Class 10 Science Chapter 6 Control and Coordination

Key Concept: Hormonal Regulation, Real-world Application

d) Abscisic acid closes stomata by inducing ion channels in guard cells.

[Solution Description] In desert environments, plants need to conserve water effectively. Abscisic acid (ABA) plays a crucial role in this adaptation by signaling the stomata to close, reducing transpiration and conserving water. This hormone increases rapidly under drought conditions, leading to stomatal closure.

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Key Concept: Impulse Transmission

a) Chemical reaction at the dendrite
[Solution Description] When specialized receptors located on the dendrites interact with environmental stimuli, it sets off a chemical reaction. This reaction generates an electrical impulse that starts from the dendritic tip and travels through the neuron.

Notes:

• Nervous System Basics:
  The nervous system coordinates body activities through electrical impulses.
• Neurons:
  Specialized cells that transmit impulses. Key parts:
  • Dendrites: Receive signals.
  • Cell Body: Processes signals.
  • Axon: Transmits signals.
• Synapse:
  • Junction between two neurons.
  • Impulse is transmitted via neurotransmitters like acetylcholine.
• Impulse Transmission Process:
  • Stimulus triggers an electrical signal in the receptor.
  • Impulse travels along the axon to the synaptic knob.
  • Neurotransmitters are released into the synaptic cleft.
  • Neurotransmitters bind to receptors on the next neuron, generating a new impulse.
• Types of Neurons:
  • Sensory Neurons: Carry impulses from sense organs to the brain/spinal cord.
  • Motor Neurons: Transmit signals from the brain/spinal cord to effectors.
  • Interneurons: Connect sensory and motor neurons.
• Speed:
  Impulse transmission occurs at high speed due to myelin sheath insulation.

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Key Concept: Plant Movement

b) Growth-independent
[Solution Description] The movement of the sensitive plant (Mimosa pudica) in response to touch is growth-independent and occurs due to changes in turgor pressure within the cells.

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Key Concept: Hormonal Control

c) Increases heart rate and energy availability

[Solution Description] Adrenaline, also known as epinephrine, is a hormone released by the adrenal glands during stress. It increases heart rate, expands air passages, and diverts blood to major muscle groups, preparing the body for a ‘fight or flight’ response.

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Key Concept: Function Identification

c) Stem elongation
[Solution Description] Gibberellins mainly help in promoting stem elongation in plants.

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Key Concept: Reflex Arc Evolution

b) To provide rapid responses without complex processing
[Solution Description] Reflex arcs likely evolved in simpler organisms as they allow for fast and efficient responses to environmental changes without relying on complex neural processing—an advantage when avoiding threats or adapting quickly to surroundings.

Notes:

• Definition of Reflex Arc:
  • A reflex arc is the neural pathway through which a reflex action occurs without conscious brain involvement.
• Components:
  • Receptor: Detects stimuli (e.g., skin).
  • Sensory Neuron: Carries signals to the spinal cord.
  • Interneuron (in Spinal Cord): Processes the signal.
  • Motor Neuron: Sends instructions to the effector.
  • Effector: Performs the action (e.g., muscle or gland).
• Evolution of Reflex Arc:
  • Early organisms responded directly to stimuli.
  • As complexity increased, spinal reflex arcs evolved for faster responses, bypassing the brain.
  • Reflex arcs ensured survival by enabling immediate reactions (e.g., withdrawing from heat).
• Advantages:
  • Saves time by avoiding the brain’s involvement.
  • Provides protection from potential harm.
• Examples:
  • Knee-jerk reflex.
  • Withdrawal of hand from a hot object.

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Key Concept: Hunger Regulation

d) Hypothalamus
[Solution Description] The hypothalamus in the fore-brain is responsible for regulating the sensation of hunger.

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Key Concept: Multi-step Solutions, Numerical and Analytical Difficulty

c) 50 N
[Solution Description] To find the remaining force experienced by the skull, we calculate: 80% reduction means only 20% of the original force is transmitted. Therefore, $20%$ of $250$ N is calculated as follows:
$\text{Remaining Force} = 0.20 \times 250 = 50 \, \text{N}$
Thus, the skull experiences a force of 50 N.

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Key Concept: Hormone Effects

c) Increases the breathing rate
[Solution Description] Adrenaline increases the breathing rate by causing contractions in the diaphragm and rib muscles to supply more oxygen to muscles.

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Key Concept: Basic Structure

b) Dendrite
[Solution Description] The dendrite of a neuron is responsible for receiving information from the environment or other neurons.

