Decoding the 2-Mark Question
The 2-mark question, a staple of Section B in the CBSE Science paper, is designed to test your conceptual clarity and ability to communicate scientific facts concisely.
To excel in this format, adhere to the following principles:
Brevity with Precision: Your answer must be to the point but should not omit essential scientific keywords. These keywords are what examiners look for.
The Power of Diagrams: A simple, neat, and accurately labeled diagram can often convey more information than a dense paragraph and is an excellent way to secure full marks.
Structured Answers: Use bullet points or numbered lists, especially when asked to state functions, list components, or provide differences. This enhances clarity and makes your answer easy to evaluate, a practice aligned with the CBSE's own marking schemes.
This question bank is more than a list of questions and answers; it is a strategic tool. Use it for active recall, to assess your preparation level, and to familiarize yourself with the type of questions you can expect in the board examination. By understanding not just what to write, but how and why to structure your answers, you will be well-equipped to demonstrate your expertise and achieve maximum marks.
The Nervous System: The Body's Command Centre
This section covers the fundamental components of the nervous system, from its basic cellular unit to the central processing hub, the brain.
The Neuron - Structure and Signal Transmission
1. Draw a neat diagram of a neuron and label its main parts.
Answer:
A neuron, or nerve cell, is the structural and functional unit of the nervous system.
Dendrites: Branch-like extensions that receive signals from other neurons.
Cell Body (Cyton): Contains the nucleus and cytoplasm; it processes the signal.
Axon: A long, slender projection that transmits the electrical impulse away from the cell body.
Nerve Ending (Axon Terminal): The end of the axon where the impulse is passed on to the next neuron.
[Image: A clearly labeled diagram of a myelinated neuron showing dendrites, cell body with nucleus, axon covered with myelin sheath, and synaptic terminals at the nerve ending.]
2. Name the parts of a neuron where (a) information is acquired, and (b) information travels as an electrical impulse.
Answer:
(a) Dendrites: Information from the environment or another neuron is acquired at the dendritic tips. These structures are specialized to receive stimuli and initiate a nerve impulse.
(b) Axon: The information, converted into an electrical impulse, travels from the cell body along the length of the axon to the nerve endings.
[Image: A diagram of a neuron with arrows indicating the direction of impulse flow, highlighting the dendrite as the point of acquisition and the axon as the path of travel.]
3. What is the correct sequence for the transmission of an electrical impulse through a neuron?
Answer:
The correct sequence for the transmission of an electrical impulse within a single neuron is:
Dendrite Cell Body Axon Nerve Ending.
The dendrite receives the initial stimulus.
The signal travels to the cell body for processing.
The impulse is then transmitted along the axon.
It reaches the nerve ending, from where it is passed to the next neuron.
[Image: A flowchart diagram showing the four key parts of the neuron in sequence with arrows indicating the unidirectional flow of the nerve impulse.]
4. What is a nerve? Name the three types of nerves.
Answer:
A nerve is a bundle of nerve fibers (axons) from multiple neurons, enclosed in a tubular sheath, that transmits impulses in the peripheral nervous system.
The three types of nerves are:
Sensory Nerves: Transmit impulses from sensory receptors (in sense organs) to the central nervous system (CNS).
Motor Nerves: Carry impulses from the CNS to effector organs like muscles and glands.
Mixed Nerves: Contain both sensory and motor fibers and can transmit signals in both directions.
[Image: A cross-section diagram of a nerve, showing multiple axons bundled together within a protective sheath.]
5. How do neurons transmit signals in the human nervous system?
Answer: Neurons transmit signals through a combination of electrical and chemical processes:
Electrical Impulse: When a neuron is stimulated, it generates an electrical impulse (action potential) at its dendrites. This impulse travels along the axon to the nerve ending.
Chemical Signal: At the nerve ending, the electrical impulse triggers the release of chemical messengers called neurotransmitters into the synapse (the gap between neurons). These chemicals then stimulate the next neuron, continuing the signal.
[Image: A simplified diagram showing an electrical signal moving down an axon, leading to the release of neurotransmitter chemicals at the synapse.]
