question: Plants do not have a nervous system, yet they respond to stimuli. Justify with examples.
Concept: Chemical coordination through hormones.
Answer: Plants respond through plant hormones (e.g. auxin causes phototropism) and show tropic movements and non-growth movements (touch-me-not leaves folding). They do not need a fast nervous system because they are fixed and respond slowly.
Final Answer: Plants coordinate chemically via plant hormones.
Example 19 (Competency)
Question: Why are reflex actions faster than thinking-based actions?
Concept: Reflex arcs are short paths through the spinal cord.
Answer: In a reflex, the impulse travels through the short spinal cord pathway (reflex arc), skipping the slower brain-processing route, so the response is faster.
Final Answer: Reflex arcs are shorter and do not involve the brain.
Example 20 (Competency)
Question: A shoot is illuminated from one side only. What will happen to auxin concentration and the growth?
Concept: Light directs auxin redistribution.
Answer: Auxin moves to the shaded side, making the shaded side elongate more. As a result the shoot bends towards light.
Final Answer: Auxin concentrates on the shaded side; shoot bends towards light.
Example 21 (Competency)
Question: Compare nervous and hormonal coordination in terms of speed and duration of effect.
Concept: Compare both coordination systems.
Answer: Nervous coordination is fast but short-lived; hormonal coordination is slow but long-lasting.
Final Answer: Nervous: fast, short-lived; Hormonal: slow, long-lasting.
Case-Based Questions (4)
Example 22 (Case-Based)
Case: A cyclist sees a dog suddenly crossing the road. He immediately applies brakes without thinking, yet his heartbeat increases.
Q1. Which pathway caused the immediate braking?
Q2. Which gland and hormone increased his heartbeat?
Q3. Why did the heartbeat increase?
Answer: Q1: Reflex action pathway (reflex arc through the spinal cord). Q2: Adrenal gland, adrenaline. Q3: Adrenaline prepares the body for an emergency by increasing the heartbeat and supplying more energy to muscles.
Final Answer: Q1 Reflex arc (spinal cord); Q2 Adrenal glands + adrenaline; Q3 To prepare the body for emergency action.
Example 23 (Case-Based)
Case: A patient has difficulty in breathing and irregular heartbeats. The doctor suspects damage to a specific part of the brain.
Q1. Which part of the brain controls breathing and heartbeat?
Q2. In which region of the brain is it located?
Q3. Name one more action controlled by this part.
Answer: Q1: Medulla oblongata. Q2: Hindbrain. Q3: It also controls blood pressure (and swallowing/coughing).
Final Answer: Q1 Medulla oblongata; Q2 Hindbrain; Q3 Blood pressure, swallowing, coughing.
Example 24 (Case-Based)
Case: A plant's roots grow towards a moist area of the soil while its shoot grows towards light through a window.
Q1. Name the tropism shown by the roots.
Q2. Name the tropism shown by the shoot.
Q3. What is the significance of these responses?
Answer: Q1: Hydrotropism (towards water). Q2: Phototropism (towards light). Q3: Roots absorb water for survival; shoots get light for photosynthesis.
Final Answer: Q1 Hydrotropism; Q2 Phototropism; Q3 Water absorption and photosynthesis.
Example 25 (Case-Based)
Case: After eating a sweet dish, a student's blood sugar rises but returns to normal in a while. His friend, who has diabetes, needs an injection afterwards.
Q1. Which hormone brings the blood sugar back to normal?
Q2. Which gland secretes it?
Q3. Why does the diabetic friend need the injection?
Answer: Q1: Insulin. Q2: Pancreas. Q3: His pancreas cannot produce enough insulin, so he needs external insulin to control blood sugar.
Final Answer: Q1 Insulin; Q2 Pancreas; Q3 Deficient insulin production in diabetes.
13. Application-Based Learning
Application Example 1
Why we withdraw our hand from a hot object: A reflex action. The spinal cord immediately commands the muscles to pull the hand away, protecting us from burns before the brain even registers pain.
Application Example 2
Why reflex actions are fast: Because the reflex arc passes through the spinal cord and avoids the longer route to and from the brain, saving time during danger.
Application Example 3
Why the cerebellum is important for balance: The cerebellum coordinates muscle activity and maintains body posture and balance, as when we cycle, walk on a straight line or climb stairs.
Application Example 4
Why shoots bend towards light: When light is from one side, auxin redistributes to the shaded side, growing that side longer so the shoot bends towards light for more photosynthesis.
Application Example 5
Why roots grow downward: By positive geotropism, roots grow towards gravity and into the soil to absorb water and minerals, anchoring the plant.
Application Example 6
Why insulin is important: Insulin helps body cells take up glucose, keeping blood sugar in a safe range. Without it (diabetes), sugar builds up in blood and harms the body.
