Overview
Introduction: Chapter 'Control and Coordination' explains how organisms detect changes in their internal and external environments and bring about appropriate responses to maintain balance and survive. It introduces the two major coordination systems in animals — the nervous system and the endocrine (hormonal) system — and shows how plants coordinate responses using chemical regulators (plant hormones). Importance: Understanding control and coordination helps students appreciate how rapid and precise responses (nervous control) and slower, long‑lasting regulatory mechanisms (hormonal control) work together to maintain homeostasis. This knowledge links physiology, health, and practical applications in agriculture and medicine. Key themes: structure and function of neurons, organization of the human nervous system (central and peripheral), reflex action and reflex arc, major parts of the brain and spinal cord, endocrine glands and key hormones with their roles, differences between nervous and hormonal coordination, and plant hormones and tropic movements. What the student will learn: students will learn to identify and describe neuron structure and synaptic transmission; draw and…
Learning Objectives
- Define control and coordination and state their significance in multicellular organisms
- Explain the structure of a neuron and draw a labeled diagram showing dendron, cell body, axon and synapse
- Describe the mechanism of nerve impulse transmission and explain the role of neurotransmitters at a synapse
- Explain reflex action and illustrate a reflex arc with labels for receptor, sensory neuron, interneuron, motor neuron and effector
- Differentiate between voluntary and involuntary actions with suitable examples
- Describe the organization of the human nervous system (central, peripheral, autonomic) and compare sympathetic and parasympathetic divisions
- Explain the structure and function of major human endocrine glands (pituitary, thyroid, adrenal, pancreas, testes/ovaries) and name key hormones they secrete
- Discuss common endocrine disorders (diabetes, goitre, hypothyroidism, hyperthyroidism) including causes, symptoms and basic preventive or remedial measures
Topics in this chapter
5 topics · tap a topic title to jump straight to it.
Nervous system (Animals)
Overview
The nervous system is a fast communication network in animals that detects stimuli, processes information and generates responses. It enables coordination of body functions and rapid reactions to the environment. Nervous control is generally rapid and short‑lived compared to hormonal control.
Basic unit: the neuron
- Structure: cell body (soma) with nucleus, dendrites (receive signals), axon (conducts impulse away), axon terminals. Many axons are wrapped in myelin sheath (insulation) produced by Schwann cells (PNS) or oligodendrocytes (CNS). Nodes of Ranvier are gaps between myelin segments.
- Types: sensory (afferent) neurons carry impulses from receptors to CNS, motor (efferent) neurons carry impulses from CNS to effectors (muscles/glands), interneurons (connector) link sensory and motor neurons in CNS.
Transmission of a nerve impulse (simplified)
- At rest: membrane has resting potential (inside negative relative to outside).
- Stimulus causes depolarization; if threshold reached, an action potential (spike) is generated — rapid depolarization followed by repolarization and short hyperpolarization.
- Action potential propagates along axon. In myelinated axons propagation is saltatory (jumps between nodes) and is much faster.
- At synapses, chemical neurotransmitters (e.g., acetylcholine, norepinephrine) carry the signal across the gap to the next neuron or effector cell.
Types of nervous systems in animals (comparative)
- Diffuse nerve net: simple radial animals (Coelenterates like Hydra) — no central brain; impulses spread in network.
- Ladder-like/nerve cords: flatworms (Platyhelminthes) have longitudinal nerve cords and transverse connections, with anterior ganglia (primitive brain).
- Segmental ganglia and nerve cords: annelids and arthropods have paired ganglia in segments and a ventral nerve cord — more localized control.
- Centralized nervous system (vertebrates): brain (forebrain, midbrain, hindbrain) and dorsal hollow spinal cord — complex processing.
Human nervous system: organization
- Central nervous system (CNS): brain + spinal cord — integration and control.
- Peripheral nervous system (PNS): cranial and spinal nerves — connect CNS to receptors and effectors.
- Functional division: somatic nervous system (voluntary control of skeletal muscles) and autonomic nervous system (involuntary control of smooth muscle, cardiac muscle, glands). The autonomic system has sympathetic (fight-or-flight) and parasympathetic (rest-and-digest) branches that often act antagonistically.
