Here are 50 short-answer questions (3 marks each) from the chapter "Control and Coordination," based on previous CBSE Class 10 board examinations.
Nervous System & Reflex Action
What is a synapse? What happens at the synapse between two neurons? How are messages carried across it?
A synapse is the junction between the axon terminal of one neuron and the dendrite of the next.
When an electrical impulse reaches the axon terminal, it triggers the release of chemical messengers called neurotransmitters.
These neurotransmitters diffuse across the gap (synaptic cleft) and bind to receptors on the dendrite of the next neuron, initiating a new electrical impulse.
Define reflex action. Draw a flowchart showing the sequence of events that occur during a reflex action like sneezing.
A reflex action is a rapid, automatic, and involuntary response to a stimulus, not under the conscious control of the brain.
Flowchart for Sneezing:
Stimulus: Irritant enters the nose (e.g., dust, pollen).
➡️ Receptor: Sensory cells in the nasal lining detect the irritant.
➡️ Sensory Neuron: Transmits the signal towards the spinal cord/brainstem.
➡️ Relay Neuron (in CNS): Processes the information.
➡️ Motor Neuron: Carries the command signal away from the CNS.
➡️ Effector: Muscles of the diaphragm, chest, and face contract forcefully.
➡️ Response: Sneezing occurs to expel the irritant.
Draw a neat diagram of a neuron and label the following parts: (a) Dendrite, (b) Axon, and (c) Myelin Sheath. *
* **(a) Dendrite:** Branched, tree-like structures at the beginning of a neuron that receive signals.
* **(b) Axon:** A long, slender projection that conducts electrical impulses away from the neuron's cell body.
* **(c) Myelin Sheath:** An insulating layer that forms around the axon, allowing nerve impulses to transmit more quickly.
Differentiate between voluntary, involuntary, and reflex actions. Give one example of each.
Voluntary Actions: Controlled by conscious thought (cerebrum). Example: Writing, walking.
Involuntary Actions: Not under conscious control, regulated by the hindbrain and midbrain. Example: Heartbeat, breathing.
Reflex Actions: A specific type of involuntary action controlled mainly by the spinal cord for a very fast response. Example: Withdrawing your hand from a hot object.
What is a reflex arc? Describe the pathway of a reflex arc with a suitable diagram.
A reflex arc is the neural pathway that controls a reflex action.
Pathway: It begins with a receptor that detects the stimulus. A sensory neuron carries the signal to the spinal cord. Here, a relay neuron passes the signal to a motor neuron. The motor neuron then carries the signal to an effector (a muscle or gland), which produces the response.
How does the nervous system control and coordinate activities in the human body?
The nervous system uses a network of specialized cells called neurons to transmit signals.
Receptors gather information from the environment (stimuli). This information travels as electrical impulses along sensory neurons to the Central Nervous System (CNS) - the brain and spinal cord.
The CNS processes the information and decides on an appropriate response. The response command is then sent via motor neurons to effectors (muscles and glands) to carry out the action.
The Human Brain 🧠
Name the three major parts of the human brain. Write one function for each.
(i) Forebrain: The largest part, with the cerebrum as its main component. Its function is thinking, memory, intelligence, and processing sensory information.
(ii) Midbrain: It acts as a bridge, connecting the forebrain and hindbrain. It controls reflexes related to sight and hearing.
(iii) Hindbrain: Consists of the cerebellum, pons, and medulla. Its functions include controlling posture, balance (cerebellum), and involuntary actions like breathing and heartbeat (medulla).
How is the human brain protected from injuries and shocks?
The brain is protected by three main layers:
(i) Bony Box (Cranium): The skull provides a hard, external protective casing.
(ii) Meninges: Three layers of protective membranes (dura mater, arachnoid mater, pia mater) that cover the brain.
(iii) Cerebrospinal Fluid (CSF): A fluid that fills the space between the meninges, acting as a shock absorber to cushion the brain against mechanical jolts.
List three functions of the forebrain.
(i) Thinking and Reasoning: It is the main thinking part of the brain, responsible for logic, problem-solving, and planning.
(ii) Memory Storage: It stores information and is the seat of intelligence and memory.
