HESI A2 Practice Test Biology

Correct Answer: B

Rationale: The correct answer is B: ATP. ATP (adenosine triphosphate) is the primary molecule responsible for storing and transferring energy in cells through its high-energy phosphate bonds. Glucose (choice A) is a source of energy but not a storage molecule. Fatty acids (choice C) are primarily used for long-term energy storage. Starch (choice D) is a polysaccharide used for energy storage in plants, but ATP is the main energy currency in all cells for immediate use.

Correct Answer: A

Rationale: The correct answer is A: Glycolysis. In the process of converting glucose to pyruvate, the first step is glycolysis. This is where glucose is broken down into two molecules of pyruvate, generating ATP and NADH. Glycolysis occurs in the cytoplasm and does not require oxygen. The Krebs cycle (B) occurs in the mitochondria and follows glycolysis, while the electron transport chain (C) and aerobic respiration (D) require oxygen and take place after glycolysis. Therefore, the correct first step in the conversion of glucose to pyruvate is glycolysis.

Correct Answer: D

Rationale: The correct answer is D: gradient. A concentration gradient is necessary for cell diffusion to occur, as it drives the movement of particles from an area of higher concentration to an area of lower concentration. This process does not require ATP (choice C) as it is a passive transport mechanism. While water (choice A) is essential for life and plays a role in cell diffusion, it is not the sole requirement. The presence of a membrane (choice B) is important for regulating the diffusion process but is not the direct driving force behind it. Therefore, the concentration gradient is the critical factor necessary for cell diffusion to take place.

Correct Answer: A

Rationale: The second part of an organism's scientific name is the species. In binomial nomenclature, developed by Carl Linnaeus, the scientific name consists of two parts: the genus and the species. The genus is the broader category that encompasses multiple species, while the species is the specific name unique to that particular organism within the genus. Therefore, the correct answer is A: species. Option B: phylum is incorrect as it is a higher taxonomic rank above the genus and species. Option C: population is incorrect as it refers to a group of organisms of the same species in a particular area. Option D: kingdom is incorrect as it is the highest taxonomic rank, encompassing all living organisms categorized into five kingdoms.

Correct Answer: C

Rationale: The correct answer is C: Selectively permeable. The phospholipid bilayer of the cell membrane allows the passage of certain molecules while restricting others based on their size, charge, and solubility. This selective permeability enables the cell to regulate the movement of substances in and out, maintaining homeostasis. Option A is incorrect because the cell membrane is not impermeable; it allows some substances to pass through. Option B is incorrect as it suggests all molecules can freely pass through, which is not the case. Option D is incorrect as it contradicts itself by combining selective and impermeable, which is not a characteristic of the cell membrane.