CBSE Class 10 · Science · board exam 2027
Chapter 6: Control and Coordination — notes
The chapter’s 10 parts in the book’s order — the first idea of each and the points Medha Ma’am writes on the board — and the summary at the end. The full lesson and a check question for each part are in the app.
1. Why living things need control and coordination
Living things move.
- • Two kinds of movement:
- • ① Movement due to growth, like a seedling pushing out of the soil
- • ② Movement as a response to a change in the environment, like a cat running after a mouse
- • Stimulus: a change in the environment to which an organism responds
- • Response: what the organism does in reply to a stimulus
- • The response is always controlled and correct
- • Control and coordination: the organs of the body working together, at the right time, in the right way
- • Animals: ① nervous system (electrical impulses) ② endocrine system (hormones)
- • Plants: hormones only (plant hormones)
2. The nervous system and the neuron
First question.
- • Receptors: tips of nerve cells in the sense organs that pick up information
- • Tongue: gustatory receptors (taste)
- • Nose: olfactory receptors (smell)
- • Also in the inner ear, eyes and skin
- • Parts of a neuron:
- • ① Dendrite ② Cell body, with its nucleus
- • ③ Axon ④ Nerve ending
- • Neuron: the structural and functional unit of the nervous system
- • Information → chemical reaction at the dendrite → electrical impulse
- • Path of the impulse: dendrite → cell body → axon → nerve ending
- • Synapse: the gap between two neurons
- • Impulse at the nerve ending → chemicals released → cross the synapse → new impulse in the next neuron
- • The chemical goes from the axon end of one neuron → to the dendrite of the next
- • Last neuron → a muscle or a gland
- • Nervous tissue: an organised network of neurons, carrying information as electrical impulses
3. Reflex actions and the reflex arc
The hand jumps back at once, without your thinking.
- • Reflex action: a sudden, involuntary, quick response to a stimulus, without thinking
- • Examples: pulling the hand back from a hot object, sneezing, blinking
- • A thought-out response: slow, because many neurons are involved
- • Reflex arc: the pathway the nerve impulse follows in a reflex action
- • Reflex arcs are formed in: the spinal cord
- • The information also goes on to the brain
- • Why evolved? The thinking process of the brain is not fast enough
- • Receptor (skin): picks up the stimulus
- • Sensory neuron: receptor → spinal cord
- • Relay neuron: sensory neuron → motor neuron
- • Motor neuron: spinal cord → muscle
- • Effector (muscle): contracts, the response
- • Stimulus → Receptor → Sensory neuron → Spinal cord (relay neuron) → Motor neuron → Effector → Response
- • Sneezing: Dust → Receptor (nose) → Sensory neuron → Medulla → Motor neuron → Breathing muscles → Sneeze
4. The human brain
The spinal cord is not only for reflexes.
- • Central nervous system: brain + spinal cord
- • Peripheral nervous system: cranial nerves (from the brain) + spinal nerves (from the spinal cord)
- • Brain: the main coordinating centre of the body
- • Voluntary actions: done by our will, after thinking, like writing, talking, walking
- • Involuntary actions: happen by themselves, like the heartbeat, breathing
- • Three parts: fore-brain, mid-brain, hind-brain
- • Hind-brain: cerebellum + pons + medulla
- • Fore-brain: the main thinking part
- • Separate areas for hearing, smell, sight
- • Interprets information, decides, controls voluntary muscles
- • Centre for hunger (hypothalamus)
- • Mid-brain: involuntary actions, like the change in pupil size
- • Medulla: blood pressure, salivation, vomiting, heartbeat, breathing (involuntary)
- • Cerebellum: precision of voluntary actions, posture and balance
5. Protection of the nervous tissue, and how muscles move
The brain is a very delicate organ, so it must be protected.
- • Brain: in the bony box of the skull, inside a fluid-filled balloon (absorbs shocks)
- • Spinal cord: inside the vertebral column (backbone)
- • Nerve impulse → special proteins in muscle cells change shape and arrangement
- • → the muscle cell becomes shorter (contracts) → movement
6. Coordination in plants: quick movement and movement due to growth
Plants have no nervous system and no muscles.
- • Movement in plants:
- • ① Immediate response to a stimulus, independent of growth
- • ② Movement due to growth
- • Touch-me-not: on touch, leaflets fold, the leaf droops
- • No growth, the movement is quick
- • Information: from cell to cell by electrical-chemical means
- • Change in the amount of water in cells → cells swell or shrink → change in shape
- • Pea tendril: sensitive to touch
- • Side touching the support: less growth
- • Side away from the support: more growth (more auxin)
- • → the tendril coils round the support (movement due to growth)
- • | Touch-me-not | Pea tendril |
- • | Quick | Slow |
- • | Independent of growth | Due to growth |
- • | Not directional | Directional (tropic) |
- • | By change in water content | By unequal growth |
7. Tropic movements: light, gravity, water and chemicals
Most plants move slowly, by growing in one direction.