Notes:

• Definition:
  Control and Coordination are vital functions of the body to regulate activities and maintain harmony in response to stimuli.
• Nervous System:
  • Composed of the brain, spinal cord, and nerves.
  • Functions via neurons that transmit electrical impulses.
  • Divided into Central Nervous System (CNS) and Peripheral Nervous System (PNS).
• Endocrine System:
  • Composed of glands that secrete hormones.
  • Works with the nervous system for coordination.
  • Example: Adrenal glands, thyroid, pituitary gland.
• Brain Structure:
  • Divided into cerebrum (thinking), cerebellum (balance), and medulla (involuntary actions).
• Reflex Action:
  • An automatic and rapid response to stimuli.
  • Involves the spinal cord.
• Hormonal Control:
  • Plants: Hormones like auxin and gibberellins.
  • Animals: Hormones like insulin and adrenaline.
• Key Coordination:
  Interaction between the nervous and endocrine systems ensures proper body function.

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Key Concept: Neural Impulse Transmission

b) Chemical transmission begins
[Solution Description] An electrical impulse triggers the release of neurotransmitters, which cross the synaptic gap to continue the signal as a chemical message.

Notes:

• Definition: Neural impulse transmission is the process of sending signals through neurons to facilitate communication between the brain, spinal cord, and body.
• Structure of a Neuron:
  • Cell Body: Contains the nucleus and cytoplasm.
  • Dendrites: Receive impulses from other neurons or sensory receptors.
  • Axon: Transmits impulses away from the cell body.
  • Axon Terminal: Releases neurotransmitters to pass the impulse to the next neuron.
• Synapse: The gap between two neurons where neurotransmitters help transfer the impulse.
• Mechanism:
  • Electrical Signal: Travels along the axon.
  • Chemical Signal: Neurotransmitters cross the synapse.
  • Impulse is converted back to an electrical signal in the next neuron.
• Direction: Neural impulses are unidirectional – from dendrites to axon terminal.
• Role: Ensures rapid response to stimuli, aiding in reflex actions and voluntary movements.

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Key Concept: Reflex and Neurons

b) They transmit impulses efficiently and rapidly
[Solution Description] Neurons swiftly transmit impulses in reflex actions, enabling the body to react promptly to external stimuli by relaying signals from sensory receptors to muscles.

Notes:

• Reflex Action:
  • Reflex action is a quick, automatic response to a stimulus.
  • It helps protect the body from harm (e.g., pulling hand away from a hot object).
  • The pathway of reflex action is called the reflex arc.
• Reflex Arc:
  • Includes a receptor, sensory neuron, spinal cord, motor neuron, and effector.
  • Reflex actions are processed in the spinal cord, not the brain, ensuring rapid responses.
• Neurons:
  • Neurons are specialized cells responsible for transmitting signals in the body.
  • Consist of three parts: Dendrites, Cell body, and Axon.
  • Signals travel in the form of electrical impulses.
• Types of Neurons:
  • Sensory Neurons: Carry signals from receptors to the brain/spinal cord.
  • Motor Neurons: Transmit signals from the brain/spinal cord to effectors.
  • Interneurons: Connect sensory and motor neurons in the spinal cord.
• Importance:
  • Reflex actions and neurons ensure efficient and timely responses, maintaining coordination and protection in the body.

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Key Concept: Reflex Arc Evolutionary Advantage, Reflex Arc Complexity

c) They offer quick response capabilities, essential for survival.

[Solution Description] Reflex arcs have evolved as simple yet highly effective pathways that prioritize speed over complex decision-making. In environments where rapid reaction times can mean the difference between life and death, such as avoiding predators or harmful stimuli, the simplicity of reflex arcs ensures survival. This efficiency is achieved because they do not require input from the entire nervous system, only utilizing sensory neurons, interneurons, and motor neurons within the spinal cord.

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Key Concept: Real-world Application, Protective Mechanisms

b) Cerebellum
[Solution Description] The cerebellum is the part of the hind-brain that is primarily responsible for coordinating voluntary movements and maintaining balance, posture, and equilibrium. It integrates sensory input concerning position and movement from the eyes, ears, and body to adjust posture and fine-tune movements.

