Class 10 Notes

Class 10 Science Notes Chapter 7 (Control and coordination) – Science Book

Philoid

Philoid

— 7 min read

Science
Alright class, let's get straight into a detailed revision of Chapter 7, 'Control and Coordination'. This is a crucial chapter, not just for your board exams but also for various government exams, as it deals with the fundamental systems that regulate life processes. Pay close attention.

Chapter 7: Control and Coordination - Detailed Notes

1. Introduction

  • All living organisms respond and react to changes in the environment around them. These changes are called stimuli (singular: stimulus). Examples: light, heat, cold, sound, smell, taste, touch, pressure, gravity, water.
  • The response of organisms to stimuli is usually in the form of movement or secretion.
  • In complex multicellular organisms, specialized tissues and systems are used to provide control and coordination activities.
  • In animals, control and coordination are carried out by the Nervous System and the Endocrine System.
  • In plants, control and coordination are primarily carried out by chemical substances called Plant Hormones or Phytohormones.

2. Nervous System in Animals

  • Function: Provides rapid coordination through electrochemical impulses.

  • Basic Unit: Neuron (Nerve Cell)

    • 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 long extension arising from the cell body that transmits nerve impulses away from the cell body. It is often covered by a myelin sheath (insulating layer, speeds up transmission).
      • Nerve Endings (Axon Terminals): Branched ends of the axon that transmit the signal to the next neuron or effector cell (muscle/gland).
    • Synapse: The junction between the nerve ending of one neuron and the dendrite of the next neuron. There is a minute gap (synaptic cleft) here. The electrical impulse arriving at the axon terminal triggers the release of chemical messengers called neurotransmitters (e.g., acetylcholine) which diffuse across the gap and initiate a similar electrical impulse in the next neuron.

  • Transmission of Nerve Impulse: Stimulus -> Receptor (sense organ) -> Sensory Neuron -> CNS (Brain/Spinal Cord) -> Motor Neuron -> Effector (muscle/gland) -> Response.

  • Types of Responses:

    • Reflex Action: A rapid, automatic, involuntary response to a stimulus, not under conscious control. Primarily controlled by the spinal cord. Example: Withdrawing hand immediately upon touching a hot object, knee-jerk reflex, blinking.
    • Reflex Arc: The pathway taken by the nerve impulse during a reflex action.
      • Pathway: Stimulus -> Receptor -> Sensory Neuron -> Relay Neuron (in Spinal Cord) -> Motor Neuron -> Effector -> Response.
    • Voluntary Action: Actions under conscious control, involving thought and decision-making by the brain. Example: Writing, walking, talking.
    • Involuntary Action: Actions not under conscious control, regulated by the mid-brain and hind-brain. Example: Heartbeat, breathing, digestion, salivation. (Note: Reflex actions are a type of involuntary action, but specifically involve the spinal cord or brainstem for rapid response).

  • Human Nervous System:

    • Central Nervous System (CNS): Main control centre.

      • Brain: The main coordinating centre of the body. Protected by the cranium (skull). Covered by three membranes called meninges. The space between meninges is filled with cerebrospinal fluid (CSF) which provides cushioning.
        • Forebrain: Largest part. Main thinking part.
          • Cerebrum: Centre of intelligence, memory, consciousness, voluntary actions, interpretation of sensations (pain, touch, sight, sound, smell).
          • Olfactory Lobes: Sense of smell (often considered part of cerebrum).
          • Diencephalon: (Includes Thalamus & Hypothalamus) - Relays sensory info, controls body temperature, urge for eating/drinking, emotions. Hypothalamus also controls the 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 at the back. Controls posture, balance, and coordination of voluntary movements (precision).
          • Pons: Relays impulses between different parts of the brain, regulates respiration.
          • Medulla Oblongata: Base of the brain, connects to the spinal cord. Controls involuntary actions like heartbeat, breathing, blood pressure, swallowing, coughing, sneezing, vomiting.
      • Spinal Cord: A cylindrical structure extending down from the Medulla Oblongata, enclosed within the vertebral column (backbone). Connects nerves to most parts of the body. Controls reflex actions below the neck. Conducts messages between the body and the brain.

