Control and Coordination
Why This Chapter Matters
Control and Coordination has 7-9 marks in board exams. The nervous system (neuron, reflex arc), human brain, hormones and their functions are all frequently tested with both theory and diagram questions.
Prerequisites
Core Concepts
1. Nervous System
#### Neuron — The Structural Unit
Types of neurons:
#### How Nerve Impulse Works
2. Central Nervous System (CNS)
Brain:
| Part | Function |
|---|
|---|---|
| Cerebrum (largest) | Thinking, memory, voluntary actions, speech, sight, hearing |
|---|---|
| Cerebellum | Balance, posture, coordination of movements |
| Medulla oblongata | Involuntary actions: breathing, heartbeat, blood pressure |
| Hypothalamus | Temperature regulation, hunger, thirst, emotions |
Spinal cord:
3. Reflex Action
Reflex action: Automatic, involuntary, rapid response to a stimulus WITHOUT involving brain.
Reflex arc (path of reflex):
Examples: Withdrawing hand from hot object, knee-jerk, blinking, pupil dilation, sneezing, coughing.
Why spinal cord, not brain?
Speed — reflex response is much faster because it doesn't travel to brain. Life-saving when there is danger.
4. Hormones and Endocrine System
Hormone: Chemical messenger secreted by endocrine gland directly into bloodstream.
Endocrine glands: Ductless — secrete directly into blood (unlike exocrine glands that have ducts).
| Gland | Hormone | Function |
|---|
|---|---|---|
| Pituitary | Growth Hormone (GH) | Growth of body |
|---|---|---|
| Pituitary | TSH, FSH, LH | Control other glands |
| Thyroid | Thyroxine | Metabolic rate, growth, development. Needs iodine. |
| Parathyroid | PTH | Calcium regulation |
| Adrenal | Adrenaline | Emergency hormone — fight or flight (increases HR, BP, breathing) |
| Pancreas | Insulin | Decreases blood glucose (glucose → glycogen) |
| Pancreas | Glucagon | Increases blood glucose (glycogen → glucose) |
| Testes | Testosterone | Male secondary sexual characters |
| Ovaries | Oestrogen, Progesterone | Female sexual characters, menstrual cycle |
5. Hormones in Plants (Phytohormones)
Plants have no nervous system — use chemical control.
| Hormone | Effect | Example |
|---|
|---|---|---|
| Auxin | Cell elongation, phototropism, geotropism | Shoot tip produces auxin; promotes growth |
|---|---|---|
| Gibberellin | Cell elongation, stem elongation, seed germination | Makes dwarf plants grow tall |
| Cytokinin | Cell division, delays aging | Found in fruits, seeds |
| Abscisic Acid (ABA) | Inhibitor — promotes dormancy, wilting | Closes stomata during drought |
| Ethylene | Fruit ripening, promotes aging | Ripening of fruits |
Phototropism: Shoot grows TOWARDS light (positive phototropism) because auxin redistributes to shaded side → unequal growth → bending.
Geotropism: Root grows DOWNWARD (positive geotropism/gravitropism); shoot grows upward (negative geotropism).
Solved Examples
Example 1 — Reflex Arc
Q: Draw and label the components of a reflex arc.
Receptor (sense organ) → Afferent nerve (sensory) → Spinal cord (nerve centre) → Efferent nerve (motor) → Effector (muscle)
Example 2 — Adrenaline
Q: Why is adrenaline called "fight or flight" hormone?
During emergency/danger, adrenal gland secretes adrenaline:
Body is prepared to either fight the threat or run from it.
PYQs
2023
Q: How do auxins help in the bending of plant towards light?
Auxin produced by shoot tip. In the presence of unidirectional light, auxin moves to shaded side. Higher auxin concentration on dark side → more cell elongation on that side → shoot bends TOWARDS light.
2022
Q: Name the hormone that controls the level of sugar in blood. What happens if it is produced in excess?
Insulin (from pancreas beta cells) controls blood glucose.
If excess: Blood glucose falls too low → hypoglycaemia → dizziness, fainting.
If deficient: Diabetes mellitus — glucose not absorbed → high blood glucose → passed in urine.
2021
Q: What is the difference between exocrine and endocrine glands?
Exocrine glands: Have ducts, secrete into specific location (e.g., salivary glands, sweat glands).
Endocrine glands: Ductless, secrete hormones directly into bloodstream (e.g., thyroid, adrenal, pituitary).
Revision Notes
Common Mistakes:
❌ Reflex arc does NOT involve brain — goes through spinal cord
❌ Auxin promotes growth on the SHADED side (not light side) → this causes bending towards light
❌ Insulin LOWERS blood glucose (not raises) — Glucagon raises it