Navigating through the CBSE Class 10 Science curriculum requires an in-depth understanding of neuromuscular coordination, neuroanatomy, reflex physiology, phytohormonal regulation, and endocrine feedback loops. Chapter 6 of Class 10 Biology, “Control and Coordination”, explores how multicellular organisms integrate environmental stimuli into regulated physiological responses. In animals, this coordination is executed via the fast, point-to-point electrical network of the Central and Peripheral Nervous System paired with the systemic, chemical communication of the Endocrine System. In plants, which lack nervous tissues, coordination relies on directional growth movements (tropisms), turgor-driven nastic responses, and plant growth regulators (auxins, gibberellins, cytokinins, abscisic acid). To help students master every aspect of this high-weightage chapter, this comprehensive solutions guide offers textbook-accurate, highly structured, and pedagogically sound responses strictly aligned with the latest CBSE evaluation standards.
Every question presented in the official NCERT textbook—ranging from all three in-text question sets to the complete chapter-end exercises (Questions 1 to 12)—has been solved with exhaustive detail. Short-answer conceptual responses follow the official 30–40 word limit, while 3-mark and 5-mark physiological comparisons use structured tables and clear neuro-chemical schematics. Key scoring terms, official CBSE board year tags, and comparative charts have been highlighted to ensure students secure maximum marks in their CBSE Board Examinations.
Master Formula & Concept Summary Tables
1. Plant Hormones (Phytohormones) and Their Functions
| Plant Hormone | Primary Physiological Role | Mechanism of Action / Key Function |
|---|---|---|
| Auxin | Growth Promoter | Synthesized at shoot and root tips; promotes cell elongation, apical dominance, and phototropism by diffusing to the shaded side of shoots. |
| Gibberellins | Growth Promoter | Promotes stem elongation, breaking of seed dormancy, and fruit enlargement. |
| Cytokinins | Growth Promoter | Promotes rapid cell division (mitosis); present in highest concentrations in areas of rapid cell division like fruits, seeds, and shoot buds. Delays leaf aging. |
| Abscisic Acid (ABA) | Growth Inhibitor | The primary stress hormone; inhibits growth, causes wilting and falling of leaves, and promotes stomatal closure during drought stress. |
| Ethylene | Fruit Ripening | Gaseous plant regulator that accelerates the ripening of fruits and leaf abscission. |
2. Major Human Endocrine Glands and Their Hormones
| Endocrine Gland | Location in Body | Hormone(s) Secreted | Primary Function in the Human Body |
|---|---|---|---|
| Pituitary Gland | Base of Brain (Master Gland) | Growth Hormone (GH) | Regulates overall somatic growth and bone development; deficiency causes Dwarfism, excess causes Gigantism. |
| Thyroid Gland | Neck / Larynx | Thyroxin | Regulates carbohydrate, protein, and fat metabolism for optimal body growth. Requires Iodine for synthesis. |
| Pancreas | Below Stomach | Insulin & Glucagon | Insulin lowers blood glucose levels; deficiency causes Diabetes mellitus. |
| Adrenal Glands | On top of Kidneys | Adrenaline | Prepares the body for emergency / fight-or-flight responses; increases heart rate, blood pressure, and breathing rate. |
| Testes (Male) | Scrotum | Testosterone | Controls development of male secondary sexual characteristics and regulates sperm production (spermatogenesis). |
| Ovaries (Female) | Pelvic Cavity | Oestrogen & Progesterone | Controls female secondary sexual characteristics, regulates menstrual cycle, and maintains pregnancy. |
3. Comparison: Nervous Coordination vs. Chemical (Hormonal) Coordination
| Parameter / Basis | Nervous Coordination | Chemical (Hormonal) Coordination |
|---|---|---|
| Nature of Signal | Electrical impulses traveling along axon membranes and chemical neurotransmitters across synapses. | Chemical messengers (Hormones) secreted directly into the bloodstream. |
| Speed of Action | Extremely rapid and immediate (milliseconds). | Slow and prolonged in response and action. |
| Target Specificity | Highly localized; affects only specific muscles or glands connected to nerves. | Wide target range; blood carries hormones to all tissues, affecting only cells with specific receptors. |
| Duration of Effect | Short-lived; ceases immediately when impulse stops. | Long-lasting and persistent effects on growth and metabolic regulation. |
NCERT In-Text Questions: Set 1 (Page No. 119)
Question 1 What is the difference between a reflex action and walking? [CBSE 2024, 2020]
Answer:
| Parameter | Reflex Action | Walking |
|---|---|---|
| Nature of Action | Involuntary, spontaneous, and unconscious automatic response to a sensory stimulus. | Voluntary, learned, and conscious motor action performed by will. |
| Control Centre | Monitored and controlled by the Spinal Cord (Central Nervous System). | Controlled and coordinated by the Forebrain (Cerebrum) and Hindbrain (Cerebellum). |
| Speed of Action | Extremely fast and instantaneous (protective mechanism). | Moderate speed, variable according to human desire. |
| Example | Pulling the hand back instantly upon touching a boiling pan. | Walking in a straight line, running, or changing direction. |
Question 2 What happens at the synapse between two neurons? [CBSE 2024, 2022]
Answer: A synapse is a microscopic gap between the axon terminal of one neuron and the dendrite of the next neuron.