Application Example 7
Why adrenaline prepares the body for emergencies: In danger, fright or excitement, adrenaline increases heartbeat, breathing and glucose supply so the body is ready to fight or run fast (fight-or-flight).
Application Example 8
Why iodine is important for thyroid function: The thyroid needs iodine to make thyroxine. Iodine-deficient diets cause goitre, slow metabolism and tiredness. This is why iodised salt is recommended.
14. Competency-Based Questions
Competency Q1
Question: If a person's sensory neurons in a reflex arc are damaged, what will happen when he touches a hot object?
Answer: The stimulus (heat) will not reach the CNS because the sensory neuron cannot carry the impulse. No reflex will occur and the person may get burnt.
Competency Q2
Question: A plant is placed in a dark room with a single window on one side. Predict the direction of shoot growth and give the reason.
Answer: The shoot bends towards the window (light). Auxin accumulates on the side away from light, elongating those cells, so the plant curves towards light.
Competency Q3
Question: Why are hormones called chemical messengers?
Answer: Because they are chemical substances produced in one place (glands) that travel through blood and deliver instructions to specific organs elsewhere in the body.
Competency Q4
Question: A person's heartbeat continues even during sleep. Which part of the brain is responsible and is this a voluntary action?
Answer: The medulla oblongata controls the involuntary (automatic) heartbeat. It is not a voluntary action because it continues without conscious control, even during sleep.
Competency Q5
Question: Compare the transmission speed and durability of nervous vs hormonal coordination with one example each.
Answer: Nervous coordination is fast and short-lived (pulling hand away from a hot object). Hormonal coordination is slow but long-lasting (hormones controlling growth).
Competency Q6
Question: Why do growing root tips bend towards water even though the whole root is in humid soil?
Answer: The root tip grows more quickly towards the side with more moisture because water acts as the stimulus and the root shows positive hydrotropism, bending towards the wetter region.
15. Case-Based Learning
Case Study 1 – Reflex Action (Hand Withdrawal)
Case: A student accidentally touches a hot pan and instantly pulls her hand back.
Q1. Trace the path of this reflex action.
Q2. Which organs act as receptor and effector here?
Q3. Why was the response faster than the pain?
Answer: Q1: Skin receptor → sensory neuron → spinal cord → motor neuron → muscles of hand. Q2: Receptor – skin; Effector – hand muscles. Q3: The impulse followed the short reflex arc through the spinal cord, faster than the longer route to the brain that produces pain sensation.
Case Study 2 – Human Brain (Balance)
Case: A gymnast walks on a narrow balance beam while performing tricks.
Q1. Which part of the brain maintains her balance and posture?
Q2. Which part carries the voluntary commands for the tricks?
Q3. What auto-coordinated roles help her finish without falling?
Answer: Q1: Cerebellum. Q2: Cerebrum (forebrain). Q3: The cerebellum coordinates Balance and smooth muscle movements, while the medulla keeps breathing and heartbeat steady during the activity.
Case Study 3 – Plant Tropism (Phototropism)
Case: A potted plant near a window grows bending towards the window over several days.
Q1. Name the tropism and the hormone involved.
Q2. Why did bending occur?
Q3. What would happen if the pot is rotated daily?
Answer: Q1: Phototropism; auxin. Q2: Auxin moved to the shaded side made those cells grow longer. Q3: Rotation keeps light roughly equal on all sides, so the auxin distribution stays fairly even and the shoot tends to grow straight.
Case Study 4 – Endocrine Hormones (Emergency)
Case: Before a board exam, Ravi feels a rise in heartbeat, cold sweat and extra alertness.
Q1. Which gland and hormone cause these changes?
Q2. Why does the body produce them?
Q3. After the exam, why does he calm down?
Answer: Q1: Adrenal glands; adrenaline. Q2: To prepare the body for an emergency (fight-or-flight): more oxygen and glucose to muscles and brain. Q3: The stress disappears, the hormone effect fades, and heartbeat gradually returns to normal.
Case Study 5 – Plant Hormones (Stress)
Case: During a drought, a plant's leaves lose less water than expected and its seeds stay dormant.
Q1. Which plant hormone helps it conserve water?
Q2. How does it reduce water loss?
Q3. Why do the seeds remain dormant?
Answer: Q1: Abscisic acid. Q2: It causes stomata to close, reducing water loss through transpiration. Q3: Abscisic acid inhibits growth and keeps the seeds dormant until conditions become favourable.
