Chapter 6: Control and Coordination

Science · CBSE Class 10 · NCERT Solutions

📖 Chapter 6 — Control and Coordination (CBSE Class 10 Science): Detailed notes — nervous system, reflex action, brain, plant movements & hormones, animal hormones.

Chapter 6 — Control and Coordination

🧠 1. Nervous System (Animals)

Neuron = functional unit of the nervous system. Parts: dendrites (receive impulse) → cell body → axon (carries impulse away) → synapse (gap between two neurons where impulse passes as a chemical).

Receptors detect stimuli: eyes (light), ears (sound/balance), nose (smell), tongue (taste), skin (touch/heat).

⚡ 2. Reflex Action

Reflex action = a quick, automatic response to a stimulus (e.g., pulling hand from a hot object). The path is the reflex arc: receptor → sensory neuron → spinal cord → motor neuron → effector (muscle). It does not need conscious thought (spinal cord manages it).

🧩 3. Human Brain

Part	Function
Fore-brain (cerebrum)	Thinking, memory, voluntary actions, senses
Mid-brain	Reflexes of eye/ear
Hind-brain: cerebellum	Balance and posture
Hind-brain: medulla	Involuntary actions (heartbeat, breathing, BP)

Brain and spinal cord are protected by bones (skull, vertebral column) and fluid.

🌿 4. Coordination in Plants

Tropic movements (directional, growth-dependent): Phototropism (light), geotropism (gravity), hydrotropism (water), chemotropism (chemicals).
Nastic movements (non-directional): e.g., touch-me-not (Mimosa) leaves fold on touch — due to change in water/turgor of cells (not growth).
Plant hormones: Auxin (growth, phototropism), Gibberellin (stem growth), Cytokinin (cell division), Abscisic acid (inhibits growth, closes stomata).

💉 5. Hormones in Animals (Endocrine System)

Hormone / Gland	Function / Deficiency
Thyroxine (thyroid)	Metabolism; needs iodine; deficiency → goitre
Insulin (pancreas)	Controls blood sugar; deficiency → diabetes
Adrenaline (adrenal)	'Fight or flight' response
Growth hormone (pituitary)	Body growth; deficiency → dwarfism
Testosterone / Oestrogen	Male / female sexual characters

🧠 Remember: Neuron: dendrite→cell body→axon→synapse. Reflex arc via spinal cord. Cerebellum=balance, medulla=involuntary. Auxin=phototropism. Iodine→thyroxine (goitre). Insulin→sugar (diabetes).

⭐ Exam Tips: ① Neuron structure & function. ② Reflex action & reflex arc. ③ Brain parts & functions. ④ Tropic vs nastic movements; plant hormones. ⑤ Hormones + deficiency diseases; nervous vs hormonal.

📘 Textbook Question Answers

Q1-3MCQs: plant hormone; gap between neurons; brain functions.

Q1: (d) Cytokinin. Q2: (b) synapse. Q3: (d) all of the above (thinking, regulating heartbeat, balancing).

Q4Function of receptors; problems if they don't work.

Receptors detect stimuli from the environment (light, sound, smell, taste, touch) and pass the information to the nervous system. If receptors don't work — e.g., damaged ear or eye — a person cannot detect that stimulus (deafness, blindness), cannot respond to danger, and may face accidents.

Q5Draw a neuron and explain its function.

A neuron has dendrites (which receive impulses), a cell body (containing the nucleus), and a long axon (which carries the impulse away to the next neuron across a synapse). Function: neurons receive, conduct and transmit electrical impulses, enabling communication and coordination in the body.

Q6How does phototropism occur?

Phototropism is the growth of a plant towards light. When light falls on one side, the hormone auxin moves to the shady side, making cells there grow longer. As the shady side grows faster, the shoot bends towards the light.

Q7-8Signals disrupted in spinal cord injury; chemical coordination in plants.

Q7: A spinal cord injury disrupts reflex actions and the signals travelling between the brain and the body (both sensory input and motor commands). Q8: In plants, chemical coordination occurs through plant hormones (auxin, gibberellin, cytokinin, abscisic acid) that diffuse from cell to cell and control growth and movement.

Q9Why is a control and coordination system needed?

It is needed so that different parts of the body work together and respond properly to changes (stimuli) in the environment, maintain internal balance and functions, and keep the organism alive and healthy.

Q10How are involuntary actions and reflex actions different?

Involuntary actions (e.g., heartbeat, breathing) are controlled by the brain (medulla) and go on continuously without our will. Reflex actions (e.g., withdrawing a hand from a hot object) are sudden, quick responses to a stimulus, controlled by the spinal cord (reflex arc), not needing conscious thought.

Q11Compare nervous and hormonal mechanisms.

Nervous: uses electrical impulses through neurons; very fast; effect is short-lived and localised to a specific part. Hormonal: uses chemical messengers (hormones) carried by blood; slower to act; effect is longer-lasting and may reach many organs.

Q12Movement in a sensitive plant vs in our legs.

In a sensitive plant (touch-me-not), leaves fold due to a change in water/turgor of cells — there is no nervous or muscle tissue and no growth. In our legs, movement is caused by muscle cells contracting, controlled by nerves, and it needs energy.

Extra practice (4× the textbook) — MCQ, short answer & long answer.

🎯 Extra MCQ

1Which gland is called the master gland?

Pituitary gland.

2Receptor for light is the —

Eye.

3The chemical released at the synapse is a —

Neurotransmitter.

4Which hormone prepares the body for emergency?

Adrenaline.

📝 Short Answer

5What is a reflex arc?

The pathway of a reflex action: receptor → sensory neuron → spinal cord → motor neuron → effector (muscle).

6Why should we take iodised salt?

Iodine is needed to make thyroxine; its deficiency causes goitre.

7Name any two tropic movements.

Phototropism (light) and geotropism (gravity).

8What is the function of the spinal cord?

It conducts impulses between the brain and body and controls reflex actions.

9How do hormones reach their target organs?

They are secreted into the blood, which carries them to target organs.

📖 Long Answer

10Explain the structure and function of a neuron.

A neuron has dendrites that receive impulses, a cell body with the nucleus, and a long axon that carries the impulse to the next neuron across a synapse. Neurons receive, conduct and pass on electrical impulses, allowing coordination between different parts of the body.

11Describe the main parts of the human brain and their functions.

Fore-brain (cerebrum) controls thinking, memory, voluntary actions and senses; mid-brain controls reflexes of the eyes and ears; hind-brain has the cerebellum (balance and posture) and the medulla (involuntary actions like heartbeat and breathing).

12How is movement in plants different from movement in animals?

Plant movements are slow, often due to growth (tropic) or changes in cell water/turgor (nastic), without nerves or muscles. Animal movements are quick, caused by muscle contraction controlled by nerves and needing energy.

13List four animal hormones and their functions.

Thyroxine — controls metabolism; Insulin — controls blood sugar; Adrenaline — emergency 'fight or flight' response; Growth hormone — controls body growth. (Testosterone/oestrogen — sexual characters.)

14What is feedback control of hormones? Give an example.

The amount of a hormone is regulated by a feedback mechanism based on its level in blood. E.g., if blood sugar rises, the pancreas releases more insulin; when sugar falls, insulin release decreases.

15Differentiate between voluntary and involuntary actions.

Voluntary actions are done consciously under our will (writing, walking), controlled by the cerebrum. Involuntary actions happen automatically without our will (heartbeat, digestion), controlled by the medulla/autonomic system.