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Where does the nerve impulses send neurotransmitters across a synapse to a muscle cell to stimulate muscle contraction?
- A. sarcomere
- B. tendon
- C. myelin sheath
- D. neuromuscular junction
Correct Answer: D
Rationale: The neuromuscular junction is the specific area where nerve impulses trigger the release of neurotransmitters that cross the synaptic gap to bind to receptors on the muscle cell membrane. This binding initiates muscle contraction by stimulating the muscle cell. The sarcomere is the basic contractile unit in a muscle fiber, not the location where nerve impulses communicate with muscle cells. Tendons are connective tissues that attach muscles to bones and are not involved in transmitting nerve impulses. The myelin sheath is a protective covering around nerve fibers but is not directly involved in transmitting neurotransmitters to muscle cells for muscle contraction.
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Which of the following describes how atomic radius varies across the periodic table?
- A. Atomic radius increases from top to bottom and left to right on the periodic table.
- B. Atomic radius increases from top to bottom and right to left on the periodic table.
- C. Atomic radius increases from top to bottom and toward the halogens on the periodic table.
- D. Atomic radius increases from top to bottom and toward the noble gases on the periodic table.
Correct Answer: A
Rationale: Atomic radius tends to increase from top to bottom and left to right on the periodic table. This is because as you move down a group (top to bottom), new energy levels are added, increasing the distance of the outer electrons from the nucleus and thus increasing the size of the atom. On the other hand, as you move from left to right across a period, the number of protons and electrons increases, leading to a stronger nuclear charge that attracts the electrons closer to the nucleus, resulting in smaller atomic radii. Choice B is incorrect as atomic radius does not increase from right to left. Choices C and D are incorrect as they incorrectly associate the trend with specific groups of elements (halogens and noble gases) rather than the general trend observed on the periodic table.
Neurotransmitters send chemical messages across the gap between one neuron and another through which of the following structures?
- A. Schwann cell
- B. ganglion
- C. synapse
- D. axon
Correct Answer: C
Rationale: Neurotransmitters send chemical messages across the gap between one neuron and another through a structure called the synapse. The synapse is a specialized junction where the axon of one neuron meets the dendrite or cell body of another neuron. Neurotransmitters are released from the axon terminal of the presynaptic neuron and travel across the synaptic cleft to bind to receptors on the postsynaptic neuron, transmitting the signal between the two neurons.
Choice A, Schwann cell, is incorrect as Schwann cells are responsible for producing myelin sheath around axons in the peripheral nervous system, not for transmitting neurotransmitters between neurons.
Choice B, ganglion, is incorrect as ganglia are clusters of nerve cell bodies outside the central nervous system and do not directly participate in the transmission of chemical messages between neurons.
Choice D, axon, is incorrect as the axon is a long, slender projection of a neuron that conducts electrical impulses away from the cell body and towards the axon terminals, where neurotransmitters are released into the synapse, but it is not the structure across which neurotransmitters travel to communicate between neurons.
Which of the following chambers of the heart receives blood returning from the lungs during pulmonary circulation?
- A. left atrium
- B. right atrium
- C. left ventricle
- D. right ventricle
Correct Answer: A
Rationale: The correct answer is A, the left atrium. During pulmonary circulation, oxygenated blood returns from the lungs to the heart and enters the left atrium through the pulmonary veins. The left atrium then contracts, pushing this oxygen-rich blood into the left ventricle. The left ventricle subsequently pumps this oxygenated blood out to the rest of the body through the aorta. Choices B, C, and D are incorrect because the right atrium receives deoxygenated blood from the body, the left ventricle receives oxygenated blood from the left atrium, and the right ventricle pumps deoxygenated blood to the lungs for oxygenation, respectively.
Two mice are both heterozygous for two traits: white fur (Ww) and short fur (Ss). Their offspring are most likely to have which of the following genotypes for these traits?
- A. wwss
- B. WWSS
- C. WwSs
- D. WWSs
Correct Answer: C
Rationale: When two mice that are heterozygous for white fur (Ww) and short fur (Ss) mate, they can produce offspring with different combinations of the two traits. The Punnett square for this cross shows that the most likely genotype for the offspring is WwSs. In this case, each offspring receives one allele for white fur (W) and one for short fur (S) from each parent, resulting in a heterozygous genotype for both traits. Choice A (wwss) is incorrect as it represents a homozygous recessive genotype for both traits. Choice B (WWSS) is also incorrect as it represents a homozygous dominant genotype for both traits. Choice D (WWSs) is incorrect as it represents a genotype where one trait is homozygous dominant (W) and the other is heterozygous (S), which is not the most likely outcome based on the given parental genotypes.
Which of the following is a true statement about dominance in genetics?
- A. All genes adhere to Mendel's law of dominance.
- B. A dominant allele will always be expressed.
- C. When two dominant alleles are present, the resulting phenotype will express both traits.
- D. There are three or more alleles possible for all genes.
Correct Answer: B
Rationale: In genetics, dominance refers to the relationship between two different alleles of a gene where one allele (dominant) masks the expression of another allele (recessive) in an individual's phenotype. The correct statement about dominance is that a dominant allele will always be expressed in the phenotype, even in the presence of a recessive allele. This means that if an individual has at least one dominant allele for a particular trait, that trait will be expressed. Choice A is incorrect because not all genes follow Mendel's law of dominance; exceptions do exist. Choice C is incorrect because when two dominant alleles are present, only one will be expressed due to complete dominance. Choice D is incorrect as there can be more than three alleles for a gene, and not all genes have three or more alleles.