(iii) Processing Sensory Information: It interprets information from sensory organs like the eyes, ears, nose, and skin (touch, pain, temperature).
Mention the roles of the following: (a) Cerebellum, (b) Medulla, (c) Cerebrum.
(a) Cerebellum: It is responsible for precision in voluntary actions and maintaining the body's posture and balance.
(b) Medulla: It controls vital involuntary actions such as heartbeat, breathing, blood pressure, and vomiting.
(c) Cerebrum: It is the center of intelligence, memory, consciousness, and willpower. It also controls all voluntary actions.
Plant Hormones & Movements 🌱
What are plant hormones (phytohormones)? Name a plant hormone that inhibits growth and mention its functions.
Plant hormones are chemical compounds produced by plants that regulate their growth, development, and responses to environmental stimuli.
Abscisic Acid (ABA) is a growth-inhibiting hormone.
Functions of ABA:
Induces dormancy in seeds and buds.
Promotes the closing of stomata to prevent water loss.
Causes the wilting and falling of leaves (abscission).
How does phototropism occur in plants? Explain with the help of a diagram.
Phototropism is the growth of a plant shoot towards a light source.
The hormone auxin is synthesized at the shoot tip. When light comes from one side, auxin diffuses towards the shaded side of the shoot.
The higher concentration of auxin on the shaded side stimulates the cells there to grow longer than the cells on the illuminated side. This differential growth causes the shoot to bend towards the light.
Differentiate between tropic movements and nastic movements in plants.
Tropic Movements: These are directional growth movements that occur in response to the direction of a stimulus. They are slow. Example: Bending of a shoot towards light (phototropism).
Nastic Movements: These are non-directional movements that are independent of the direction of the stimulus. They are relatively fast. Example: Folding of the leaves of a 'touch-me-not' plant when touched.
Name four major types of plant hormones. Write one function for each.
(i) Auxins: Promote cell elongation and are responsible for phototropism.
(ii) Gibberellins: Promote stem and fruit growth; also involved in breaking seed dormancy.
(iii) Cytokinins: Promote cell division and delay the aging of leaves.
(iv) Abscisic Acid: Inhibits growth, causes stomatal closure, and promotes dormancy.
Explain geotropism in plants. Describe an experiment to demonstrate it.
Geotropism is the growth of plant parts in response to gravity. Roots show positive geotropism (grow downwards), while shoots show negative geotropism (grow upwards).
Experiment:
Take a potted plant and place it horizontally on its side for a few days.
Observation: The shoot will bend and grow upwards, away from the pull of gravity (negative geotropism). The roots will bend and grow downwards, towards the pull of gravity (positive geotropism).
Conclusion: This demonstrates that plant parts respond to the stimulus of gravity.
How is the movement of leaves of a sensitive plant different from the movement of a shoot towards light?
Movement of Sensitive Plant Leaves (Thigmonasty):
It is a nastic movement (non-directional).
It is a rapid response to touch, caused by changes in turgor pressure in the cells of the pulvinus.
It is not a growth movement.
Movement of Shoot Towards Light (Phototropism):
It is a tropic movement (directional).
It is a slow response to light, caused by differential cell growth due to the hormone auxin.
It is a growth movement.
What is chemotropism? Give an example.
Chemotropism is the movement or growth of a part of a plant in response to a chemical stimulus.
Example: The growth of the pollen tube from the stigma, through the style, towards the ovule in a flower. This growth is guided by chemical signals (sugars) secreted by the ovule. This process is essential for fertilization.
Endocrine System in Humans 👨⚕️
Why is the pituitary gland called the 'master gland'? Name the hormone it secretes that regulates growth.
The pituitary gland is called the master gland because it produces hormones that control the functioning of several other important endocrine glands (like the thyroid, adrenal glands, testes, and ovaries).
It acts as the command center for the endocrine system.
The hormone it secretes to regulate overall body growth is called Growth Hormone (GH).
How is the timing and amount of hormone release regulated? Explain with the help of an example.
The release of hormones is regulated by a feedback mechanism. This system ensures that hormones are secreted in precise quantities and only when needed.
Example (Blood Sugar Regulation):
When blood sugar levels rise (e.g., after a meal), the pancreas is stimulated to secrete insulin.
