Control and Coordination Class 10: Comprehensive Study Notes

Control and Coordination in Living Organisms

Control and coordination are essential life processes that enable organisms to respond appropriately to changes in their environment. In Class 10 Biology Chapter 7, we explore how both animals and plants maintain internal balance and react to external stimuli through specialized systems the nervous system and endocrine system in animals, and hormonal responses in plants.

Nervous System vs Endocrine System: Key Differences and Roles

Living organisms require two major coordination systems to function efficiently: the nervous system and the endocrine system. While both systems regulate body functions, they differ significantly in their mechanisms, speed, and duration of action.

Nervous System

The nervous system is composed of specialized cells called neurons that transmit information rapidly through electrical impulses. This system is responsible for:

• Quick responses to stimuli (within milliseconds)
• Localized effects targeting specific organs or muscles
• Short-duration actions that cease once the stimulus is removed
• Voluntary and involuntary movements, including reflex actions

The nervous system includes the central nervous system (CNS) comprising the brain and spinal cord and the peripheral nervous system (PNS), which consists of cranial and spinal nerves connecting the CNS to the rest of the body.

Endocrine System

The endocrine system operates through hormones—chemical messengers secreted by ductless glands directly into the bloodstream. Key characteristics include:

• Slower transmission compared to nerve impulses (seconds to hours)
• Widespread effects throughout the body via blood circulation
• Long-lasting actions that may persist even after hormone secretion stops
• Regulation of growth, metabolism, reproduction, and stress responses

Major endocrine glands include the pituitary, thyroid, parathyroid, adrenal, pancreas, and gonads (testes and ovaries).

Comparative Table: Nervous System vs Endocrine System

Both systems often work together. For example, the hypothalamus (part of the brain) produces releasing and inhibiting hormones that control the pituitary gland, demonstrating neuro-endocrine coordination.

Structure and Function of a Neuron

The neuron (or nerve cell) is the structural and functional unit of the nervous system. Despite variations in size and shape, all neurons share a common basic structure designed for receiving, processing, and transmitting information.

Parts of a Neuron

1. Cell Body (Cyton/Soma)
   • Contains the nucleus and abundant cytoplasm (neuroplasm)
   • Houses Nissl's granules (rough endoplasmic reticulum) responsible for protein synthesis
   • Serves as the metabolic center of the neuron
2. Dendrites (Dendrons)
   • Short, branched projections extending from the cell body
   • Receive incoming signals from other neurons or sensory receptors
   • Conduct nerve impulses toward the cell body
   • Increase the surface area for receiving multiple inputs
3. Axon (Nerve Fiber)
   • A single, long cylindrical extension from the cell body
   • Conducts nerve impulses away from the cell body toward other neurons or effectors
   • Covered by protective layers:
     • Axolemma: Innermost membrane
     • Myelin sheath: Insulating fatty layer (in myelinated neurons)
     • Neurilemma: Outermost protective sheath
   • Nodes of Ranvier: Gaps in the myelin sheath that allow faster impulse transmission (saltatory conduction)
   • Terminal branches end in synaptic knobs containing neurotransmitters

Types of Neurons Based on Function

1. Sensory Neurons (Afferent Neurons)
   • Carry impulses from receptors toward the CNS
   • Example: Neurons transmitting pain signals from skin to spinal cord
2. Motor Neurons (Efferent Neurons)
   • Carry impulses from CNS to effectors (muscles or glands)
   • Example: Neurons causing muscle contraction
3. Relay Neurons (Interneurons/Association Neurons)
   • Connect sensory and motor neurons within the CNS
   • Process and integrate information
   • Most abundant type in the brain and spinal cord

How Neurons Function

1. A stimulus activates receptors (specialized sensory cells)
2. Receptors generate an electrical impulse
3. The impulse travels along the dendrite → cell body → axon
4. At the axon terminal, the impulse reaches a synapse (gap between two neurons)
5. Neurotransmitters (e.g., acetylcholine) are released to transmit the signal across the synapse
6. The impulse continues to the next neuron or effector organ

Key Features of Nerve Transmission

• Unidirectional: Impulses travel in one direction only (dendrite → axon)
• Synaptic transmission: Chemical neurotransmitters bridge the synaptic gap
• Speed variation: Myelinated neurons conduct impulses faster than unmyelinated ones
• All-or-none principle: A neuron either fires completely or not at all

This specialized structure enables rapid, precise, and coordinated responses essential for survival.

Reflex Actions and Their Pathways: Examples and Mechanism

Reflex actions are spontaneous, automatic, and involuntary responses to specific stimuli that occur without conscious thought. They are among the fastest responses in the nervous system, designed to protect the body from harm.

