Control and Coordination
Introduction
Have you ever touched a hot object and pulled your hand away instantly—even before realizing it's hot? Or noticed how plants grow toward sunlight even though they can't "see"? These are examples of control and coordination—the systems that help living organisms detect changes in the environment (stimuli) and respond appropriately. Understanding these systems (nervous system in animals, hormones in both, and tropisms in plants) makes this chapter easy to score in Board 2026 because most questions are direct.
What is control and coordination?
All living organisms respond to stimuli (changes in environment) to survive. This response requires control and coordination between different body parts.
• Animals use nervous system (fast, electrical signals) and endocrine system (slow, chemical signals via hormones).
• Plants use only hormones (chemical coordination) and growth movements.
Nervous system in animals
The nervous system is the network of nerve cells (neurons) that detects, processes, and responds to stimuli using electrical signals.
Neuron (nerve cell)
Structure of neuron:
· Dendrites: Receive signals from other neurons or receptors
· Cell body: Contains nucleus and cytoplasm
· Axon: Long fiber that transmits signals away from cell body
· Nerve endings (axon terminal): Release chemicals to pass signal to next neuron
Function: Neurons transmit information as electrical impulses throughout the body.
Synapse
The gap between two neurons is called a synapse. At the synapse, electrical signals are converted into chemical signals (neurotransmitters) which cross the gap and trigger electrical signals in the next neuron.
Why is synapse important? It ensures one-way transmission of
signals and allows signal regulation.
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Reflex action
Reflex action is an automatic, involuntary, and rapid response to a stimulus that is controlled by the spinal cord without involving the brain.
Example: Pulling hand away from a hot object instantly.
Reflex arc pathway (step-by-step)
|
Step |
What happens |
Part involved |
|
1. Detection |
Stimulus (heat) detected by receptors in skin |
Receptor |
|
2. Sensory neuron |
Signal travels to spinal cord |
Sensory neuron |
|
3. Processing |
Spinal cord processes and generates response |
Spinal cord |
|
4. Motor neuron |
Signal travels to effector organ |
Motor neuron |
|
5. Response |
Muscle contracts, hand pulled away |
Effector (muscle) |
Role of brain in reflex action: Reflex is controlled by spinal cord, but information also reaches the brain where it is stored for future reference.
Table: Voluntary vs involuntary vs reflex actions
|
Action type |
Controlled by |
Speed |
Examples |
|
Voluntary |
Brain (conscious) |
Slower |
Walking, writing, picking up objects |
|
Involuntary |
Brain (unconscious) |
Continuous |
Heartbeat, breathing, digestion |
|
Reflex |
Spinal cord |
Very fast |
Hand withdrawal from hot object, blinking |
Human Brain
The brain is the control center of the nervous system, located inside the skull (cranium) and protected by three membranes called meninges.
Structure: Three main parts
|
Part |
Sub-parts |
Functions |
|
Forebrain |
Cerebrum, Olfactory lobes |
Thinking, memory, reasoning, vision, hearing, touch, smell, voluntary movements |
|
Midbrain |
Small region |
Controls involuntary reflexes (eye movement, head turning toward sound) |
|
Hindbrain |
Cerebellum, Pons, Medulla oblongata |
Balance & posture (cerebellum), involuntary actions like heartbeat, breathing, blood pressure (medulla) |
Cerebrum is the largest part of the brain and controls thinking, intelligence, sensory perception, and voluntary actions.
Cerebellum maintains posture and balance of the body.
Medulla oblongata controls involuntary actions like heartbeat,
breathing, coughing, swallowing, salivation, vomiting.
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Protection of nervous system
Brain: Protected by bony skull (cranium) and cerebrospinal fluid (acts as shock absorber)
Spinal cord: Protected by vertebral column (backbone)
What happens in spinal cord injury? Signals between brain and body are disrupted; reflex
actions may also be affected.
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Endocrine system (hormonal coordination)
Hormones are chemical messengers secreted by endocrine glands (ductless glands) directly into the blood. They travel to target organs and control growth, development, and metabolism.
