HESI A2
HESI A2 Biology Practice Test
1. Which one of the following best describes the function of a cell membrane?
- A. It controls the substances entering and leaving the cell.
 - B. It maintains the cell's shape.
 - C. It controls the substances entering the cell.
 - D. It supports the cell's structures.
 
Correct answer: A
Rationale: The correct answer is A. The function of a cell membrane is to control the substances entering and leaving the cell. The cell membrane is selectively permeable, allowing it to regulate the movement of ions and molecules in and out of the cell to maintain internal balance and proper function. Choice B is incorrect because while the cell membrane does provide some structural support, its primary function is not to maintain the cell's shape. Choice C is incorrect because the cell membrane controls both the substances entering and leaving the cell, not just those entering. Choice D is incorrect as the primary function of the cell membrane is not to support the cell's structures but to regulate the movement of substances.
2. Which of the following is true of heterozygous traits?
- A. They are haploid
 - B. They are denoted AA
 - C. They are denoted aa
 - D. They are denoted Aa
 
Correct answer: D
Rationale: Heterozygous traits are denoted by having two different alleles for a particular gene, represented as Aa. This means that they are not haploid (A), not denoted AA (B), and not denoted aa (C). Therefore, the correct answer is D, as heterozygous traits are represented as Aa.
3. The mixture of gases surrounding a planet is referred to as its ______.
- A. Atmosphere
 - B. Stratosphere
 - C. Biosphere
 - D. Troposphere
 
Correct answer: A
Rationale: The mixture of gases surrounding a planet is referred to as its atmosphere. The atmosphere plays a crucial role in supporting life on Earth by providing oxygen, regulating carbon dioxide levels, and shielding the planet from harmful radiation. While the stratosphere, troposphere, and other layers are part of the atmosphere, the term 'atmosphere' encompasses the entire gaseous envelope surrounding a planet. The stratosphere, troposphere, mesosphere, thermosphere, and exosphere are specific layers within the atmosphere, each with distinct characteristics and functions.
4. 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.
5. Which is true of the term Phenotype?
- A. It is the genetic code
 - B. Phenotype determines genotype
 - C. Genotype determines phenotype
 - D. Genotype, epigenetic factors, and environmental factors determine phenotype
 
Correct answer: D
Rationale: The term "phenotype" refers to the observable characteristics or traits of an organism, which are determined by a combination of genotype (genetic makeup), epigenetic factors (modifications to gene expression), and environmental factors (external influences and experiences). Genotype, epigenetic factors, and environmental factors all play a role in determining an individual's phenotype, making option D the correct statement. Options A, B, and C are incorrect because the phenotype is not the genetic code, the phenotype does not determine the genotype, and it is the genotype that influences the phenotype, not the other way around.
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