Control and Coordination — NCERT Solutions, AI Tutor & Practice

Understand: Both are responses of the body, but they differ in how the nervous system controls them.

Analyze:

| Reflex action | Walking | |---|---| | It is an involuntary, automatic response to a stimulus. | It is a voluntary action performed under conscious control. | | Controlled by the spinal cord (reflex arc). | Controlled by the brain (especially cerebellum for balance). | | Very quick and does not need thinking. | Comparatively slower and requires thinking/decision. | | Example: pulling the hand away from a hot object. | Example: deciding to walk to school. |

Conclude: A reflex action is a rapid, automatic protective response managed by the spinal cord, whereas walking is a deliberate, conscious activity managed mainly by the brain.

Understand: A synapse is the microscopic gap between the axon terminal of one neuron and the dendrite of the next neuron.

Analyze (step-by-step):

1. An electrical impulse (nerve signal) travels along the axon of the first neuron.
2. On reaching the axon terminal, this electrical signal triggers the release of chemical substances called neurotransmitters into the synaptic gap.
3. These chemicals diffuse across the gap and reach the dendrite of the next neuron.
4. They start a new electrical impulse in the next neuron.

Conclude: At the synapse, the impulse is converted from electrical → chemical → electrical, ensuring the signal moves in only one direction (from axon to dendrite).

Understand: A neuron (nerve cell) is the structural and functional unit of the nervous system, specialised to carry messages.

Main parts and functions:

1. Dendrites – short, branched projections that receive information (stimulus) and pass it to the cell body.
2. Cell body (Cyton) – contains the nucleus and cytoplasm; processes the received information.
3. Axon – a long fibre that carries the impulse away from the cell body towards the next cell.
4. Nerve endings / Axon terminals – release neurotransmitters to pass the message across the synapse.

Direction of impulse: Dendrite → Cell body → Axon → Nerve ending → Synapse → next neuron.

(Diagram: an oval cell body with branching dendrites on one side and a single long axon ending in fine terminal branches.)

Understand: Plants show two kinds of movements — those that involve growth and those that do not.

Analyze:

| Mimosa leaf folding | Shoot bending towards light | |---|---| | A nastic movement, independent of growth. | A tropic (phototropic) movement, dependent on growth. | | Very fast response to touch (stimulus). | Slow response occurring over time. | | Caused by rapid changes in water content of cells at the base of leaves. | Caused by unequal growth: cells on the shaded side elongate more due to the hormone auxin. | | Not directional (does not depend on the direction of touch). | Directional (towards the light). |

Conclude: Leaf folding in Mimosa is a quick, non-growth movement due to water movement, while bending of a shoot towards light is a slow, growth-dependent tropic movement controlled by auxin.

Plant hormones (phytohormones) are chemical compounds that control growth and development in plants.

1. Auxin – promotes cell elongation; helps in bending of shoots towards light (phototropism).
2. Gibberellin – promotes growth of the stem, seed germination, and flowering.
3. Cytokinin – promotes cell division; delays ageing of leaves; more concentrated in growing areas like fruits and seeds.
4. Abscisic acid (ABA) – inhibits growth; causes closing of stomata; promotes dormancy and wilting/falling of leaves (a stress hormone).

Conclude: Auxin, gibberellin, and cytokinin are mainly growth-promoting hormones, while abscisic acid is a growth-inhibiting hormone.

Understand: In animals, coordination is achieved through two systems — nervous (electrical) and hormonal (chemical). Chemical coordination is done by the endocrine system.

Analyze (step-by-step):

1. Special glands called endocrine glands (e.g., pituitary, thyroid, adrenal, pancreas) produce chemical messengers called hormones.
2. These glands are ductless — they secrete hormones directly into the blood.
3. The blood carries hormones to all parts of the body.
4. Only the specific target organs/tissues respond to a particular hormone.
5. Hormones are needed in very small amounts and their timing and quantity are precisely regulated.

Example: Adrenaline secreted by the adrenal gland prepares the body for emergencies ("fight or flight").

Conclude: Chemical coordination in animals is carried out by hormones released by endocrine glands into the blood, which act on target organs to control body functions.

Understand: The brain is the main coordinating centre of the body and has three major regions.

