Control and Coordination – Class 10 Biology Chapter 6 NCERT Notes
Class 10 Biology Control and Coordination notes: nervous system, reflex arc, brain structure, hormones, and plant movements for CBSE & ICSE.
Chapter 6: Control and Coordination
6.1 The Nervous System
The nervous system provides rapid, precise control using electrical impulses transmitted through specialised cells called neurons.
Structure of a Neuron
A neuron consists of three main parts:
- Cell Body (Cyton): Contains the nucleus and most of the cytoplasm.
- Dendrites: Short, branched projections that receive signals from other neurons or from the environment.
- Axon: A long, slender projection that transmits impulses away from the cell body to other neurons, muscles, or glands. The axon ends in axon terminals that form synapses with the next neuron.
Stimulus → Receptor (Dendrite tip) → Dendrite → Cell Body → Axon → Axon Terminal → Synapse → Next Neuron (or Effector organ: muscle/gland)
Synapse
A synapse is the tiny gap between two neurons. When an electrical impulse reaches the axon terminal, it triggers the release of neurotransmitter chemicals into the synaptic cleft. These chemicals cross the gap and generate a new electrical impulse in the dendrite of the next neuron.
6.2 Reflex Action and Reflex Arc
A reflex action is an involuntary, rapid, and automatic response to a stimulus. Examples: pulling your hand away from a hot surface, blinking when something approaches your eye.
Receptor (in skin/sense organ) → Sensory (Afferent) Neuron → Relay Neuron (in spinal cord) → Motor (Efferent) Neuron → Effector (muscle/gland)
The brain is not directly involved in reflex actions — the spinal cord processes the response. This makes reflex actions much faster than voluntary actions.
6.3 Human Brain
The brain is the main coordinating centre of the body. It is protected by a bony structure called the cranium (skull) and is surrounded by three membranes called meninges. A fluid called cerebrospinal fluid (CSF) cushions the brain against mechanical shocks.
Parts of the Brain and Their Functions
| Part | Location | Functions |
|---|---|---|
| Cerebrum (Forebrain) | Largest part, upper region | Thinking, memory, intelligence, voluntary actions, sensations (sight, hearing, smell, taste, touch) |
| Cerebellum (Hindbrain) | Below cerebrum, at the back | Balance, posture, coordination of voluntary movements (e.g., walking, riding a bicycle) |
| Medulla Oblongata (Hindbrain) | Lowest part, connects to spinal cord | Controls involuntary actions: breathing, heartbeat, blood pressure, vomiting, sneezing |
| Hypothalamus (Forebrain) | Below cerebrum | Body temperature regulation, hunger, thirst, sleep; links nervous system to endocrine system |
6.4 Coordination in Plants
Plants do not have a nervous system. They coordinate their behaviour using plant hormones (phytohormones).
Types of Plant Movements
A. Tropic Movements (Directional — Growth-dependent)
- Phototropism: Growth towards or away from light. Shoots are positively phototropic (grow towards light); roots are negatively phototropic.
- Geotropism (Gravitropism): Growth in response to gravity. Roots are positively geotropic (grow downward); shoots are negatively geotropic.
- Hydrotropism: Growth towards water. Roots are positively hydrotropic.
- Chemotropism: Growth towards or away from a chemical. Example: pollen tube growing towards the ovule.
- Thigmotropism: Growth in response to touch. Example: tendrils of climbers coiling around a support.
B. Nastic Movements (Non-directional)
These movements are independent of the direction of the stimulus. Example: the leaves of the Mimosa pudica (touch-me-not) plant fold when touched. This is due to changes in water pressure in the cells at the base of the leaf (pulvinus).
Plant Hormones
| Hormone | Function |
|---|---|
| Auxin | Promotes cell elongation; involved in phototropism (produced at shoot tip, moves to shaded side causing differential growth) |
| Gibberellin | Promotes stem elongation, seed germination, and flowering |
| Cytokinin | Promotes cell division; found mainly in areas of rapid cell division (roots, fruits, seeds) |
| Abscisic Acid (ABA) | Inhibits growth; promotes wilting of leaves, dormancy; known as the "stress hormone" |
6.5 Hormones in Animals — The Endocrine System
The endocrine system uses chemical messengers called hormones that are secreted directly into the blood by endocrine glands (ductless glands).
| Gland | Hormone | Function |
|---|---|---|
| Pituitary | Growth hormone | Regulates growth of the body; controls other endocrine glands (master gland) |
| Thyroid | Thyroxine | Regulates metabolism of carbohydrates, fats, and proteins. Iodine is needed for its synthesis. Deficiency causes goitre. |
| Pancreas | Insulin | Lowers blood sugar by converting excess glucose to glycogen. Deficiency causes diabetes mellitus. |
| Adrenal | Adrenaline | Prepares the body for emergency ("fight or flight") — increases heart rate, blood pressure, breathing rate |
| Testes (Male) | Testosterone | Development of male secondary sexual characteristics during puberty |
| Ovaries (Female) | Estrogen | Development of female secondary sexual characteristics; regulation of menstrual cycle |
• Nervous system: fast, precise, short-lived responses via electrical impulses
• Endocrine system: slow, widespread, long-lasting responses via chemical hormones in blood
• Both work together — e.g., adrenaline release during fear is triggered by the nervous system acting on the adrenal gland.
Indexed Topics & Examination Keywords
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