Notes:

• Control and Coordination:
  • It is vital for the body to respond to stimuli efficiently.
  • Involves the nervous system, endocrine system, and sense organs.
• Real-world Applications:
  • Traffic Light Response: Quick reflexes in crossing the road showcase nervous coordination.
  • Sports Performance: Athletes rely on muscle coordination for precise movements.
  • Technology Use: Finger movements while typing or gaming reflect fine motor coordination.
• Protective Mechanisms:
  • Reflex Actions: Involuntary actions like blinking protect eyes from dust.
  • Pain Sensation: Alerts the body to withdraw from harmful stimuli like hot objects.
  • Tear Production: Protects eyes from irritants.
  • Adrenaline Hormone: Prepares the body for “fight or flight” in emergencies.
• Examples in Nature:
  • Plants: Mimosa leaves fold when touched, a protective response.
  • Humans: Sweating regulates body temperature.

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Key Concept: Growth Promotion

c) Auxin
[Solution Description] Auxins are responsible for the elongation of cells in the shoots. They work by loosening the cell wall tissues, allowing the cells to expand and grow longer, thereby contributing to the lengthening of the shoot.

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Key Concept: Shape Change

b) Filament structures slide over each other due to electrical stimulation.

[Solution Description] Muscle cells change shape by sliding filament theory. Upon receiving a nerve impulse, calcium ions are released, which interact with regulatory proteins on actin filaments. This interaction allows myosin heads to bind to actin and perform a power stroke, pulling actin filaments inward, thereby shortening the muscle fiber.

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Key Concept: Signal Limitation

b) They require connections to nervous tissue
[Solution Description] Electrical impulses in animals can only reach cells that are connected by nervous tissue. They cannot reach every cell in the body because not all cells are connected via neurons.

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Key Concept: Reflex Arc Pathway

c) Spinal cord
[Solution Description]
Reflex arcs are typically formed in the spinal cord. The reflex arc enables a quick response to stimuli without needing to be processed by the brain first, allowing for faster reactions to potentially harmful situations.

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Key Concept: Hormonal Coordination Complexity, Feedback Mechanism

c) Assertion is true, but Reason is false.
[Solution Description]
The assertion states that growth regulation involves multiple hormones and feedback mechanisms, which is valid because not only the growth hormone but also other hormones like testosterone, oestrogen, and regulatory factors are involved in complex interactions for growth regulation. Feedback mechanisms also play a crucial role in maintaining hormonal balance. However, the reason, stating that growth hormone acts through a simple linear pathway, is incorrect. The regulation of growth hormone itself involves the hypothalamus releasing growth hormone-releasing factor, making it part of a more intricate network, including feedback loops.

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Key Concept: Simple Functions

c) Cerebellum
[Solution Description] The cerebellum is part of the hind-brain and is responsible for the precision of voluntary actions and maintains posture and balance in the body.

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Key Concept: Hormone Regulation

c) Is reduced
[Solution Description] When blood sugar levels decrease, the pancreas detects this change and reduces the secretion of insulin. Insulin is responsible for lowering blood glucose by promoting its uptake by cells, so less insulin is needed when blood glucose is low.

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Key Concept: Effect on Growth

a) Promote stem elongation
[Solution Description] Auxins promote the growth and elongation of cells on the side of the plant away from light, causing the plant to bend toward the light source. This process is part of the plant’s phototropic response.

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Key Concept:Reflex Action Pathway

b) Stimulus → Spinal cord → Muscle
[Solution Description] In a typical reflex action, the stimulus is detected by sensory neurons which send an impulse directly to the spinal cord. An interneuron in the spinal cord relays the impulse to motor neurons, which then prompt an immediate response from an effector such as muscle or gland. Therefore, the correct pathway is: Stimulus → Spinal cord → Muscle.

Notes:

• Definition: Reflex action is an automatic and rapid response to a stimulus that does not involve conscious thought.
• Purpose: Protects the body from harm and minimizes injury by quickly responding to harmful stimuli.
• Pathway (Reflex Arc):
  • Stimulus: Any external or internal change that triggers a response.
  • Receptor: Sensory organs (e.g., skin) detect the stimulus.
  • Sensory Neuron: Carries the signal from the receptor to the spinal cord.
  • Relay Neuron (Interneuron): Processes the signal in the spinal cord and bypasses the brain.
  • Motor Neuron: Sends the signal from the spinal cord to the effector organ.
  • Effector: Muscles or glands that carry out the response.
• Example: Pulling your hand away when touching a hot object.
• Significance: Reflex actions are crucial for survival, providing immediate and involuntary responses to harmful situations.

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Key Concept: Role in Development

c) Delaying leaf senescence
[Solution Description] Cytokinins are crucial in delaying leaf senescence by maintaining chlorophyll levels and promoting nutrient mobilization within leaves, thus prolonging their green state and function.