16. Self-Practice Questions
A. Multiple Choice Questions (1–6)
- The functional unit of the nervous system is: (a) Nephron (b) Neuron (c) Axon (d) Dendrite
- Smallest gap between two neurons across which impulses pass is called: (a) Axon (b) Synapse (c) Dendrite (d) Myelin
- Sudden, involuntary response to a stimulus is: (a) Voluntary action (b) Reflex action (c) Tropism (d) Hormone
- Bending of a shoot towards light is: (a) Geotropism (b) Phototropism (c) Hydrotropism (d) Chemotropism
- Which hormone is secreted by the pancreas? (a) Thyroxine (b) Adrenaline (c) Insulin (d) Growth hormone
- Balance and coordination of body movements are controlled by: (a) Cerebrum (b) Cerebellum (c) Medulla (d) Midbrain
B. Very Short Answer Questions (7–12)
- Name the three main parts of a neuron.
- What is a reflex arc?
- Name the largest part of the human brain.
- Which plant hormone is responsible for seed dormancy?
- Name the hormone that regulates blood sugar level.
- What is the role of the iodine in our body?
C. Short Answer Questions (13–18)
- Differentiate between receptors and effectors with examples.
- Explain phototropism with the role of auxin.
- Why is the pituitary gland called the master gland?
- Write the functions of thyroxine and adrenaline.
- Why are reflex actions important for the survival of animals?
- Differentiate between geotropism and hydrotropism with one example each.
D. Assertion-Reason Questions (19–20)
- Assertion (A): Reflex actions are very fast.
Reason (R): They are carried out through the reflex arc without involving the brain.
(a) Both A and R are true and R explains A (b) Both A and R are true but R does not explain A (c) A is true, R is false (d) A is false, R is true - Assertion (A): Plants do not have a nervous system.
Reason (R): Plants coordinate through plant hormones.
(a) Both A and R are true and R explains A (b) Both A and R are true but R does not explain A (c) A is true, R is false (d) A is false, R is true
E. Competency-Based Questions (21–24)
- A cyclist applies brakes without thinking on seeing a dog. Is this a reflex or voluntary action? Give a reason.
- Why is a hormonal response slower but longer lasting than a nervous response?
- An injury damages a person's cerebellum. What consequences do you expect from the child for the person's body movements?
- In diabetes, why does a patient need insulin injections even though insulin is produced in the human body?
F. Case-Based / Diagram-Based Questions (25–27)
- Case: A seed is placed in a pot with moist soil on one side only. Predict the direction of root growth. Name the tropism.
- Diagram: Draw a labelled diagram of a neuron. Label dendrites, cell body, axon and nerve endings.
- Diagram: Draw a labelled diagram of the reflex arc and label receptor, sensory neuron, spinal cord and effector.
G. Application / Higher-Order Questions (28–30)
- Application: Why does a person sweat and feel pounding of the heart before an important presentation? Name the endocrine gland involved.
- Application: A farmer rotates a potted seedling daily under even light. What will be the growth pattern of the shoot? Give the reason.
- HOTS: If a person's motor neurons of a reflex arc are cut, will he be able to feel pain when he touches a hot object? Will he be able to withdraw his hand? Explain.
Answer Key
| Q.No | Answer |
|---|---|
| 1 | (b) Neuron |
| 2 | (b) Synapse |
| 3 | (b) Reflex action |
| 4 | (b) Phototropism |
| 5 | (c) Insulin |
| 6 | (b) Cerebellum |
| 7 | Dendrites, cell body, axon |
| 8 | Path taken by nerve impulse during a reflex action |
| 9 | Cerebrum |
| 10 | Abscisic acid |
| 11 | Insulin |
| 12 | Thyroid needs iodine to form thyroxine |
| 13 | Receptor detects stimulus (skin); effector executes response (muscle) |
| 14 | Auxin collects on shaded side and elongates it; shoot bends towards light |
| 15 | It regulates and controls many other endocrine glands |
| 16 | Thyroxine: metabolism; Adrenaline: emergency response |
| 17 | They give rapid protection from danger without consuming thinking time |
| 18 | Geotropism (root to gravity) vs hydrotropism (root to water) |
| 19 | (a) Both true, R explains A |
| 20 | (a) Both true, R explains A |
| 21 | Reflex (fast, involuntary, spinal cord) |
| 22 | Hormones travel by blood; effect lasts; impulses are quick but brief |
| 23 | Loss of balance, coordination and smooth movement control / posture problems |
| 24 | Pancreas cannot produce enough insulin |
| 25 | Root bends towards moist soil; positive hydrotropism |
| 26–27 | Refer to Fig. 1 and Fig. 2 diagrams of this page |
| 28 | Adrenal gland; adrenaline prepares the body for stress (increased heartbeat and sweating) |
| 29 | Shoot grows straight because auxin distribution stays even under equal light from all sides |