Characteristics of Reflex Actions

• Immediate: Occur within milliseconds
• Involuntary: Not under conscious control
• Protective: Often safeguard the body from injury
• Mediated by spinal cord: Do not require brain involvement (though the brain receives information later)
• Stereotyped: Same stimulus produces the same response

Common Examples of Reflex Actions

1. Withdrawing hand from a hot object
   • Prevents burn injury through rapid muscle contraction
2. Blinking when an object approaches the eye
   • Protects the cornea from damage
3. Knee-jerk reflex
   • Tested by tapping below the kneecap
4. Sneezing or coughing
   • Clears airways of irritants
5. Salivation at the sight of food
   • Prepares digestive system for food intake
6. Pupil constriction in bright light
   • Protects retina from excessive light

The Reflex Arc: Pathway of Reflex Action

A reflex arc is the neural pathway that controls reflex actions. It consists of five essential components:

1. Receptor
   • Sensory organ that detects the stimulus
   • Example: Pain receptors in the skin
2. Sensory (Afferent) Neuron
   • Carries impulses from receptor to the spinal cord
   • Enters through the dorsal root of spinal nerve
3. Relay Neuron (Interneuron)
   • Located in the grey matter of the spinal cord
   • Connects sensory and motor neurons
   • Processes information and determines response
4. Motor (Efferent) Neuron
   • Carries impulses from spinal cord to effector
   • Exits through the ventral root of spinal nerve
5. Effector
   • Muscle or gland that executes the response
   • Example: Arm muscles that pull hand away from heat

Step-by-Step: How a Reflex Action Occurs

Example: Touching a Hot Object

1. Stimulus Reception: Heat receptors in skin detect high temperature
2. Signal Generation: Sensory neurons generate electrical impulse
3. Transmission to Spinal Cord: Impulse travels via sensory neuron to spinal cord's dorsal root
4. Processing: Relay neuron in spinal cord's grey matter receives signal
5. Response Signal: Motor neuron receives signal from relay neuron
6. Muscle Activation: Motor neuron sends impulse through ventral root to arm muscles
7. Action: Muscles contract, pulling hand away from hot object
8. Brain Notification (parallel): Information also sent to brain, producing sensation of pain (after reflex occurs)

Why Reflex Actions Don't Require the Brain

• Time-saving: Brain processing would delay response
• Protective mechanism: Reduces injury risk
• Automatic: Doesn't require decision-making
• Spinal cord control: Acts as a "mini-brain" for reflexes

However, the brain is informed afterward, allowing us to feel pain or become aware of what happened.

Types of Reflexes

1. Simple (Unconditioned) Reflexes
   • Inborn, automatic responses
   • Example: Blinking, knee-jerk
2. Conditioned Reflexes
   • Learned through experience
   • Example: Salivating at the sound of a bell (Pavlov's dog experiment)
3. Somatic Reflexes
   • Involve skeletal muscles
   • Example: Withdrawal reflex
4. Visceral Reflexes
   • Involve internal organs
   • Example: Regulation of heart rate

Reflex actions demonstrate the efficiency of the nervous system in protecting the body through rapid, pre-programmed responses.

Control and Coordination in Plants

Unlike animals, plants lack a nervous system, muscles, and specialized sense organs. Yet they respond remarkably to environmental stimuli such as light, gravity, water, touch, and chemicals. Plant coordination is achieved through hormones (phytohormones) and specialized movements.

Plant Hormones (Phytohormones)

Plant hormones are naturally occurring chemical substances produced in low concentrations that regulate growth, development, and physiological processes. They are synthesized in one part of the plant and translocated to target sites.

Types of Plant Hormones

1. Growth Promoters

a) Auxins (Example: Indole-3-Acetic Acid - IAA)

• Functions:
  • Promote cell enlargement and differentiation
  • Stimulate stem and root growth
  • Control phototropism (growth toward light) and geotropism (growth in response to gravity)
  • Induce parthenocarpy (seedless fruit formation)
  • Maintain apical dominance (suppressing lateral bud growth)
• Mechanism in Phototropism:
  • When light falls on one side of the shoot, auxin migrates to the shaded side
  • Higher auxin concentration on shaded side causes cells to elongate more
  • Plant bends toward light source

b) Gibberellins (Example: Gibberellic Acid - GA₃)

• Functions:
  • Promote stem elongation and bolting (rapid stem growth)
  • Break seed and bud dormancy
  • Stimulate flowering in some plants
  • Work synergistically with auxins

c) Cytokinins

• Functions:
  • Promote cell division (cytokinesis)
  • Break seed dormancy
  • Delay aging of plant organs
  • Promote opening of stomata
  • Stimulate fruit growth

2. Growth Inhibitors

a) Abscisic Acid (ABA) - "Stress Hormone"

