HESI A2 Biology Practice Test

Correct Answer: D

Rationale: The correct answer is D because all the choices - the pituitary gland, the thyroid gland, and the adrenal glands - are indeed components of the endocrine system. Each of these glands secretes hormones directly into the bloodstream to regulate various bodily functions. The pituitary gland controls other endocrine glands, the thyroid gland regulates metabolism, and the adrenal glands manage stress responses. Therefore, all of these glands play vital roles in the endocrine system. The other choices (A, B, C) are incorrect because they are all components of the endocrine system.

Correct Answer: A

Rationale: The correct answer is A: A segment of DNA. Genes are segments of DNA that contain the instructions for building proteins and controlling various processes in an organism. DNA is the genetic material that carries hereditary information and is passed down from parents to offspring. Option B is incorrect because genes are not bead-like structures on chromosomes but are located within chromosomes. Option C is incorrect because genes are not protein molecules themselves but may code for proteins. Option D is incorrect because genes are not made up of RNA but rather DNA.

Correct Answer: B

Rationale: Thymine is not present in RNA because thymine is a pyrimidine base found in DNA instead of RNA. RNA contains uracil as its complementary base to adenine, while DNA contains thymine. Adenine, uracil, and cytosine are all present in RNA, making them incorrect choices. Thymine is the only base not present in RNA, making option B the correct answer.

Correct Answer: D

Rationale: The correct answer is D: species. Within the biological hierarchical system, species is the least inclusive category. A species consists of organisms that can interbreed and produce fertile offspring. Moving up the hierarchy, species are grouped into genera, then families, orders, classes, phyla, and finally kingdoms. Phylum (A), order (B), and kingdom (C) are all more inclusive categories than species. Phylum includes multiple classes, order includes multiple families, and kingdom includes multiple phyla. Therefore, species is the least inclusive category within this system.

Correct Answer: C

Rationale: The correct answer is C because plant cells have a rigid cell wall that prevents them from forming a contractile ring during cell division. The cell wall provides structural support, making it challenging for plant cells to constrict and pinch apart like animal cells. This rigidity limits the flexibility needed for the contractile ring to form and function effectively. Plant cells primarily rely on other mechanisms such as cell plate formation for division. Choices A and B are incorrect as they do not address the specific structural difference between plant and animal cells. Choice D is incorrect as it does not provide any relevant information on the topic.