The Synapse - The Crucial Junction
6. What is a synapse? What happens at the synapse between two neurons?
Answer:
A synapse is the microscopic gap between the nerve ending of one neuron and the dendrite of the next neuron.
At the synapse, the transmission of the nerve impulse changes from electrical to chemical:
When the electrical impulse reaches the axon terminal, it stimulates the release of neurotransmitters into the synaptic cleft.
These chemicals diffuse across the gap and bind to receptors on the dendrites of the adjacent neuron, initiating a new electrical impulse in it.
[Image: A detailed diagram of a synapse, showing the pre-synaptic terminal releasing neurotransmitters (dots) into the synaptic cleft, which then bind to receptors on the post-synaptic dendrite.]
7. Why is the flow of signals in a synapse from the axonal end of one neuron to the dendritic end of another, but not the reverse?
Answer: The flow of signals in a synapse is unidirectional due to its specialized structure and function:
Neurotransmitter Release: Neurotransmitters are stored in vesicles and released only from the pre-synaptic terminal (axonal end).
Receptor Location: The protein receptors that can detect and respond to these neurotransmitters are located only on the post-synaptic membrane (dendritic end).
This arrangement ensures that nerve impulses are transmitted in a single, coordinated direction, preventing chaotic signal flow.
8. In a nerve cell, what is the site where the electrical impulse is converted into a chemical signal?
Answer:
The site where an electrical impulse is converted into a chemical signal is the synapse, specifically at the nerve ending or axon terminal of the pre-synaptic neuron.
[Image: A close-up view of an axon terminal, showing vesicles fusing with the membrane and releasing neurotransmitters in response to an incoming electrical signal (represented by a lightning bolt symbol).]
The Human Brain - The Central Processor
9. Name the three major parts or regions of the human brain.
Answer: The human brain is divided into three major parts:
Forebrain: The largest and most prominent part, consisting of the cerebrum, thalamus, and hypothalamus. It is the main thinking part of the brain.
Midbrain: A small, central part that connects the forebrain and hindbrain and is involved in auditory and visual responses.
Hindbrain: Located at the back, it consists of the cerebellum, pons, and medulla oblongata, controlling vital functions and coordination.
[Image: A simplified side-view diagram of the human brain, clearly color-coding and labeling the Forebrain, Midbrain, and Hindbrain regions.]
10. Which part of the brain is responsible for (a) maintaining posture and equilibrium, and (b) regulating involuntary actions like heartbeat and breathing?
Answer:
(a) Cerebellum: Located in the hindbrain, the cerebellum is responsible for maintaining the posture, balance, and equilibrium of the body. It coordinates voluntary movements, making them smooth and precise.
(b) Medulla Oblongata: Also part of the hindbrain, the medulla controls essential involuntary actions such as heartbeat, breathing, blood pressure, and swallowing.
[Image: A diagram of the hindbrain, highlighting and labeling the Cerebellum and the Medulla Oblongata.]
11. What are the main functions of the cerebrum?
Answer: The cerebrum, the largest part of the forebrain, is the main thinking part of the brain and is responsible for higher-order functions, including:
Voluntary Actions: It controls all voluntary movements, such as walking and writing.
Cognitive Functions: It is the seat of intelligence, thinking, memory, learning, and reasoning.
Sensory Perception: It processes and interprets sensory information from sense organs, such as sight, hearing, touch, and smell.
[Image: A diagram of the human brain with the cerebrum highlighted, and icons representing thinking (a lightbulb), memory (a brain with a gear), and sensory input (eye, ear symbols) pointing to it.]
12. Name the part of the brain which is the main thinking part. A student is learning to play the piano. Which part of his brain is coordinating the movement of his fingers?
Answer:
The main thinking part of the brain is the forebrain, specifically the cerebrum.
The cerebellum, a part of the hindbrain, is responsible for coordinating the precise and voluntary movements of his fingers while learning to play the piano. It ensures the actions are smooth and balanced.
[Image: A split image showing a brain with the cerebrum highlighted on one side, and on the other side, a diagram showing signals from the cerebrum being fine-tuned by the cerebellum to control finger movements on a piano.]
