Control and Coordination

Introduction

• Living organisms respond to environmental changes with controlled movements, distinct from growth-related movements (e.g., seed germination) or non-growth movements (e.g., a cat running).
• Movement is often a response to environmental stimuli, aimed at benefiting the organism (e.g., plants growing toward sunlight, animals withdrawing from danger).
• Control and coordination involve recognizing environmental events and responding with appropriate movements, facilitated by specialized tissues in multicellular organisms.
• This chapter explores how animals and plants achieve control and coordination through nervous systems and chemical signals, respectively.

6.1 Animals - Nervous System

• Control and coordination in animals are managed by nervous and muscular tissues, enabling rapid detection and response to environmental stimuli.
• Receptors: Specialized nerve cell tips in sense organs (e.g., inner ear, nose, tongue) detect environmental changes (e.g., gustatory receptors for taste, olfactory for smell).
• Neuron Structure and Function (Fig. 6.1a):
  • Dendrite: Acquires information via environmental stimuli, initiating a chemical reaction that generates an electrical impulse.
  • Axon: Transmits the electrical impulse from the cell body to the axon’s end.
  • Synapse: Converts the impulse into a chemical signal, releasing chemicals that cross the gap to stimulate the next neuron or target cell (e.g., muscle, gland) (Fig. 6.1b).
  • Neurons form an organized network, conducting information as electrical impulses across the body.
• Activity 6.1:
  • Taste sugar with and without blocking your nose. Blocking the nose reduces taste perception because smell contributes significantly to taste.
  • During a cold, nasal congestion similarly impairs taste, highlighting the role of olfactory receptors.
  • This demonstrates sensory integration in the nervous system.

6.1.1 Reflex Actions

• Reflex actions are rapid, involuntary responses to environmental stimuli without conscious thought (e.g., pulling hand from a flame).
• Reflex Arc (Fig. 6.2):
  • A direct connection between sensory (input) and motor (output) nerves, bypassing the brain for speed.
  • Formed in the spinal cord, where nerves from the body converge.
  • Process: Stimulus → Sensory neuron → Spinal cord (relay neuron) → Motor neuron → Muscle action.
  • Reflex arcs evolved for quick responses, especially in animals with limited thinking capacity, and remain efficient even in complex organisms.
• Example: Bright light on eyes triggers pupil constriction via a reflex arc, protecting the retina.
• Thinking involves complex neural interactions, which are too slow for urgent responses like avoiding burns.

6.1.2 Human Brain

• The brain and spinal cord form the central nervous system (CNS), integrating information from the body (Fig. 6.3).
• Peripheral Nervous System: Includes cranial nerves (from brain) and spinal nerves (from spinal cord), facilitating communication between CNS and body.
• Brain Regions:
  • Fore-brain: Main thinking center, processes sensory inputs (hearing, smell, sight), interprets via association areas, and controls voluntary muscle movements (e.g., leg muscles). Includes hunger sensation centers.
  • Mid-brain: Controls some involuntary actions (e.g., pupil size adjustment).
  • Hind-brain:
    • Medulla: Regulates involuntary actions (e.g., blood pressure, salivation, vomiting).
    • Cerebellum: Ensures precision in voluntary actions (e.g., walking, cycling) and maintains posture/balance.
  • The brain enables voluntary actions (e.g., writing, clapping) based on decision-making, unlike reflex actions.
• Action Types:
  • Voluntary: Planned actions (e.g., moving a chair).
  • Involuntary: Unconscious actions (e.g., heartbeat, digestion).
  • The hind-brain’s medulla and cerebellum manage involuntary and precise voluntary actions, respectively.

6.1.3 Protection of Nervous Tissues

• Brain: Encased in a bony skull, cushioned by fluid-filled membranes for shock absorption.
• Spinal Cord: Protected by the vertebral column (backbone), a hard, bumpy structure.
• These protective structures safeguard delicate nervous tissues critical for control and coordination.

6.1.4 Nervous Tissue and Muscle Action

• Nervous tissue collects, processes, and transmits information to muscles for action.
• Muscle Movement:
  • Nerve impulses trigger muscle fibers to change shape, shortening via special proteins that rearrange in response to electrical signals.
  • This chemical process distinguishes muscle movement from nervous signal transmission.
• Voluntary vs. Involuntary Muscles:
  • Voluntary: Controlled consciously (e.g., skeletal muscles for walking).
  • Involuntary: Operate without conscious control (e.g., heart, digestive muscles).
  • The nervous system’s interaction with muscle types determines action control.

6.2 Coordination in Plants

• Plants lack nervous or muscle tissues but respond to stimuli via growth-dependent and growth-independent movements.
• Growth-Independent Movement:
  • Example: Sensitive plant (Mimosa pudica) leaves fold rapidly upon touch (Fig. 6.4).
  • Mechanism: Touch triggers electrical-chemical signals between cells, causing cells to change shape by altering water content (swelling/shrinking).
  • Unlike animals, plants use non-specialized cells for signal transmission and movement.
• Growth-Dependent Movement:
  • Example: Pea plant tendrils curl around supports due to differential growth (slower on contact side).
  • Directional growth mimics movement, driven by environmental stimuli.

