Nokea
Which two bases are purines?
- A. Adenine (A)
- B. Cytosine (C)
- C. Thymine (T)
- D. Guanine (G)
Correct Answer: A
Rationale: Adenine (A) and guanine (G) are the two bases that are purines. Purines are characterized by a double-ring structure containing two carbon rings, distinguishing them from pyrimidines. Adenine and guanine are purines because they possess this unique double-ring structure. Therefore, choices A and D, adenine and guanine, respectively, are the correct answers. Choices B and C, cytosine and thymine, are pyrimidines and do not exhibit the double-ring structure characteristic of purines.
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Which of the following is true of optical microscopy?
- A. Utilizes scanning electrons
- B. Utilizes visible light
- C. Utilizes dye for samples
- D. More than one of the above is true
Correct Answer: D
Rationale: The correct answer is D, 'More than one of the above is true.' Optical microscopy utilizes visible light (Choice B) and often involves the use of dyes for samples (Choice C). Using dyes helps enhance contrast, making it easier to visualize the structures being observed. Choice A is incorrect as optical microscopy does not utilize scanning electrons, but rather visible light.
Which of the following is not true about enzymes?
- A. They catalyze reactions
- B. They lower the activation energy needed
- C. They have an active site
- D. They are typically proteins
Correct Answer: B
Rationale: Enzymes lower the activation energy needed for a reaction to occur, not raise it. By lowering the activation energy, enzymes facilitate reactions, making them occur more easily and rapidly. Choice A is correct as enzymes indeed catalyze reactions. Choice C is correct as enzymes have specific active sites where substrates bind. Choice D is correct as enzymes are commonly proteins, although some RNA molecules also exhibit catalytic properties.
What type of cells possess a cell membrane?
- A. Prokaryotic cells only
- B. Eukaryotic cells only
- C. Both prokaryotic and eukaryotic cells
- D. None of the above
Correct Answer: C
Rationale: Cell membranes are present in both prokaryotic and eukaryotic cells. The cell membrane serves as a barrier that encloses the cell contents and regulates the entry and exit of substances in and out of the cell. It is a fundamental structure found in all types of cells, regardless of whether they are prokaryotic (lacking a nucleus) or eukaryotic (containing a nucleus).
Choice A is incorrect because eukaryotic cells also possess cell membranes. Choice B is incorrect as prokaryotic cells, such as bacteria, also have cell membranes. Choice D is incorrect as both prokaryotic and eukaryotic cells have cell membranes.
A cell from heart muscle would more than likely contain an unusually high proportion of which of the following?
- A. lysosomes
- B. mitochondria
- C. mRNA
- D. ribosomes
Correct Answer: B
Rationale: A cell from heart muscle would more than likely contain an unusually high proportion of mitochondria because the heart muscle requires a significant amount of energy to function properly. Mitochondria are the powerhouse of the cell and are responsible for producing energy in the form of ATP through cellular respiration. Therefore, to meet the high energy demands of the heart muscle, it would need a higher concentration of mitochondria compared to other cell types. Choices A, C, and D are incorrect because while lysosomes, mRNA, and ribosomes are essential components of a cell, they do not play as direct a role in meeting the high energy demands of heart muscle as mitochondria do.
Why doesn't an antibiotic work for treating the flu?
- A. The antibiotic is for a different type of infection
- B. The antibiotic is not effective against viruses
- C. The antibiotic is not prescribed in a high enough dosage
- D. None of the above
Correct Answer: B
Rationale: The correct answer is B. Antibiotics are used to treat bacterial infections, not viral infections like the flu. The flu is caused by a virus, and antibiotics are ineffective against viruses. Choice A is incorrect because it does not address the fact that antibiotics do not work on viruses. Choice C is incorrect as the issue is not related to the dosage amount, but rather the nature of the infection. Choice D is incorrect as there is a specific reason why antibiotics do not work for the flu.