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Key Concept: Growth Promotion

d) Cytokinin
[Solution Description] Cytokinins are plant hormones that encourage cell division and are typically concentrated in regions of active growth like fruits and seeds.

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Key Concept: Integrated Protection, Advanced Functionality

d) By transferring shock waves away from critical areas and preserving vital functions.

[Solution Description] The vertebral column encases the spinal cord providing a sturdy structure that absorbs and distributes forces from impacts, while the skull encloses the brain within a rigid cavity that prevents direct traumatic injury. Together, they form a continuous protective barrier that guards the central nervous system against external damage by maintaining stability and preventing excessive movement during high-impact situations.

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Key Concept: Reflex Arc Pathway

b) Sensory neuron -> Spinal cord -> Motor neuron
[Solution Description] When a finger touches something hot, sensory neurons first detect this change. The signal then travels via sensory neurons to the spinal cord where it’s relayed through interneurons to motor neurons. These motor neurons send signals to the muscles of the hand to withdraw it immediately.

Notes:

• Definition: A reflex arc is the pathway through which reflex actions occur, allowing for a quick, automatic response to stimuli without conscious brain involvement.
• Stimulus: The process begins when a sensory receptor detects a stimulus (e.g., heat, pain).
• Sensory Neuron: The sensory neuron transmits the signal from the receptor to the spinal cord.
• Spinal Cord (Control Center): The spinal cord processes the signal and sends instructions through motor neurons.
• Interneuron: Located in the spinal cord, interneurons act as a link between sensory and motor neurons.
• Motor Neuron: The motor neuron carries the response signal from the spinal cord to the effector organ.
• Effector Organ: The effector (e.g., muscle or gland) executes the response, such as withdrawing a hand from a hot object.
• Key Feature: Reflex arcs bypass the brain, ensuring rapid response to potentially harmful stimuli.

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Key Concept: Sensory Integration

c) Fore-brain
[Solution Description]

The fore-brain, particularly its different regions, is responsible for integrating various sensory inputs such as sight, sound, and smell. It processes these inputs and helps in forming a cohesive response or perception based on the integrated information.

Notes:

• Sensory Integration:
  • Refers to the coordination of sensory inputs (sight, sound, touch, taste, and smell) and their processing in the brain to produce an appropriate response.
• Sense Organs:
  • Humans have five sense organs: eyes (vision), ears (hearing and balance), skin (touch), tongue (taste), and nose (smell).
• Sensory Receptors:
  • Specialized cells in sense organs that detect specific stimuli (light, sound waves, chemicals, or touch).
  • Types: Photoreceptors (eyes), Mechanoreceptors (skin, ears), Chemoreceptors (tongue, nose), and Thermoreceptors (skin).
• Role of Nervous System:
  • Sensory neurons carry signals from receptors to the brain/spinal cord.
  • Brain integrates information and sends motor responses via motor neurons.
• Importance of Coordination:
  • Ensures survival by responding to external stimuli (e.g., avoiding danger).
  • Maintains internal balance (homeostasis) through reflex actions and voluntary responses.
• Disorders:
  • Dysfunction in sensory integration can lead to challenges in perception and coordination.

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Key Concept: Muscle Movement

b) Nervous electrical impulses
[Solution Description] Muscle contraction is initiated by nervous electrical impulses, leading to changes in muscle cell shape through protein interactions within the cell.

Notes:

• Muscle Movement Overview:
  • Muscles are responsible for body movements by contracting and relaxing.
  • Movement occurs due to coordination between muscles, nerves, and the brain.
• Types of Muscles:
  • Voluntary Muscles: Skeletal muscles under conscious control.
  • Involuntary Muscles: Smooth muscles not under conscious control, e.g., in the digestive system.
• How Muscles Work:
  • Muscles work in pairs: one contracts while the other relaxes (antagonistic action).
  • Example: Biceps and triceps during arm movement.
• Role of Nervous System:
  • Motor neurons transmit signals from the brain/spinal cord to muscles.
  • Neurotransmitters like acetylcholine help in communication between nerves and muscles.
• Energy for Muscle Movement:
  • Muscles use ATP (adenosine triphosphate) as energy.
  • Anaerobic conditions may lead to lactic acid buildup, causing muscle fatigue.
• Reflex Actions:
  • Quick muscle responses to stimuli, controlled by the spinal cord.

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Key Concept: Puberty Changes

c) Oestrogen
[Solution Description] Oestrogen is the primary female sex hormone responsible for the development of secondary sexual characteristics during puberty in females.

