MCAT: Missed Questions 3
How do blood clots form
1. platelets form a plug and they know where to form the plug by identifying collegen which is typically outside the blood vessel 2. a protein called fibrinogen forms a mesh, it turns into fibrin which it allows the strands to stick together
The electrons in the pi bond of an alkene have what kind of character and what kind of energy
100% p character and are at a higher energy level than the electron pair in the sigma bond
The maximum number of optically active isomers that a single compound can have is related to the number of its chiral centers by the following formula
2^(n)
Assuming that the breating rate is 10 breaths/ min, the tidal volume is 800 mL/breath, and the nonalveolar respiratory system volume (dead space) is 150 mL, what is the net volume of fresh air that enters the alveoli each minute
6,500 mL; you say 10 times 800. From the resulting 8000, you subtract the dead space volume 150 mL multiplied by 10 (breaths). The result is 6500
On an oxygen hemoglobin curve, what does a left shift mean? How would pH relate to this?
A left shift of the oxygen dissociation curve indicates an increase in the affinity of oxygen for hemoglobin, and a decrease in oxygen's ability to dissociate from hemoglobin. A higher pH would cause a left shift
A 25.00 mL sample of 0.1050 M H2SO4 is titrated with a NaOH solution of unknown concentration. The phenolphthalein endpoint was reached when 17.23 mL of the NaOH solution had been added. What is the concentration of the NaOH? (A) 0.07617 M (B) 0.1447 M (C) 0.1524 M (D) 0.3047 M
For Acid/Base Neutralization, you want to have the same number of moles of acid and base. For this problem, you need to find the original number of moles you would have of acid. Bc sulfuric acid is diprotic, you need twice the moles of base. Then use the moles with the liters to find the molarity
The atmospheric pressure of carbon dioxide and oxygen is .3 mmHg and 160 mmHg respectively, but the partial pressures of these gases of carbon dioxide and oxygen in blood leaving the lungs are 40 mmHg and 95 mmHg respectively. What explains this?
Henry's law states that the amount of gas that dissolves in a given liquid is directly proportional to the partial pressure of the gas in equilibrium with that liquid. If the only factor influencing dissolved gas concentrations is the partial pressure of the gas in the air in contact with the liquid, then we would assume that the ratio of oxygen to carbon dioxide would be equal both within and outside of the liquid. However, if a given gas were more soluble in a given liquid, a greater proportion of the gas could be dissolved within that liquid.
What is the relationship between oxygen concentration and carbon dioxide concentration and the relative affinity of hemoglobin (Hb) for each of these molecules?
High oxygen concentration reduces the affinity of hemoglobin for CO2, and high CO2 reduces the affinity of hemoglobin for oxygen
How would an increase in bicarbonate relative to all other molecules in the blood affect the oxygen affinity of hemoglobin and why?
Increase oxygen affinity by binding with free protons
What is the relationship between lung elastic recoil and alveolar surface tension
Increased lung elastic recoil and increased alveolar surface tension are more or less synonymous. Increasing either increases the pressure of the alveolar wall on the gas within the alveolar space
What is the key point about the lac operon
It is an inducible system in which an inducer binds to a repressor; the repressor is constitutively made
When does laminar flow occur
Laminar flow occurs when the velocity is low or the fluid is very viscous. Laminar flow is where the fluid flows in layers or lamina without much mixing of the layers. Within each layer, the velocity, pressure, and other hydrodynamic properties remain unchanged.
Can you know which direction an R or S rotates plane polarized light
No, you have to determine that experimentally
How much heat is given off when 1.0 g of steam condenses at 100 degrees celsius? How do you solve this?
Since condensation is the opposite of vaporization, you use the heat of vaporization, but with the opposite sign to indicate that this heat is released. Then you say that q = the number of moles times the heat of condensation
According to your understanding of Bernoulli's principle and continuity equation, which of the following statements accurately describes the phenomenon of vascular flutter which occurs when an artery becomes constricted due to the accumulated plaque in its inner walls?
The constriction causes the pressure to drop and the vessel to collapse
There is a 1-liter container filled with 500 milliliters of water placed on top of a scale displaying 80 pounds. When a metal cube is submerged tied to a string end into the container, which of the following statements accurately describes the result?
The scale will register a weight greater than 80 pounds due to Newton's Third Law.
What are conformational isomers? Which form has the highest potential energy?
They are not true isomers. They are different spatial orientations of the same molecule . Eclipsed form
Astrocytes do what for neurons in the CNS
They provide nutrients
What is the difference between relative configuration and absolute configuration
absolute configuration has to do with R and S. Relative configuration happens when two molecules have the same orientation but differ in one of the substituent atoms
How do you find the heat of sublimation
add the heat of fusion and the heat of vaporization
Describe the dipole moments of cis / trans molecules
cis have a dipole moment, while trans do not
Structural isomers have
different carbon skeletons, chemical properties altered due to differences in functional groups, and functional groups may occupy different positions on the carbon skeleton
nitro group; is it electron withdrawing or electron donating
electron withdrawing
sulfonic acid ; electron withdrawing or electron donating
electron withdrawing
What stages of translation require ATP
every stage: initiation, elongation, and termination all require ATP
In human females, mitotic divisions of oogonia that lead to formation of presumptive eggs cells (primary oocytes) occur between?
fertilization and birth
For eukaryotes, the total yield of ATP from NADH is not always maximized when the NADH is manufactured by which process
glycolysis; glycolysis occurs in the cytosol, and so it takes energy to transport that NADH to the mitochondrion
The most stable bond is the one with the
highest bond energy; this means that the higher the bond energy, the lower the energy of the compound
If a question says how long will it take for 90 percent of the reactant to react, how do you translate that mathematically
if 90% has reacted, there is only 10% of the reactant left, which is what you need to use for your concentration at time T
For the arrhenius equation, if the activation rate goes up, what happens to the rate constant
it goes down
How do you calculate the degree of rotation of plane polarized light in a racemic mixture
it is always zero
How does the sympathetic nervous system affect the bronchi
it relaxes the bronchi so they open up
What about when enantiomers are mixed in unequal concentrations?
light is rotated in the same direction as it would be in a pure sample of the enantiomer in excess but only to a fraction of the degree. The ratio of actual rotation to the rotation of a pure sample is called optical purity
In decrease in blood pH lowers or increases hemoglobin's affinity for oxygen
lowers
If you have a molecule with sp3d2 hybridization, what are the possible shapes
octahedral, square pyramidal, or square planar (every one has angles of 90 degrees)
Which are more reactive, sigma bonds or pi bonds
pi bonds ; pi bonds have a higher energy, and are less strong and stable
If you are doing a problem on a melting ice cube, what must you include to find the heat gained
remember you have to ADD the mass times the heat of fusion with the regular mcat equation to raise the melted cube to a certain temperature
Shorter bonds are always
stronger
A molecule will be meso if it contains the same atoms as substituents and the absolute configuration of the two chiral carbons are
the same. R and S or S and R
The bonds of benzene are what compared to the carbon-carbon bonds of an alkene
they are longer and weaker
What does the internal structure of erythrocytes tell you about it's energy production
they lack mitochondria and so they can only perform glycolysis, meaning they need glucose exclusively; the only substrates for glycolysis are monosaccharides - not amino acids or fatty acids
If you have a molecule with sp3d hybridization , what are the possible shapes
trigonal bipyramidal, see-saw, t-shaped, or linear
A triple bond has how many pi and how many sigma bonds
two pi bonds and 1 sigma bond