Table: Important endocrine glands and hormones
|
Gland |
Hormone |
Function |
Deficiency/Excess effect |
|
Pituitary (master gland) |
Growth hormone |
Controls body growth |
Deficiency → dwarfism; Excess → gigantism |
|
Thyroid |
Thyroxine (needs iodine) |
Controls metabolism of carbs, fats, proteins |
Deficiency → goitre (neck swelling), slow growth |
|
Pancreas |
Insulin, Glucagon |
Insulin lowers blood sugar; Glucagon raises it |
Deficiency → diabetes (high blood sugar) |
|
Adrenal |
Adrenaline |
Emergency hormone; increases heartbeat, breathing, blood sugar |
Prepares body for fight/flight response |
|
Testes (male) |
Testosterone |
Male sex hormone; sperm production, male secondary sexual characters |
— |
|
Ovaries (female) |
Oestrogen, Progesterone |
Female sex hormones; egg maturation, menstruation, pregnancy |
— |
Why is iodised salt advisable? Thyroid gland needs iodine to produce thyroxine; deficiency causes goitre.
Why are insulin injections given to diabetic patients? Their pancreas secretes less insulin, so external insulin is needed to lower blood sugar.
What
happens when adrenaline is secreted?
Heart rate, breathing rate, and blood sugar increase to provide energy for
emergency situations.
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Difference between nervous and hormonal control
|
Feature |
Nervous control |
Hormonal control |
|
Signal type |
Electrical impulses |
Chemical signals (hormones) |
|
Speed |
Very fast (milliseconds) |
Slow (seconds to minutes) |
|
Duration |
Short-lived |
Long-lasting effect |
|
Pathway |
Through neurons |
Through blood |
|
Target |
Specific (connected by nerves) |
Specific target organs |
Coordination in plants
Plants don't have a nervous system, so they coordinate using hormones and growth-related movements.
Plant hormones
|
Hormone |
Function |
|
Auxin |
Promotes cell elongation; causes phototropism (growth toward light) and geotropism (root growth toward gravity) |
|
Gibberellins |
Promotes stem growth |
|
Cytokinins |
Promotes cell division |
|
Abscisic acid |
Inhibits growth; causes stomata closure (prevents water loss) |
Tropic movements (growth movements)
Tropism is directional growth movement in response to a stimulus.
|
Type |
Stimulus |
Example |
|
Phototropism |
Light |
Shoot grows toward light (positive); root grows away from light (negative) |
|
Geotropism (Gravitropism) |
Gravity |
Root grows downward (positive); shoot grows upward (negative) |
|
Hydrotropism |
Water |
Root grows toward water (positive) |
|
Chemotropism |
Chemicals |
Pollen tube grows toward ovule |
|
Thigmotropism |
Touch/contact |
Tendrils coil around support |
How does phototropism occur? When light falls on one side of the shoot, auxin hormone moves to the shaded side, causing faster growth on that side; the shoot bends toward light.
Nastic movements (non-directional)
Nastic movements do not depend on the direction of stimulus.
Example: Touch-me-not plant (Mimosa pudica) leaves fold when touched; this is caused by change in water content in cells, not by growth.
Difference between tropic and nastic movements:
· Tropic: directional, permanent (growth-related)
· Nastic: non-directional, temporary (reversible)
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MCQs (PYQ)
1. The gap between two neurons is called:
(a) Dendrite
(b) Synapse
(c) Axon
(d) Impulse
Answer:
(b) Synapse.
(CBSE 2020)
2. Posture and equilibrium of the body
are maintained by:
(a) Cerebrum
(b) Medulla
(c) Cerebellum
(d) Pons
Answer:
(c) Cerebellum.
(Board Term I, 2017)
3. Which plant hormone is responsible for
phototropism?
(a) Gibberellin
(b) Cytokinin
(c) Auxin
(d) Abscisic acid
Answer:
(c) Auxin.
(CBSE 2020)
4. Insulin is secreted by:
(a) Thyroid
(b) Pituitary
(c) Pancreas
(d) Adrenal
Answer:
(c) Pancreas.
