1. Which of the following is a plant hormone?
(a) Insulin
(b) Thyroxin
(c) Oestrogen
(d) Cytokinin
Answer: (d) Cytokinin.
2. The gap between two neurons is called a:
(a) dendrite.
(b) synapse.
(c) axon.
(d) impulse.
Answer: (b) synapse.
3. The brain is responsible for:
(a) thinking.
(b) regulating the heart beat.
(c) balancing the body.
(d) all of the above.
Answer: (d) all of the above.
4. What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?
Answer:
- Function: Receptors are specialized nerve cell tips located in sense organs (like the eyes, ears, nose, tongue, and skin) that detect changes in the environment (stimuli) and convert them into electrical impulses for the nervous system.
- Problems when malfunctioning: If receptors fail, the body cannot detect specific stimuli. For example, damaged gustatory receptors would prevent tasting food, while faulty olfactory receptors would prevent smelling (e.g., failing to detect a gas leak or smoke), potentially leading to dangerous situations.
5. Draw the structure of a neuron and explain its function.
Answer:
- Structure: A neuron consists of a cell body, dendrites (short branched fibers that receive signals), and an axon (a long fiber that transmits signals). The end of the axon has nerve endings that release chemicals at the synapse.
- Function: It is the structural and functional unit of the nervous system. It acquires information at the dendritic tips, creates an electrical impulse, conducts it along the axon, and transmits it to the next neuron or a muscle/gland through chemical signals at the synapse.
6. How does phototropism occur in plants?
Answer: Phototropism is the directional growth of a plant part in response to light.
- When a plant detects light from one side, the hormone auxin (synthesized at the shoot tip) diffuses toward the shady side.
- The higher concentration of auxin on the shady side stimulates cells to grow longer than those on the sunny side, causing the shoot to bend toward the light source.
7. Which signals will get disrupted in case of a spinal cord injury?
Answer: A spinal cord injury will disrupt:
- Reflex actions: Rapid, involuntary responses that are processed in the spinal cord.
- Sensory signals: Information traveling from the body parts to the brain.
- Motor signals: Commands from the brain to the muscles and glands for voluntary movements.
8. How does chemical coordination occur in plants?
Answer: Plants use hormones (phytohormones) for chemical coordination. These are synthesized in small quantities at certain locations and diffuse to their site of action. Examples include auxins (growth), gibberellins (stem growth), cytokinins (cell division), and abscisic acid (growth inhibition/wilting).
9. What is the need for a system of control and coordination in an organism?
Answer: It is essential for survival and efficiency. It allows an organism to:
- Respond appropriately to environmental changes (stimuli).
- Integrate the activities of various organs and tissues so they work together harmoniously.
- Protect the body from harm (e.g., reflex actions).
- Maintain internal balance (homeostasis) and regulate growth.
10. How are involuntary actions and reflex actions different from each other?
Answer:
- Reflex Actions: Rapid, automatic responses to a specific stimulus, often processed in the spinal cord without conscious thought (e.g., pulling your hand from a flame).
- Involuntary Actions: Ongoing internal body processes that occur without our conscious control, usually regulated by the mid-brain and hind-brain (medulla), such as heartbeat, breathing, and blood pressure.
11. Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
Answer:
- Nervous Mechanism: Uses electrical impulses, signals travel very fast along nerve fibers, effects are localized to specific cells (muscles/glands), and the action is short-lived.
- Hormonal Mechanism: Uses chemical messengers (hormones) secreted into the blood, signals travel slower, can reach all cells in the body, and the effects are often long-lasting and widespread.
12. What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?
Answer:
- Sensitive Plant: Movement is independent of growth. It is caused by changes in the amount of water in specific cells (turgor pressure), leading to swelling or shrinking of cells. No specialized muscle or nervous tissue is involved.
- Movement in Legs: It is a voluntary movement controlled by the nervous system. It involves specialized muscle tissues where proteins change shape and arrangement in response to electrical impulses, causing the muscle cells to shorten and produce movement.