• Functions:
  • Promotes dormancy in seeds and buds (inhibits growth)
  • Induces stomatal closure during water stress
  • Causes leaf abscission (falling)
  • Promotes senescence (aging)

b) Ethylene (a gaseous hormone)

• Functions:
  • Promotes fruit ripening and maturation
  • Accelerates leaf abscission
  • Breaks seed dormancy in some species
  • Used commercially to ripen fruits like bananas and mangoes

Summary Table: Plant Hormones and Functions

Plant Movements

Plants exhibit two main types of movements:

1. Tropic Movements (Tropisms)

Definition: Directional growth movements in response to external stimuli. Growth occurs toward (positive tropism) or away from (negative tropism) the stimulus.

Types of Tropisms:

a) Phototropism (response to light)

• Positive: Shoots grow toward light (due to auxin accumulation on shaded side)
• Negative: Roots grow away from light
• Importance: Maximizes photosynthesis

b) Geotropism/Gravitropism (response to gravity)

• Positive: Roots grow downward toward gravity
• Negative: Shoots grow upward against gravity
• Mechanism: Auxin distribution affected by gravity

c) Hydrotropism (response to water)

• Positive: Roots grow toward moisture
• Example: Root growth toward water sources in soil

d) Chemotropism (response to chemicals)

• Example: Pollen tube growth toward ovule (attracted by sugars secreted by stigma)

e) Thigmotropism (response to touch/contact)

• Positive: Tendrils of climbing plants coil around support
• Mechanism: Differential growth—side in contact grows slower than opposite side
• Example: Pea plant tendrils, Cuscuta (dodder)

2. Nastic Movements (Nasties)

Definition: Non-directional movements in response to stimuli. The direction of movement is independent of the stimulus direction.

Characteristics:

• Rapid (seconds to minutes)
• Reversible
• Independent of growth
• Caused by changes in turgor pressure (water movement in/out of cells)

Types of Nastic Movements:

a) Thigmonasty (response to touch)

• Example: Mimosa pudica (Touch-me-not plant)
• Mechanism: Touch triggers loss of turgor pressure in pulvini (swollen base of leaves), causing leaves to fold
• Function: Possible defense mechanism

b) Photonasty (response to light)

• Example: Opening and closing of dandelion flowers
• Morning: Flowers open in bright light
• Evening: Flowers close in darkness

c) Nyctinasty (sleep movements)

• Example: Bean leaves fold at night, open during day

Comparison: Tropisms vs Nastic Movements

Additional Factors Affecting Plant Growth

Photoperiodism (response to day length)

• Affects flowering time
• Short-day plants: Flower when day length is shorter than critical period (e.g., tobacco, chrysanthemum)
• Long-day plants: Flower when day length exceeds critical period (e.g., cabbage, wheat)
• Day-neutral plants: Flowering independent of photoperiod (e.g., tomato, cucumber)

Vernalization (exposure to cold)

• Cold treatment required for flowering in some plants (e.g., winter wheat)

Plant control and coordination, though different from animals, is equally sophisticated, enabling plants to thrive, compete, and reproduce successfully in diverse environments.

Important Formulas and Concepts

While Control and Coordination is primarily conceptual, here are key relationships and formulas for quick reference:

10 Important Exam Questions on Control and Coordination

1. What is the difference between nervous and hormonal control in animals? Give two points.

Expected Answer:

Additional points:

• Nervous control is voluntary or involuntary; hormonal control is always involuntary
• Example: Reflex action (nervous) vs. growth regulation (hormonal)

2. Draw a neat labeled diagram of a neuron and explain its three main parts.

Diagram Requirements:

• Cell body/cyton with nucleus
• Dendrites
• Axon with myelin sheath, nodes of Ranvier, and axon terminal

Explanation:

1. Cell Body (Cyton): Contains nucleus and Nissl's granules; metabolic center
2. Dendrites: Short branched projections; receive signals and conduct impulses toward cell body
3. Axon: Long fiber; conducts impulses away from cell body; covered by myelin sheath in many neurons; ends in synaptic knobs

3. What is a reflex action? With the help of a flow chart, show the pathway of reflex action when you touch a hot object.

Definition: A reflex action is a spontaneous, automatic, and involuntary response to a stimulus, controlled by the spinal cord without conscious thought.

Flow Chart:

Hot Object (Stimulus)↓Heat Receptors in Skin↓Sensory Neuron (Afferent)↓Spinal Cord (Relay Neuron in Grey Matter)↓Motor Neuron (Efferent)↓Arm Muscles (Effector)↓Hand Withdrawn (Response)

Explanation: The reflex arc bypasses the brain for faster response. Information is simultaneously sent to the brain, causing pain sensation after the reflex occurs.