================================================================================ NEUROTRANSMISSION AT THE SYNAPSE: -------------------------------------------------------------------------------- 1. Arrival of Impulse: An electrical impulse travels along the axon and reaches the terminal nerve endings. 2. Chemical Release: The electrical impulse triggers the release of chemical messengers called Neurotransmitters (e.g., Acetylcholine) into the synaptic cleft. 3. Diffusion & Reception: These chemical molecules diffuse across the microscopic gap and bind to specific receptor sites on the dendrite of the adjacent neuron. 4. Generation of New Impulse: This binding initiates a fresh electrical impulse in the next neuron, ensuring strictly unidirectional transmission of signals. ================================================================================
Question 3 Which part of the brain maintains the posture and equilibrium of the body? [CBSE 2023]
Answer: The Cerebellum, which is an integral part of the Hindbrain, is responsible for coordinating voluntary muscle movements, maintaining bodily posture, balance, and physical equilibrium (e.g., while riding a bicycle or walking in a straight line).
Question 4 How do we detect the smell of an agarbatti (incense stick)? [CBSE 2024, 2020]
Answer: We detect the smell of an incense stick through specialized sensory mechanisms:
- Volatile aromatic particles released by the burning incense stick diffuse through the air and enter the nasal cavity.
- These odor molecules bind to specialized Olfactory Receptors located in the epithelial lining of the nose, triggering an electrical impulse.
- Sensory neurons transmit this nerve impulse to the Olfactory Lobes of the Forebrain (Cerebrum), which interprets the signal and retrieves past memories to identify the pleasant scent of the agarbatti.
Question 5 What is the role of the brain in reflex action? [CBSE 2023]
Answer: The brain has no active role in initiating or executing a reflex action:
- Reflex arcs are completed and executed entirely at the level of the Spinal Cord to ensure the fastest possible defensive response to prevent tissue injury.
- The brain’s role is purely informative and secondary: sensory signals traveling through the spinal cord relay information to the brain so that the event is registered, recorded in conscious memory, and processed for future learning.
NCERT In-Text Questions: Set 2 (Page No. 122)
Question 1 What are plant hormones? [CBSE 2024, 2020]
Answer: Plant hormones (also known as Phytohormones) are naturally occurring, specialized chemical compounds synthesized in minute quantities in one part of the plant (such as root or shoot tips) that diffuse to other parts to control, coordinate, and regulate growth, development, cell division, and environmental responses.
Question 2 How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light? [CBSE 2024, 2022]
Answer:
| Parameter | Movement in Sensitive Plant (Mimosa pudica) | Movement of Shoot Towards Light (Phototropism) |
|---|---|---|
| Type of Movement | Nastic Movement (Non-directional, immediate response). | Tropic Movement (Directional, growth-related response). |
| Growth Dependency | Independent of growth; reversible. | Dependent on growth; irreversible. |
| Mechanism | Caused by sudden changes in turgor pressure (water loss) in cells of the pulvinus at the leaf base. | Caused by unequal distribution of Auxin hormone, stimulating cell elongation on the shaded side. |
| Response Speed | Extremely rapid (leaves fold within seconds of touch). | Slow and gradual (takes several days to bend). |
Question 3 Give an example of a plant hormone that promotes growth.