Reflex action and reflex arc
A reflex is a rapid, involuntary response to a stimulus that does not require conscious brain activity. Components of a reflex arc: receptor → sensory neuron → interneuron (in spinal cord or brainstem) → motor neuron → effector. Example: withdrawal reflex on touching a hot object.
Coordination with endocrine system
Nervous and endocrine systems work together: nervous system gives fast, short-term control (e.g., moving hand away), endocrine system gives slower, long-term control (e.g., stress hormones like adrenaline affecting heart rate). Hypothalamus is a major link between the two.
Common disorders (brief)
Examples include neuritis, paralysis from spinal cord injury, epilepsy (abnormal neuronal discharge), Parkinson’s disease (dopamine deficiency), and multiple sclerosis (loss of myelin).
Key points for Class 10: understand neuron structure, concept of action potential qualitatively, reflex arc with steps, differences between nervous and hormonal control, and basic organization (CNS/PNS, somatic/autonomic).
- Touching a hot pan: pain receptor → sensory neuron → spinal cord interneuron → motor neuron → withdrawal of hand (reflex arc).
- Knee-jerk (patellar) reflex: doctor taps tendon, stretch receptors produce quick leg extension via spinal reflex.
- Pupillary reflex: bright light causes pupil to constrict (autonomic reflex).
- Fight-or-flight: perceived danger → sympathetic activation → increased heart rate and adrenaline release.
- Hydra’s nerve net: a simple stimulus causes body-wide contraction because there is no central brain.
- Simple relation for conduction or reaction calculations: speed (conduction velocity) = distance / time
- Reaction time (experiment): reaction time = time of response − time of stimulus
- Typical conduction speed (useful reference, not a strict formula): myelinated axons ≈ up to 100–120 m/s; unmyelinated axons ≈ 0.5–2 m/s
Endocrine system (Chemical coordination in animals)
What is the endocrine system? The endocrine system is a collection of ductless glands that secrete chemical messengers called hormones directly into the blood. Hormones travel in the bloodstream to target cells/organs and regulate growth, metabolism, reproduction, stress response and homeostasis.
Major endocrine glands and main hormones
- Hypothalamus: releasing and inhibiting hormones that control the pituitary.
- Pituitary (master gland): growth hormone (GH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), FSH, LH, prolactin.
- Thyroid: thyroxine (T4) and triiodothyronine (T3) — regulate metabolic rate.
- Parathyroid: parathyroid hormone (PTH) — controls blood Ca2+ levels.
- Adrenal glands: adrenaline (epinephrine) and cortisol — stress and metabolic regulation.
- Pancreas (islets): insulin and glucagon — blood glucose regulation.
- Gonads: estrogen, progesterone, testosterone — reproduction and secondary sexual characteristics.
How hormones act
- Lipid-soluble hormones (e.g., steroid, thyroid hormones) pass through cell membranes, bind intracellular receptors and change gene transcription.
- Water-soluble hormones (e.g., insulin, adrenaline) bind membrane receptors and use second messengers (cAMP, Ca2+) to alter cell activity quickly.
Comparison with nervous system
- Nervous: fast, electrical signals, local & short-lived effects. Endocrine: slower, chemical signals via blood, often widespread & longer-lasting.
Regulation and feedback Most endocrine functions are controlled by negative feedback loops. Example: low blood thyroxine stimulates hypothalamus & pituitary to release TRH and TSH; TSH raises thyroxine which then inhibits TRH/TSH release.
Common disorders Diabetes mellitus (insulin deficiency or resistance), goitre (iodine deficiency → low thyroxine → high TSH), hyperthyroidism and hypothyroidism, dwarfism/gigantism (GH problems), Addison's disease, Cushing's syndrome, acromegaly.
Importance for homeostasis The endocrine system maintains internal balance (blood glucose, calcium, water & electrolyte balance, growth and stress response) by coordinating slow but sustained changes across the body.
- Fight-or-flight: Stress triggers adrenal medulla to release adrenaline → increased heart rate, dilation of bronchioles, glucose release for immediate energy.
- Blood glucose regulation: After a meal blood glucose rises → pancreas secretes insulin → cells absorb glucose and liver stores glycogen; during fasting glucagon stimulates glycogen breakdown.
- Goitre: Iodine deficiency reduces thyroxine production → pituitary increases TSH → thyroid enlarges (goitre).
