Survey of Natural Sciences Answers &
Explanations
1.
The answer is B.
Explanation:
The P680 molecule is involved in noncyclic electron flow. Light
striking P680 excites electrons which rush off to fill the
electron "holes" in the P700 chlorophyll. The P680 with its
electron "holes" is a strong enough oxidizing agent to oxidize
water, filling its electron holes and producing
O2.
Choice A is incorrect because glucose is oxidized in cellular
respiration. Photosynthesis is a reductive process. Choice C is
incorrect because P680 is named according to its preferred
absorption wavelength, namely 680nm. P700 absorbs best at 700nm.
Choice D is incorrect because P700, when excited by light,
provides the electrons that reduce NADH+. Choice E is
incorrect because only choice B is correct.
2. The answer is D.
Explanation:
In order to determine the genotype of an individual with dominant
phenotype, a test cross must be conducted with a homozygous
recessive individual which will display the recessive phenotype.
If any offspring have the recessive phenotype (and are thus
homozygous recessive), this will indicate that the tested
individual was heterozygous. Test crosses with other individuals
will not provide conclusive results.
3. The answer is D.
Explanation:
The endoderm will develop into the epithelial linings of the
digestive and respiratory tracts, parts of the liver, pancreas,
thyroid, and the bladder lining.
Choice (A) is incorrect because the lens of the eye will
develop from the ectoderm.
Choice (B) is incorrect because the gonads are developed from the
mesoderm.
Choice (C) is incorrect because the nervous system is developed
from the ectoderm.
Choice (E) is incorrect because the connective tissue is
developed from the mesoderm.
4. The answer is C.
Explanation:
The difference in electronegativity of two species determines the
ionic character of a bond between them. The greater the
difference in electronegativity, the greater the ionic character.
Recall that electronegativity increases up and to the right on
the periodic table. Thus, Fluorine (F) is the most
electronegative element, while Cesium (Cs) is the least
electronegative. A bond between these two elements would have the
greatest ionic character because the difference in
electronegativity would be the greatest. A bond between two atoms
of the same element would be completely covalent, with no polar
character, because the nuclei will share the electrons equally.
Thus, a carbon-carbon bond would have the least ionic
character.
5. The answer is E.
Explanation:
While this question can be answered by calculations based on the
ideal gas law, as usual shortcuts can be applied. Decreasing
pressure increases the volume of a gas. Increasing temperature
increases the volume. If the pressure is cut in half, the volume
will double, while doubling the temperature will also double the
volume. Thus if both changes occur, the volume will be multiplied
by 4. Since the volume of one mole of a gas at STP can be
approximated as 22.4 liters, four times this volume will be 89.6
liters. Solving this problem via the ideal gas law (to calculate
the volume) requires that we insert all of the numerical values P
= 0.5 atm, n = 1 mole, R = 0.08206 L atm/mol.K, and T = 546 K
into PV = nRT, then rearrange to solve for V = 89.6 liters.
6. The answer is E.
Explanation:
A mole of ideal gas, regardless of the species, occupies 22.4 L
at STP, which corresponds to 1 atm pressure at 0 degrees C (or
273 K). The conditions specified in the question stem are thus
STP conditions. The mixture occupies a volume of 44.8 L, which
means there are two moles of gas present. If the mixture contains
1.5 moles of argon, then there must be 2.0-1.5=0.5 mol Ne
present.
7. The answer is D.
Explanation:
The compounds listed (except for the alcohol listed as Choice E)
are all alkanes, and the alkane with the lowest boiling point
will be that with the smallest molecular weight and the greatest
amount of branching. For similar molecular weights, alcohols will
always have higher boiling points than alkanes due to the
intermolecular hydrogen bonding made possible by the alcohol's OH
group; choice E is thus the compound with the HIGHEST boiling
point of the compounds offered, and should thus be
eliminated.
The remaining choices can be compared pair-wise to arrive at
the credited choice: Comparing choices A and D, which both have
six carbons and thus the same molecular weight, the unbranched
n-hexane of choice A will have the higher boiling point since the
lack of branching allows the molecules to pack more closely in
the liquid phase and thus maximizes dispersion forces of
attraction. Choice A can be eliminated based on this comparison.
Comparing choices B and C, we see that the compound in B has more
carbon atoms and therefore a higher molecular weight; compound B,
as a result, will have a higher boiling point than the compound
offered in choice C, and choice B can be disposed of. Likewise,
when we compare choice C to choice D, we find that the compound
in choice C has the higher molecular weight and thus the higher
boiling point; disposing of choice C leaves us with the correct
choice. Note that it is not necessary to actually calculate the
molecular weights — the alkane with more carbons is more
massive.
8. The answer is B.
Explanation
Alcohols have higher boiling points than their analogous ethers
and hydrocarbons because alcohols have a polarized O-H bond where
the oxygen is partially negative and the hydrogen is partially
positive. This enables the oxygen atoms of other alcohol
molecules to be attracted to the hydrogen to form a weak hydrogen
bond. These hydrogen bonds make it difficult for the alcohol to
vaporize, thereby increasing the boiling point. The analogous
hydrocarbons and ethers do not form hydrogen bonds and therefore
vaporize at lower temperatures. Choice A is a nonsense choice.
The bond length of the oxygen is not a factor in determining the
boiling point of a substance. Choice C is incorrect because
although alcohols are more acidic than their analogous ethers or
hydrocarbons, this property does not affect the boiling point of
a substance.
9. The answer is D.
Explanation:
Both aldehyde and carboxylic acid functional groups are located
on the terminal ends of carbon backbones. As a result, the carbon
to which they are attached is named C-1, and choice D is correct.
Ketones are always internal to the carbon chain.
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