Answer: Auxin (or Gibberellin / Cytokinin) is a primary plant hormone that promotes cell elongation, apical dominance, and overall plant growth.
Question 4 How do auxins promote the growth of a tendril around a support? [CBSE 2024, 2023]
Answer: Tendrils are sensitive, thread-like climbing organs of plants like peas and bitter gourd:
- When a tendril comes into physical contact with a solid support, auxin synthesised at the tip diffuses away from the point of contact toward the side of the tendril facing away from the support.
- The higher concentration of auxin on the outer, shaded side stimulates rapid cell elongation compared to the side in direct contact with the object.
- This unequal growth causes the tendril to bend and coil tightly around the support, anchoring the climbing plant firmly.
Question 5 Design an experiment to demonstrate hydrotropism. [CBSE 2024, 2020]
Answer:
================================================================================
EXPERIMENTAL DEMONSTRATION OF HYDROTROPISM:
--------------------------------------------------------------------------------
1. Procedure:
• Take a shallow wooden trough containing dry soil or sawdust.
• Plant a few germinating bean/pea seeds at one end of the trough (End A).
• At the opposite end (End B), place a porous clay pot filled with water.
2. Observation:
• Initially, the radicles (young roots) grow downward due to positive geotropism.
• After several days, as the roots extend, they distinctly bend and grow
horizontally TOWARD the porous clay pot (the source of water).
3. Conclusion:
• Plant roots exhibit POSITIVE HYDROTROPISM, actively bending and growing
toward water, showing that water stimulus can overcome gravitational pull.
================================================================================
NCERT In-Text Questions: Set 3 (Page No. 125)
Question 1 How does chemical coordination take place in animals? [CBSE 2024]
Answer: Chemical coordination in animals is mediated by the Endocrine System:
- Ductless endocrine glands secrete specialized chemical messengers called Hormones directly into the circulating bloodstream.
- The blood carries these hormones throughout the body to specific target organs or tissues equipped with complementary molecular receptors.
- Hormones regulate long-term processes such as metabolic rate (Thyroxin), blood glucose levels (Insulin), growth and development (Growth Hormone), and emergency responses (Adrenaline).
Question 2 Why is the use of iodised salt advisable? [CBSE 2024, 2020]
Answer: The use of iodised salt is essential because Iodine is a mandatory chemical element required by the Thyroid Gland to synthesize the hormone Thyroxin:
- Thyroxin regulates carbohydrate, protein, and fat metabolism in the body to ensure balanced physical and mental development.
- A deficiency of iodine in the daily diet prevents thyroxin synthesis, causing the thyroid gland to enlarge abnormally in the neck, resulting in a disease called Simple Goitre.
Question 3 How does our body respond when adrenaline is secreted into the blood? [CBSE 2024, 2022]
Answer: Adrenaline (secreted by the adrenal medulla during fear, stress, or danger) triggers the “fight-or-flight” response through the following coordinated physiological changes:
- Increased Heart Rate: The heart beats faster to pump larger volumes of oxygen-rich blood to skeletal muscles.
- Diversion of Blood Supply: Blood supply to the skin and digestive system is reduced due to vasoconstriction of small arteries, diverting maximum blood to the skeletal muscles.
- Increased Breathing Rate: The diaphragm and rib muscles contract rapidly, accelerating oxygen intake.
- Elevated Blood Glucose: The liver breaks down stored glycogen into glucose, providing muscles with instant energy to confront or escape the emergency.
Question 4 Why are some patients of diabetes treated by giving injections of insulin? [CBSE 2023, 2020]
Answer: Diabetes mellitus is a metabolic disorder caused by the deficient secretion or absence of the hormone Insulin by the beta-cells of the pancreas:
- Insulin is responsible for regulating blood sugar levels by promoting the uptake and conversion of excess blood glucose into stored glycogen in the liver and muscle cells.