- Diabetes mellitus: Insulin deficiency (type 1) or insulin resistance (type 2) leads to high blood glucose, frequent urination, and fatigue.
- Puberty: Increased sex hormones (testosterone, estrogen) cause development of secondary sexual characteristics like voice change, breast development, body hair.
- Gigantism vs acromegaly: Excess growth hormone before growth plate closure causes gigantism; after closure it causes acromegaly (bone thickening).
- Simple feedback equilibrium (conceptual): at steady state synthesis_rate = degradation_rate ⇒ H_ss = Synthesis/k, where H_ss is steady hormone level and k is degradation constant.
- Dose–response (receptor binding approximation): Response R = Rmax × [H] / (Kd + [H]) (similar to Michaelis–Menten/Hill equation).
- Simple blood-glucose dynamics (conceptual differential equation): dG/dt = Intake(t) - a·[Insulin]·G + b·[Glucagon] - basal_use, where G is blood glucose and a, b are proportionality constants.
- Hormone kinetics (first-order decay): dH/dt = r(t) - k·H, where r(t) is time-dependent secretion rate and k is elimination rate constant.
Control and coordination in plants
Overview
Plants do not have a nervous system like animals. They control and coordinate growth, development and responses to the environment mainly by chemical signals (plant hormones), local chemical changes and, in some cases, electrical signals. Coordination mechanisms act over different timescales: rapid (seconds — e.g. Venus flytrap), intermediate (minutes to hours — nastic movements, stomatal responses) and slow (hours to days — growth, tropisms, flowering).
Main mechanisms
- Plant hormones (growth regulators): Small organic substances produced in one part of the plant and transported to other parts where they change the rate of cell division, elongation or differentiation. Major hormones: auxins, gibberellins, cytokinins, ethylene and abscisic acid (ABA). Each has characteristic functions that often interact.
- Tropisms: Directional growth responses toward or away from a stimulus. Example types: phototropism (light), geotropism/gravitropism (gravity), hydrotropism (water), chemotropism (chemicals). Tropic responses usually result from asymmetric distribution of auxin causing differential cell elongation.
- Nastic movements: Non-directional responses to stimuli where the direction is independent of stimulus direction (e.g., folding of Mimosa leaves, opening/closing of some flowers). These often depend on rapid turgor changes in specialized motor cells (pulvini) and ion movement.
- Electrical signals: Some plants generate action-potential–like electrical signals that cause rapid movements (Venus flytrap, Mimosa pudica). These are produced by ion fluxes across membranes and trigger turgor changes or rapid cell wall changes.
Key hormones and roles
- Auxins (indole-3-acetic acid, IAA): Promote cell elongation in shoots (acid-growth mechanism), maintain apical dominance, promote root initiation; involved in phototropism and geotropism by asymmetric distribution.
- Gibberellins (e.g., GA3): Promote stem elongation, seed germination, flowering in some plants and fruit development.
- Cytokinins: Promote cell division, delay leaf senescence, interact with auxins to control organ formation.
- Ethylene (C2H4): A gaseous hormone that promotes fruit ripening, leaf abscission and some stress responses.
- Abscisic acid (ABA): Promotes stomatal closure during water stress, induces seed dormancy and inhibits growth.
Mechanisms in practice
- Phototropism (shoot bending toward light): Light is perceived by photoreceptors in the tip; auxin redistributes to the shaded side. Higher auxin on shaded side → increased cell elongation there → shoot bends toward light.
- Geotropism (root downward): Gravity-sensing statoliths in root cap cells help concentrate auxin on the lower side; in roots high auxin inhibits elongation, so the upper side grows faster and the root bends downward.
- Stomatal regulation: Light, CO2 and ABA regulate guard cell turgor by controlling ion fluxes (K+, Cl–). Light opens stomata (K+ influx, water follows); ABA closes stomata during drought (ion efflux, water loss).
- Seed germination and dormancy: ABA maintains dormancy; gibberellins break dormancy and stimulate synthesis of enzymes (e.g., amylases) to mobilize food reserves for germination.
- Rapid movements: Mimosa pudica folds its leaflets on touch because mechanical stimulation triggers electrical signals and rapid ion movement out of pulvinus cells → water efflux → loss of turgor and movement. Venus flytrap closes its trap similarly after two touches within a short interval.
