CG Board Class 10 Science Chapter 8 Solutions: Life Processes: Control and Coordination (जैविक प्रक्रियाएँ: नियंत्रण एवं समन्वय) (2026-27)

(i) Which of the following is a plant hormone?**

• (a) Insulin
• (b) Thyroxine
• (c) Estrogen
• (d) Cytokinin

(d) Cytokinin

Explanation: Cytokinin is a plant hormone promoting cell division. Insulin, thyroxine, and estrogen are animal hormones secreted by pancreas, thyroid, and ovaries respectively.

Answer: (d) cellulosic cell wall

Explanation: Nerve cells are animal cells and lack cell walls; cellulosic cell walls are present only in plant cells. Dendrites, nucleus, and axons are structural parts of neurons.

Answer: (a) Pituitary

Explanation: The pituitary gland located at the base of the brain is known as the ‘master gland’ because its secretions control the hormone release of thyroid, adrenals, and gonads.

Answer: (b) Pancreas

Explanation: The endocrine part of the pancreas secretes the hormone Insulin, which regulates and lowers blood glucose levels.

Answer: (b) spinal cord and brain

Explanation: The sensory stimulus of a mosquito bite triggers a reflex response handled by the spinal cord, while processing and learned motor actions involve brain pathways.

Description: A Reflex Action** is an extremely fast, automatic, involuntary response of the body to an external sensory stimulus, controlled primarily by the spinal cord without conscious involvement of the brain.

• Components of Reflex Arc:

1. Receptor (Sensory Organ): Detects stimulus (e.g., skin detects heat/pain).
2. Sensory Neuron: Carries electrical nerve impulse to the spinal cord.
3. Spinal Cord (Integration Center): Processes signal instantly and relays command.
4. Motor Neuron: Carries response command from spinal cord to effector.
5. Effector (Muscle/Gland): Contracts muscle to produce response (e.g., pulling hand away).

• Schematic Diagram:

Stimulus (Heat) → Skin Receptor → [Sensory Nerve] Spinal Cord → [Motor Nerve] Arm Muscle → Response (Hand Withdrawal)

1. Role of Spinal Cord: The spinal cord is the main control center for most reflex actions. Because thinking by the brain requires time, the spinal cord directly connects sensory pathways to motor pathways, enabling instantaneous responses to dangerous stimuli to prevent body injury.
2. Role of Brain: Although the reflex response is executed by the spinal cord, information about the reflex action and pain signals are simultaneously transmitted upward to the brain. The brain records the event in memory, perceives pain, and modifies future conscious responses to avoid similar hazards. Some complex reflexes (like pupil constriction in bright light) are directly controlled by the brain.

The nervous system and endocrine system work together as an integrated neuro-endocrine network to control body processes

1. Hypothalamus-Pituitary Link: Structural nerve connections in the brain connect directly with the pituitary gland, allowing nerve impulses to trigger or inhibit hormone release.
2. Emergency Response: Under stress or fear, the nervous system stimulates the adrenal medulla to release adrenaline rapidly into the blood, increasing heart rate and blood flow to muscles.
3. Feedback Mechanisms: The nervous system monitors internal conditions and regulates endocrine glands, while circulating hormones feed back into brain centers to adjust neural output.

Description:** A nerve cell (Neuron) is the structural and functional unit of the nervous system, specialized for conducting electrochemical messages.

• Main Parts of Neuron:

1. Cell Body (Cyton): Contains cytoplasm, a central nucleus, Golgi bodies, and mitochondria.
2. Dendrites: Highly branched, short projections extending from the cell body that receive signals from other neurons or receptors.
3. Axon: A long single tubular projection that conducts electrical impulses away from the cell body toward target cells or muscle tissues.
4. Myelin Sheath & Schwann Cells: Insulating fatty layer formed by Schwann cells covering many axons, protecting them and increasing impulse speed.
5. Synapse: Junction gap between axon terminal of one neuron and dendrite of the next.

• Diagram Structure:

Dendrites → Cell Body (Nucleus) → Axon (Myelin Sheath) → Axon Terminals → Synapse

Control Mechanism: Involuntary actions (heartbeat, peristalsis, breathing, blood vessel constriction) occur automatically without conscious thought. They are controlled by autonomic nerves connected directly to the Spinal Cord and the Lower Part / Hindbrain (Medulla Oblongata)**.

• Path: Receptors in internal organs → Autonomic sensory nerves → Spinal cord / Lower brain (Medulla) → Autonomic motor nerves → Smooth muscles / Cardiac muscles / Glands.
• Diagrammatic Scheme:

Internal Organ Receptor → [Sensory Nerve] Spinal Cord / Lower Brain → [Autonomic Motor Nerve] Smooth/Cardiac Muscle → Involuntary Response

A classic example of chemical control in plants is Phototropism (bending of plant shoot towards light) controlled by the plant hormone Auxin. When sunlight falls on one side of a plant shoot tip, Auxin synthesized at the tip diffuses to the shaded side. Auxin stimulates rapid cell elongation on the dark side, causing the stem to bend towards the light source. Other chemical controls include fruit ripening induced by Ethylene and leaf senescence caused by Abscisic acid.

Control and coordination are essential for survival, enabling organisms to integrate internal body functions, maintain homeostasis, and respond effectively to environmental changes

1. Preventing Conflicts: During swallowing food, breathing stops momentarily to prevent choking-a precise coordination between digestive and respiratory tracts.
2. Resource Efficiency: While exercising, the muscular system requires more energy. The nervous system coordinates with the circulatory and respiratory systems to increase heart rate and breathing rate simultaneously.
3. Protection from Injury: Reflex withdrawal of hand from a hot utensil protects tissues from destruction.

Experiment (Darwin’s Phototropism Experiment):**

1. Take potted oat/canary grass seedlings and place them near a window with light coming from one side.
2. Set A (Normal): The intact stem tip bends towards the light source.
3. Set B (Tip Removed): If the stem tip is cut off, no bending occurs.
4. Set C (Opaque Cap): If the tip is covered with an opaque foil cap, the stem grows straight without bending.
5. Set D (Transparent Cap): If covered with a clear glass cap, bending towards light occurs normally.

• Conclusion: This proves that the stem tip detects light stimuli and produces Auxin hormone to bend towards light, confirming light sensitivity in plants.

1. Response to Touch (Thigmonasty): Drooping and folding of leaves in ‘Touch-Me-Not’ (Mimosa pudica) plant immediately upon touch due to turgor pressure changes in leaf cells.
2. Response to Light (Phototropism): Bending of shoot tips toward light (positive phototropism) and growing of roots away from light (negative phototropism).
3. Response to Gravity (Geotropism): Downward growth of roots toward gravity and upward growth of shoots away from gravity.
4. Response to Chemical Stimuli (Chemotropism): Growth of pollen tube down the style toward the ovary induced by sugary chemicals released by the carpel.
5. Response to Water (Hydrotropism): Bending of plant roots toward moist soil regions.