Insulin helps cells absorb glucose, thus lowering blood sugar.
When blood sugar falls to a normal level, the pancreas reduces insulin secretion. This is a negative feedback loop.
Why are some patients of diabetes treated by giving injections of insulin?
Diabetes is a condition where the pancreas does not produce enough insulin, or the body cannot effectively use the insulin it produces.
Insulin is a protein hormone that is essential for regulating blood sugar levels.
If taken orally, insulin would be digested by the protein-digesting enzymes in the stomach and small intestine, rendering it ineffective. Therefore, it must be injected directly into the bloodstream to perform its function.
Name the gland and the hormone secreted for the following conditions:
(a) A person has stunted growth.
(b) A person's blood sugar level is high.
(c) A person is suffering from goitre.
(a) Gland: Pituitary Gland; Hormone: Growth Hormone (deficiency).
(b) Gland: Pancreas; Hormone: Insulin (deficiency).
(c) Gland: Thyroid Gland; Hormone: Thyroxine (deficiency due to lack of iodine).
What happens when adrenaline is secreted into the blood? How does it help the body cope with emergency situations?
Adrenaline is the "fight or flight" hormone, preparing the body for emergencies.
Effects of Adrenaline Secretion:
Heart beats faster to supply more oxygen to muscles.
Blood flow is diverted to skeletal muscles and away from the digestive system.
Breathing rate increases, and the diaphragm and rib muscles contract more.
Liver releases more glucose into the blood to provide energy.
These rapid changes provide the body with a burst of energy and heightened alertness to either fight or flee from a dangerous situation.
List the functions of testosterone and oestrogen.
Testosterone (in males):
Stimulates the development of male reproductive organs (testes, prostate).
Responsible for the development of male secondary sexual characteristics (deep voice, beard, body hair).
Regulates sperm production.
Oestrogen (in females):
Stimulates the development of female reproductive organs (uterus, fallopian tubes).
Responsible for the development of female secondary sexual characteristics (breast development, wider hips).
Regulates the menstrual cycle.
Why is it important for us to have iodized salt in our diet?
Iodine is an essential mineral required by the thyroid gland to produce the hormone thyroxine.
Thyroxine regulates the metabolism of carbohydrates, fats, and proteins, which is crucial for overall growth and development.
A deficiency of iodine in the diet leads to insufficient production of thyroxine, causing a condition called goitre, which is characterized by a swollen neck. Therefore, using iodized salt prevents this deficiency disease.
Q25. Explain the mechanism of phototropism in plants.
Solution:
Phototropism is the directional growth of a plant part in response to a light stimulus. The mechanism is regulated by the hormone auxin:
Synthesis of Auxin: Auxin is synthesized at the tip of the shoot.
Diffusion and Distribution: When light is coming from all directions (or directly from above), auxin diffuses evenly down the shoot, causing uniform growth.
Unilateral Light Response: When light shines on the plant from one side, the auxin hormone diffuses towards the shaded side of the shoot. This leads to a higher concentration of auxin on the side away from the light.
Differential Growth: Auxin promotes cell elongation. The higher concentration of auxin on the shaded side stimulates the cells there to elongate more rapidly than the cells on the illuminated side. This unequal growth causes the shoot to bend towards the light source. This response is a survival strategy to maximize light absorption for photosynthesis.
Q26. How do auxins help a tendril to coil around a support?
Solution:
The coiling of a tendril around a support is a form of thigmotropism, also mediated by auxin.
Contact with Support: When a tendril, which is a modified sensitive stem, comes into contact with a support, the side of the tendril touching the support experiences a stimulus.
Redistribution of Auxin: Auxin is sensitive to touch. Upon contact, auxin moves from the side of the tendril that is in contact with the support to the side that is away from it.
Differential Growth Rate: This results in a lower concentration of auxin on the contact side and a higher concentration on the non-contact side. Since auxin promotes growth, the side away from the support grows much faster than the side in contact.
Coiling Action: This differential growth causes the tendril to bend and coil around the support, providing anchorage for the climbing plant.
Q27. How does the movement in a 'touch-me-not' plant differ from the movement of a shoot towards light?