6.2.1 Immediate Response to Stimulus

• Sensitive plant movement occurs at a point different from the touch site, requiring signal communication.
• Plants use electrical-chemical signals, transmitted cell-to-cell, to coordinate responses.
• Movement results from cells changing shape via water content adjustments, not specialized proteins as in animals.
• This highlights plants’ unique coordination strategy without nervous tissue.

6.2.2 Movement Due to Growth

• Tropisms: Directional growth responses to stimuli.
  • Phototropism: Shoots bend toward light, roots away (Activity 6.2, Fig. 6.5).
  • Geotropism: Roots grow downward, shoots upward in response to gravity (Fig. 6.6).
  • Hydrotropism: Growth toward water (e.g., roots toward moisture).
  • Chemotropism: Growth toward chemicals (e.g., pollen tubes toward ovules).
• Activity 6.2:
  • Place germinated bean seeds in a flask within a box open toward light. Shoots bend toward light, roots away.
  • Rotate the flask; new growth adjusts to the new light direction, while old parts remain unchanged.
  • Conclusion: Plants exhibit phototropism, optimizing light capture for photosynthesis.
• Tropisms enhance plant survival by directing growth toward favorable conditions.

6.3 Hormones in Animals

• Animal hormones, part of the endocrine system, provide chemical coordination, complementing the nervous system.
• Hormonal vs. Nervous Coordination:
  • Nervous: Fast, electrical impulses, limited to nerve-connected cells, requires reset time.
  • Hormonal: Slower, chemical signals (hormones) diffuse to all cells, persistent, no reset needed.
  • Hormones enable widespread, sustained responses, unlike localized neural signals.
• Example: Adrenaline (Fig. 6.7):
  • Secreted by adrenal glands in stressful situations (e.g., fear).
  • Effects: Increases heart rate (more oxygen to muscles), diverts blood from digestion/skin to skeletal muscles, boosts breathing rate.
  • Prepares the body for “fight or flight” responses.
• Other Hormones (Table 6.1):
  • Growth Hormone (Pituitary): Stimulates growth; deficiency causes dwarfism.
  • Thyroxin (Thyroid): Regulates metabolism; requires iodine (deficiency causes goitre).
  • Insulin (Pancreas): Regulates blood sugar; deficiency leads to diabetes.
  • Testosterone (Testes): Develops male sex organs, secondary sexual characteristics.
  • Oestrogen (Ovaries): Develops female sex organs, regulates menstrual cycle.
  • Releasing Hormones (Hypothalamus): Stimulate pituitary hormone release.
• Feedback Mechanisms:
  • Regulate hormone secretion (e.g., high blood sugar triggers insulin release; falling levels reduce it).
  • Ensures precise hormone levels for coordinated responses.
• Activity 6.3: Identify endocrine glands in Fig. 6.7 (e.g., pituitary, thyroid, adrenal, pancreas, testes, ovaries).
• Activity 6.4: Complete Table 6.1 with hormones, glands, and functions.

Key Questions and Answers

1. Plant Hormones: Chemical compounds (e.g., auxin, gibberellins, cytokinins, abscisic acid) that coordinate growth, development, and environmental responses.
2. Sensitive Plant vs. Shoot Movement:
   • Sensitive plant: Rapid, growth-independent, due to water content changes in cells.
   • Shoot: Slow, growth-dependent, due to differential cell elongation (e.g., phototropism).
3. Plant Hormone Promoting Growth: Auxin (promotes cell elongation).
4. Auxins in Tendrils: Auxin concentrates on the side away from the support, promoting faster growth there, causing the tendril to curl around the support.
5. Hydrotropism Experiment:
   • Place a plant in a pot with a water source (e.g., moist sponge) on one side.
   • Observe roots growing toward the water source over days, demonstrating hydrotropism.

Exercises

1. Plant Hormone: (d) Cytokinin.
2. Gap Between Neurons: (b) Synapse.
3. Brain Functions: (d) All of the above (thinking, heart rate, balance).
4. Receptors’ Role:
   • Detect environmental stimuli (e.g., light, sound, touch).
   • Issues if defective: Impaired sensory perception (e.g., blindness, deafness, numbness).
5. Neuron Structure and Function:
   • Structure: Dendrite (receives signal), cell body, axon (transmits signal), synapse (chemical transfer).
   • Function: Transmits electrical impulses to coordinate responses.
6. Phototropism: Auxin accumulates on the shaded side of the shoot, promoting cell elongation, causing the shoot to bend toward light.
7. Spinal Cord Injury: Disrupts reflex arcs and signals to/from limbs, causing paralysis or loss of reflexes.
8. Chemical Coordination in Plants: Hormones (e.g., auxin, gibberellins) diffuse to target cells, regulating growth and responses.
9. Need for Control and Coordination: Ensures appropriate responses to environmental changes, optimizing survival and function.
10. Involuntary vs. Reflex Actions:
    • Involuntary: Automatic, not always stimulus-driven (e.g., heartbeat).
    • Reflex: Rapid, involuntary responses to specific stimuli (e.g., withdrawing from heat).
11. Nervous vs. Hormonal Mechanisms:
    • Nervous: Fast, electrical, localized, short-term.
    • Hormonal: Slow, chemical, widespread, persistent.
12. Sensitive Plant vs. Leg Movement:
    • Sensitive Plant: Growth-independent, water-based cell shape change, no nervous system.
    • Leg: Nervous system-driven, muscle contraction via specialized proteins.