SZABMU MDCAT 2024 past paper, Blue Booklet

Answer: B. Lecithin

The plasma membrane is primarily composed of a phospholipid bilayer. Lecithin, a type of phospholipid, has a hydrophilic head and a hydrophobic tail, enabling it to form this crucial membrane structure. While other lipids are present in cells, phospholipids are the fundamental building blocks of the membrane's bilayer.

Answer: A. ATP synthetase

The knob-like structures on the inner mitochondrial membrane are the F1 components of ATP synthase. These enzymes are responsible for synthesizing ATP by utilizing the proton gradient generated during the electron transport chain. While cytochromes and coenzyme Q are involved in the electron transport chain, they are integral membrane proteins and not the knob-like structures observed. Mesosomes are found in bacteria, not mitochondria.

Answer: C. ileocolic

The ileocolic sphincter is located at the junction of the ileum (the final section of the small intestine) and the cecum (the beginning of the large intestine). Its role is to regulate the passage of chyme from the small intestine into the large intestine. The hepatic, cardiac, and pyloric sphincters are located in different parts of the digestive system and serve different functions.

Answer: C. twenty times

The resting membrane potential is primarily established by the differential distribution of ions across the cell membrane. Potassium ions (K+) are about twenty times more concentrated inside the cell than outside, which is crucial for maintaining the negative charge within the neuron. While other ions are involved, the significant concentration gradient of K+ inside the cell is the most substantial factor in setting the resting potential.

Answer: D. ΔE = qv

The first law of thermodynamics states that the change in internal energy ($\Delta E$) of a system is equal to the heat added to the system ($q$) plus the work done on the system. At constant volume, no work is done ($P\Delta V = 0$), so $\Delta E = q$. Since the volume is constant, this heat exchange is specifically referred to as heat at constant volume, $q_v$. Option B is incorrect because $P$ alone is not the work done.

Answer: A. 1st order kinetics

Unimolecular nucleophilic substitution (SN1) reactions involve a rate-determining step that only depends on the concentration of the substrate, making them first-order reactions. The nucleophile's concentration does not affect the rate of the reaction because it attacks after the rate-determining step. Option B, 2nd order kinetics, is characteristic of bimolecular nucleophilic substitution (SN2) reactions.

Answer: D. Ethanol

LiAlH4 is a strong reducing agent that reduces carboxylic acids to primary alcohols. Acetic acid, a carboxylic acid, is reduced to ethanol, a primary alcohol. Ethane is formed from the reduction of alkyl halides, and ethanal is an aldehyde, which would be an intermediate in the reduction of acetic acid to ethanol if a milder reducing agent were used.

Answer: A. 250 J

The energy stored in a capacitor is given by the formula $E = \frac{1}{2}CV^2$. Plugging in the given values of capacitance ($C = 20 \, \text{F}$) and potential difference ($V = 5 \, \text{V}$), we get $E = \frac{1}{2}(20 \, \text{F})(5 \, \text{V})^2 = \frac{1}{2}(20)(25) = 250 \, \text{J}$. Option A is therefore correct. Option C might be tempting if one incorrectly forgets to square the voltage or multiply by $\frac{1}{2}$, as $20 \times 5 = 100$ which is close to 250.

Answer: B. Germanium

Materials with negative temperature coefficients of resistance (like semiconductors) experience a decrease in resistance as temperature increases. Germanium, a semiconductor, exhibits this behavior due to increased charge carrier concentration with rising temperature. Copper, sulphur, and zinc are conductors or insulators that generally show an increase in resistance with temperature.

Answer: A. at

The preposition "at" is used to indicate a specific point or location. In this context, "at my classroom door" signifies being precisely at the doorway. Option D, "to," implies movement towards something, which isn't the case here as the person is already nearing the door.