Solution:
The movement in a 'touch-me-not' plant (Mimosa pudica) and the movement of a shoot towards light differ fundamentally in their mechanism, nature, and purpose.
Q28. Design a simple experiment to demonstrate hydrotropism in plants.
Solution:
Aim: To demonstrate that roots of a plant grow towards water (positive hydrotropism).
Materials: A wire mesh sieve or a transparent container with a perforated base, soil/sawdust, a few bean seeds, water.
Procedure:
Take the sieve and fill it with moist sawdust or soil.
Sow a few germinating bean seeds in the moist sawdust.
Suspend the sieve in the air. For a few days, observe the seedlings. The radicles (young roots) will grow downwards through the holes in the mesh due to gravity (geotropism).
After the roots have emerged, stop watering the sawdust from above. Place a source of water, like a beaker of water or a wet cloth, touching the mesh on one side only.
Leave the setup for a few more days and observe the direction of root growth.
Observation: It will be observed that the roots, after emerging downwards, bend and start growing sideways towards the source of water.
Conclusion: This experiment demonstrates that roots are positively hydrotropic, as they grow towards the stimulus of water, even against the pull of gravity.
Q29. Name the plant hormones responsible for: (a) inhibiting growth, (b) promoting cell division, and (c) breaking seed dormancy.
Solution:
(a) Inhibiting growth: Abscisic Acid (ABA) is the primary growth-inhibiting hormone. It promotes dormancy and causes the wilting of leaves. (b) Promoting cell division: Cytokinins are the hormones that promote rapid cell division, especially in fruits and seeds. (c) Breaking seed dormancy: Gibberellins play a crucial role in breaking the dormancy of seeds and buds, allowing them to germinate.
Q30. Mention three important functions of gibberellins.
Solution:
Three important functions of gibberellins in plants are:
Stem Elongation: Gibberellins promote the elongation of internodes (the part of the stem between two nodes). This leads to an increase in the height of the plant. This effect is particularly noticeable in genetically dwarf plants.
Breaking Dormancy: They are instrumental in breaking the dormancy of seeds and buds. They stimulate the production of enzymes that mobilize stored food reserves in the seed, facilitating germination.
Promoting Flowering: In some plants, gibberellins can induce flowering, even under conditions that would normally be unfavorable. They also play a role in fruit development and can be used to increase fruit size.
Q31. State the functions of the plant hormone Abscisic Acid (ABA).
Solution:
Abscisic Acid (ABA) is primarily a growth inhibitor hormone with the following key functions:
Induces Dormancy: ABA promotes and maintains dormancy in seeds and buds, preventing them from germinating or sprouting during unfavorable conditions (like winter or drought).
Stress Hormone: It helps plants cope with environmental stress, particularly water scarcity. It triggers the closure of stomata on the leaves to reduce water loss through transpiration.
Promotes Abscission: ABA promotes the aging (senescence) and shedding (abscission) of leaves, flowers, and fruits from the plant.
Q32. What is chemotropism? Give one example.
Solution:
Chemotropism: It is the directional growth movement of a plant part in response to a chemical stimulus. The movement can be positive (towards the chemical) or negative (away from the chemical).
Example: The most common example of chemotropism is the growth of the pollen tube towards the ovule during fertilization in flowering plants. The stigma secretes sugary chemical substances that act as a stimulus, guiding the pollen tube through the style to reach the ovule for fertilization.
Q33. Explain geotropism in plants with a suitable diagram.
Solution:
Geotropism: It is the directional growth of a plant in response to the force of gravity. Plant parts that grow in the direction of gravity are called positively geotropic, while those that grow against it are negatively geotropic.
Mechanism and Examples:
Positive Geotropism: The roots of a plant always grow downwards, into the soil. This is positive geotropism. It is a vital survival mechanism that anchors the plant and helps it absorb water and minerals from the soil.
Negative Geotropism: The shoot (stem) of a plant always grows upwards, away from the soil and against the pull of gravity. This is negative geotropism. This response ensures that the leaves are positioned to receive maximum sunlight for photosynthesis.