13. What constitutes the Central Nervous System (CNS) in humans?
Answer: The Central Nervous System (CNS) is the primary control center of the body. It is composed of two main parts:
The Brain: The main processing center that controls thoughts, emotions, memory, and most bodily functions.
The Spinal Cord: A long, thin, tubular bundle of nervous tissue that extends from the brainstem. It transmits nerve signals between the brain and the rest of the body and mediates reflexes.
Protection of the Central Nervous System (CNS)
14. How is the brain protected in the human body?
Answer: The brain is a delicate organ and is protected by a multi-layered system:
Bony Protection: The brain is enclosed within the cranium (or skull), a hard bony box that provides a rigid shield against physical injury.
Meninges: Inside the cranium, the brain is covered by three protective membranes called meninges.
Fluid Cushion: A fluid called cerebrospinal fluid (CSF) fills the space between the meninges. This fluid acts as a shock absorber, cushioning the brain from mechanical shocks and jolts.
[Image: A cross-section diagram of the head showing the layers: scalp, skull (cranium), meninges, and the brain, with the space for cerebrospinal fluid indicated.]
15. How is the spinal cord protected in the human body?
Answer: The spinal cord is protected in a manner similar to the brain:
Bony Protection: It is encased within the vertebral column (or backbone), which is a flexible series of bones (vertebrae) that provides a strong, protective armor.
Meninges and Fluid: Like the brain, the spinal cord is also surrounded by the three meningeal layers and cushioned by cerebrospinal fluid, which protects it from injury and shock.
[Image: A diagram showing a section of the vertebral column with the spinal cord running through the central canal, illustrating its bony protection.]
Reflexes: The Involuntary Safeguard Mechanism
This section explores the body's rapid, automatic response system designed for immediate protection from harm.
Defining Reflex Action and its Pathway
16. What is a reflex action? Give two examples.
Answer:
A reflex action is a rapid, automatic, and involuntary response to a stimulus that occurs without conscious thought. It is a protective mechanism to prevent injury.
Examples include:
Immediately pulling your hand away after touching a hot object.
Blinking of eyes when a bright light is suddenly focused on them or an object quickly approaches.
[Image: A two-panel cartoon showing (1) a hand touching a cactus and (2) the hand instantly pulling back with a surprised expression.]
17. Define a reflex arc and draw a schematic diagram to show the path of a reflex action.
Answer:
A reflex arc is the neural pathway that a nerve impulse follows during a reflex action.
The schematic pathway is:
Stimulus Receptor Organ Sensory Neuron Spinal Cord (Relay Neuron) Motor Neuron Effector Organ (Muscle/Gland) Response.
18. Draw a diagram of a reflex arc showing the withdrawal of a hand from a hot object. Label the key components.
Answer: The diagram should illustrate the following components involved in the reflex arc:
Receptor: Heat and pain receptors in the skin of the hand detect the stimulus (hot object).
Sensory Neuron: Transmits the nerve impulse from the receptor to the spinal cord.
Relay Neuron (Interneuron): Located in the spinal cord, it processes the signal and passes it from the sensory neuron to the motor neuron.
Motor Neuron: Carries the impulse from the spinal cord to the effector.
Effector: The muscle in the arm, which contracts to pull the hand away from the hot object.
[Image: A complete diagram showing a hand touching a flame, with the entire neural pathway traced: sensory neuron from hand to spinal cord, a relay neuron within the spinal cord, and a motor neuron from the spinal cord to the arm muscle, causing it to contract.]
19. Name the components of a reflex arc in the correct sequence.
Answer: The correct sequence of components in a reflex arc is:
Receptor: Detects the stimulus.
Sensory Neuron: Carries the signal towards the CNS.
Spinal Cord (or Brainstem): Acts as the integration center, often involving a relay neuron.
Motor Neuron: Carries the command away from the CNS.
Effector: The muscle or gland that carries out the response.
[Image: A series of five simple icons arranged in a line with arrows, representing: a sensor (like an eye or skin), a neuron, the spinal cord, another neuron, and a muscle.]
20. What is the significance of reflex actions?
Answer: Reflex actions are significant for survival due to two main reasons:
Speed: They provide extremely fast responses to harmful stimuli, as the nerve impulse travels a short path via the spinal cord, bypassing conscious thought in the brain. This minimizes potential damage or injury to the body.
