OAT Study Guide 2026

A nonsense mutation changes a codon that encodes an amino acid into a stop codon (UAA, UAG, or UGA), causing premature termination of translation.

Acetylcholine (ACh) is a neurotransmitter that transmits signals across the synaptic cleft. After binding to receptors on the postsynaptic membrane, its action is terminated by the enzyme acetylcholinesterase (AChE), which degrades ACh in the synaptic cleft. If all enzymes in the synaptic cleft, including AChE, are denatured, they will lose their function. This means acetylcholine will not be broken down and will persist in the cleft, continuing to bind to receptors and prolonging its effect.

This is a combination problem because the order in which the people are selected for the committee does not matter. The formula for combinations is nCr = n! / (r! * (n-r)!), where n is the total number of items to choose from, and r is the number of items to choose. Here, n=10 and r=3. So, 10C3 = 10! / (3! * (10-3)!) = 10! / (3! * 7!) = (10 * 9 * 8) / (3 * 2 * 1) = 720 / 6 = 120.

The Hardy-Weinberg equation (p² + 2pq + q² = 1) predicts genotype frequencies under the assumption of no evolution (no selection, drift, gene flow, or mutation).

Plasmodesmata are microscopic channels that traverse the cell walls of plant cells, connecting the cytoplasm of adjacent cells. These channels allow for the direct transport of water, nutrients, and signaling molecules between cells, facilitating intercellular communication and coordination within plant tissues. Desmosomes, gap junctions, and hemidesmosomes are types of cell junctions found in animal cells, not plant cells.

The ladder, the wall, and the ground form a right-angled triangle. The ladder itself is the hypotenuse (20 feet). The distance from the wall to the base of the ladder is the adjacent side relative to the angle with the ground (12 feet). The cosine of an angle in a right triangle is defined as the ratio of the adjacent side to the hypotenuse (SOH CAH TOA). Therefore, cos(θ) = Adjacent / Hypotenuse = 12 / 20. This fraction simplifies to 3/5.