- In diabetic patients, insufficient insulin causes blood glucose levels to rise dangerously high (hyperglycemia), leading to organ damage. Injections of insulin restore normal metabolic regulation.
NCERT Chapter-End Exercises (Page No. 126-127)
Question 1 Which of the following is a plant hormone? (a) Insulin (b) Thyroxin (c) Oestrogen (d) Cytokinin
Answer: (d) Cytokinin Explanation: Cytokinin is a plant growth hormone that promotes cell division, while insulin, thyroxin, and oestrogen are animal hormones.
Question 2 The gap between two neurons is called a: (a) dendrite (b) synapse (c) axon (d) impulse
Answer: (b) synapse Explanation: The microscopic functional junction across which nerve impulses pass from the axon terminal of one neuron to the dendrite of an adjacent neuron is called a synapse.
Question 3 The brain is responsible for: (a) thinking (b) regulating the heartbeat (c) balancing the body (d) all of the above
Answer: (d) all of the above Explanation: The cerebrum is responsible for thinking and memory; the medulla oblongata in the hindbrain regulates involuntary actions like heartbeat and breathing; the cerebellum maintains posture and body balance.
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? [CBSE 2024, 2020]
Answer:
- Function of Receptors: Receptors are specialized sensory nerve cells located in sense organs (photoreceptors in eyes, phonoreceptors in ears, olfactory in nose, gustatory on tongue, thermoreceptors in skin) that detect external environmental stimuli and convert them into electrical nerve impulses.
- Problems When Receptors Fail:
- If skin thermoreceptors fail, a person cannot feel heat or pain, risking severe accidental burns or physical injuries without awareness.
- If gustatory receptors fail, spoiled or poisonous food cannot be detected by taste, causing severe food poisoning.
- If auditory or visual receptors fail, spatial awareness is lost, endangering physical safety in traffic and daily life.
Question 5 Draw the structure of a neuron and explain its function. [CBSE 2024, 2023]
Answer: A Neuron (nerve cell) is the basic structural and functional unit of the nervous system.
================================================================================
STRUCTURE AND FUNCTION OF A NEURON:
--------------------------------------------------------------------------------
1. Structural Components:
• Dendrites: Branch-like projections that receive sensory information and
stimuli, generating an electrical chemical signal.
• Cyton (Cell Body): Contains the nucleus and cytoplasm; processes the
incoming impulse from dendrites.
• Axon: A long, cylindrical single fiber insulated by a myelin sheath that
conducts the electrical impulse away from the cyton to the nerve endings.
• Axon Terminal (Nerve Endings): Releases chemical neurotransmitters across
the synapse to trigger the next neuron or activate a muscle/gland.
2. Primary Function:
To rapidly acquire, conduct, and transmit electrical nerve impulses across
the body, coordinating sensory perception with motor muscular responses.
================================================================================
Question 6 How does phototropism occur in plants? [CBSE 2024, 2020]
Answer: Phototropism is the directional growth movement of plant organs in response to the direction of light:
- When growing plant shoot tips receive directional sunlight from one side, the plant hormone Auxin synthesised at the shoot tip diffuses toward the shaded side of the stem.
- The higher concentration of auxin on the shaded side stimulates the cells in that region to elongate and grow faster than the cells on the illuminated side.
- This unequal growth causes the shoot to bend toward the light source, demonstrating positive phototropism. In contrast, roots grow away from light, exhibiting negative phototropism.
Question 7 Which signals will get disrupted in case of a spinal cord injury? [CBSE 2024, 2022]
Answer: In case of an injury to the spinal cord, two critical neural pathways are severely disrupted:
- Reflex Actions: All involuntary spinal reflex arcs below the level of injury will be abolished, preventing rapid protective responses.
- Sensory and Motor Communication with Brain: Sensory nerve impulses carrying sensations (pain, touch, temperature) from the lower body to the brain will fail to reach the cerebrum, and voluntary motor commands from the brain to skeletal muscles of the legs and pelvic organs will be blocked, resulting in paralysis and loss of sensation.
