ETEA MDCAT 2022 past paper

Answer: C. They do not have the ability to reproduce.

Viruses are obligate intracellular parasites, meaning they cannot reproduce on their own and require a host cell's machinery to replicate. While they don't respire or excrete in the traditional sense, and can be crystallized, the inability to reproduce independently is a defining characteristic that distinguishes them from cellular organisms. Option C directly contradicts this fundamental aspect of viral biology.

Answer: D. Alveoli

The alveoli are tiny air sacs with thin walls and a large surface area, specifically adapted for the efficient diffusion of oxygen into the blood and carbon dioxide out of the blood. The trachea, larynx, and bronchi are primarily involved in conducting air to the lungs, not in gas exchange.

Answer: C. Peptidoglycan

The cell wall of bacteria is primarily composed of peptidoglycan, a unique polymer providing structural integrity. Chitin is found in the cell walls of fungi, and cellulose makes up the cell walls of plant cells. Pectin is a component of plant cell walls but not the primary structural element of bacterial cell walls.

Answer: C. 17 carbon atoms

Steroids are characterized by a specific four-ring structure. This structure, known as the steroid nucleus or gonane, is composed of 17 carbon atoms arranged in three six-membered rings and one five-membered ring. Option C correctly identifies this fundamental carbon count for the steroid backbone.

Answer: B. Neither heat nor any mass are transferred to the environment

Option B is correct because an isolated system, by definition, exchanges neither energy (in the form of heat or work) nor mass with its surroundings. Option D is incorrect because while an isolated system does not transfer mass, it also cannot transfer energy.

Answer: B. This proves law of conservation of momentum

The initial state has zero momentum since the electron and positron are typically at rest. To conserve momentum, the two photons must have equal and opposite momenta, thus traveling in opposite directions. While energy is also conserved, the direction of the photons is directly dictated by the conservation of momentum.

Answer: D. Doppler effect

The Doppler effect describes the change in frequency of a wave in relation to an observer, which is exactly what happens with sound when the source or listener is moving. The Compton, Zeeman, and Stark effects are all phenomena related to quantum mechanics and light or atomic energy levels, not sound waves.

Answer: C. 2-chloro-2-methylpropane

The rate of an S_N1 reaction is primarily determined by the stability of the carbocation intermediate. Option C, 2-chloro-2-methylpropane, forms a tertiary carbocation, which is the most stable due to hyperconjugation and inductive effects from the surrounding alkyl groups. This stability makes it the easiest to form, thus leading to the fastest S_N1 reaction. The other options form less stable primary or secondary carbocations, which are energetically less favorable.

Answer: B. Trigonal pyramidal

The central nitrogen atom in ammonia has three bonding pairs and one lone pair of electrons, arranged tetrahedrally. Due to the lone pair's repulsion, the molecule adopts a trigonal pyramidal shape. Option A is incorrect because a trigonal bipyramidal shape requires five electron domains.

Answer: C. through

The preposition "through" is correct because it indicates movement from one side to the other of an enclosed space, like a tunnel. Option D, "into," suggests entering the tunnel but not necessarily exiting it.