HESI A2 Biology Practice Test

Correct Answer: D

Rationale: The correct answer is D because in DNA, adenine (A) always pairs with thymine (T), forming two hydrogen bonds. This is known as complementary base pairing, essential for DNA replication and maintenance. Options A, B, and C are incorrect as they do not demonstrate the complementary base pairing rule observed in DNA. Option A (A and G) is incorrect because adenine pairs with thymine, not guanine. Option B (A and C) is incorrect because adenine pairs with thymine, not cytosine. Option C (A and A) is incorrect because in DNA, adenine always pairs with thymine, not with itself.

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: Bacteria. Eukaryotic cells have a defined nucleus and membrane-bound organelles, which bacteria lack. Dogs, humans, and onions are all multicellular organisms that possess eukaryotic cells. Bacteria, being prokaryotic, do not have a distinct nucleus or membrane-bound organelles, leading to the conclusion that they do not have eukaryotic cells.

Correct Answer: D

Rationale: Failed to generate a rationale after 5 retries.

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.