HESI A2
Biology HESI A2 2024
1. What kind of symbiosis exists between a pneumonia bacterium and a human?
- A. Mutualism
- B. Parasitism
- C. Commensalism
- D. Competition
Correct answer: B
Rationale: In the case of a pneumonia bacterium and a human, the relationship is best described as parasitism. The bacterium benefits by causing harm to the human host, while the human is negatively affected by the presence of the bacterium, leading to illness or infection. This is a classic example of a parasitic relationship where one organism benefits at the expense of the other. Mutualism (Choice A) is a type of symbiotic relationship where both organisms benefit from each other. Commensalism (Choice C) is a symbiotic relationship where one organism benefits, and the other is neither helped nor harmed. Competition (Choice D) refers to a relationship where both organisms are negatively affected by each other as they compete for resources.
2. Duchenne muscular dystrophy is a recessive sex-linked trait carried on the X chromosome. In an example of an unaffected father and a female carrier who have two daughters and two sons, which is the predicted outcome?
- A. Both daughters will carry the disease.
- B. Both sons will carry the disease.
- C. One daughter may have the disease.
- D. One son may have the disease.
Correct answer: C
Rationale: Duchenne muscular dystrophy is a recessive sex-linked trait carried on the X chromosome. Since the father is unaffected and does not carry the disease, he must have a normal X chromosome. The mother is a carrier, which means she has one normal X chromosome and one X chromosome with the disease allele. The daughters will inherit one X chromosome from each parent; one would be normal, and the other has a chance of carrying the disease allele. So, there is a 50% chance that one daughter may have the disease, as she could inherit the X chromosome with the disease allele. The sons will inherit the Y chromosome from the father and the X chromosome from the mother, so they will not be affected by the disease. Therefore, the predicted outcome is that one daughter may have the disease, while the sons will not carry the disease. This rules out choices A, B, and D.
3. Which organelle is found in protists but not in monerans?
- A. Golgi apparatus
- B. Chromosome
- C. Cytoplasm
- D. Cell membrane
Correct answer: A
Rationale: The Golgi apparatus is the correct answer. The Golgi apparatus is a cellular organelle responsible for processing and packaging proteins before they are transported to their final destination. Protists, being eukaryotic organisms, have membrane-bound organelles including the Golgi apparatus, which are absent in monerans. Monerans are prokaryotic organisms that lack membrane-bound structures such as the Golgi apparatus. Choices B, C, and D are incorrect as chromosomes, cytoplasm, and cell membranes are present in both protists and monerans.
4. Which organelle is the site of photosynthesis in plant cells?
- A. Mitochondria
- B. Chloroplasts
- C. Ribosomes
- D. Endoplasmic Reticulum
Correct answer: B
Rationale: The correct answer is B: Chloroplasts. Chloroplasts are responsible for conducting photosynthesis in plant cells. They contain chlorophyll, a pigment that captures light energy and converts it into chemical energy through the process of photosynthesis. Mitochondria (choice A) are known as the powerhouse of the cell and are involved in cellular respiration, not photosynthesis. Ribosomes (choice C) are responsible for protein synthesis. The endoplasmic reticulum (choice D) is involved in protein and lipid synthesis and transport within the cell, not photosynthesis.
5. Select the option that best shows complementary base pairing in DNA:
- A. A and G
- B. A and C
- C. A and A
- D. A and T
Correct answer: D
Rationale: The correct answer is D. A purine (A) must pair with a pyrimidine (T) in DNA. This eliminates options A and C as they do not follow the rule of complementary base pairing. Adenine (A) always pairs with thymine (T) due to their specific shape and bonding properties in DNA structure. Choice B is incorrect because adenine does not pair with cytosine in DNA.
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