Summary
Control and coordination in plants rely mainly on hormones, localized chemical/turgor changes and sometimes electrical signaling. Responses are adaptive: directing growth toward resources, protecting against stress, coordinating development (flowering, fruiting, seed dormancy).
- Sunflower stems bending toward sunlight (phototropism): auxin accumulates on the shaded side causing longer cells there.
- Roots growing downward (geotropism): higher auxin concentration on the lower side inhibits root cell elongation, making the root bend down.
- Ripening of fruits (ethylene action): climacteric fruits like banana and apple produce ethylene, accelerating ripening.
- Closing of stomata during drought (ABA action): ABA causes ion efflux from guard cells, reducing turgor and closing stomata to reduce water loss.
- Folding of Mimosa pudica leaves on touch: mechanical stimulus triggers electrical and ionic changes in pulvini leading to rapid turgor loss and folding.
- Seed germination of barley: gibberellins from the embryo induce aleurone cells to produce amylase, which converts starch to sugars for the growing embryo.
- Indole-3-acetic acid (IAA): C10H9NO2 (common naturally occurring auxin)
- Ethylene: C2H4 (gaseous hormone involved in fruit ripening and abscission)
- Abscisic acid (ABA): C15H20O4 (hormone for stomatal closure and seed dormancy)
- Gibberellic acid (GA3): C19H22O6 (one common gibberellin promoting germination and stem elongation)
- Cytokinin example — Zeatin: C10H13N5O
- Simple rate relation for transpiration (practical/experimental): Transpiration rate ≈ ΔW / (A · Δt), where ΔW = water loss (mass or volume), A = leaf area, Δt = time interval
Comparison: Nervous vs Chemical (Hormonal) coordination
Overview: Living organisms coordinate internal activities using two main systems: the nervous system (electrical + chemical signals) and the endocrine system (hormones). Both bring about purposeful responses, but they differ in how fast, how long, how specifically and by which routes they act.
| Feature | Nervous coordination | Chemical (hormonal) coordination |
|---|---|---|
| Mode of transmission | Electrical impulse along neurons; chemical at synapses | Chemical messengers (hormones) secreted into the blood |
| Nature of signal | Rapid electrical signal (action potentials) often with neurotransmitter at synapse | Biochemical molecules (peptides, steroids, amines) |
| Medium | Neural fibers and synaptic clefts | Blood (circulatory system) |
| Speed of response | Very fast (milliseconds to seconds) | Slower (seconds to minutes to hours or days) |
| Duration of effect | Short-lived (stops when stimulus stops or neurotransmitter removed) | Often long-lasting (minutes to days; effects may persist after secretion ends) |
| Specificity | Highly specific: targeted cells connected by nerves | Less specific: hormones circulate and affect all cells with appropriate receptors |
| Area affected | Local (specific muscle/gland/organ) | Widespread (many organs or whole body) |
| Examples of actions | Reflex withdrawal, voluntary movement, sensory perception | Metabolic rate control (thyroxine), blood sugar regulation (insulin), stress response (adrenaline) |
| Control of effect | Neural networks, reflex arcs, inhibitory/excitatory synapses | Feedback loops (negative/positive), receptor regulation, hormone degradation |
How they complement each other: Nervous coordination gives immediate, precise control (e.g., withdrawing a hand from a hot object). Hormonal coordination maintains long-term processes like growth, metabolism, reproduction and stress adaptation (e.g., increased blood glucose via glucagon/insulin balance). Many responses involve both systems—for example, the fight-or-flight response uses sympathetic nerves plus adrenal hormones.
Key terms: action potential, synapse, neurotransmitter, hormone, endocrine gland, receptor, feedback regulation.
- Touching a hot pan → immediate withdrawal via a spinal reflex (nervous coordination).
- Seeing a car coming → rapid leg movement to step back (nervous coordination + brain processing).
- Sudden fright → adrenal medulla secretes adrenaline, raising heart rate and blood glucose (hormonal).
- After a meal → pancreas secretes insulin; cells take up glucose and blood sugar falls (hormonal).
- Long-term growth and metabolic rate regulated by thyroid hormones like thyroxine (hormonal).
- Phototropism in plants: auxin redistribution causes bending toward light (plant hormone action).