    • 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).
      • PNS includes the Somatic Nervous System (controls voluntary muscles) and the Autonomic Nervous System (controls involuntary functions like heartbeat, glands - further divided into Sympathetic and Parasympathetic, usually not detailed in Class 10).

  • How Nervous Tissue Causes Action: When a nerve impulse reaches a muscle fibre via a motor neuron at the neuromuscular junction, it triggers the release of neurotransmitters. This causes electrical changes in the muscle cell membrane, leading to the rearrangement of special proteins (Actin and Myosin) within the muscle cell, resulting in muscle contraction (shortening) and movement.

3. Coordination in Plants

  • Plants lack a nervous system but show responses to stimuli, often in the form of growth movements.

  • Coordination is achieved through chemical substances called Plant Hormones (Phytohormones).

  • 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 phototropism); roots grow away from light (negative phototropism). Mediated mainly by Auxin.
      • Geotropism (Gravitropism): Response to gravity. Roots grow downwards (positive geotropism); shoots grow upwards, against gravity (negative geotropism). Also involves Auxin.
      • Hydrotropism: Response to water. Roots grow towards water (positive hydrotropism).
      • Chemotropism: Response to chemicals. Example: Growth of pollen tube towards the ovule (due to chemical signals).
      • Thigmotropism: Response to touch or contact. Example: Climbing tendrils coiling around a support.

    • Nastic Movements: Non-directional movements in response to a stimulus (the direction of response is independent of the direction of stimulus). Usually involve changes in turgor pressure.

      • Thigmonasty (Seismonasty): Response to touch. Example: Folding of leaves in Mimosa pudica (touch-me-not plant) upon touching. Caused by rapid loss of water (change in turgor) from cells at the base of leaflets (pulvini).
      • Nyctinasty: "Sleep movements" of leaves/petals in response to light/dark cycles (e.g., closing at night, opening during the day).

  • Plant Hormones (Phytohormones): Chemical messengers regulating growth, development, and responses.

    • Auxins: Synthesized at shoot tips. Promote cell elongation, stem and root growth, phototropism, geotropism, apical dominance (suppression of lateral buds).
    • Gibberellins: Promote stem elongation (especially internodal elongation), seed germination, breaking dormancy, flowering, fruit development.
    • Cytokinins: Synthesized mainly in roots. Promote cell division, overcome apical dominance, delay leaf senescence (aging), promote fruit growth, help in opening of stomata. Often work in conjunction with auxins.
    • Abscisic Acid (ABA): Growth inhibitor. Promotes dormancy in seeds and buds, causes closing of stomata (during water stress), promotes leaf senescence and abscission (falling of leaves/fruits). Often acts antagonistically to Gibberellins.
    • Ethylene: (Gaseous hormone) Promotes fruit ripening, senescence, and abscission.

4. Hormones in Animals (Endocrine System)

  • Function: Provides chemical coordination, often slower but longer-lasting than nervous coordination.

  • Endocrine Glands: Ductless glands that secrete chemical messengers called hormones directly into the bloodstream.

  • Hormones: Chemical substances that act as messengers, transported by blood to target organs/tissues where they regulate specific physiological processes.

  • Major Endocrine Glands, Hormones, and Functions (in Humans):