Parts and functions:

1. Fore-brain (Cerebrum):

   • Main thinking part of the brain.
   • Controls voluntary actions, memory, reasoning, intelligence.
   • Receives sensory impulses (sight, hearing, smell, taste).

2. Mid-brain:

   • Connects fore-brain and hind-brain.
   • Controls certain reflex actions (e.g., changes in pupil size, movements of the head).

3. Hind-brain (has three parts):

   • Cerebellum – maintains posture and balance; coordinates precise voluntary movements (e.g., writing).
   • Pons – regulates respiration.
   • Medulla oblongata – controls involuntary actions like heartbeat, blood pressure, breathing, vomiting, salivation.

Conclude: The cerebrum controls thinking and voluntary actions, the cerebellum controls balance and coordination, and the medulla controls vital involuntary functions.

Understand: A reflex arc is the pathway followed by a nerve impulse during a reflex action.

Path (step-by-step):

1. Receptor (skin of hand) detects the stimulus (heat).
2. Impulse travels along the sensory (afferent) neuron to the spinal cord.
3. In the spinal cord, the sensory neuron connects to a relay (interneuron).
4. The relay neuron passes the impulse to a motor (efferent) neuron.
5. The motor neuron carries the impulse to the effector (arm muscle).
6. The muscle contracts and the hand is pulled away.

Summary: Stimulus → Receptor → Sensory neuron → Spinal cord (relay) → Motor neuron → Effector (muscle) → Response.

Why fast: Because the message is processed by the spinal cord and does not have to travel to the brain and back for a decision, saving time and protecting the body from harm.

Understand: The thyroid gland produces the hormone thyroxine, which requires iodine for its synthesis.

Analyze:

1. Thyroxine regulates carbohydrate, protein, and fat metabolism in the body for balanced growth.
2. If the diet lacks iodine, the thyroid cannot make enough thyroxine.
3. This causes a deficiency disease called goitre, in which the neck (thyroid gland) becomes swollen and enlarged.

Conclude: Since iodine is essential for making thyroxine, using iodised salt ensures adequate iodine intake and prevents goitre.

Understand: Animals coordinate their activities using two systems that differ in speed and mode of action.

Analyze:

| Feature | Nervous control | Hormonal (endocrine) control | |---|---|---| | Messenger | Electrical impulses (and neurotransmitters) | Chemical substances (hormones) | | Medium of transport | Neurons | Blood | | Speed | Very fast | Slow | | Duration of effect | Short-lived | Long-lasting | | Area affected | Localised (specific muscle/gland) | Can be widespread (target organs) | | Example | Withdrawing hand from a pin | Growth controlled by growth hormone |

Conclude: The nervous system gives quick, short-lasting, localised responses, while the endocrine system gives slow, long-lasting, and often more widespread responses; both work together for complete coordination.

Understand: Involuntary actions are those we do not consciously control, such as heartbeat and breathing.

Analyze:

1. Involuntary actions are chiefly controlled by the medulla oblongata, located in the hind-brain.
2. It controls the beating of the heart, breathing rate, blood pressure, vomiting, salivation, etc.

Protection of the brain:

1. The brain is enclosed inside a bony box called the cranium (skull).
2. It is surrounded by three membranes called meninges.
3. A fluid called cerebrospinal fluid (CSF) fills the space between the meninges, acting as a shock absorber to cushion the brain against injury.

Conclude: The medulla oblongata regulates vital involuntary functions, and the brain is protected by the skull, meninges, and cerebrospinal fluid.

Understand: Phototropism is the growth movement of a plant part in response to the direction of light.

Activity (step-by-step):

1. Take a healthy potted plant and place it in a cardboard box with a small hole cut on one side.
2. Keep the box near a window so that light enters only through the hole.
3. Leave it for a few days and observe.

Observation: The shoot of the plant bends and grows towards the direction of light (through the hole).

Role of auxin (explanation):

1. Auxin is a plant hormone made at the shoot tip.
2. When light falls from one side, auxin moves towards the shaded (darker) side of the shoot.
3. The higher auxin concentration on the shaded side makes those cells elongate more.
4. Since the shaded side grows faster than the lighted side, the shoot bends towards the light.

Conclude: Unequal distribution of auxin causes unequal growth, which bends the shoot towards light — demonstrating positive phototropism.