(CBSE 2024)
5. Reflex action is controlled by:
(a) Brain
(b) Spinal cord
(c) Medulla
(d) Cerebellum
Answer:
(b) Spinal cord.
(Board Term I, 2016)
6. Iodised salt is advisable because:
(a) It prevents goitre
(b) It increases growth
(c) It controls diabetes
(d) It strengthens bones
Answer:
(a) Thyroid needs iodine to make thyroxine; deficiency causes goitre. (CBSE 2020)
7. Which hormone is called emergency
hormone?
(a) Insulin
(b) Thyroxine
(c) Adrenaline
(d) Growth hormone
Answer:
(c) Adrenaline.
(CBSE 2023)
8. Movement of shoot toward light is:
(a) Positive phototropism
(b) Negative phototropism
(c) Geotropism
(d) Thigmotropism
Answer:
(a) Positive phototropism.
(CBSE 2024)
9. Which gland is called master gland?
(a) Thyroid
(b) Pituitary
(c) Pancreas
(d) Adrenal
Answer:
(b) Pituitary controls other glands.
(Board Term I, 2015)
10.
The
largest part of the brain is:
(a) Cerebrum
(b) Cerebellum
(c) Medulla
(d) Midbrain
Answer:
(a) Cerebrum.
(CBSE 2020)
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Short Answer Questions (PYQ with answers)
Q1. What happens at synapse between
two neurons?
Answer: At synapse, electrical signal is converted to chemical signal (neurotransmitter) which crosses the gap and triggers electrical signal in next neuron. (Board Term I, 2017)
Q2. Differentiate between reflex
action and walking.
Answer: Reflex action is involuntary, controlled by spinal cord, very fast (e.g., hand withdrawal from hot object). Walking is voluntary, controlled by brain, slower. (Board Term I, 2014)
Q3. What are plant hormones?
Answer: Chemical substances produced naturally by plants to regulate growth and physiological processes (e.g., auxin, gibberellins, cytokinins, abscisic acid). (CBSE 2020)
Q4. Why is iodised salt advisable?
Answer: Thyroid gland needs iodine to produce thyroxine, which regulates metabolism. Iodine deficiency causes goitre (thyroid swelling). (Board Term I, 2016)
Q5. Name the three main parts of the
brain and one function each.
Answer: Forebrain (thinking, memory),
Midbrain (involuntary eye/head reflexes), Hindbrain (balance, posture,
involuntary actions like breathing). (CBSE
2020).
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Long Answer Questions (PYQ with answers)
Q1. Explain reflex arc with diagram.
Give one example.
Answer: Reflex arc: Receptor → Sensory neuron → Spinal cord → Motor neuron → Effector. Example: Touching hot object: heat receptor in skin → sensory neuron → spinal cord → motor neuron → muscle contracts, hand pulled away. Brain gets information later. (Delhi 2019)
Q2. (a) What role does
brain play in reflex action? (b) State functions of forebrain, midbrain,
hindbrain.
Answer: (a) Reflex controlled by spinal cord, but information reaches brain and is stored for future. (b) Forebrain: thinking, sensory, voluntary actions. Midbrain: involuntary reflexes. Hindbrain: balance (cerebellum), involuntary actions like heartbeat, breathing (medulla). (CBSE 2020)
Q3. How does phototropism occur in
plants? Name the hormone responsible.
Answer: Auxin hormone moves to the shaded side of the shoot when light falls from one direction. Shaded side grows faster, causing the shoot to bend toward light. This is positive phototropism. (CBSE 2023)
Q4. How is chemical coordination
different from nervous coordination?
Answer: Nervous: electrical signals, very
fast, short-lived, through neurons. Chemical (hormonal): chemical signals
(hormones), slow, long-lasting, through blood to target organs. (CBSE 2020).
Class 10 Science Chapter-1: Chemical Reactions and Equations.
Conclusion
Control and Coordination becomes easy when you connect three systems: (1) nervous system for fast responses (neurons, synapse, reflex arc, brain parts), (2) endocrine system for slow, long-term control (hormones from pituitary, thyroid, pancreas, adrenal, gonads), and (3) plant coordination through hormones and tropisms (auxin causing phototropism, nastic movements).
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