Question #1
A tone from a tuning fork travels down the ear canal of a listening musician. Given that the musician's ear canal can be thought of as a pipe with one closed end with a length of 2.5 cm, what is the wavelength of this tone's third harmonic in the ear canal?
Answer:
(C) 3.3 cm is correct.
(C) 3.3 cm is correct.
This question gives us a closed pipe with a length of 2.4 cm and asks us to calculate the wavelength of the third harmonic. Wavelengths of harmonics for closed pipes are given by the formula wavelength = 4L/n, where L is the length of the pipe, and n is any odd integer. Plugging in our values we get wavelength = 4(2.5)/3 = 3.3 Since our length was in cm, our wavelength will also be in cm making (C) the best choice.
Question #2
The net charge of a particular amino acid is 'x'. If three copies of this amino acid are equidistant from point A, what is the electric potential at A?
Answer:
(D) is correct.
(D) is correct.
This question asks us to determine the electric potential at a point equidistant from three identical charges. The electric potential is given by V=kQ/r where k is a constant, Q is the charge, and r is the distance between the point in question and the charge. Electric potential is a scalar quantity, and thus the electric potential at point A is the sum of the electric potential from each of the three charges. The charges are identical (each carrying a charge of x), so the electric potential can be expressed as V=3k(x/r). This matches perfectly with choice (D).
Question #3
In order to transmit an action potential, a neuron requires stimulation from multiple presynaptic cells at the same time. Which of the following concepts best describes this phenomenon?
Answer:
(D) is correct.
(D) is correct.
This is a fairly direct question regarding summation of action potentials to trigger a response. Think of the difference between temporal summation and spatial summation. Threshold potential is the potential each individual neuron must achieve to initiate a single action potential, just as dendritic stimulation is simply the postsynaptic reception of a signal. The two answer choices we should be drawn to are Choices C and D. Temporal summation is where a high frequency of action potentials from a single presynaptic neuron are required to generate a response from a postsynaptic neuron. Spatial summation is where a postsynaptic neuron requires input from multiple presynaptic neurons. Therefore, the answer is choice (D).
Question #4
Apoptosis is induced in a cell, and small pores are created in the mitochondrial membrane. What is the effect of this process on oxidative phosphorylation?
Answer:
(C) is correct.
(C) is correct.
The question is asking about an effect, not the cause, so there is no need to focus on apoptosis (other than remembering it is programmed cell death. To answer the question, we must think about what role the mitochondrial membrane plays in oxidative phosphorylation. How would the small pores affect this role? A key part of the oxidative phosphorylation process is the electrochemical gradient established across the mitochondrial membrane. It is the gradient and the movement of protons through the membrane that drives ATP production. If there were small pores in the membrane, the protons could pass through by means other than the proper ATP-synthase channels and thus the process would not be able to continue. Answer choice (C) matches this reasoning.