Class 10 Science Notes Chapter 7 (Chapter 7) – Examplar Problems (English) Book

Detailed Notes with MCQs of Chapter 7, 'Control and Coordination', from your NCERT Exemplar. This chapter is crucial not just for your board exams but also forms a foundation for many questions in competitive government exams. Pay close attention as we break down the key concepts.

Chapter 7: Control and Coordination - Detailed Notes for Government Exam Preparation

Introduction:
All living organisms respond and react to changes in their environment. This ability to respond to stimuli is a fundamental characteristic of life. In multicellular organisms, specialized tissues and systems are involved in providing control and coordination. In animals, this is done by the nervous system and the endocrine (hormonal) system. In plants, it's primarily achieved through chemical coordination (plant hormones).

1. Control and Coordination in Animals: The Nervous System

• Stimulus: Any change in the environment to which an organism responds. (e.g., light, heat, sound, smell, taste, touch, pressure).

• Response: The reaction of the organism to a stimulus.

• Receptors: Specialized cells or tips of nerve cells that detect stimuli. They are usually located in sense organs.

  • Phonoreceptors: Detect sound (Inner ear).
  • Photoreceptors: Detect light (Eyes).
  • Thermoreceptors: Detect heat/cold (Skin).
  • Olfactory Receptors: Detect smell (Nose).
  • Gustatory Receptors: Detect taste (Tongue).
  • Tangoreceptors: Detect touch (Skin).

• Effectors: Parts of the body that produce the response. Usually muscles or glands.

• Neuron (Nerve Cell): The structural and functional unit of the nervous system.

  • Structure:
    • Cell Body (Cyton/Soma): Contains the nucleus and cytoplasm.
    • Dendrites: Short, branched extensions arising from the cell body that receive signals from other neurons.
    • Axon: A single, long extension arising from the cell body that transmits signals away from the cell body. It may be covered by a myelin sheath.
    • Myelin Sheath: An insulating layer around the axon (formed by Schwann cells) that speeds up nerve impulse transmission. Gaps in the myelin sheath are called Nodes of Ranvier.
    • Nerve Ending (Axon Terminal): Branched ends of the axon that transmit signals to the next neuron or effector cell.
  • Synapse: The junction between the axon terminal of one neuron and the dendrite of the next neuron (or an effector cell). There is a minute gap called the synaptic cleft.
  • Nerve Impulse: The electrical and chemical signal that travels along a neuron.
    • Transmission: Dendrite → Cell Body → Axon → Nerve Ending.
    • Across Synapse: At the axon terminal, electrical impulse triggers the release of chemical messengers called neurotransmitters (e.g., Acetylcholine) into the synaptic cleft. These chemicals bind to receptors on the next neuron's dendrite, initiating an electrical impulse in it.

• Types of Neurons:

  • Sensory Neurons: Transmit impulses from receptors to the CNS (Brain/Spinal Cord).
  • Motor Neurons: Transmit impulses from the CNS to effectors (Muscles/Glands).
  • Relay Neurons (Interneurons): Found within the CNS, connecting sensory and motor neurons.

• Reflex Action: A rapid, automatic, involuntary response to a stimulus, not under conscious control. It is a protective mechanism.

  • Examples: Withdrawing hand from a hot object, blinking, sneezing, coughing, knee-jerk reflex.
  • Reflex Arc: The pathway taken by the nerve impulse during a reflex action.
    • Pathway: Receptor → Sensory Neuron → Relay Neuron (in Spinal Cord) → Motor Neuron → Effector.
    • Note: The brain is informed after the reflex action has occurred, though it can sometimes override or modify reflexes.

• Human Nervous System:

  • Central Nervous System (CNS): Brain and Spinal Cord. Receives information, processes it, and generates responses.
  • Peripheral Nervous System (PNS): Nerves arising from the CNS that connect it to the rest of the body.
    • Cranial Nerves: Arise from the brain (12 pairs in humans).
    • Spinal Nerves: Arise from the spinal cord (31 pairs in humans).
    • Somatic Nervous System: Controls voluntary actions (skeletal muscles).
    • Autonomic Nervous System: Controls involuntary actions (smooth muscles, cardiac muscles, glands). Further divided into:
      • Sympathetic: Prepares body for 'fight or flight' (increases heart rate, breathing rate, etc.).
      • Parasympathetic: Controls 'rest and digest' functions (slows heart rate, stimulates digestion, etc.).

• Human Brain: The main coordinating centre of the body. Protected by the cranium (skull), and surrounded by three membranes called meninges, with cerebrospinal fluid (CSF) filling the space between them (provides cushioning, nourishment).