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Key Concept: Midbrain Reflexes

b) Pupil dilation
[Solution Description] The midbrain mediates certain involuntary reflexes related to visual stimuli, such as pupil dilation, which adjusts light entry into the eye.

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Key Concept: Duration of Responses, Hormone Interaction

c) Auxin and Gibberellin
[Solution Description] The duration and speed of response depend on the type of stimulus and the mechanism through which it acts. Auxins are known for promoting cell elongation and are involved in phototropic responses. Gibberellins also promote stem elongation and are more effective when combined with cytokinins that promote cell division. Together, they facilitate complex growth patterns but typically act slowly.

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Key Concept: Hormone Synthesis

b) Iodine
[Solution Description] Thyroxin is a hormone produced by the thyroid gland, and iodine is essential for its synthesis. Without sufficient iodine, the thyroid gland cannot produce enough thyroxin, which can lead to goitre.

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Key Concept: Growth Mechanism

d) By slower growth of the part in contact with the support
[Solution Description] Tendrils of a pea plant use differential growth to climb up supports. When tendrils come in contact with an object, the part of the tendril touching the object grows more slowly compared to the opposite side, causing it to curve around and cling to the support.

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Key Concept: Hormonal Interactions, Hormonal Pathways

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
The Assertion states that gibberellins and cytokinins work together to promote plant growth. Gibberellins are known for stimulating stem elongation while cytokinins promote cell division. Together, they contribute significantly to overall growth. The Reason suggests that gibberellins and cytokinins act through distinct pathways. While both hormones have unique signaling mechanisms, their actions can be complementary without necessarily sharing pathways. Thus, both the Assertion and Reason are true, but the Reason does not explain why the Assertion is true as it focuses on separate pathways rather than the combined effect of both hormones.

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Key Concept: Hormone Interaction

d) By receiving signals from the hypothalamus through GHRF
[Solution Description] The hypothalamus plays a crucial role in regulating hormone secretions. When there is a low level of growth hormone in the blood, the hypothalamus releases growth hormone releasing factor (GHRF). This stimulates the pituitary gland to release more growth hormone which then acts on various tissues to promote growth and development.

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Key Concept: Real-world Application

c) Medulla
[Solution Description] The medulla oblongata controls autonomic functions such as heart rate and breathing. Difficulty in breathing can indicate an issue with this area of the brain.

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Key Concept: Critical Thinking, Synthesis of Information

a) Enhanced downward shoot growth, inhibited root growth

[Solution Description] When a plant is placed upside down, geotropism plays a significant role. Auxins tend to accumulate on the lower side of a root, inhibiting its growth due to sensitivity at high concentrations, thus encouraging upward curvature. Conversely, gibberellins generally promote growth, especially in shoots. An increase in both auxins and gibberellins would lead to enhanced shoot growth but inhibited root growth, resulting in the shoot growing further downward and roots not correcting their position efficiently.

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Key Concept: Advanced Reasoning, Multi-step Solutions

c) Chemical gradient detection $\rightarrow$ directed tube growth $\rightarrow$ successful fertilization.
[Solution Description] Chemotropism in plants involves detecting chemical gradients, such as those emitted by ovules. Pollen tubes grow directionally by sensing these chemicals, triggering cellular changes that guide the tube’s path toward the ovule, ensuring successful fertilization.

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Key Concept: Involuntary Actions

b) Medulla
[Solution Description] The medulla in the hind-brain is responsible for controlling involuntary actions like blood pressure and salivation.

Notes:

Key Concept: Brain Regions

c) Fore-brain
[Solution Description] The fore-brain is the main thinking part of the brain, which receives and processes sensory inputs from various receptors and is involved in decision making.

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Key Concept: Hormone Source

c) Adrenal gland
[Solution Description] Adrenaline is a hormone responsible for preparing the body for ‘fight or flight,’ and it is secreted from the adrenal glands.

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Key Concept: Basic Function

b) It maintains posture and balance.
[Solution Description] The cerebellum is a part of the hind-brain responsible for precision of voluntary actions and maintaining posture and balance.

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Key Concept: Hormonal Basis of Diseases

c) Diabetes mellitus

[Solution Description]

Diabetes mellitus is the condition characterized by insufficient production or action of insulin, leading to elevated blood sugar levels. It can be due to autoimmune destruction of the pancreas (Type 1 diabetes) or insulin resistance (Type 2 diabetes).

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Key Concept: Decision Making

c) Decision making
[Solution Description] The forebrain is primarily involved in decision-making processes because it serves as the main thinking part of the brain. It interprets sensory information and combines it with stored knowledge to make decisions.

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