- • Tropic movement: a directional growth movement in response to a stimulus
- • Towards the stimulus: positive Away from it: negative
- • Phototropism: growth movement in response to light
- • Shoot: towards light (positive), root: away from light
- • Geotropism: growth movement in response to gravity
- • Root: down, towards gravity (positive), shoot: up (negative)
- • Hydrotropism: growth towards water, like roots
- • Chemotropism: growth towards chemicals, like the pollen tube growing towards the ovule
- • Auxin: made at the shoot tip
- • Light from one side → auxin diffuses to the shady side
- • Cells on the shady side grow longer → the shoot bends towards light
8. Plant hormones
In plants, growth, development and responses are controlled by chemical compounds called plant hormones, or phytohormones.
- • Plant hormones (phytohormones): chemicals made in plants that control growth and development
- • | Hormone | Function |
- • | Auxin (IAA) | cells grow longer; made at the shoot tip |
- • | Gibberellins | growth of the stem |
- • | Cytokinins | cell division; more in fruits and seeds |
- • | Abscisic acid | inhibits growth; wilting of leaves |
- • Promote growth: auxin, gibberellins, cytokinins
- • Inhibits growth: abscisic acid
9. Hormones in animals: adrenaline
Animals need chemical messages besides the nervous system.
- • Limitations of electrical impulses:
- • ① They reach only the cells connected by nervous tissue
- • ② After an impulse, the cell takes time to reset
- • Hormone: a chemical messenger secreted by an endocrine gland into the blood, which regulates the function of target organs
- • Reaches all cells through the blood, steadily and continuously
- • Scary situation → adrenal gland → adrenaline directly into the blood
- • Adrenal gland: the stress gland
- • Effects of adrenaline:
- • ① Heart beats faster → more oxygen to the muscles
- • ② Less blood to the digestive system and skin → diverted to skeletal muscles
- • ③ Diaphragm and rib muscles contract → breathing rate increases
10. Endocrine glands and the feedback mechanism
The figure, the endocrine glands of the human body.
- • Endocrine glands: pineal, hypothalamus, pituitary, thyroid, parathyroid, thymus, pancreas, adrenal, testes, ovaries
- • Thyroid → thyroxin: metabolism of carbohydrates, proteins, fats
- • Iodine is needed to make thyroxin
- • Iodine deficiency → goitre (swollen neck)
- • So: iodised salt
- • Pituitary → growth hormone: growth and development
- • Deficiency in childhood → dwarfism
- • Testes → testosterone (males), ovaries → oestrogen (females): changes of puberty
- • Pancreas → insulin: regulates blood sugar
- • Too little insulin → blood sugar rises → diabetes
- • Treatment: insulin injections
- • | Gland | Hormone | Function |
- • | Adrenal | Adrenaline | prepares the body for an emergency |
- • | Thyroid | Thyroxin | regulates metabolism |
- • | Pituitary | Growth hormone | growth and development |
- • | Testes | Testosterone | changes of puberty in males |
- • | Ovaries | Oestrogen | changes of puberty in females |
- • | Pancreas | Insulin | regulates blood sugar |
- • Feedback mechanism: regulates the timing and amount of hormone released
- • Blood sugar rises → pancreas makes more insulin → sugar falls → insulin secretion reduced
- • | Nervous control | Hormonal control |
- • | messages as electrical impulses | messages as chemicals (hormones) |
- • | carried by neurons | carried by the blood |
- • | quick, short-lived response | slow, long-lasting response |
- • | reaches only cells joined to nerves | reaches all cells |
Summary
Very good! You learnt a lot today, so let us revise it once together. Movement is of two kinds, due to growth, and as a response to a stimulus. In animals the neuron carries the impulse from the dendrite to the cell body, along the axon to the nerve ending, and at the synapse chemicals carry it on. For a quick response, the reflex arc is formed in the spinal cord. The brain has three parts. The fore-brain thinks, the medulla runs involuntary actions, and the cerebellum keeps balance. In plants, the touch-me-not folds by changing water content, and tropic movements happen by growth, with auxin, gibberellins, cytokinins and abscisic acid at work. And in animals the endocrine glands make hormones, adrenaline, thyroxin, growth hormone, insulin, and the feedback mechanism keeps their amount right. Draw the neuron, the reflex arc and the brain once in your notebook without looking, and label every part. If anything was not clear, press the Ask button and ask me. Done, you worked very well today!
AskMedha · Medha Ma’am — CBSE Class 10 Science, Chapter 6. Written from the textbook, checked twice.
Questions parents and students ask
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