Ans: A reflex action is a rapid, automatic, involuntary response to a stimulus. It does not involve conscious thinking by the brain. Example: Withdrawing hand from a hot object. Reflex arc pathway: Stimulus (hot object) → Receptor (skin) → Sensory neuron → Spinal cord (relay neuron processes) → Motor neuron → Effector (muscle contracts) → Response (hand withdrawn). The spinal cord coordinates the reflex, making it faster. The brain only becomes aware after the action is complete.

Ans: The brain is enclosed in the skull and protected by meninges and cerebrospinal fluid. Forebrain — Cerebrum: largest part; controls intelligence, memory, voluntary actions, sensory interpretation (sight, hearing, smell, touch, taste), speech. Hypothalamus: controls body temperature, hunger, thirst, sleep; links nervous and endocrine systems. Midbrain: controls eye movements and auditory reflexes. Hindbrain — Cerebellum: coordinates balance, posture, and smooth muscle movement. Pons: relay station between cerebrum and cerebellum. Medulla oblongata: controls involuntary vital functions — breathing, heartbeat, blood pressure, swallowing, vomiting.

Ans: Plant hormones (phytohormones) are chemical substances produced in small quantities that regulate plant growth and development. Auxin: produced at shoot tip; promotes cell elongation; causes phototropism (shoot bends toward light because auxin accumulates on shaded side, causing those cells to elongate more). Gibberellin: promotes stem elongation, seed germination, and fruit development; used to increase size of seedless grapes. Abscisic acid: inhibits growth; promotes dormancy in seeds and closing of stomata during water stress — called the "stress hormone". Cytokinin: promotes cell division; delays leaf ageing. Ethylene: promotes fruit ripening; used commercially to ripen bananas.

Ans: Nervous system: transmits electrical signals through neurons; fast response (milliseconds); short-term effect; specific (targets exact muscles/glands); does not use chemicals in blood. Endocrine system: releases hormones into blood; slow response (seconds to hours); long-lasting effects; widespread (affects many tissues); hormones travel throughout the body. Both work together — hypothalamus coordinates nervous and endocrine systems, and the pituitary gland (master gland) controls most other endocrine glands.

Ans: Adrenaline (epinephrine) is a hormone secreted by the adrenal glands (located above kidneys) in response to stress, fear, excitement, or danger — called the "fight or flight" hormone. Effects: increases heart rate, dilates blood vessels and air passages, raises blood pressure, speeds up breathing, raises blood glucose levels (more energy available), diverts blood from digestion to muscles, dilates pupils. All these prepare the body to either face the threat (fight) or run away (flight). Example: feeling your heart race before a race or during a scary moment.

Ans: The cerebellum, part of the hind-brain, controls posture, balance and coordination of voluntary movements.

Ans: The medulla controls involuntary actions such as blood pressure, salivation and vomiting.

Ans: Insulin, produced by the pancreas.

Ans: Cytokinin.

Ans: A tropic movement is a directional growth movement of a plant part in response to an external stimulus such as light, gravity, water, chemicals or touch.

Ans: The pituitary gland, because it secretes hormones that control the working of other endocrine glands.

Ans: Iodine is needed by the thyroid gland to make thyroxine, which regulates metabolism. Deficiency of iodine can cause goitre (swelling of the neck), so salt is iodised to prevent it.

Ans: The movement of Mimosa leaves is a quick nastic movement caused by changes in the water content (turgor) of cells at the base of the leaf; it does not involve growth and is not directional. The bending of a shoot towards light (phototropism) is a slow, directional growth movement caused by the hormone auxin.

Ans: The spinal cord conducts sensory information to the brain and motor commands from the brain to the body. It also controls reflex actions independently of the brain.

Ans: Receptors are specialised cells or nerve endings in sense organs that detect changes in the environment. Examples: photoreceptors in the eye detect light; olfactory receptors in the nose detect smell; taste receptors in the tongue detect taste.

Ans: The brain is enclosed in the bony skull (cranium), which protects it from mechanical injury. Inside, it is covered by three membranes (meninges), and the space between them is filled with cerebrospinal fluid, which acts as a shock absorber and keeps the brain cushioned.

Ans: Gibberellins promote stem elongation, seed germination and flowering; they are growth promoters. Abscisic acid inhibits growth and causes wilting and falling of leaves and closing of stomata in stress; it is a growth inhibitor. Their effects are opposite: gibberellins promote growth while abscisic acid retards it.

Ans: The person would lose the ability to maintain posture and balance and coordinate voluntary movements. Actions like walking in a straight line, picking up a pencil or riding a bicycle would become jerky and uncoordinated, and the body might be unsteady.

Ans: A neuron has dendrites that receive signals, a cell body with the nucleus, a long axon that carries the impulse away from the cell body, and nerve endings. Information acquired at the dendrite creates an electrical impulse that travels through the cell body and along the axon to its end. At the axon end, the electrical impulse triggers the release of chemicals (neurotransmitters) into the synapse, a tiny gap between two neurons. These chemicals diffuse across the gap and start a similar electrical impulse in the dendrite of the next neuron. In this way the information is relayed from one neuron to another.

Ans: Pituitary: growth hormone; growth and development; deficiency causes dwarfism. Thyroid: thyroxine; regulates metabolism; iodine deficiency causes goitre. Pancreas: insulin; lowers blood sugar; deficiency causes diabetes. Adrenal: adrenaline; prepares the body for emergencies. Testes: testosterone; controls male puberty changes. Ovaries: oestrogen; controls female puberty changes and the menstrual cycle.