MCAT Exam Questions & Answers 2026 (11–20)

✓ Correct answer: B. Their secretions contain zymogens.

The pancreas produces multiple zymogens that are activated within the small intestine; the gastric glands produce pepsinogen, which is converted to pepsin under acidic conditions.

✓ Correct answer: D. E inbred plants were found, on average, to be less attractive to pollinators than outbred plants, which could reduce their fitness.

The inbred plants attracted fewer pollinators and experienced fewer probes per visit than outbred plants. This could result in further reduced fitness of inbred plants and effectively select for future out-crossing. On average, the outbred plants were more attractive to pollinators than inbred plants—but both inbred and outbred plants were capable of attracting pollinators.

✓ Correct answer: A. Three

Benzylamine consists of a benzene ring with a -CH₂NH₂ substituent. The benzene ring contains three double bonds, and the substituent has none.<br/><br/>Each bond in a compound represents a sigma bond. Each additional bond represents a pi bond; thus, double binds result from one sigma and one pi bond, and triple bonds from one sigma and two pi bonds. In benzylamine, there are three double bonds and seventeen total bonds, three of which are double bonds. The compound will have a total of seventeen sigma bonds and three pi bonds.

✓ Correct answer: D. Antidiuretic hormone (ADH)

Of all the hormones listed, antidiuretic hormone (ADH) is the only one that neither acts on, nor is released by, the adrenal cortex. ADH is released from the posterior pituitary and causes the kidneys to retain more water.<br/><br/>Aldosterone (a mineralcorticoid) and cortisol (a glucocorticoid) are both incorrect choices because they are released by the adrenal cortex and would be greatly affected by trauma to that area. ACTH is released by the anterior pituitary and acts to stimulate the adrenal cortex; these hormones act as part of a negative feedback chain, so damage to the target area would temporarily cause more ACTH to be produced. The same goes for CRH, which is released by the hypothalamus and stimulates secretion of ACTH.

✓ Correct answer: B. 3

Ephedrine has two stereocenters (carbons 1 and 2), meaning there would be <tex>\displaystyle 2^2</tex>, or <tex>\displaystyle 4</tex>, total possible stereoisomers. One is already shown, so there would be three others.

✓ Correct answer: A. Component of sarcomere scaffold structure

Microtubules are made of the tubulin protein and play integral roles in cell structure. They are prominent in the cytoskeleton and form the fundamental structures for cilia and flagella. The mitotic spindles are also comprised of microtubules, and are used to draw apart the sister chromatids of each chromosome during cell division.<br/><br/>Microtubules do not play a significant role in the structure or function of sarcomeres. Actin and myosin compose the main functional basis of the sarcomere, while titin and the Z disc proteins provide the sarcomere structure.

✓ Correct answer: D. <tex>\frac{1}{3}\text{N}</tex>

This question can be answered using conservation of energy. Having an understanding of the work-energy theorem allows us the knowledge that changing kinetic energy is a form of work, and that work can be a form of energy. In this particular question, the only force acting on the block to slow it down is the force of friction from the rough surface. As we know, work is equal to force times distance.<br/><br/><tex>\displaystyle W=Fd</tex><br/><br/>Because the block started with a certain amount of kinetic energy, and then is brought to a complete stop, all of that kinetic energy is transferred to work done by the force of friction over a distance of six meters.<br/><br/><tex>\displaystyle W=\Delta KE=\frac{1}{2}m(\Delta v)^2</tex><br/><br/>Because the <tex>\displaystyle 1.0kg</tex> block had a velocity of <tex>\displaystyle 2\frac{m}{s}</tex> on a smooth surface and ends with a velocity of <tex>\displaystyle 0\frac{m}{s}</tex> at rest, we can calculate the change in kinetic energy.<br/><br/><tex>\displaystyle \Delta KE=\frac{1}{2}(1.0kg)(0\frac{m}{s}-2\frac{m}{s})^2=\frac{1}{2}(1.0kg)(4\frac{m^2}{s^2})</tex><br/><br/><tex>\displaystyle \Delta KE=2J</tex><br/><br/>The kinetic energy is completely converted to the work done by friction.<br/><br/><tex>\displaystyle W=\Delta KE=2J</tex><br/><br/>We can then use the first equation for work to determine the force of friction.<br/><br/><tex>\displaystyle W=Fd=F_f(6m)=2J</tex><br/><br/><tex>\displaystyle F_f=\frac{2J}{6m}=\frac{1}{3}N</tex>

✓ Correct answer: C. It will decrease by a factor of 4.

The gravitational force between two objects is inversely proportional to the distance between them squared.

✓ Correct answer: D. The principle of optical dispersion, such that the velocity of a wave in a given medium depends on its frequency.

The interaction of the light and the electrons in the medium varies with frequency.<br/><br/>Choice B is incorrect because while the description of the photoelectric effect in this answer is accurate, it is not relevant to the noted difference in refractive indices. The two refractive indices were measured separately for light at 350 and 800 nm, so there is no interference between waves playing a role here.

✓ Correct answer: D. The formal charge increases by 1.

In NH₃, nitrogen has a formal charge of 0 because the nitrogen is surrounded by three bonded hydrogens and one lone electron pair. In the Lewis adduct, nitrogen is surrounded by four bonds, so its new formal charge is +1. The nitrogen gives up two electrons to form the coordinate bond with boron, but its formal charge increases in the process. Converting a lone electron pair on an atom to a bonding electron pair will inevitably change the formal charge of that atom.