HESI A2 Practice Test Biology

Correct Answer: B

Rationale: The correct answer is B: oxygen. Oxygen is not a product of the Krebs cycle; it is used as the final electron acceptor in the electron transport chain. Carbon dioxide (A) is a product of the Krebs cycle, produced during decarboxylation reactions. Adenosine triphosphate (ATP) (C) and energy carriers (D) such as NADH and FADH2 are also products of the Krebs cycle, as they are generated through the oxidation of substrates. Oxygen's role is crucial for the efficient functioning of aerobic respiration, but it is not a direct product of the Krebs cycle.

Correct Answer: C

Rationale: The correct answer is C: Hydrogen. Water molecules are bonded to each other through hydrogen bonds. In a water molecule, oxygen is more electronegative than hydrogen, creating a partial negative charge on oxygen and a partial positive charge on hydrogen. These opposite charges allow hydrogen bonding to occur between water molecules, where the partially positive hydrogen atom of one molecule is attracted to the partially negative oxygen atom of another molecule. This type of bond is weaker than covalent bonds but crucial for the unique properties of water, such as high surface tension and cohesion. Summary of other choices: A: Ionic - Water molecules do not form ionic bonds with each other. B: Covalent - While water molecules are held together by covalent bonds within the molecule itself, they are not bonded to each other through covalent bonds. D: Molecular - This choice is vague and does not accurately describe the specific type of bonding between water molecules.

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: C

Rationale: The correct answer is C: covalent. In DNA, the bond connecting sugar and phosphate is a covalent bond. This is because covalent bonds involve the sharing of electrons between atoms, which is essential for forming the strong backbone structure of the DNA molecule. Hydrogen bonds (choice A) are important for holding the nitrogenous bases together in the DNA double helix, but they do not connect sugar and phosphate. Ionic bonds (choice B) involve the transfer of electrons between atoms, not sharing, and are not typically found in the structure of DNA. "Overt" (choice D) is not a type of chemical bond and is an incorrect term in this context. Thus, the correct choice is covalent based on the nature of the bond required to connect sugar and phosphate in DNA.

Correct Answer: B

Rationale: The correct answer is B: oxygen. Oxygen is not a product of the Krebs cycle; it is used as the final electron acceptor in the electron transport chain. Carbon dioxide (A) is a product of the Krebs cycle, produced during decarboxylation reactions. Adenosine triphosphate (ATP) (C) and energy carriers (D) such as NADH and FADH2 are also products of the Krebs cycle, as they are generated through the oxidation of substrates. Oxygen's role is crucial for the efficient functioning of aerobic respiration, but it is not a direct product of the Krebs cycle.