Science Chapter 6: Control and Coordination

Principles of Movement and Life Processes

• Initial Notion of Life: A common observation for identifying life is movement.

• Types of Movements in Living Organisms:

  • Growth-Related Movement: In plants, a seed germinates and grows; the seedling pushes soil aside to emerge. These movements cease if growth is stopped.

  • Non-Growth Related Movement: Many activities are not connected to growth, such as a cat running, children playing on swings, or buffaloes chewing cud.

• Rationale for Movement:

  • Response to Environmental Change: Movement is often a reaction to a change in surroundings (e.g., a cat running after seeing a mouse).

  • Advantageous Adaptation: Organisms use movement to their advantage. Plants grow toward sunshine to facilitate photosynthesis; buffaloes chew cud to break down tough food for better digestion; children swing for pleasure.

  • Protection: Organisms detect and respond to dangerous stimuli, such as pulling a hand away from a hot object or blinking in bright light.

• Control and Coordination:

  • Movement in response to the environment is carefully controlled and appropriate to the stimulus.

  • Example: Whispering in class rather than shouting depends on the specific social context.

  • Multicellular organisms use specialized tissues to provide control and coordination systems.

Animals – Nervous System

• Function: Control and coordination in animals are provided by nervous and muscular tissues.

• Detection of Stimuli: Information from the environment is detected by specialized tips of nerve cells called receptors, typically located in sense organs.

  • Gustatory Receptors: Specialized for detecting taste.

  • Olfactory Receptors: Specialized for detecting smell.

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

  • Information Acquisition: Occurs at the dendritic tip of the nerve cell.

  • Signal Transmission:

    1. A chemical reaction at the dendrite sets off an electrical impulse.

    2. The impulse travels from the dendrite to the cell body.

    3. It then travels along the axon to its end.

  • The Synapse: At the end of the axon, the electrical impulse triggers the release of certain chemicals. These chemicals cross the gap, or synapse, to start a similar electrical impulse in the dendrite of the next neuron.

  • Neuromuscular Junction: This same process allows the delivery of impulses from neurons to other cells, such as muscle cells or glands.

• Activity 6.1 (Taste and Smell): Blocking the nose while eating sugar or food demonstrates the interaction between olfactory and gustatory receptors. When the nose is blocked (common during a cold), the full flavor of food cannot be appreciated because smell contributes significantly to perceived taste.

Reflex Actions and the Reflex Arc

• Definition of Reflex: A sudden, involuntary action in response to something in the environment, performed without conscious thought or control.

  • Examples: Jumping out of the way of a bus, pulling a hand back from a flame, or the mouth watering at the sight of food.

• The Problem of Conscious Thinking: Thinking is a complex activity involving dense networks of neurons in the brain. If we had to think consciously before reacting to a hot object, the time taken for the brain to process signals and instruct muscles would be too long, resulting in injury.

• The Reflex Arc: A shorter, faster connection between the input (sensory) nerve and the output (motor) nerve.

  • Pathway: Stimulus $\rightarrow$ Receptor $\rightarrow$ Sensory Neuron $\rightarrow$ Spinal Cord (Relay Neuron) $\rightarrow$ Motor Neuron $\rightarrow$ Effector (Muscle) $\rightarrow$ Response.

  • Location: Nerves from the body meet in a bundle in the spinal cord on their way to the brain. Reflex arcs are formed in the spinal cord because it is the quickest meeting point.

• Evolutionary Significance: Reflex arcs evolved as efficient ways of functioning because the thinking process of the brain is not fast enough for immediate survival. Even in complex animals, reflex arcs remain the most efficient mechanism for quick responses.

The Human Brain

• Central Nervous System (CNS): Comprises the brain and the spinal cord. It receives and integrates information from all parts of the body.

• Peripheral Nervous System (PNS): Facilitates communication between the CNS and the rest of the body. It consists of:

  • Cranial Nerves: Arise from the brain.

  • Spinal Nerves: Arise from the spinal cord.

• Major Regions of the Brain:

  • Fore-brain: The main thinking part of the brain.

    • Sensory Areas: Separate regions for hearing, smell, and sight.

    • Association Areas: Interpret sensory information by combining it with input from other receptors and stored information.

    • Motor Areas: Control the movement of voluntary muscles (e.g., leg muscles).

    • Hunger Centre: A separate part of the fore-brain specifically associated with the sensation of feeling full.

  • Mid-brain and Hind-brain: Control many involuntary actions.

  • Medulla (Hind-brain): Specifically controls involuntary actions such as blood pressure, salivation, and vomiting.