Diagram: (A simple diagram of a potted plant placed horizontally on its side should be drawn. The diagram should show the shoot bending upwards (away from gravity) and the roots bending downwards (towards gravity), with labels indicating "Negative Geotropism" for the shoot and "Positive Geotropism" for the root.)
Q34. Give two examples of functions in plants that are regulated by light.
Solution:
Two important functions in plants that are regulated by light are:
Phototropism: This is the directional growth of a plant shoot towards a light source. Light acts as a stimulus that causes the redistribution of the hormone auxin, leading to differential growth and the bending of the stem. This ensures the plant maximizes its exposure to light for photosynthesis.
Photosynthesis: This is the fundamental process by which plants convert light energy into chemical energy (glucose). Light is the essential energy source that drives this reaction in the chloroplasts of plant cells. The rate of photosynthesis is directly dependent on the intensity and duration of light.
Q35. How does chemical coordination occur in plants?
Solution:
Chemical coordination in plants is carried out by a group of chemical messengers called phytohormones or plant hormones. The process occurs as follows:
Synthesis: Phytohormones are synthesized in specific regions of the plant, such as the shoot apex, root tips, or developing fruits.
Translocation: Unlike animals, plants lack a circulatory system. These hormones are transported from their site of synthesis to their site of action through vascular tissues (xylem and phloem) or by simple diffusion from cell to cell.
Action at Target Cells: At the target site, these hormones bind to specific receptors on or within the cells, triggering a physiological response. This response could be cell elongation (auxin), cell division (cytokinin), stomatal closure (ABA), or fruit ripening (ethylene). This coordinated action of various hormones regulates all aspects of a plant's life cycle, from germination to senescence.
Q36. Name the plant hormone that (a) promotes ripening of fruits, (b) causes wilting of leaves, and (c) promotes growth of tendrils.
Solution:
(a) Promotes ripening of fruits: The gaseous hormone Ethylene is responsible for promoting fruit ripening. (b) Causes wilting of leaves: The growth-inhibiting hormone Abscisic Acid (ABA) causes the wilting and shedding of leaves. (c) Promotes growth of tendrils: The hormone Auxin promotes the differential growth that causes tendrils to coil around a support.
Table: Key Phytohormones and Their Primary Roles
Table: Differentiating Tropic and Nastic Movements
Conceptual Primer
Alongside the nervous system, animals possess a second major control system: the endocrine system. This system consists of a network of ductless glands called endocrine glands, which synthesize and secrete chemical messengers known as hormones directly into the bloodstream.
Key endocrine glands and their secretions in humans include
Pituitary Gland: Often called the 'master gland' because it secretes hormones that control the functioning of other endocrine glands (e.g., TSH, FSH) as well as growth hormone.
Thyroid Gland: Secretes thyroxine, which regulates the body's overall metabolic rate. Iodine is essential for its synthesis.
Adrenal Glands: Secrete adrenaline, the 'emergency hormone' that prepares the body for 'fight-or-flight' responses.
Pancreas: Functions as both an exocrine and endocrine gland. Its endocrine part secretes insulin and glucagon, which regulate blood sugar levels.
Testes (in males): Secrete testosterone, responsible for the development of male secondary sexual characteristics.
Ovaries (in females): Secrete estrogen and progesterone, which control the development of female secondary sexual characteristics and the menstrual cycle.
A critical concept governing the endocrine system is the feedback mechanism. This is a self-regulating process that ensures hormones are secreted in precise quantities and at the right time to maintain homeostasis (a stable internal environment).
Curated Questions & Solutions
Q37. Why are some patients of diabetes treated by giving injections of insulin?
Solution:
Diabetes is a metabolic disorder characterized by high blood sugar levels. Patients are treated with insulin injections for the following reasons:
Cause of Diabetes: In diabetic patients, the pancreas either does not produce enough insulin or the body's cells do not respond effectively to the insulin produced.
Function of Insulin: Insulin is the hormone responsible for regulating blood glucose (sugar) levels. It signals the liver, muscle, and fat cells to take up glucose from the blood and use it for energy or store it as glycogen.
Restoring Balance: By administering insulin through injections, the deficiency is compensated. The injected insulin helps the body's cells to absorb the excess glucose from the blood, thereby lowering the high blood sugar level back to a normal range and preventing the complications associated with prolonged high blood sugar.
