Practice questions without fighting the page.

<b>Answer: D. Lymphocytes</b> <ul> <li><b>Why correct:</b> Lymphocytes are white blood cells that circulate in the blood and lymph, contributing to immune surveillance as they move through the circulatory system.</li> <li><b>Key concept:</b> Circulation involves movement of cells and plasma through vessels; white blood cells continuously travel in blood to reach tissues.</li> <li><b>Brief note on others:</b> <ul> <li>A) Erythrocytes carry oxygen but are not primarily responsible for “circulating” the blood itself—oxygen transport is their main function.</li> <li>B) Platelets aid in clotting, not circulation per se.</li> <li>C) Monocytes are immune cells, but not the general circulatory facilitator.</li> </ul> </li> <li><b>Exam tip:</b> If a question asks about cells in the bloodstream with immune roles, lymphocytes are key; pandas of circulation are all blood cells, but functionally they differ.</li> </ul>

<b>Correct option: A</b> – U-235 <ul> <li><b>Key concept:</b> U-235 is a <i>fissile</i> isotope that undergoes fission with slow (thermal) neutrons, releasing energy and neutrons to sustain a chain reaction.</li> <li><b>Why others are incorrect:</b> U-238 is mostly fertile (becomes Pu-239); U-234 and U-236 are not practical fissile fuels for reactors.</li> <li><b>Formula/logic (brief):</b> E = energy from fission; one fission event releases ~200 MeV and about 2–3 neutrons.</li> </ul> <b>Exam tip:</b> Remember: fissile isotopes (like U-235) sustain chain reactions with thermal neutrons; fertile ones (U-238) require conversion.

<b>Correct option: B</b> <ul> <li><b>Why:</b> White blood cells (leukocytes) are the primary cells of the immune system that recognize and attack pathogens.</li> <li><b>Key concept:</b> Immune response is carried out by leukocytes (e.g., neutrophils, lymphocytes, macrophages).</li> <li><b>Other options:</b> <ul> <li>A) Red blood cells transport oxygen, not immunity.</li> <li>C) Epithelical/epithelial cells form barriers, not active immune cells.</li> <li>D) Adipose cells store fat and have other roles, not direct immune response.</li> </ul> </li> <li><b>Exam tip:</b> Remember “WBC = white blood cells = immune defense.”</li> </ul>

<b>Correct answer: B. Graphite</b> <ul> <li><b>Why it conducts:</b> Graphite has delocalized electrons in its layered structure, allowing easy movement of charge along the planes.</li> <li><b>Key concept:</b> Electrical conductivity from delocalized (free) electrons in a crystal lattice.</li> <li><b>Why others don’t:</b> Glass, rubber, and PVC are insulators with localized electrons; they resist current flow.</li> <li><b>Exam tip:</b> Distinguish conductors vs insulators by bonding: metals/graphite conductors vs polymers/ glasses insulators.</li> </ul>

<b>Answer: C. Radiation</b> <ul> <li><b>Why correct:</b> In space with no gravity, there is no medium for conduction or natural convection. Heat moves mainly by electromagnetic waves (radiation).</li> <li><b>Key concept:</b> Heat transfer by radiation follows the Stefan–Boltzmann law: P = εσA(T^4 − T_env^4).</li> <li><b>Exam tip:</b> If there is no medium, assume radiation dominates.</li> <li><b>Why others are wrong:</b> <ul> <li>Conduction requires contact between substances.</li> <li>Convection requires a fluid and gravity to drive buoyancy (natural convection) or an external force.</li> <li>“Cannot be heated” is incorrect; heating occurs by radiation. </li> </ul> </li> </ul>

<b>Correct option: A</b> <ul> <li><b>Why</b>: A bus accelerates forward. Passengers tend to keep their state of rest (inertia of rest) while the bus moves, so they lean backward relative to the bus.</li> <li><b>Key concept</b>: Newton's first law of motion — object at rest stays at rest unless acted on by a net external force; a change in velocity is resisted.</li> <li><b>Formula/idea</b>: If a = acceleration, the tendency to resist change in motion causes a backward tilt when the bus speeds up.</li> <li><b>Exam tip</b>: Remember inertia types: rest vs. motion; here the initial state is rest, so inertia of rest explains backward lean.</li> <li><b>Why others are incorrect</b>: Momentum is about moving objects; gravity is vertical; inertia of motion would apply if the bus suddenly stopped.</li> </ul>

<b>Correct answer: D</b> <ul> <li><b>Explanation</b>: A sphygmomanometer measures <b>blood pressure</b> using a cuff and gauge to read systolic/diastolic pressures (in mmHg). Concept: arterial pressure in the circulatory system. </li> <li><b>Why the others are incorrect</b>: <ul> <li>A) Heart beat is assessed by auscultation/palpation, not this device.</li> <li>B) Vision is checked with a refractometer/eye exam tools.</li> <li>C) Blood sugar is measured with a glucometer.</li> </ul> </li> <li><b>Exam tip</b>: Remember “cuff + gauge = blood pressure.”</li> </ul>

<b>Correct answer: A</b> <br> <ul> <li><b>Spam</b> is junk or unsolicited email sent to many recipients.</li> <li>Key concept: mass unsolicited messaging in email systems.</li> <li>Formula/logic: none needed here; recognition by common term.</li> <li>Exam tip: Remember that “spam” refers to junk mail, not spoofing or scripts.</li> <li>Why others are incorrect: <ul> <li>B. spoof = faking sender identity, not the message itself.</li> <li>C. sniffer script = code used to capture data, not junk mail.</li> <li>D. spool = queue or storage area; not the term for junk email.</li> </ul> </li> </ul>

<b>Correct answer: B. Neil Armstrong</b> <ul> <li>Why correct: Armstrong was the first human to set foot on the Moon during Apollo 11 (1969). He stepped onto the lunar surface first while Buzz Aldrin followed; Michael Collins orbited above in the Command Module.</li> <li>Key concept: lunar landing sequence; order matters in human spaceflight events.</li> <li>Tip: Remember the famous line “one small step for man, one giant leap for mankind.”</li> <li>Why others are incorrect: Aldrin was second on the Moon; Collins did not land on the Moon; Gagarin never reached the Moon (first human in space).</li> </ul>

<b>Correct option: C - Sodium</b> <ul> <li><b>Why</b>: Nerve impulses travel as action potentials. Opening Na+ channels allows Na+ influx, depolarizing the membrane and transmitting the signal along the fiber.</li> <li><b>Key concept</b>: Resting potential and depolarization trigger the action potential; the Na+/K+ pump restores resting state.</li> <li><b>Formula/logic</b>: Membrane potential changes when Na+ moves in; threshold reached → rapid depolarization.</li> <li><b>Exam tip</b>: Remember “Sodium for signal” to link Na+ with nerve impulse transmission.</li> <li><b>Why others are incorrect</b>: Calcium mainly triggers neurotransmitter release at synapses; Iron and Zinc are not primary carriers of nerve impulse along axons.</li> </ul>