    • Hypothalamus: (Part of the brain) Produces releasing hormones and inhibiting hormones that regulate the secretions of the pituitary gland. Often called the 'master of the master gland'.
    • Pituitary Gland (Master Gland): Located at the base of the brain. Secretes several hormones:
      • Growth Hormone (GH): Regulates growth and development. Deficiency causes Dwarfism; excess causes Gigantism.
      • Other hormones regulate thyroid, adrenals, ovaries, testes (TSH, ACTH, FSH, LH - details less critical for Class 10).
    • Thyroid Gland: Located in the neck region.
      • Thyroxine: Regulates carbohydrate, protein, and fat metabolism, essential for growth. Requires Iodine for its synthesis. Deficiency leads to Goitre (swelling of the thyroid gland). Hypothyroidism can also cause cretinism (in children) or myxoedema (in adults).
    • Parathyroid Glands: Embedded in the thyroid gland.
      • Parathormone: Regulates calcium and phosphate levels in the blood. (Less emphasized in Class 10).
    • Adrenal Glands: Located on top of the kidneys. Two parts: Cortex and Medulla.
      • Adrenaline (Epinephrine): Secreted by Adrenal Medulla. "Emergency hormone" or "Fight or Flight" hormone. Prepares the body for stress situations by increasing heart rate, blood pressure, breathing rate, blood glucose levels, diverting blood to muscles.
    • Pancreas: Located below the stomach. Acts as both endocrine and exocrine gland. Endocrine part (Islets of Langerhans) secretes:
      • Insulin: Lowers blood glucose levels (promotes uptake of glucose by cells, conversion of glucose to glycogen in liver/muscles). Deficiency causes Diabetes Mellitus (high blood sugar).
      • Glucagon: Raises blood glucose levels (promotes breakdown of glycogen to glucose in the liver).
    • Testes (in Males): Located in the scrotum.
      • Testosterone: Responsible for development of male secondary sexual characteristics (deep voice, beard, body hair) during puberty, sperm production.
    • Ovaries (in Females): Located in the abdominal cavity.
      • Estrogen: Responsible for development of female secondary sexual characteristics (breast development, menstruation cycle onset) during puberty, egg development.
      • Progesterone: Maintains pregnancy.

  • Feedback Mechanism: The regulation of hormone secretion based on the levels of the hormone or the substance it controls in the blood. Ensures hormones are secreted in precise quantities.

    • Example: If blood sugar level rises, pancreas secretes more insulin. Insulin helps lower blood sugar. If blood sugar falls too low, insulin secretion is reduced. If blood sugar falls further, pancreas secretes glucagon to raise it. This maintains blood glucose homeostasis.

Multiple Choice Questions (MCQs)

  1. Which part of the neuron receives information?
    (a) Axon
    (b) Dendrite
    (c) Cell Body
    (d) Nerve Ending

  2. The gap between two neurons is called a:
    (a) Synapse
    (b) Dendrite
    (c) Axon
    (d) Impulse

  3. Which part of the human brain is the main thinking part?
    (a) Cerebellum
    (b) Medulla
    (c) Cerebrum
    (d) Pons

  4. The pathway taken by a nerve impulse in a reflex action is called:
    (a) Reflex Impulse
    (b) Reflex Arc
    (c) Reflex Pathway
    (d) Reflex Stimulus

  5. Which plant hormone promotes cell division?
    (a) Auxin
    (b) Gibberellin
    (c) Cytokinin
    (d) Abscisic Acid

  6. The growth of a pollen tube towards the ovule is an example of:
    (a) Phototropism
    (b) Geotropism
    (c) Chemotropism
    (d) Hydrotropism

  7. Which endocrine gland is known as the 'Master Gland'?
    (a) Thyroid Gland
    (b) Adrenal Gland
    (c) Pituitary Gland
    (d) Pancreas

  8. Which hormone is responsible for regulating blood sugar levels by lowering them?
    (a) Glucagon
    (b) Thyroxine
    (c) Adrenaline
    (d) Insulin

  9. Deficiency of Iodine in the diet can lead to:
    (a) Diabetes
    (b) Goitre
    (c) Dwarfism
    (d) Gigantism

  10. The 'Fight or Flight' response is triggered by the hormone:
    (a) Insulin
    (b) Estrogen
    (c) Adrenaline
    (d) Growth Hormone

Answer Key for MCQs:

  1. (b) Dendrite
  2. (a) Synapse
  3. (c) Cerebrum
  4. (b) Reflex Arc
  5. (c) Cytokinin
  6. (c) Chemotropism
  7. (c) Pituitary Gland
  8. (d) Insulin
  9. (b) Goitre
  10. (c) Adrenaline

Make sure you understand these concepts thoroughly. Remember the structure of the neuron, the parts of the brain and their functions, the reflex arc pathway, different types of plant movements, and the roles of various plant and animal hormones. Good luck with your preparation!

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