which of the following describes the gene in which one allele takes a different form from another

HESI A2

Biology HESI A2 Practice Test

1. Which of the following describes the situation where one allele takes a different form from another in a gene?

A. phenotype
B. heterozygous
C. homolog
D. homozygous

Correct answer: B

Rationale: Heterozygous is the term used to describe the genotype of an individual with two different alleles for a specific gene. In this case, one allele takes a different form from another, resulting in genetic diversity and variation in trait expression. The other choices are incorrect: 'phenotype' refers to the observable traits of an organism, 'homolog' typically refers to chromosomes that are similar in structure, and 'homozygous' describes the genotype where both alleles for a gene are the same.

2. Which of the following is true of homozygous traits?

A. They are haploid
B. They are denoted AA
C. They are denoted aa
D. They are denoted Aa

Correct answer: B

Rationale: Homozygous traits have two identical forms of the gene, either both dominant (AA) or both recessive (aa). Therefore, choices B and C are true for homozygous traits. Choice A is incorrect because being haploid refers to having a single set of chromosomes, not necessarily homozygous traits. Choice D is incorrect as homozygous traits have identical alleles, so they are not denoted as Aa.

3. Why are bacteria and blue-green algae often classified together?

A. Both are gymnosperms.
B. Both are prokaryotes.
C. Both are autotrophs.
D. Both are pathogens.

Correct answer: B

Rationale: Bacteria and blue-green algae (cyanobacteria) are often classified together because they are both prokaryotes. Prokaryotes are unicellular organisms that lack a membrane-bound nucleus and other membrane-bound organelles. This characteristic distinguishes them from eukaryotic organisms, which have these membrane-bound structures. Choice A is incorrect because gymnosperms are seed-producing plants with naked seeds, not bacteria or blue-green algae. Choice C is incorrect because being an autotroph (able to produce its own food) is not a reason for classifying them together. Choice D is incorrect because not all bacteria and blue-green algae are pathogens; many of them are beneficial or neutral to other organisms.

4. What is the initial step in the metabolism of food to cellular energy?

A. Citric Acid Cycle
B. Glycolysis
C. Electron Transport Chain
D. Photosynthesis

Correct answer: B

Rationale: The correct answer is B: Glycolysis. Glycolysis is the initial step in the metabolism of food to cellular energy. During glycolysis, glucose is broken down into pyruvate, generating ATP and NADH. Choices A, C, and D are incorrect because the Citric Acid Cycle and Electron Transport Chain occur later in cellular respiration, while Photosynthesis is the process by which plants convert light energy into chemical energy.

5. 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.