| 30 | Yes, he will feel pain (sensory pathway to brain is intact), but he cannot withdraw the hand because the motor impulse cannot reach the muscle |
17. Common Mistakes Students Make
| Common Mistake | Correct Understanding |
|---|---|
| Impulse flows from axon to dendrite | Impulse flows from dendrites → cell body → axon → nerve endings |
| Synapse described as a solid connection | Synapse is a microscopic gap; impulse crosses it chemically |
| Writing reflex arc without the spinal cord | Reflex arc passes through the spinal cord (receptor → sensory → spinal cord → motor → effector) |
| Confusing cerebrum with cerebellum | Cerebrum is for thinking/memory/voluntary action; cerebellum is for balance/coordination |
| Saying brain controls all reflexes | Most reflex actions are coordinated by the spinal cord (reflex arc) |
| Root grows up, shoot grows down | Root is positively geotropic (downwards); shoot is negatively geotropic (upwards) |
| Saying all plant growth is due to auxin | Different hormones have different roles: auxin, gibberellin, cytokinin, abscisic acid |
| Reversing positive/negative tropism definitions | Positive = towards stimulus; Negative = away from stimulus |
| Insulin secretion blamed on liver | Insulin is secreted by the pancreas; it regulates blood sugar |
| Thyroxine said to be iodine-free | Thyroxine requires iodine; deficiency causes goitre |
| Adrenaline said to work slowly | Adrenaline works quickly to prepare the body for emergencies |
| Growth hormone attributed to thyroid | Growth hormone is secreted by the pituitary; thyroxine by the thyroid |
18. CBSE Board Exam Tips
Labelled Diagrams
- Practise the neuron, reflex arc, brain and endocrine-in-position diagrams until you can draw them quickly.
- Draw large, clear labels with pencil rules; label the four-direction impulse on the neuron.
Reflex Arc Questions
- Always write in the pathway form: Receptor → Sensory neuron → Spinal cord → Motor neuron → Effector.
- Mention that the brain is not involved in the reflex arc so the response is fast.
Brain-Function Questions
- Match each function to its region: cerebrum (thinking/voluntary), cerebellum (balance), medulla (involuntary), hypothalamus (temperature/hunger), pons (respiration-relay).
Tropism Questions
- Write stimulus, direction and example for each tropism. State positive/negative clearly.
- For phototropism, always mention auxin redistribution to the shaded side.
Hormone-Function Questions
- Give gland + hormone + function in one line, e.g. “Pancreas secretes insulin, which regulates blood sugar.”
Comparison Questions
- Use a two/three-column table: basis of comparison, feature 1, feature 2. Include speed, duration and carrier as key rows.
Assertion-Reason Strategy
- Judge whether A is true, then whether R is true, then whether R correctly explains A. Watch out for correct statements that do not explain the assertion.
Case-Based Questions
- Read the case, underline the stimuli/organs involved, then map them to topics such as reflex arc, brain region, tropism or hormone.
Writing Biological Explanations
- Order: define the term, state the mechanism, then give the example. Keep answers compact and neat.
Important Diagrams to Practise
- Neuron, Reflex Arc, Human Brain, Endocrine glands in human body, and Phototropism/Geotropism sketches.
19. Quick Revision – Control and Coordination
Nervous System Summary
- Neuron is the functional unit; impulse travels dendrite → cell body → axon → nerve endings → synapse.
- CNS = brain + spinal cord; PNS = nerves radiating out.
Reflex Arc
- Receptor → Sensory neuron → Spinal cord → Motor neuron → Effector → Response.
- Fast, automatic, protective; brain not directly involved.
Brain Parts and Functions
- Cerebrum: thinking, memory, reasoning, voluntary actions.
- Hypothalamus: temperature, hunger, thirst, emotions.
- Midbrain: visual/auditory reflex relay.
- Cerebellum: balance, posture, movement coordination.
- Pons: breathing regulation, relay.
- Medulla: heartbeat, breathing, blood pressure (involuntary).
Plant Movements
- Growth (tropic): phototropism, geotropism, hydrotropism, chemotropism.
- Non-growth: touch-me-not leaf folding (turgor change).
Plant Hormones
- Auxin – growth/phototropism; Gibberellin – elongation, germination; Cytokinin – cell division; Abscisic acid – inhibition/dormancy/stomatal closure.
Endocrine Glands and Hormones
- Pituitary – growth hormone (master gland).
- Thyroid – thyroxine (needs iodine; goitre on deficiency).
- Adrenal – adrenaline (emergency).
- Pancreas – insulin (blood sugar; diabetes on deficiency).
- Testes – testosterone; Ovaries – oestrogen (secondary sexual characters).
Important Comparisons
- Nervous coordination: fast, short-lived. Hormonal coordination: slow, long-lasting.
- Reflex action: involuntary, automatic. Voluntary action: conscious, deliberate.
- Positive tropism: growth towards stimulus. Negative tropism: growth away.