- Nerve impulse (average) speed: v = d / t (where v = velocity, d = distance along neuron, t = time taken).
- Concentration of hormone in blood: C = amount / volume (useful for simple dilution calculations).
- \[Hormone clearance (first-order approximation): C(t) = C0 · e^{−kt}\]\[where k is clearance rate constant\]\[half-life t1/2 = ln(2)/k.\]
- Simple reflex time decomposition (not a precise formula, but useful): Reaction time ≈ afferent conduction time + synaptic delay + efferent conduction time + effector response time.
Sense organs and receptors (overview)
What are receptors and sense organs?
Receptors are specialised cells or nerve endings that detect specific types of external or internal stimuli (light, sound, chemical molecules, pressure, temperature, pain) and convert them into electrical signals. A sense organ is a structure that houses receptors and associated accessory parts to collect and transmit stimuli to the nervous system (for example, the eye, ear, nose, tongue and skin).
Main types of receptors
- Photoreceptors: detect light (rods and cones in the retina of the eye).
- Chemoreceptors: detect chemical stimuli (taste buds on tongue, olfactory receptors in nose).
- Mechanoreceptors: detect mechanical changes like pressure, touch, stretch and vibration (Pacinian corpuscles, Meissner's corpuscles, hair cells in inner ear).
- Thermoreceptors: detect temperature changes (free nerve endings in skin).
- Nociceptors: detect damaging or potentially damaging stimuli that cause pain.
How receptors work (sensory transduction)
1) Stimulus acts on the receptor. 2) The receptor converts the physical/chemical stimulus into a change in membrane potential called a receptor (generator) potential. 3) If the receptor potential crosses threshold, it triggers action potentials in sensory neurons. 4) Frequency and pattern of action potentials encode stimulus intensity and quality and travel to the brain for interpretation.
Important concepts
- Threshold: minimum stimulus intensity that produces a detectable receptor response.
- Adaptation: decrease in receptor response during a continuous stimulus. Phasic receptors adapt quickly (e.g., smell, light touch), tonic receptors adapt slowly (e.g., pain, proprioceptors).
- Acuity / discrimination: ability to distinguish two close stimuli; higher receptor density gives better spatial acuity (e.g., fingertips vs back).
- Frequency coding: stronger stimuli produce larger receptor potentials and higher frequencies of action potentials (until saturation).
Pathway to perception
Sensory receptors → sensory neurons → spinal cord/brainstem (may relay/synapse) → thalamus (except olfaction) → specific cortical area for perception (visual cortex, auditory cortex, somatosensory cortex, gustatory/olfactory areas).
Summary: Sense organs contain receptors specialized for particular stimulus types. Receptors transduce stimuli into electrical signals; the nervous system encodes intensity, location and modality and produces perception and/or reflex responses.
- Touching a hot plate: thermoreceptors and nociceptors in skin detect high temperature and tissue damage; rapid withdrawal reflex protects the hand.
- Seeing a bright lamp: photoreceptors in the retina absorb light; pupil constriction reduces light entry (reflex) and visual cortex interprets the image.
- Smelling gas: olfactory chemoreceptors detect gas molecules; a small concentration may be noticed because olfactory receptors are highly sensitive.
- Hearing a bell: mechanoreceptors (hair cells) in the cochlea detect sound vibrations, convert them into nerve impulses whose frequency and intensity encode pitch and loudness.
- Tasting a lemon: taste buds (chemoreceptors) on the tongue detect acidic compounds, producing a sour taste sensation.
- Weber's law (just noticeable difference): ΔI / I = k (ΔI is the smallest detectable change in stimulus I; k is Weber fraction)
- Fechner's law (perceived sensation): S = k · log(I / I0) (S is sensation magnitude, I is stimulus intensity, I0 is threshold intensity, k is a constant)
- Decibel scale for sound intensity: L(dB) = 10 · log10(I / I0) where I0 is reference intensity (commonly 10^-12 W/m^2)
- Qualitative relation used in coding: firing frequency ∝ stimulus intensity (up to saturation)
Key Concepts
- Stimulus
- Any change in the internal or external environment that is detected by a receptor and elicits a response.
- Response
- The action or change in behavior of an organism or cell as a result of a stimulus.
- Receptor
- Specialized cells or nerve endings that detect specific stimuli (like light, heat, touch) and convert them into nerve impulses.