Q38. Why is the consumption of iodised salt advisable? Name the disease that can be caused by a deficiency of iodine.
Solution:
Reason for Advisability: The consumption of iodised salt is advisable because iodine is an essential mineral required by the thyroid gland to synthesize the hormone thyroxine. Thyroxine regulates the metabolism of carbohydrates, fats, and proteins in the body, which is crucial for balanced growth. Iodised salt provides the necessary amount of iodine in the diet to ensure proper functioning of the thyroid gland.
Deficiency Disease: A deficiency of iodine in the diet leads to a condition called hypothyroidism. This impairs the production of thyroxine. To compensate, the thyroid gland enlarges in an attempt to capture more iodine from the blood. This enlargement of the thyroid gland, visible as a swelling in the neck, is known as Goitre.
Q39. Describe how our body responds when adrenaline is secreted into the blood.
Solution:
Adrenaline is the 'emergency' or 'fight-or-flight' hormone secreted by the adrenal glands in response to stress, fear, or excitement. When secreted into the blood, it triggers a series of rapid physiological changes to prepare the body for intense physical activity:
Increased Heart Rate: The heart beats faster, pumping more blood to the muscles and brain, thus increasing the supply of oxygen and glucose for rapid energy production.
Increased Breathing Rate: The rate of breathing increases, and the airways dilate, allowing for more oxygen to be taken into the lungs and delivered to the blood.
Diversion of Blood Flow: Blood vessels to the digestive system and skin constrict, redirecting blood flow towards the skeletal muscles where it is needed most for action. This is why the skin can appear pale during a state of fear.
Q40. Justify why the pituitary gland is referred to as the 'master gland'.
Solution:
The pituitary gland, a small pea-sized gland located at the base of the brain, is called the 'master gland' of the endocrine system because it produces and secretes several hormones that control the functioning of most other endocrine glands.
Control of Other Glands: It secretes tropic hormones, which act on other glands. For example:
Thyroid-Stimulating Hormone (TSH): Stimulates the thyroid gland to produce thyroxine.
Adrenocorticotropic Hormone (ACTH): Stimulates the adrenal glands.
Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH): Control the functions of the testes and ovaries.
Direct Functions: In addition to controlling other glands, it also secretes hormones that have direct effects on the body, such as Growth Hormone (GH), which regulates the growth of bones and muscles.
Link with Nervous System: It is controlled by the hypothalamus, forming a crucial link between the nervous and endocrine systems. This central regulatory role justifies its title as the 'master gland'.
Q41. Name the hormones secreted by the (i) Testes, (ii) Ovaries, and (iii) Pancreas, and state one function of each.
Solution:
(i) Testes:
Hormone: Testosterone
Function: Responsible for the development of male secondary sexual characteristics (e.g., beard, deep voice) and stimulates sperm production.
(ii) Ovaries:
Hormone: Estrogen
Function: Responsible for the development of female secondary sexual characteristics (e.g., breast development) and regulates the menstrual cycle.
(iii) Pancreas:
Hormone: Insulin
Function: Regulates blood sugar levels by promoting the uptake of glucose from the blood into cells, thus lowering blood glucose.
Q42. Explain the feedback mechanism that regulates the timing and amount of hormone release, using the example of blood sugar regulation.
Solution:
A feedback mechanism is a biological regulatory system where the output of a process influences its own operation, ensuring homeostasis. Most hormonal regulation occurs via negative feedback.
Mechanism of Blood Sugar Regulation:
High Blood Sugar (Stimulus): After a meal, blood glucose levels rise. This increase is detected by the beta cells of the pancreas.
Hormone Release: In response, the pancreas secretes the hormone insulin into the bloodstream.
Response: Insulin acts on body cells, causing them to absorb glucose from the blood, and on the liver, causing it to convert glucose into glycogen for storage. This lowers the blood sugar level.
Negative Feedback: As the blood sugar level falls back to the normal range, this drop is detected by the pancreas, which then reduces the secretion of insulin. This prevents the blood sugar from dropping too low. If blood sugar drops too low, alpha cells in the pancreas secrete glucagon, which raises blood sugar, and this rise in turn inhibits further glucagon secretion. This constant interplay maintains blood sugar within a narrow, healthy range.
