Vardaan Learning Institute
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Control and Coordination

1. Animal Nervous System

A. The Neuron (Structural Unit)

Neuron Structure
Figure 2.1: Structure of Neuron
Structure & Function:
The Synapse (Crucial Definition):
It is the microscopic gap between the nerve ending of one neuron and the dendrite of the next.
Mechanism: At the nerve ending, the electrical impulse releases chemicals (Neurotransmitters like Acetylcholine). These chemicals diffuse across the gap and start a similar electrical impulse in the dendrite of the next neuron.
Why do we need Chemical Communication (Hormones) if we have Nerves?
Limitations of Electrical Impulses:
1. They reach only those cells connected by nervous tissue.
2. Once an impulse is generated, the cell takes time to reset (cannot continuously create impulses).
Chemical communication (Hormones) overcomes this by reaching every cell and acting steadily.

B. Reflex Action & Reflex Arc

Reflex Arc
Figure 2.2: Reflex Arc Pathway
Why are Reflex Arcs formed in the Spinal Cord?
Thinking processes in the brain are complex and slow. To save time and prevent tissue damage during emergencies, nerves connect directly in the spinal cord for a quicker response. (The signal still goes to the brain later for memory).

The Pathway (Reflex Arc):

Stimulus (Heat)
→
Receptor (Skin)
→
Sensory Neuron
→
Spinal Cord (Relay Neuron)
→
Motor Neuron
→
Effector (Muscle)
→
Response (Movement)

2. The Human Brain (The Thinking Center)

Human Brain
Figure 2.3: Human Brain
Region Part Function (Matches PYQ 2025)
Forebrain
(Main thinking part)		 Cerebrum • Voluntary actions.
• Sensory processing (Hearing, Smell, Sight).
• Seat of Intelligence, Memory, Learning.
• Hypothalamus: Satiety Center (Hunger/Thirst).
Midbrain - Involuntary reflexes of head/neck/eyes. (e.g., Pupil size change).
Hindbrain Cerebellum • Precision of voluntary actions (e.g., Threading a needle).
• Maintains Posture and Balance (e.g., Riding a bike).
(Damage leads to loss of balance, drunk-like walk).
Medulla Controls Involuntary life processes: Blood Pressure, Heartbeat, Salivation, Vomiting.
Pons Regulates Respiration (Rate of breathing).

C. Protection of the CNS

How are these delicate organs protected?
1. Brain: sits inside a bony box (Cranium/Skull). Inside the box, the brain is contained in a fluid-filled balloon (Cerebrospinal Fluid) for shock absorption.
2. Spinal Cord: Protected by the Vertebral Column (Backbone).

3. Coordination in Plants

Plants use Electrical-Chemical means to convey information from cell to cell, but lack specialized tissue.

A. Types of Movements

Feature Nastic Movements Tropic Movements
Direction Non-directional. Directional.
Growth Growth Independent. Growth Dependent.
Speed Immediate/Fast. Slow.
Mechanism Change in Turgor Pressure. Cell division/elongation (Auxin).
Example Mimosa pudica (Touch-me-not). Shoot bending to light (Phototropism).

B. Mechanism of Phototropism (Auxin Action)

How does a plant bend towards light?
1. Auxin is synthesized at the shoot tip.
2. When light comes from one side, Auxin diffuses towards the shady side of the shoot.
3. High concentration of Auxin stimulates cells on the shady side to grow longer.
4. As one side grows longer than the other, the plant appears to bend towards light.

C. Various Tropic Movements

Movement Stimulus Response (Example)
Phototropism Light Shoot bends towards light (Positive). Root bends away (Negative).
Geotropism Gravity Roots grow down (Positive). Shoots grow up (Negative).
Hydrotropism Water Roots grow towards water (Positive).
Chemotropism Chemicals Growth of Pollen Tube towards Ovule.
Thigmotropism Touch Growth of Tendrils around a support (climbing plants).

D. Plant Hormones (Phytohormones)

Hormone Function
Auxin Helps cells to grow longer (Phototropism).
Gibberellins Helps in the growth of the stem.
Cytokinins Promotes cell division. Rapid in fruits and seeds.
Abscisic Acid Inhibits growth. Causes wilting of leaves.

4. Animal Hormones (Endocrine System)

Endocrine Glands
Figure 2.4: Endocrine Glands in Humans
Gland Hormone Function/Deficiency Disease
Pituitary Growth Hormone Regulates growth. Deficiency: Dwarfism. Excess: Gigantism.
Thyroid Thyroxin Regulates Metabolism. Deficiency: Goitre. Requires Iodine.
Adrenal Adrenaline "Fight or Flight": Increases heart rate, breathing, alert.
Pancreas Insulin Lowers blood sugar. Deficiency: Diabetes.
Testes Testosterone Sperm production + Puberty changes.
Ovary Oestrogen Egg production + Puberty changes.
Feedback Mechanism (Example):
Blood sugar rises → Detected by Pancreas → More Insulin secreted → Sugar falls → Insulin secretion reduced.
🎯 TRICKY PRACTICE ZONE (Control & Coordination)
  1. A person is walking in a drunken manner (loss of balance). Which part of the brain is likely affected? How is this part different from the part that helps you think? Hint: Balance = Cerebellum (Hindbrain); Thinking = Cerebrum (Forebrain).
  2. Why does a tendril circle around a support? Explain the role of Auxin in this specific case. Hint: Auxin diffuses to the side AWAY from support, causing it to grow faster, making the tendril bend/coil.
  3. In a Reflex Arc, what happens at the Synapse? Why can't the signal travel backwards? Hint: Electrical signal converts to Chemical. Receptors for chemicals are only on the next dendrite, ensuring one-way flow.

🧪 NCERT EXPERIMENT ZONE (Control & Coordination)

1. Phototropism (Response to Light):
• Setup: Conical flask with water, wire mesh covering, germinating bean seeds. Keep in cardboard box open from one side.
• Observation: Shoots bend towards light (Positive Phototropism). Roots bend away (Negative Phototropism).
Phototropism in a Box
Figure 2.E1: Phototropism (Response to Light)
2. Geotropism (Response to Gravity):
• Setup: Potted plant laid horizontally.
• Observation: Shoot bends Upwards (Negative Geotropism). Root bends Downwards (Positive Geotropism).
Geotropism Pot Experiment
Figure 2.E2: Geotropism (Response to Gravity)
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