Biology HESI A2 Practice Test

Correct Answer: A

Rationale: The correct answer is A: hypothesis. A hypothesis is a statement that proposes an explanation for a phenomenon based on available evidence. It helps guide scientific inquiry by providing a testable prediction. Observations (B) are simply data collected through senses. Experiments (C) involve testing hypotheses through controlled conditions. Conclusions (D) are interpretations drawn from the data collected. Therefore, a hypothesis is the initial statement or explanation of certain events or happenings in the scientific process.

Correct Answer: B

Rationale: Cytosine and thymine are pyrimidines because they are smaller, single-ring nitrogenous bases found in DNA and RNA. Purines have a double-ring structure, which includes adenine and guanine. Choice A is incorrect because purines have a different structure. Choice C is incorrect because cytosine and thymine are specifically pyrimidines, not both. Choice D is incorrect as they are classified as pyrimidines.

Correct Answer: A

Rationale: The correct answer is A: Through a contractile ring. Animal cells divide through a process called cytokinesis, where a contractile ring made of actin and myosin filaments constricts the cell membrane, leading to cell division. This process is specific to animal cells. Choice B, via a cell plate, is characteristic of plant cells, not animal cells. Choice C, both methods, is incorrect as animal cells do not divide using a cell plate. Choice D, none of the above, is incorrect as animal cells do divide through a contractile ring.

Correct Answer: B

Rationale: The correct answer is B: Taxonomy. Taxonomy is the science of classifying organisms based on their physical characteristics and presumed natural relationships. It involves categorizing organisms into different groups to reflect their evolutionary history. Biology (A) is the broader study of living organisms, not specifically focused on classification. Grouping (C) is a generic term and does not encompass the systematic categorization process of taxonomy. Nomenclature (D) refers to the naming of organisms, not their classification based on physical characteristics and relationships.

Correct Answer: B

Rationale: The correct answer is B: heterozygous. In a heterozygous situation, an individual carries two different alleles for a particular gene, resulting in different forms of the allele. This creates genetic diversity and can lead to varying phenotypic expressions. The term phenotype (A) refers to the physical characteristics of an organism, not specifically related to different forms of alleles. Homolog (C) refers to chromosomes that are similar in structure and function but not necessarily different forms of alleles. Homozygous (D) describes a situation where an individual carries two identical alleles for a gene, which does not involve different forms of alleles.