Q1. Why do living organisms need control and coordination? Explain using everyday examples and the idea of homeostasis.
Answer:
Living organisms constantly face changing surroundings. They must detect a change (a stimulus) and produce a suitable response to survive. This requires both control (regulating body activities) and coordination (making different organs work together without conflict).
The body also needs to keep its internal conditions stable, a process called homeostasis. Even when the outside temperature, light, or water changes, the body tries to maintain a steady internal environment for proper functioning.
Examples you know:
Touching a hot pan: skin receptors detect heat, signals pass via nerves to the spinal cord, and muscles pull the hand back — a fast reflex action.
Sweating during exercise: the nervous system detects heat and signals sweat glands; sweat cools the body.
Hearing your name: ears send impulses to the brain, which signals neck muscles to turn.
Without efficient communication between different body parts through the nervous and endocrine systems, survival, defense, and normal functioning would be impossible.
Q2. Describe the human nervous system and show how it enables both voluntary and involuntary actions with examples.
Answer:
The nervous system uses fast electrical impulses to carry information. Its main parts are the brain, spinal cord, and nerves. It includes:
Sensory nerves that carry messages from receptors (eyes, skin, ears) to the brain/spinal cord.
Motor nerves that carry commands from the brain/spinal cord to muscles and glands (effectors).
It controls:
Voluntary actions (under our control): writing, walking, turning the head when someone calls your name.
Involuntary actions (automatic): blinking when something approaches the eyes, heartbeat adjustments, knee-jerk reflex at the doctor’s clinic.
A classic example is the reflex arc. When touching something hot, receptors send impulses to the spinal cord, which immediately sends motor signals to withdraw the hand. This is fast because it does not wait for the brain.
The system’s speed and precision help in quick responses, safety, and adaptation, ensuring the body reacts correctly to both expected and sudden changes.
Q3. Explain the endocrine system: how hormones work, how endocrine responses differ from nervous responses, and give suitable examples.
Answer:
The endocrine system uses hormones, which are chemical messengers made by endocrine glands. Hormones travel through the blood to specific target organs with the right receptors.
Compared to the nervous system:
Hormonal responses are usually slower to start but long-lasting.
They influence growth, metabolism, mood, and long-term development.
Key examples:
Adrenaline from the adrenal glands during fear or anger: raises heart rate and oxygen supply for a rapid “fight or flight” response.
Growth hormone from the pituitary: supports height increase and tissue development during childhood.
Insulin from the pancreas: helps maintain blood sugar balance after meals by allowing cells to use glucose.
Hormones ensure the body runs smoothly over time, complementing the nervous system. When both systems coordinate, the body achieves complete control — quick responses when needed and steady regulation for long-term health.
Q4. How do plants show control and coordination without a nervous system? Explain the roles of plant hormones and tropisms with examples.
Answer:
Plants lack a brain or nerves, so they use phytohormones for control and coordination. Major plant hormones include:
Auxins: help shoots bend towards light.
Gibberellins: promote stem and seed growth.
Cytokinins: promote cell division.
Abscisic acid (ABA): helps in stress responses and causes leaf fall.
Ethylene: helps in fruit ripening.
Plants respond directionally to stimuli (tropisms):
Phototropism: shoots bend towards light. Auxin accumulates on the shaded side, making cells there elongate more, so the stem bends towards the light. Examples: sunflower heads tracking the sun, houseplants leaning toward windows.
Geotropism (gravitropism): roots grow down (positive geotropism), and shoots grow up (negative geotropism).
Thigmotropism (touch response): climbers like pea tendrils coil around supports; the Venus flytrap closes quickly on touch to trap insects.
These controlled responses help plants secure light, water, and support for survival and growth.
Q5. Using the “jar-on-its-side” activity, explain how to investigate geotropism in seeds. Include method, observations, and scientific reasoning.
Answer:
Method:
Take a transparent jar, fill it halfway with moist cotton/tissue, and place soaked bean seeds along one visible side.
