Nokea
Which laboratory method is most useful to separate genomic DNA fragments by size?
- A. Titration
- B. Spectrophotometry
- C. Electrophoresis
- D. Filtration
Correct Answer: C
Rationale: Electrophoresis is the most suitable laboratory method for separating genomic DNA fragments by size. It works by subjecting DNA fragments to an electric field, causing them to migrate through a gel matrix based on size differences. Smaller fragments move faster and travel farther than larger ones, allowing for separation and analysis based on size. Titration is a technique used to determine the concentration of a solution, not to separate DNA fragments by size. Spectrophotometry is used to measure the amount of light absorbed by a substance at different wavelengths, not for DNA fragment size separation. Filtration is a method used to separate solid particles from a liquid or gas by passing it through a filter medium, not for separating DNA fragments by size.
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Which of the following allows the skull to rotate on the neck?
- A. Vertebral foramen
- B. Spinous process
- C. Atlas
- D. Sacrum
Correct Answer: C
Rationale: The atlas is the first cervical vertebra that supports the skull and allows it to rotate on the neck. The vertebral foramen is an opening in the vertebra for the spinal cord, and the spinous process is a bony projection, not involved in rotation.
In scientific inquiry, experiments can only falsify hypotheses, not validate them. Which of the following statements is an accurate restatement of this idea?
- A. Proving a hypothesis exempts it from further testing
- B. Until disapproved, an explanation for an observation is valid
- C. Certain concepts cannot be subjected to direct experimentation
- D. A hypothesis that has not been falsified remains provisional
Correct Answer: D
Rationale: The core concept in scientific inquiry is that experiments can only disprove or falsify hypotheses but cannot definitively validate them. Choice D is the accurate restatement of this idea since it emphasizes that a hypothesis, until proven false, is considered provisional and open to further testing. Options A, B, and C do not align with this principle. Choice A incorrectly suggests that proving a hypothesis stops it from needing further testing, which goes against the idea of continuous testing and refinement in science. Choice B is incorrect as it implies that an explanation remains valid until disproved, which is not in line with the scientific approach of questioning and testing hypotheses. Choice C is irrelevant to the original idea about experiments falsifying hypotheses, as it introduces concepts about direct experimentation rather than focusing on the validation of hypotheses.
What is the approximate threshold value for mammalian neurons?
- A. -80 mV
- B. -55 mV
- C. 0 mV
- D. +35 mV
Correct Answer: B
Rationale: The approximate threshold value for mammalian neurons is around -55 mV. At this membrane potential, the neuron becomes more excitable and is more likely to generate an action potential. If the membrane potential reaches this level or depolarizes beyond it, it triggers the opening of voltage-gated ion channels, leading to the initiation of an action potential. Values below this threshold are considered subthreshold and do not usually result in action potential generation. Understanding the threshold potential is crucial in assessing the excitability and firing properties of neurons, as it represents the critical point at which the neuron transitions from a resting state to an active state, enabling the transmission of electrical signals.
In order to determine the effects of energy drinks on women's running speed, researchers gave 300 women an energy drink and then recorded the time it took each of them to run 2 miles. After collecting the results, researchers concluded that energy drinks increase the speed of running in women. Which of the following further tests would best help to support this conclusion? Repeat the same experiment, using 300 men.
- A. Repeat the experiment, giving half of the men water and the other half the energy drink.
- B. Repeat the experiment having half of the men run 2 miles and the other half run 5 miles.
- C. Repeat the experiment, giving the men two different energy drinks.
- D. Repeat the experiment, giving the men two different energy drinks.
Correct Answer: B
Rationale: To further support the conclusion that energy drinks increase running speed in women, the best approach would be to repeat the experiment with men. By having half of the men run 2 miles (similar to the original experiment with women) and the other half run a longer distance such as 5 miles, researchers can determine if the effects of energy drinks on running speed are consistent across different distances. This design allows for a comparative analysis between genders and varying running distances, providing a more comprehensive understanding of the impact of energy drinks on running performance.
Which of the following demonstrates a chemical reaction involving water?
- A. Water and oil separate when combined
- B. Water boils to produce steam at 100 degrees Celsius
- C. Water dissolves sugar
- D. Water produces gas when reacting with sodium metal
Correct Answer: D
Rationale: The correct answer is D because when water reacts with sodium metal, it produces hydrogen gas, indicating a chemical reaction. Options A, B, and C involve physical changes or processes like separation, phase change, and dissolution, respectively, which do not involve a chemical reaction. In option A, oil and water separating is a physical change due to differences in polarity. Option B describes a physical change where water undergoes a phase change from liquid to gas. Option C involves a physical change as sugar dissolves in water through a physical process without a chemical reaction occurring.