SZABMU MDCAT 2024 past paper, Re-Conduct · Code C

Answer: A. Viral envelope

The viral envelope, if present, has glycoproteins that are specifically shaped to bind to receptors on the surface of host cells, acting like a lock and key. While the viral genome is essential for replication, it's the interaction between the envelope and host cell surface that dictates host specificity. The host cytoplasm and genome are internal components and are not the initial recognition sites for viral entry.

Answer: C. Parietal cell — Pepsin

The correct answer is C because parietal cells secrete hydrochloric acid (HCl) and intrinsic factor, not pepsin. Pepsinogen is secreted by chief cells and is activated into pepsin by the acidic environment created by parietal cells. Option A is correct as chief cells produce pepsinogen. Option B is correct as endocrine cells in the stomach release hormones like gastrin. Option D is correct as mucus cells produce mucus for protection.

Answer: C. Self-eating process

Autophagy is a cellular process where the cell breaks down and recycles its own damaged or unnecessary components. This "self-eating" mechanism is crucial for maintaining cellular health and adapting to stressful conditions. Option B, intracellular food digestion, is too narrow; while autophagy can digest intracellular material, it's not limited to "food" in the typical sense.

Answer: C. The form of appearance of a trait

The phenotype refers to the observable characteristics or traits of an organism, which result from the interaction of its genotype (genetic makeup) and the environment. Option C correctly defines phenotype as the expressed form of a trait. Option A describes the genotype, which is the underlying genetic code, not the observable outcome.

Answer: D. 1 Nm A⁻¹

The Weber (Wb) is the SI unit of magnetic flux. Magnetic flux can be defined as the product of magnetic field strength (measured in Tesla, T) and area (measured in square meters, m²), so 1 Wb = 1 T⋅m². Since a Tesla is defined as 1 Newton per Ampere-meter (1 T = 1 N/(A⋅m)), substituting this into the equation gives 1 Wb = (1 N/(A⋅m))⋅m² =

Answer: B. De excitation of nucleus

Gamma radiation is a form of electromagnetic radiation emitted when an atomic nucleus transitions from a higher energy state to a lower energy state. This process is called de-excitation of the nucleus. Option A is incorrect because while atoms can de-excite, this typically involves the emission of visible or ultraviolet light, not gamma rays. Option D is tempting because excitation of the nucleus is the preceding step to de-excitation, but it's the release of energy during de-excitation that produces gamma radiation.

Answer: D. 180º

Work done is calculated as $W = Fd \cos(\theta)$, where $\theta$ is the angle between the force and displacement. For work to be negative, $\cos(\theta)$ must be negative, which occurs when $\theta$ is between 90º and 180º. Among the given options, 180º results in $\cos(180º) = -1$, making the work done negative. Option C (90º) results in zero work because $\cos(90º) = 0$.

Answer: C. Zero order reaction

The decomposition of ammonia on heated tungsten is a surface-catalyzed reaction. At high pressures of ammonia, the tungsten surface becomes saturated with adsorbed ammonia molecules. This means the rate of decomposition depends only on the surface area available and not on the concentration of ammonia in the gas phase, making it a zero-order reaction. A tempting wrong answer is "First order reaction" because many decomposition reactions are first order, but the specific conditions here lead to a different order.

Answer: A. CO₂

Carbon dioxide (CO₂) is a non-polar molecular solid because its molecules are symmetrical, resulting in no net dipole moment. Silicon carbide (SiC) and magnesium oxide (MgO) are covalent network and ionic solids, respectively, while ice (H₂O) is a polar molecular solid due to the polar nature of its covalent bonds and its bent molecular geometry.

Answer: C. , (Comma)

The comma is used to separate independent clauses when they are joined by a coordinating conjunction like "when." In this sentence, "When I was a bachelor" is a dependent clause and "I lived by myself" is an independent clause. The colon and semicolon are incorrect because they are not used to join a dependent clause to an independent clause in this manner. The apostrophe is used for possession or contractions, which is not relevant here.