Reduced Brain Overload: By handling these automatic responses, the spinal cord frees up the brain to focus on more complex, voluntary, and conscious activities.
The Role of the Brain and Spinal Cord
21. What is the role of the brain in a reflex action?
Answer: In a typical reflex action, the brain's role is secondary and occurs after the response has been executed.
The primary reflex arc is managed by the spinal cord to ensure a rapid response.
However, the signal is also sent from the spinal cord to the brain. This allows the brain to become aware of the event, process the sensation (like pain), and potentially store it in memory for future learning.
[Image: A diagram showing the reflex arc pathway to the spinal cord and back to the muscle, with a separate, secondary arrow showing the signal continuing up the spinal cord towards the brain.]
22. Which signal will get disrupted in case of a spinal cord injury?
Answer: A spinal cord injury will primarily disrupt:
Reflex Actions: Signals for reflexes below the point of injury will be blocked, as the spinal cord acts as the relay center for the reflex arc.
Communication with the Brain: The transmission of sensory signals from the body to the brain, and motor signals from the brain to the body, will be interrupted. This can lead to paralysis and loss of sensation below the site of injury.
[Image: A diagram of the human nervous system with a "break" symbol on the spinal cord, showing arrows from the brain unable to pass the break to the legs, and arrows from the legs unable to pass the break to the brain.]
23. How does the body's response in a reflex action differ from a response initiated by the thinking part of the brain?
Answer: The key differences lie in the control center and the nature of the response:
Reflex Action: Controlled by the spinal cord. The response is involuntary, automatic, and extremely rapid, designed for immediate protection.
Voluntary Action (Thinking): Controlled by the brain (cerebrum). The response is voluntary, deliberate, and slower, as it involves conscious thought, analysis, and decision-making.
Differentiating Types of Actions
24. How are involuntary actions and reflex actions different from each other?
Answer: While both are not under conscious control, they differ in their purpose and control center:
25. Differentiate between walking and a reflex action.
Answer:
[Image: A side-by-side comparison. On the left, a person is shown walking thoughtfully. On the right, a person is shown instantly jerking their foot away after stepping on a sharp object.]
The Endocrine System: Chemical Messengers of the Body
This section delves into the system of chemical coordination, where hormones act as messengers to regulate various bodily functions.
Endocrine Glands and Hormones
26. What are hormones? Name the system responsible for producing them.
Answer:
Hormones are chemical messengers secreted in small amounts by specialized glands. They are transported by the blood to target organs where they regulate physiological processes like growth, development, and metabolism.
The system responsible for producing and secreting hormones is the endocrine system, which consists of several ductless glands.
[Image: A simple diagram showing a gland releasing hormone molecules (dots) into the bloodstream, which then travel to and act on a distant target cell.]
27. Why is the pituitary gland often called the 'Master Gland'?
Answer:
The pituitary gland, located at the base of the brain, is called the 'Master Gland' because it secretes several hormones that control the functioning of most other endocrine glands in the body, such as the thyroid gland, adrenal glands, testes, and ovaries.
[Image: A central pituitary gland with arrows pointing to other endocrine glands (thyroid, adrenal, ovary, testis), indicating its controlling role.]
28. Name the hormone secreted by the thyroid gland. State the mineral necessary for its synthesis and mention its function.
Answer:
Hormone: The thyroid gland secretes thyroxine.
Mineral: Iodine is essential for the synthesis of thyroxine.
Function: Thyroxine regulates the metabolism of carbohydrates, fats, and proteins in the body, thereby controlling the overall metabolic rate and contributing to growth.
[Image: A diagram showing the location of the thyroid gland in the neck, with a chemical symbol for Iodine (I) pointing to it.]
29. Which organ secretes a hormone when blood sugar rises? Name the hormone.
Answer:
The pancreas is the organ that secretes a hormone when blood sugar levels rise.
insulin. Insulin helps the body's cells to absorb glucose from the blood and also signals the liver to convert excess glucose into glycogen for storage, thus lowering blood sugar levels.