Question 8 How does chemical coordination occur in plants? [CBSE 2023]
Answer: Chemical coordination in plants occurs through Phytohormones:
- Plant cells synthesize specific chemical messengers (Auxins, Gibberellins, Cytokinins, Abscisic Acid) in response to environmental cues like light, gravity, water, and touch.
- These hormones diffuse through plant tissues from their site of origin to target cells, where they bind to cellular receptors and regulate processes like cell division, elongation, directional bending (tropisms), seed dormancy, and leaf abscission.
Question 9 What is the need of a system of control and coordination in an organism? [CBSE 2024, 2020]
Answer: A multicellular organism consists of billions of specialized cells organized into diverse organs and organ systems (digestive, respiratory, circulatory, excretory):
- Functional Integration: Various body organs must work together in a synchronized, harmonious manner; for instance, during digestion, gastric secretion, enzyme release, and peristalsis must occur in strict sequence.
- Environmental Adaptation: Organisms must detect external changes (danger, food, temperature) and produce appropriate, rapid responses to survive and maintain internal homeostasis.
Question 10 How are involuntary actions and reflex actions different from each other? [CBSE 2024, 2023]
Answer:
| Parameter | Involuntary Actions | Reflex Actions |
|---|---|---|
| Definition | Regular, continuous physiological activities occurring automatically without conscious will. | Sudden, rapid, and automatic protective motor responses to a specific external stimulus. |
| Control Centre | Controlled by the Midbrain and Hindbrain (Medulla Oblongata). | Controlled and executed primarily by the Spinal Cord. |
| Stimulus Requirement | Does not require a sudden external sensory stimulus (runs continuously). | Triggered specifically by an immediate external stimulus (e.g., heat, pinprick). |
| Examples | Beating of the heart, peristalsis of the gut, secretion of saliva, blood pressure regulation. | Blinking of eyes when an object approaches, withdrawing hand from a hot flame. |
Question 11 Compare and contrast nervous and hormonal mechanisms for control and coordination in animals. [CBSE 2024, 2020]
Answer:
| Basis of Comparison | Nervous Mechanism | Hormonal (Endocrine) Mechanism |
|---|---|---|
| Mediating Agent | Electrical impulses along neurons and neurotransmitters at synapses. | Chemical substances (Hormones) secreted directly into the bloodstream. |
| Pathway of Transmission | Dedicated network of nerves and spinal cord tracks. | Circulatory system (blood vascular system). |
| Speed and Response | Instantaneous and ultra-rapid (milliseconds). | Slow, gradual, and progressive response. |
| Specificity and Area | Highly localized (affects only target muscle or gland). | Widespread (affects multiple tissues and organs expressing specific receptors). |
| Duration of Effect | Short-lived; ceases as soon as the impulse stops. | Persistent and long-lasting regulatory action. |
Question 12 What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs? [CBSE 2024, 2022]
Answer:
| Parameter | Movement in Sensitive Plant (Touch-Me-Not) | Movement in Human Legs |
|---|---|---|
| Nature of Tissue | Involves plant cells; lacks nervous and muscular tissues. | Involves specialized muscle cells and motor neurons. |
| Mechanism of Movement | Plant cells change shape by altering the amount of water (turgor pressure) in them, swelling or shrinking. | Muscle cells change shape by the contraction and relaxation of specialized muscle proteins (Actin and Myosin). |
| Transmission of Signal | Electrical-chemical signals diffuse slowly from cell to cell. | Nerve impulses travel rapidly along dedicated motor nerve fibers at high speed. |
| Voluntary Control | Involuntary plant movement triggered by touch. | Voluntary motor movement under conscious brain control. |
Frequently Asked Questions (FAQs) – Class 10 Biology Chapter 6
Question 1: What is a reflex arc? Name the components in correct sequence. [CBSE 2024] Answer: A reflex arc is the neural pathway that mediates a reflex action. The correct sequence is: Receptor (Sense Organ) → Sensory Neuron → Relay Neuron (Spinal Cord) → Motor Neuron → Effector (Muscle/Gland)
Question 2: What is the main thinking part of the human brain? [CBSE 2023] Answer: The Forebrain (specifically the Cerebrum) is the main thinking, learning, intelligence, conscious thought, and sensory-interpretation center of the human brain.