  • Major Parts:
    • Forebrain:
      • Cerebrum: Largest part. Centre of intelligence, memory, learning, thinking, reasoning, consciousness, and voluntary actions. Divided into two cerebral hemispheres. Has distinct areas for sensory perception (touch, sight, hearing, smell) and motor control.
      • Olfactory Lobes: Sense of smell (reduced in humans compared to other mammals).
      • Diencephalon: Includes Thalamus (relay centre for sensory information) and Hypothalamus (controls body temperature, urge for eating/drinking, emotions, links nervous system to endocrine system via pituitary gland).
    • Midbrain: Connects forebrain and hindbrain. Controls reflex movements of the head, neck, and trunk in response to visual and auditory stimuli; controls reflex movements of the eye muscles.
    • Hindbrain:
      • Cerebellum: Located below the cerebrum. Coordinates voluntary movements (e.g., walking, picking up objects), maintains posture and body balance (equilibrium).
      • Pons: Relays impulses between different parts of the brain, particularly the cerebellum and cerebrum. Helps regulate respiration.
      • Medulla Oblongata: Connects to the spinal cord. Controls involuntary actions like heartbeat, breathing rate, blood pressure, swallowing, coughing, sneezing, vomiting.

• Spinal Cord: A cylindrical structure extending from the medulla oblongata down through the vertebral column (backbone). Protected by the vertebrae and meninges.

  • Functions:
    • Conducts nerve impulses between the brain and the rest of the body.
    • Centre for most reflex actions.

2. Coordination in Plants

Plants lack a nervous system but exhibit coordination through chemical means (hormones) and respond to stimuli.

• Plant Movements:

  • Tropic Movements (Tropisms): Directional growth movements in response to a directional stimulus. Can be positive (towards stimulus) or negative (away from stimulus).
    • Phototropism: Response to light. Shoots grow towards light (positive), roots grow away (negative).
    • Geotropism (Gravitropism): Response to gravity. Roots grow downwards (positive), shoots grow upwards (negative).
    • Hydrotropism: Response to water. Roots grow towards water (positive).
    • Chemotropism: Response to chemicals. Growth of pollen tube towards ovule (due to chemical signals).
    • Thigmotropism: Response to touch. Growth of tendrils around a support.
  • Nastic Movements: Non-directional movements in response to a stimulus, independent of the direction of stimulus. Usually involve changes in turgor pressure.
    • Thigmonasty: Response to touch. E.g., Folding of leaves in Mimosa pudica (touch-me-not plant).
    • Photonasty: Response to light intensity. E.g., Opening/closing of petals in Dandelion flowers.

• Plant Hormones (Phytohormones): Chemical substances produced in small quantities that regulate growth, development, and responses to stimuli.

  • Growth Promoters:
    • Auxins: Synthesized at shoot/root tips. Promote cell elongation, stem/root growth, phototropism, geotropism, apical dominance (suppression of lateral buds). Involved in fruit development. (e.g., Indole-3-acetic acid - IAA).
    • Gibberellins: Promote stem elongation (especially internodes), break seed/bud dormancy, promote flowering and fruit development (e.g., parthenocarpy in grapes).
    • Cytokinins: Promote cell division (cytokinesis), promote lateral bud growth (counteract apical dominance), delay leaf senescence (ageing). Found in areas of rapid cell division (fruits, seeds).
  • Growth Inhibitors:
    • Abscisic Acid (ABA): Inhibits growth, promotes seed/bud dormancy, causes stomatal closure (response to water stress), promotes leaf senescence and abscission (falling of leaves/fruits). Often called the 'stress hormone'.
  • (Ethylene - Sometimes considered separately): A gaseous hormone. Promotes fruit ripening, senescence, and abscission.

3. Hormones in Animals: The Endocrine System

• Endocrine System: Consists of endocrine glands that produce and secrete chemical messengers called hormones directly into the bloodstream (ductless glands). Hormones travel via blood to target organs/tissues where they exert specific effects.

• Hormones: Chemical messengers regulating various physiological processes like growth, metabolism, development, reproduction, and response to stress. Act in small concentrations.

• Comparison with Nervous Control:

  • Nervous: Fast, short-lived response, transmitted electrically/chemically via neurons, localized effect.
  • Hormonal: Slow, long-lasting response, transmitted chemically via blood, widespread effect (on target organs).

• Major Endocrine Glands and Hormones in Humans:

  • Hypothalamus: Part of the brain; produces releasing hormones and inhibiting hormones that control the pituitary gland. Also produces ADH and Oxytocin (stored and released by posterior pituitary).
  • Pituitary Gland (Master Gland): Located below the brain.
    • Anterior Pituitary: Produces Growth Hormone (GH), Thyroid Stimulating Hormone (TSH), Adrenocorticotropic Hormone (ACTH), Follicle Stimulating Hormone (FSH), Luteinizing Hormone (LH), Prolactin.
    • Posterior Pituitary: Stores and releases Antidiuretic Hormone (ADH/Vasopressin - regulates water balance) and Oxytocin (stimulates uterine contractions during childbirth, milk ejection).
  • Thyroid Gland: Located in the neck. Produces Thyroxine (T4) and Triiodothyronine (T3).
    • Function: Regulates basal metabolic rate (carbohydrate, protein, fat metabolism), promotes growth.
    • Requirement: Iodine is essential for thyroxine synthesis.
    • Disorders: Hypothyroidism (causes Goitre - swelling of thyroid, Cretinism in children, Myxedema in adults), Hyperthyroidism.
  • Parathyroid Glands: Four small glands embedded in the thyroid. Produce Parathyroid Hormone (PTH) or Parathormone.
    • Function: Regulates calcium and phosphate levels in the blood (increases blood calcium).
  • Adrenal Glands: Located on top of kidneys (Suprarenal glands). Have two parts:
    • Adrenal Cortex (Outer): Produces corticosteroids (e.g., Cortisol - regulates metabolism, stress response; Aldosterone - regulates salt/water balance).
    • Adrenal Medulla (Inner): Produces Adrenaline (Epinephrine) and Noradrenaline (Norepinephrine).
      • Function: Released during stress/emergency ('fight or flight' hormones). Increase heart rate, blood pressure, breathing rate, blood glucose levels, divert blood to skeletal muscles.
  • Pancreas: Located below the stomach. Has both exocrine (digestive enzymes) and endocrine functions (Islets of Langerhans).
    • Endocrine Function: Produces Insulin (secreted by β-cells) and Glucagon (secreted by α-cells).
      • Insulin: Lowers blood glucose levels (promotes uptake by cells, conversion to glycogen in liver/muscles).
      • Glucagon: Raises blood glucose levels (promotes breakdown of glycogen to glucose in liver).
    • Disorder: Diabetes Mellitus (due to insulin deficiency or insensitivity; results in high blood sugar - hyperglycemia).
  • Testes (in Males): Produce Testosterone.
    • Function: Development of male secondary sexual characteristics (deep voice, beard, body hair), sperm production.
  • Ovaries (in Females): Produce Estrogen and Progesterone.
    • Function:
      • Estrogen: Development of female secondary sexual characteristics (breast development, wider hips), regulates menstrual cycle, maturation of eggs.
      • Progesterone: Maintains pregnancy, further development of uterus lining.

• Feedback Mechanism: The regulation of hormone secretion. The level of a hormone (or the response of the target organ) in the blood can inhibit or stimulate further secretion of that hormone (or its releasing hormone). Mostly negative feedback (e.g., high blood glucose → insulin secretion → lower blood glucose → reduced insulin secretion). This maintains homeostasis.

Key Takeaways for Exams:

• Know the structure and function of a neuron, synapse, and reflex arc.
• Understand the divisions of the nervous system (CNS, PNS, Somatic, Autonomic).
• Memorize the main parts of the human brain and their specific functions.
• Differentiate between tropic and nastic movements in plants with examples.
• Learn the names, sources, functions, and deficiency/excess effects (where applicable) of major plant and animal hormones.
• Understand the concept of feedback mechanism in hormone regulation.
• Compare nervous and hormonal control mechanisms.

Multiple Choice Questions (MCQs)

Here are 10 MCQs based on Chapter 7, keeping competitive exams in mind:

1. Which sequence correctly represents a reflex arc?
   (a) Receptor → Motor Neuron → Spinal Cord → Sensory Neuron → Effector
   (b) Effector → Sensory Neuron → Spinal Cord → Motor Neuron → Receptor
   (c) Receptor → Sensory Neuron → Spinal Cord/Relay Neuron → Motor Neuron → Effector
   (d) Sensory Neuron → Receptor → Motor Neuron → Spinal Cord → Effector

2. The growth of tendrils around a support is an example of:
   (a) Phototropism
   (b) Geotropism
   (c) Thigmotropism
   (d) Hydrotropism

3. Which part of the human brain is the main centre for thinking, intelligence, and memory?
   (a) Cerebellum
   (b) Medulla Oblongata
   (c) Cerebrum
   (d) Pons

4. Which plant hormone promotes cell division and is found abundantly in areas of rapid growth like fruits and seeds?
   (a) Auxin
   (b) Gibberellin
   (c) Cytokinin
   (d) Abscisic Acid

5. A person meets with an accident and loses the ability to maintain posture and equilibrium. Which part of the hindbrain is likely affected?
   (a) Pons
   (b) Medulla Oblongata
   (c) Cerebellum
   (d) Thalamus

6. Which endocrine gland is responsible for secreting 'fight or flight' hormones?
   (a) Thyroid Gland
   (b) Pituitary Gland
   (c) Pancreas
   (d) Adrenal Gland

7. Iodine is essential for the synthesis of which hormone?
   (a) Insulin
   (b) Adrenaline
   (c) Thyroxine
   (d) Growth Hormone

8. The gap between two neurons where chemical signals are transmitted is called:
   (a) Axon terminal
   (b) Synapse
   (c) Dendrite
   (d) Myelin Sheath

9. Which of the following is NOT a function of Auxins in plants?
   (a) Promoting cell elongation
   (b) Initiating rooting in stem cuttings
   (c) Promoting fruit ripening
   (d) Mediating phototropism

10. Diabetes Mellitus is caused due to the deficiency or improper functioning of:
    (a) Glucagon
    (b) Thyroxine
    (c) Insulin
    (d) Adrenaline

Answers to MCQs:

1. (c)
2. (c)
3. (c)
4. (c)
5. (c)
6. (d)
7. (c)
8. (b)
9. (c) (Fruit ripening is primarily promoted by Ethylene)
10. (c)

Study these notes thoroughly. Remember to correlate the functions with the structures in the nervous system and the specific roles of each hormone in both plants and animals. Good luck with your preparation!