  • Cerebellum (Hind-brain): Responsible for the precision of voluntary actions and maintaining the posture and balance of the body (e.g., walking in a straight line, riding a bicycle, picking up a pencil).

• Voluntary vs. Involuntary Actions:

  • Voluntary: Decided actions like writing or moving a chair.

  • Involuntary: Actions we cannot easily control by thinking, such as heartbeats, digestion, or the changing size of the pupil.

Protection of Nervous Tissue and Mechanism of Action

• Protection of the Brain: The brain is housed in a bony box (the skull). Inside the skull, it is contained in a fluid-filled balloon that acts as a shock absorber.

• Protection of the Spinal Cord: The spinal cord is protected by the vertebral column or backbone.

• How Muscles Move:

  • When a nerve impulse reaches a muscle, the muscle fibre must move by changing its shape.

  • Cellular Level: Muscle cells contain specialized proteins that change their shape and arrangement in response to electrical impulses.

  • This causes the muscle cell to shorten (contract), effecting movement.

Coordination in Plants

• Absence of Nervous System: Plants have neither a nervous system nor muscles. They show two types of movement:

  • Growth-Independent Movement: Immediate response to stimuli (e.g., the folding of leaves in the Mimosa pudica or 'touch-me-not' plant).

  • Growth-Dependent Movement: Directional movement caused by growth (e.g., a seedling growing toward light).

• Immediate Response (Non-Growth):

  • Information about a stimulus (like touch) is communicated via electro-chemical means from cell to cell.

  • Unlike animals, plants have no specialized tissue for this conduction.

  • Mechanism of Shape Change: Plant cells change shape by altering the amount of water in them, causing swelling or shrinking.

• Movement Due to Growth (Tropic Movements):

  • Thigmotropism: Tendrils (e.g., in pea plants) are sensitive to touch. The side of the tendril in contact with a support grows slower than the side away from it, causing the tendril to circle and cling to the support.

  • Phototropism: Shoots bend toward light ($+\text{ve}$ phototropism), while roots bend away from light ($-\text{ve}$ phototropism).

  • Geotropism: Response to gravity. Roots grow downward ($+\text{ve}$ geotropism), and shoots grow upward ($-\text{ve}$ geotropism).

  • Hydrotropism: Growth movement in response to water.

  • Chemotropism: Growth movement in response to chemicals (e.g., the growth of pollen tubes toward ovules).

Chemical Communication and Plant Hormones

• Limitations of Electrical Impulses:

  1. They only reach cells connected by nervous tissue.

  2. Cells need time to reset their mechanisms after an impulse; they cannot transmit continually.

• Chemical Communication: Diffusible chemical compounds reach all cells, regardless of nervous connections, and provide steady, persistent signaling.

• Plant Hormones (Phytohormones):

  • Auxin: Synthesized at the shoot tip. When light comes from one side, auxin diffuses to the shady side, stimulating those cells to grow longer, causing the plant to bend toward the light.

  • Gibberellins: Help in the growth of the stem.

  • Cytokinins: Promote cell division; found in high concentrations in fruits and seeds.

  • Abscisic Acid: Inhibits growth; responsible for effects like the wilting of leaves.

Hormones in Animals

• The Endocrine System: Provides a second way of control and coordination via hormones secreted directly into the blood.

• Adrenaline (The Fight or Flight Hormone):

  • Secreted by the adrenal glands.

  • Target Organs: The heart (beats faster to supply more oxygen).

  • Physiological Changes: Blood is diverted from the digestive system and skin to skeletal muscles; breathing rate increases due to diaphragm and rib muscle contraction.

• Thyroxin:

  • Secreted by the thyroid gland.

  • Function: Regulates carbohydrate, protein, and fat metabolism for growth balance.

  • Iodine Requirement: Iodine is essential for thyroxin synthesis. Deficiency leads to goitre, characterized by a swollen neck.

• Growth Hormone:

  • Secreted by the pituitary gland.

  • Function: Regulates growth and development. Deficiency in childhood leads to dwarfism.

• Puberty Hormones:

  • Testosterone: Produced in males (testes).

  • Oestrogen: Produced in females (ovaries).

• Insulin:

  • Produced by the pancreas.

  • Function: Regulates blood sugar levels. Deficiency leads to diabetes.

• The Role of the Hypothalamus: Plays a crucial role in releasing factors (e.g., growth hormone releasing factor) that stimulate the pituitary gland.

• Feedback Mechanisms: Regulate the timing and amount of hormone release. Example: Pancreatic cells detect rising blood sugar and produce insulin; as sugar levels fall, insulin secretion is reduced.

Summary Table of Animal Hormones