Q43. How does chemical coordination take place in animals?
Solution:
Chemical coordination in animals is carried out by the endocrine system through chemical messengers called hormones.
Secretion: Specialized endocrine glands (like the pituitary, thyroid, adrenal glands) synthesize and secrete hormones directly into the bloodstream.
Transport: The circulatory system (blood) transports these hormones throughout the body. Unlike nerve impulses, which travel along fixed paths, hormones reach virtually all cells of the body.
Action on Target Organs: Hormones act only on specific target cells or organs that have receptors for that particular hormone. The binding of the hormone to its receptor triggers a specific metabolic or physiological change within the target cell, regulating processes like growth, metabolism, and stress responses.
Q44. A person, while climbing a hill, comes into a panic state. His breathing becomes fast and blood pressure increases. Which hormone is released in his body and from which gland?
Solution:
The physiological changes described—panic, fast breathing, and increased blood pressure—are characteristic of the 'fight-or-flight' response.
Hormone Released: The hormone responsible is Adrenaline (also known as epinephrine).
Gland: Adrenaline is released from the Adrenal Glands, which are located on top of the kidneys.
Function: The release of adrenaline prepares the body for an emergency or a stressful situation by rapidly increasing the supply of oxygen and energy to the muscles, enabling the person to cope with the physical exertion and panic of climbing.
Q45. Dwarfism results due to the deficiency of which hormone? Which gland secretes this hormone?
Solution:
Hormone: Dwarfism, a condition characterized by stunted growth, results from the deficiency of Growth Hormone (GH) during childhood.
Gland: Growth Hormone is secreted by the anterior lobe of the Pituitary Gland. Insufficient secretion of this hormone during the growing years leads to inadequate development of bones and muscles, resulting in a very short stature.
Q46. Name the hormone that regulates carbohydrate, protein, and fat metabolism in our body. Which gland secretes it and what is essential for its synthesis?
Solution:
Hormone: The hormone that regulates the metabolism of carbohydrates, proteins, and fats is Thyroxine.
Gland: Thyroxine is secreted by the Thyroid Gland, located in the neck region.
Essential Element: The mineral Iodine is essential for the synthesis of the thyroxine hormone by the thyroid gland.
Q47. Name any two heterocrine glands and mention their endocrine and exocrine functions.
Solution:
Heterocrine (or mixed) glands are glands that have both endocrine (ductless) and exocrine (with ducts) functions.
Pancreas:
Endocrine Function: Secretes the hormones insulin and glucagon directly into the blood to regulate blood sugar levels.
Exocrine Function: Secretes pancreatic juice, containing digestive enzymes, through a duct into the small intestine to aid in digestion.
Testes (in males):
Endocrine Function: Secrete the hormone testosterone into the blood to control male secondary sexual characteristics.
Exocrine Function: Produce sperms, which are released through a system of ducts.
Q48. How does our body maintain blood sugar levels?
Solution:
The body maintains blood sugar (glucose) levels through a negative feedback mechanism involving two hormones secreted by the pancreas: insulin and glucagon.
When Blood Sugar is High (e.g., after a meal): The pancreas secretes insulin. Insulin promotes the uptake of glucose by body cells and stimulates the liver to convert excess glucose into glycogen for storage. This lowers the blood sugar level.
When Blood Sugar is Low (e.g., during fasting): The pancreas secretes glucagon. Glucagon stimulates the liver to break down stored glycogen into glucose and release it into the bloodstream. This raises the blood sugar level.
Homeostasis: This antagonistic (opposing) action of insulin and glucagon ensures that the blood glucose concentration is maintained within a narrow, healthy range.
Q49. Name the fluid-filled space between the meninges of the brain. What is its function?
Solution:
Fluid: The fluid that fills the space between the meninges (the protective membranes covering the brain) is called Cerebrospinal Fluid (CSF).
Function: The primary function of the cerebrospinal fluid is protection. It acts as a shock absorber or cushion, protecting the delicate brain and spinal cord from mechanical shocks, jerks, and injuries. It also helps in nourishing the brain tissue and removing waste products.