4. Name five plant hormones and write one function of each.

5. Differentiate between tropic and nastic movements in plants with examples.

6. Explain how auxin helps in phototropism of shoot.

Answer:

When light falls on a plant shoot from one side:

1. Auxin synthesis occurs at the shoot tip
2. Unequal distribution: Auxin migrates to the shaded side (away from light)
3. Differential growth: Higher auxin concentration on shaded side causes cells to elongate more
4. Bending response: Faster growth on shaded side causes shoot to bend toward light
5. Positive phototropism: This ensures maximum light absorption for photosynthesis

Diagram suggestion: Show shoot with light source on one side, auxin concentration higher on opposite side, and resulting bending.

7. What are the three main parts of the human brain? Write one function of each.

Additional details:

• Cerebrum: Largest part, controls voluntary actions
• Cerebellum: Second largest, maintains equilibrium
• Medulla oblongata: Connects brain to spinal cord

8. Why is the use of iodized salt advisable? Name the disease caused by iodine deficiency.

Answer:

Importance of iodized salt:

• Iodine is essential for synthesis of thyroxine hormone by the thyroid gland
• Thyroxine regulates carbohydrate, protein, and fat metabolism
• It is crucial for physical and mental growth
• Deficiency leads to goitre (enlarged thyroid gland)

Disease: Goitre (Simple/Iodine-deficiency goitre)

Symptoms:

• Swelling in the neck region
• Fatigue and weakness
• Weight gain
• In children: Cretinism (stunted growth, mental retardation)

Prevention: Regular consumption of iodized salt provides adequate iodine.

9. How does our body respond when adrenaline is secreted into the blood?

Answer:

Adrenaline (also called epinephrine) is the "emergency hormone" or "fight or flight hormone" secreted by the adrenal medulla during stress or danger.

Effects of adrenaline:

1. Heart rate increases → More blood pumped to muscles
2. Blood pressure rises → Better oxygen supply
3. Breathing rate increases → More oxygen intake
4. Pupils dilate → Better vision
5. Blood glucose level rises → More energy available
6. Blood diverted from digestive system to skeletal muscles → Muscles contract with more power
7. Liver converts glycogen to glucose → Instant energy
8. Sweat production increases → Body cooling

Overall effect: Body is prepared to face emergency situations by either fighting or fleeing.

10. A potted plant is placed horizontally on its side. After a few days, what changes will you observe in the plant? Explain with reasons.

Answer:

Observations:

1. Stem will bend upward (away from gravity)
2. Root will bend downward (toward gravity)

Explanation:

This response is due to geotropism (gravitropism) controlled by plant hormones, especially auxin.

Mechanism:

For Stem (Negative Geotropism):

• When placed horizontally, auxin accumulates on the lower side of stem
• Lower side grows faster
• Stem bends upward (against gravity)

For Root (Positive Geotropism):

• Auxin accumulates on lower side of root
• High auxin concentration inhibits root cell growth
• Upper side grows faster
• Root bends downward (toward gravity)

Biological significance:

• Ensures shoots reach sunlight for photosynthesis
• Ensures roots reach soil for water and mineral absorption

Additional Study Tips for Control and Coordination

Diagrams to Practice:

1. Structure of neuron with all parts labeled
2. Reflex arc pathway
3. Human brain (sagittal section) with parts labeled
4. Phototropism experiment showing auxin distribution
5. Endocrine glands in human body

Key Terms to Remember:

• Stimulus, Response, Receptor, Effector
• Synapse, Neurotransmitter, Reflex arc
• Hormone, Endocrine gland, Target organ
• Tropism, Nastic movement, Photoperiodism
• Cerebrum, Cerebellum, Medulla oblongata
• Thyroxine, Insulin, Adrenaline, Growth hormone

Common Exam Mistakes to Avoid:

1. Confusing tropic with nastic movements
2. Mixing up sensory and motor neurons
3. Incorrectly labeling neuron parts
4. Forgetting that reflex actions involve spinal cord, not brain
5. Not mentioning specific hormone names (using generic terms)

Conclusion

Control and coordination are fundamental processes that enable living organisms to maintain homeostasis and respond appropriately to environmental changes. Understanding the complementary roles of the nervous and endocrine systems in animals, along with hormonal coordination in plants, provides essential insights into how life sustains itself.

For CBSE Class 10 students, mastering this chapter requires:

• Clear understanding of neuron structure and function
• Ability to explain reflex actions with diagrams
• Knowledge of major hormones and their functions
• Differentiation between tropic and nastic movements
• Practice of labeled diagrams

This comprehensive guide covers all major concepts with scientific accuracy, making it an authoritative resource for exam preparation.