30. Name the endocrine gland associated with the kidneys. What is the hormone it secretes in a scary situation?
Answer:
The endocrine glands associated with the kidneys are the adrenal glands, located on top of each kidney.
adrenaline (also known as epinephrine).
[Image: A diagram of the human kidneys with the adrenal glands clearly labeled on top of them.]
31. Name the endocrine gland which is present in males but not in females. Name the hormone it secretes.
Answer:
The endocrine gland present in males but not in females is the testis (plural: testes).
testosterone. Testosterone is responsible for the development of male secondary sexual characteristics during puberty, such as the growth of facial hair, deepening of the voice, and sperm production.
[Image: A simple diagram of the male reproductive system with the testes clearly labeled.]
32. Name the hormone responsible for changes in females during puberty. Which gland secretes it?
Answer:
The primary hormone responsible for the development of female secondary sexual characteristics during puberty is estrogen.
ovaries. Estrogen stimulates changes such as the development of breasts, the start of the menstrual cycle, and the broadening of hips.
[Image: A simple diagram of the female reproductive system with the ovaries clearly labeled.]
Hormonal Imbalances and Disorders
33. Why is the use of iodised salt advisable? Name the disease caused by iodine deficiency.
Answer:
The use of iodised salt is advisable because iodine is a necessary component for the thyroid gland to produce the hormone thyroxine.
goitre, which is characterized by a swollen neck due to the enlargement of the thyroid gland.
[Image: A photograph or illustrative drawing of a person with a visibly swollen neck, characteristic of goitre.]
34. Why are some patients of diabetes treated by giving injections of insulin?
Answer:
Diabetes is a condition where the pancreas does not produce sufficient amounts of insulin, or the body cannot effectively use the insulin it produces. Insulin is essential for regulating blood sugar levels. Therefore, diabetic patients are given insulin injections to supplement the deficiency, which helps their bodies manage blood glucose and prevent the harmful effects of high blood sugar.
[Image: A diagram showing an insulin injection being administered, with a corresponding graph showing blood sugar levels decreasing after the injection.]
35. What is the cause of (a) dwarfism and (b) gigantism?
Answer:
Both conditions are caused by an imbalance in the secretion of Growth Hormone (GH) from the pituitary gland during childhood:
(a) Dwarfism: This is caused by the under-secretion or deficiency of growth hormone, leading to stunted growth.
(b) Gigantism: This is caused by the over-secretion of growth hormone, resulting in abnormal and excessive growth, particularly in height.
[Image: A silhouette comparison of three figures: one of average height, one showing dwarfism (much shorter), and one showing gigantism (much taller).]
Feedback Mechanisms and Fight-or-Flight Response
36. With the help of an example, explain how the feedback mechanism regulates hormone secretion.
Answer: A feedback mechanism is a self-regulating process where the level of a hormone in the blood controls its own secretion. For example, the regulation of blood sugar by insulin:
High Blood Sugar: After a meal, blood sugar levels rise. This stimulates the pancreas to secrete more insulin.
Action of Insulin: Insulin helps cells absorb glucose and the liver to store it, thus lowering blood sugar.
Low Blood Sugar: As blood sugar levels fall back to normal, the pancreas reduces the secretion of insulin. This negative feedback loop ensures that blood sugar levels are maintained within a narrow, healthy range.
[Image: A circular flowchart illustrating the negative feedback loop for blood sugar regulation, showing the roles of the pancreas, insulin, and glucose levels.]
37. Name the hormone secreted in scary situations. List any two responses it generates in the body.
Answer:
The hormone secreted in scary or emergency situations is adrenaline, released by the adrenal glands.
Two responses it generates are:
Increased Heart Rate: The heart beats faster to supply more oxygenated blood to the muscles.
Increased Breathing Rate: Breathing becomes faster and deeper to take in more oxygen. Blood flow is also diverted from the skin and digestive system to the skeletal muscles.
[Image: A diagram of a person in a "fight or flight" stance, with icons next to them indicating a rapidly beating heart and expanding lungs.]
38. How does our body respond when adrenaline is secreted into the blood?
Answer: When adrenaline is secreted into the blood, it triggers a coordinated response to prepare the body for intense physical activity:
The heartbeat increases, raising blood pressure and pumping more blood to the muscles.