Q50. Name the hormones secreted by the following endocrine glands and specify one function of each: (a) Thyroid, (b) Pituitary, (c) Adrenal.
Solution:
(a) Thyroid Gland:
Hormone: Thyroxine
Function: Regulates the basal metabolic rate of the body, influencing the metabolism of carbohydrates, proteins, and fats for balanced growth.
(b) Pituitary Gland:
Hormone: Growth Hormone (GH)
Function: Stimulates the growth and development of bones and muscles in the body.
(c) Adrenal Gland:
Hormone: Adrenaline
Function: Prepares the body for emergency situations ('fight-or-flight' response) by increasing heart rate, breathing rate, and blood flow to muscles.
Table: Major Human Endocrine Glands, Their Hormones, and Functions
Conclusion - Synthesizing Knowledge for Exam Success
Summary of High-Yield Concepts
This comprehensive analysis of 50 high-yield 3-mark questions reveals several core themes that are central to mastering the chapter 'Control and Coordination'. Success in the board examination hinges not on rote memorization but on a deep, conceptual understanding of these overarching principles.
Integrated Control Systems: The nervous and endocrine systems are not isolated entities but are two components of a single, integrated control network. The nervous system provides rapid, targeted responses, while the endocrine system manages slower, systemic changes. Their synergy, exemplified by the 'fight-or-flight' response, is a recurring and critical concept.
Evolutionary Purpose of Mechanisms: Biological structures and pathways are shaped by evolutionary pressures. The reflex arc's design, which bypasses the brain for speed, is a prime example of a mechanism optimized for survival. Similarly, plant tropisms are not passive movements but active strategies to maximize resource acquisition (light, water) and ensure reproductive success. Understanding the 'why' behind a mechanism provides a more profound and memorable learning experience.
The Universality of Chemical Signalling: The principle of a chemical messenger binding to a specific receptor to elicit a response is a unifying theme across biology. This concept is seen at the microscopic level in the synapse (neurotransmitters), at the systemic level in animals (hormones), and throughout the plant kingdom (phytohormones). Recognizing this parallel helps in building a cohesive understanding of biological communication.
Homeostasis and Feedback Loops: The maintenance of a stable internal environment, or homeostasis, is the ultimate goal of control and coordination. The feedback mechanism is the primary tool used by the endocrine system to achieve this balance. Common questions on diseases like diabetes and goitre are, at their core, case studies on the failure of these critical feedback loops.
Blueprint for a Perfect 3-Mark Answer
To consistently score full marks in 3-mark questions, students should adopt a systematic approach to answer writing. The following checklist serves as a practical blueprint for constructing a high-quality response in the examination hall.
Deconstruct the Question: Read the question carefully and identify all its sub-parts. A 3-mark question often asks for two or three distinct pieces of information (e.g., "Define..., name the gland..., and state its function."). Ensure every part is addressed explicitly.
Keyword Integration: Use precise biological terms. Instead of "chemical that passes between nerves," write "neurotransmitter crosses the synaptic cleft." Instead of "plant bends to light," use "the shoot exhibits positive phototropism." Underline these keywords.
The Power of Diagrams: Whenever a question involves a pathway (reflex arc), a structure (neuron), or a process (phototropism experiment), support your answer with a simple, neat, and clearly labeled diagram or flowchart. A good diagram can often communicate more effectively than a paragraph of text.
Structure for Clarity: Organize your answer into distinct points, preferably using bullets or numbering (1, 2, 3 or a, b, c). This makes your answer easy for the examiner to read and assess, ensuring you get credit for each valid point you have made.
Provide Examples: When explaining a concept (e.g., tropism, reflex action, hormone function), always include a specific and relevant example. Examples demonstrate a concrete understanding of the abstract concept.
Highlight for Impact: Use an underline to draw the examiner's attention to the most critical terms and phrases in your answer. This shows confidence and helps ensure that the key aspects of your knowledge are not overlooked.
By internalizing these principles and strategies, students can approach the CBSE Class 10 Science examination with confidence, equipped not just with knowledge, but with the skills to present that knowledge in a clear, precise, and effective manner.