Lay the jar horizontally in a warm, shaded place. Keep the cotton moist but not waterlogged.
Observations (after 3–5 days):
Roots curve downward (towards gravity), and shoots curve upward (against gravity), even though the jar lies sideways.
Scientific reasoning:
Roots show positive geotropism, allowing them to anchor and absorb water and minerals.
Shoots show negative geotropism, helping leaves reach light for photosynthesis.
Precautions and variables:
Keep light and temperature similar each day; avoid rotating the jar.
Use multiple seeds to reduce error.
Record growth direction and measure curvature if possible.
Conclusion:
The activity shows that plants can sense gravity and adjust growth through internal hormonal signals, ensuring proper orientation and survival.
High Complexity (Analytical & Scenario-Based)
Q6. A student suddenly spots a snake near the footpath and steps back quickly. Analyze how the nervous and endocrine systems coordinate this “fight or flight” response.
Answer:
Step-by-step coordination:
Eyes detect danger; sensory nerves send impulses to the brain.
The brain processes the threat and immediately sends motor commands to leg muscles to step back — a rapid protective response.
At the same time, the brain signals the adrenal glands to release adrenaline into the blood.
Effects of adrenaline:
Heart rate and breathing increase to supply more oxygen to muscles.
More glucose becomes available for quick energy.
Pupils may dilate; attention becomes sharp.
Why integration matters:
The nervous system gives immediate, targeted action (step back).
The endocrine system supports the body for sustained readiness if danger continues.
After the event, signals reduce and the body returns to homeostasis. This integrated control protects life by combining speed with sustained support.
Q7. After a long run, you are very hot and start sweating. Trace the stimulus–response pathway and explain how homeostasis is achieved. What happens if this system fails?
Answer:
Pathway:
Running generates heat. Temperature receptors in the skin and inside the body detect the rise.
The nervous system processes this information and signals sweat glands to release sweat.
As sweat evaporates, it removes heat from the skin surface, cooling the body.
Additional adjustments:
Skin blood vessels may dilate to lose heat faster.
Breathing rate may increase to remove warm air and maintain oxygen supply.
Result:
Body temperature returns to its normal range (homeostasis), allowing enzymes and cells to function properly.
If the system fails:
Temperature may rise too high, leading to heat exhaustion or heat stroke.
Fatigue, dizziness, and confusion can occur because cells cannot work well at high temperatures.
Thus, coordinated detection, signaling, and effector action (sweat glands, blood vessels) protect the body during and after exercise.
Q8. Using the “touching a hot pan” example, explain the reflex arc in detail. Why is it faster than voluntary actions, and what is its survival value?
Answer:
Reflex pathway:
Receptors in the skin detect harmful heat.
Sensory neurons carry impulses to the spinal cord.
An interneuron in the spinal cord links to a motor neuron.
The motor neuron carries impulses to muscles, which contract and pull the hand away.
Speed advantage:
The pathway is short and often does not wait for the brain to decide, so it is very fast.
Less processing time and fewer synapses make the withdrawal almost immediate.
Survival value:
Prevents or reduces tissue damage by acting before serious burns occur.
Leaves the brain free to process the event afterward (pain perception, learning to avoid).
Comparison with voluntary actions:
Voluntary actions (like carefully placing a hot pot) are slower because they need conscious brain processing.
Reflexes are automatic, protective, and essential for safety in daily life.
Q9. A potted plant is kept near a window with light coming from one side. Predict its growth over two weeks. Explain the role of auxin and describe what changes if you rotate the pot daily or provide light from all sides.
Answer:
One-sided light:
The shoot will bend towards the window. Auxin accumulates on the shaded side of the stem, causing those cells to elongate more, so the shoot curves toward the light (phototropism). Leaves become larger and greener on the lighted side.
If you rotate the pot daily:
The direction of the shaded side keeps changing. The plant may show gentler, zig-zag bending or more upright growth...