- Effector
- Muscle or gland that carries out the response commanded by the nervous or endocrine system.
- Neuron
- A nerve cell that transmits electrical impulses; basic structural and functional unit of the nervous system.
- Sensory neuron
- Neuron that carries impulses from receptors toward the central nervous system.
- Motor neuron
- Neuron that carries impulses away from the central nervous system to effectors (muscles or glands).
- Synapse
- The gap between two neurons where the nerve impulse is transmitted chemically (by neurotransmitters) or electrically.
- Neurotransmitter
- Chemical substances released at synapses to transmit nerve impulses from one neuron to another or to an effector.
- Nerve impulse
- An electrochemical signal that travels along the membrane of a neuron carrying information.
- Reflex action
- A rapid, automatic, and involuntary response to a stimulus that does not involve conscious thought.
- Reflex arc
- The neural pathway followed by a reflex action typically involving receptor, sensory neuron, spinal cord (relay neuron), motor neuron, and effector.
- Central Nervous System (CNS)
- Part of the nervous system consisting of the brain and spinal cord; integrates information and coordinates responses.
- Autonomic Nervous System (ANS)
- Part of the nervous system that controls involuntary actions (like heartbeat, digestion) and maintains internal balance.
- Brain
- The principal organ of the nervous system responsible for processing information, thinking, memory, and voluntary actions.
- Spinal cord
- A long bundle of nerve tissue within the vertebral column that transmits impulses between the brain and the rest of the body and mediates many reflexes.
- Hormone
- Chemical messenger secreted by endocrine glands into the blood to regulate physiological processes at distant target organs.
- Endocrine gland
- Gland that secretes hormones directly into the bloodstream rather than through ducts.
- Auxin
- A class of plant hormones (e.g., indole-3-acetic acid) that regulate plant growth, cell elongation, and responses to light and gravity.
- Tropism
- Directional growth movement of a plant in response to an external stimulus (toward or away from the stimulus).
End-of-Chapter Trial Paper & Test Questions
Topic-wise questions to test your understanding of every concept in this chapter.
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Define a reflex action and explain its survival importance with an example. / प्रतिवर्ती क्रिया को परिभाषित कीजिए तथा उदाहरण सहित इसके उत्तरजीविता महत्व को समझाइए।
Show answer
A reflex action is a rapid, automatic and involuntary response to a stimulus without involving conscious thought of the brain. It protects the body from harm, for example, instantly withdrawing the hand on touching a hot object. / प्रतिवर्ती क्रिया किसी उद्दीपन के प्रति एक तीव्र, स्वचालित तथा अनैच्छिक अनुक्रिया है जिसमें मस्तिष्क की सचेत सोच शामिल नहीं होती। यह शरीर को हानि से बचाती है, जैसे गर्म वस्तु को छूते ही हाथ का तुरंत पीछे हट जाना।
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Draw and label the components of a reflex arc, naming them in correct sequence. / प्रतिवर्ती चाप के घटकों को सही क्रम में नाम देते हुए बनाइए तथा नामांकित कीजिए।
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The reflex arc consists of: receptor → sensory (afferent) neuron → spinal cord (relay neuron) → motor (efferent) neuron → effector (muscle/gland). The impulse travels in this sequence to produce a quick response. / प्रतिवर्ती चाप में होते हैं: ग्राही → संवेदी (अभिवाही) तंत्रिका → मेरुरज्जु (सहचारी तंत्रिका) → प्रेरक (अपवाही) तंत्रिका → प्रभावक (पेशी/ग्रंथि)। आवेग इसी क्रम में चलकर त्वरित अनुक्रिया उत्पन्न करता है।
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How is information transmitted across a synapse from one neuron to another? / एक तंत्रिका कोशिका से दूसरी तक सूचना युग्मानुबंध (सिनैप्स) के पार कैसे संचारित होती है?