The breathing rate increases due to the contraction of the diaphragm and rib muscles, providing more oxygen.
The liver is stimulated to release more glucose into the blood, providing a quick source of energy for the muscles.
[Image: An infographic showing the effects of adrenaline on different body parts: heart (beating faster), lungs (breathing deeper), liver (releasing glucose), and muscles (receiving more blood).]
Table 1: Summary of Major Human Endocrine Glands and Hormones
| Gland Name | Location | Hormone(s) Secreted | Principal Function / Disorder |
| Pituitary Gland | Base of the brain | Growth Hormone (GH), TSH, etc. | Controls growth and other glands; Dwarfism/Gigantism |
| Thyroid Gland | Throat/Neck region | Thyroxine | Regulates metabolism; Goitre |
| Pancreas | Behind the stomach | Insulin, Glucagon | Regulates blood sugar levels; Diabetes |
| Adrenal Glands | On top of kidneys | Adrenaline | Prepares body for "fight or flight" response |
| Testes (in males) | Scrotum | Testosterone | Controls male secondary sexual characteristics |
| Ovaries (in females) | Lower abdomen | Estrogen, Progesterone | Controls female secondary sexual characteristics and menstrual cycle |
Coordination in Plants: Responding to the Environment
This section explores how plants, despite lacking a nervous system, coordinate their growth and behavior in response to environmental stimuli.
Plant Hormones (Phytohormones) and their Functions
39. What are phytohormones? Name any two.
Answer:
Phytohormones (or plant hormones) are chemical compounds produced by plants that regulate their growth, development, and responses to the environment. They are active in very small concentrations.
Two examples of phytohormones are:
Auxin: Promotes cell elongation and growth.
Cytokinin: Promotes cell division.
[Image: A simple diagram of a plant with labels pointing to different areas where hormones act, such as the shoot tip (auxin) and roots/fruits (cytokinins).]
40. Name a plant hormone that promotes growth. How does it promote the growth of a tendril around a support?
Answer:
Auxin is a plant hormone that promotes growth.
When a tendril comes into contact with a support, the auxin hormone diffuses to the side of the tendril that is away from the support. This higher concentration of auxin causes the cells on the non-contact side to grow and elongate faster than the cells on the contact side. This differential growth causes the tendril to coil around the support.
41. Name a plant hormone responsible for (a) promoting cell division, and (b) inhibiting growth.
Answer:
(a) Cytokinin: This hormone is found in high concentrations in areas of rapid cell division, such as in fruits and seeds, and its primary function is to promote cell division (cytokinesis).
(b) Abscisic Acid (ABA): This hormone acts as a growth inhibitor. It promotes dormancy in seeds and buds and causes the wilting of leaves, especially during stressful conditions like drought.
42. List two functions of the plant hormone gibberellin.
Answer: Two important functions of gibberellins are:
Stem Elongation: They promote the elongation of the stem, especially in dwarf plants, causing an increase in height.
Breaking Dormancy: They help in breaking the dormancy of seeds and buds, allowing them to germinate and grow.
43. Which plant hormone is found in a gaseous state? What is its primary function?
Answer:
Ethylene is a plant hormone that exists as a gas.
Its primary function is to promote the ripening of fruits. It triggers the changes in color, texture, and sugar content that are characteristic of ripe fruit.
[Image: A diagram showing green, unripe bananas on the left and yellow, ripe bananas on the right, with an arrow labeled 'Ethylene' between them.]
44. How do plants respond to external stimuli without a nervous system?
Answer:
Plants respond to external stimuli through the action of chemical messengers called phytohormones. These hormones are synthesized in one part of the plant and diffuse to other parts, where they coordinate growth and development. This chemical coordination allows plants to respond to stimuli like light, gravity, water, and touch, albeit much more slowly than animals.
[Image: An infographic showing a plant with arrows indicating various stimuli (sunlight, water, gravity) and the resulting growth responses (bending, root growth).]
Tropic Movements - Directional Growth
45. What is phototropism? How does it occur in a plant shoot?
Answer:
Phototropism is the directional growth movement of a plant part in response to a light stimulus.