Question 3: Which part of the brain controls involuntary functions like blood pressure, salivation, and vomiting? [CBSE 2024] Answer: The Medulla Oblongata located in the Hindbrain controls essential involuntary actions including heartbeat, blood pressure, salivation, swallowing, and vomiting.
Question 4: What is the protective covering of the human brain? [CBSE 2022] Answer: The brain is protected by a bony box called the Cranium (Skull), lined with three protective membranes called Meninges, and cushioned by shock-absorbing Cerebrospinal Fluid (CSF).
Question 5: What is thigmotropism? Give an example. [CBSE 2024] Answer: Thigmotropism is the directional growth movement of a plant in response to physical touch or contact with a solid support, as seen in the coiling of tendrils in pea plants.
Question 6: Why is Abscisic Acid called the stress hormone in plants? [CBSE 2023] Answer: Abscisic acid (ABA) is called the stress hormone because it is produced under adverse environmental conditions (like drought) to induce stomatal closure to conserve water and inhibit growth.
Question 7: How does a feedback mechanism regulate hormone secretion? Give an example. [CBSE 2024, 2020] Answer: A feedback mechanism regulates the timing and quantity of hormone release: when blood glucose rises after a meal, pancreatic beta-cells detect it and secrete more insulin; as glucose drops to normal, insulin secretion is switched off.
Question 8: What is chemotropism? Give a classic example. [CBSE 2024] Answer: Chemotropism is the directional growth movement of a plant part in response to a chemical stimulus. A classic example is the growth of the pollen tube toward the ovule through the style during fertilization.
Question 9: What is geotropism? Which plant parts show positive and negative geotropism? [CBSE 2023] Answer: Geotropism is the growth movement of plants in response to gravity. Roots grow downward toward gravity (Positive Geotropism), while shoots grow upward away from gravity (Negative Geotropism).
Question 10: Which hormone is responsible for puberty changes in boys and girls? [CBSE 2022] Answer:
- In Boys: Testosterone (secreted by the Testes).
- In Girls: Oestrogen (secreted by the Ovaries).
Question 11: What is the difference between an endocrine gland and an exocrine gland? [CBSE 2024] Answer: Endocrine glands are ductless glands that secrete hormones directly into the bloodstream (e.g., Pituitary, Thyroid); exocrine glands have ducts to release secretions locally (e.g., Salivary glands, Sweat glands).
Question 12: Why is the pancreas called a heterocrine (mixed) gland? [CBSE 2023] Answer: The pancreas functions as both an exocrine gland (secreting digestive pancreatic juice containing trypsin and lipase via pancreatic duct) and an endocrine gland (secreting hormones insulin and glucagon directly into blood).
Question 13: What causes dwarfism and gigantism in humans? [CBSE 2022] Answer:
- Dwarfism: Caused by the under-secretion (deficiency) of Growth Hormone (GH) from the anterior pituitary during childhood.
- Gigantism: Caused by the over-secretion (excess) of Growth Hormone (GH) during childhood, leading to abnormal bone growth.
Question 14: What is the function of the myelin sheath in a neuron? [BOARD EXAM FAVORITE] Answer: The myelin sheath is an insulating fatty layer surrounding the axon that prevents electrical leakage and significantly increases the transmission speed of nerve impulses.
Question 15: What are gustatory and olfactory receptors? [CBSE 2024] Answer:
- Gustatory Receptors: Located on taste buds on the tongue to detect taste (sweet, salty, sour, bitter, umami).
- Olfactory Receptors: Located in the mucous membrane of the nasal cavity to detect smell.
Mastering the NCERT Solutions for Class 10 Science Chapter 6, “Control and Coordination”, equips students with the neuroanatomical concepts, endocrine feedback mechanisms, and phytohormonal pathways required for the CBSE Board Examination. Review the reflex arc sequence, the master endocrine table, and the 15 board-level FAQs above to secure full marks in your biology evaluations.