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When an electrical impulse reaches the nerve ending, it releases chemicals (neurotransmitters) into the synaptic gap. These chemicals diffuse across and start a new electrical impulse in the next neuron's dendrite. / जब विद्युत आवेग तंत्रिका के सिरे तक पहुँचता है, तो वह युग्मानुबंध की दरार में रसायन (तंत्रिका-प्रेषक) मुक्त करता है। ये रसायन दूसरी ओर विसरित होकर अगली तंत्रिका के द्रुमिका में नया विद्युत आवेग प्रारंभ करते हैं।
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Distinguish between the functions of the cerebrum and the cerebellum. / प्रमस्तिष्क तथा अनुमस्तिष्क के कार्यों में अंतर स्पष्ट कीजिए।
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The cerebrum is the main thinking part responsible for voluntary actions, memory, reasoning and sensory perception. The cerebellum maintains posture, balance and coordinates precise voluntary movements. / प्रमस्तिष्क मुख्य सोचने वाला भाग है जो ऐच्छिक क्रियाओं, स्मृति, तर्क तथा संवेदी बोध के लिए उत्तरदायी है। अनुमस्तिष्क शरीर की मुद्रा, संतुलन को बनाए रखता है तथा सूक्ष्म ऐच्छिक गतियों में समन्वय करता है।
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Name the plant hormone responsible for phototropism and explain how a shoot bends toward light. / प्रकाशानुवर्तन के लिए उत्तरदायी पादप हार्मोन का नाम लिखिए तथा समझाइए कि प्ररोह प्रकाश की ओर कैसे झुकता है।
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Auxin is the hormone responsible for phototropism. When light falls on one side, auxin moves to the shaded side and causes faster cell elongation there, so the shoot bends toward the light. / प्रकाशानुवर्तन के लिए ऑक्सिन उत्तरदायी हार्मोन है। जब एक ओर प्रकाश पड़ता है, तो ऑक्सिन छाया वाली ओर चला जाता है और वहाँ कोशिकाओं की तीव्र वृद्धि करता है, जिससे प्ररोह प्रकाश की ओर झुक जाता है।
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Why is the thyroid gland's secretion dependent on iodine, and what disorder results from its deficiency? / थायरॉइड ग्रंथि का स्राव आयोडीन पर निर्भर क्यों होता है तथा इसकी कमी से कौन-सा रोग होता है?
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The thyroid gland needs iodine to synthesise the hormone thyroxine, which regulates carbohydrate, protein and fat metabolism. Deficiency of iodine causes goitre, in which the thyroid gland becomes enlarged. / थायरॉइड ग्रंथि को थायरॉक्सिन हार्मोन बनाने के लिए आयोडीन की आवश्यकता होती है, जो कार्बोहाइड्रेट, प्रोटीन तथा वसा के उपापचय का नियमन करता है। आयोडीन की कमी से गलगंड (घेंघा) रोग होता है, जिसमें थायरॉइड ग्रंथि बढ़ जाती है।
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Compare nervous coordination and hormonal coordination in animals. / जंतुओं में तंत्रिकीय समन्वय तथा हार्मोनी समन्वय की तुलना कीजिए।
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Nervous coordination uses electrical impulses through neurons, acts very rapidly, and its effect is short-lived. Hormonal coordination uses chemical messengers carried in blood, acts slowly, and its effect lasts longer. / तंत्रिकीय समन्वय तंत्रिकाओं द्वारा विद्युत आवेगों का उपयोग करता है, बहुत तीव्र होता है तथा इसका प्रभाव अल्पकालिक होता है। हार्मोनी समन्वय रक्त में वहन किए जाने वाले रासायनिक संदेशवाहकों का उपयोग करता है, धीमा होता है तथा इसका प्रभाव अधिक समय तक रहता है।
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Explain the role of adrenaline as the 'emergency hormone' during a frightening situation. / भयावह परिस्थिति में 'आपातकालीन हार्मोन' के रूप में एड्रिनेलिन की भूमिका समझाइए।
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When a person is frightened, adrenaline is secreted by the adrenal glands into the blood, which increases heart rate, breathing rate and blood supply to muscles. This prepares the body to deal with the emergency by a 'fight or flight' response. / जब कोई व्यक्ति भयभीत होता है, तो अधिवृक्क ग्रंथियाँ रक्त में एड्रिनेलिन स्रावित करती हैं, जो हृदय गति, श्वसन दर तथा पेशियों को रक्त की आपूर्ति बढ़ा देता है। यह शरीर को 'संघर्ष या पलायन' अनुक्रिया द्वारा आपातकाल से निपटने के लिए तैयार करता है।
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