In a plant shoot, this occurs due to the hormone auxin:
Auxin is synthesized at the shoot tip.
When light comes from one direction, auxin diffuses towards the shaded side of the shoot.
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.
46. What is geotropism? Differentiate between positive and negative geotropism with examples.
Answer:
Geotropism (or gravitropism) is the growth movement of a plant part in response to the stimulus of gravity.
Positive Geotropism: Growth in the direction of gravity (downwards). Example: The roots of a plant grow downwards into the soil.
Negative Geotropism: Growth against the direction of gravity (upwards). Example: The shoot or stem of a plant grows upwards, away from the soil.
47. Give an example of chemotropism in plants. Explain its significance.
Answer:
An example of chemotropism is the growth of the pollen tube towards the ovule during fertilization in a flower.
Significance: The ovule secretes a chemical (sugary substance) that acts as a stimulus. The pollen tube responds by growing towards this chemical, ensuring that the male gametes are delivered to the ovule for successful fertilization and seed formation. This directional growth is essential for plant reproduction.
[Image: A diagram of the pistil of a flower, showing a pollen grain on the stigma germinating and its pollen tube growing down the style towards the ovule, guided by chemical signals.]
48. Define hydrotropism. Which part of a plant shows positive hydrotropism?
Answer:
Hydrotropism is the directional growth of a plant part in response to the stimulus of water or moisture.
The roots of a plant show positive hydrotropism. They will grow towards areas with higher moisture content in the soil to ensure the plant gets an adequate supply of water for its survival and metabolic processes.
[Image: A diagram showing plant roots in soil, bending and growing towards a pocket of water, while growing away from a dry area.]
Nastic Movements and Other Responses
49. How is the movement of leaves of a sensitive plant (Mimosa pudica) different from the movement of a shoot towards light?
Answer: The two movements differ in their nature and mechanism:
[Image: A side-by-side comparison. On the left, a touch-me-not plant with its leaves folded after being touched. On the right, a plant shoot bending towards a light source.]
50. How does a touch-me-not plant respond on being touched? What is this movement called?
Answer:
When the leaves of a touch-me-not plant (Mimosa pudica) are touched, they rapidly fold inwards and droop.
This response is caused by a sudden loss of water (and thus turgor pressure) from specialized cells in a swelling at the base of the leaf called the pulvinus. The plant cells change shape due to this water movement.
This type of non-directional movement in response to a touch stimulus is called thigmonasty.
Table 2: Overview of Key Plant Hormones (Phytohormones)
| Hormone Name | Primary Function | Specific Actions |
| Auxin | Growth Promoter | Promotes cell elongation, apical dominance, root formation, phototropism |
| Gibberellin | Growth Promoter | Promotes stem elongation, breaks seed dormancy, stimulates flowering |
| Cytokinin | Growth Promoter | Promotes cell division, delays leaf aging, promotes fruit and seed growth |
| Abscisic Acid (ABA) | Growth Inhibitor | Induces seed dormancy, causes stomatal closure (stress hormone), promotes wilting of leaves |
| Ethylene | Both (mainly inhibitory) | Promotes fruit ripening, promotes senescence and abscission (shedding) of leaves and flowers |
Conclusion:
We hope this list of 50 important 2-mark questions from the Control and Coordination chapter helps you feel more confident for your Class 10 board exams. Remember, consistent practice is the key to success. Go through these answers, understand the concepts behind them, and you'll be well-prepared to tackle any question that comes your way.
All the best for your exams! 👍
FAQs on Control and Coordination Class 10
Q1: What is the weightage of the Control and Coordination chapter in the Class 10 board exam? A: The chapter is part of the 'Life Processes' unit, which carries a significant weightage. Typically, you can expect questions worth 5-6 marks from this specific chapter, including 2-mark short answer questions.
Q2: What is the difference between tropic and nastic movements in plants? A: Tropic movements are directional growth movements in response to a stimulus (like light or gravity), while nastic movements are non-directional movements that are independent of the stimulus's direction (like the closing of a touch-me-not plant's leaves).
Q3: Which diagrams are important from the Control and Coordination chapter? A: The most important diagrams to practice are the structure of a neuron, the reflex arc, and the human brain.
