HESI A2 Practice Test Biology

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: Ribosome. Ribosomes are responsible for organizing protein synthesis by translating mRNA into protein. They are the cellular machinery where protein synthesis occurs. The nucleus (A) houses the genetic material but does not directly participate in protein synthesis. Lysosomes (C) are responsible for cellular waste digestion, not protein synthesis. Vacuoles (D) are primarily storage organelles and do not play a direct role in organizing protein synthesis. In summary, the ribosome is the correct answer as it is the key organelle directly involved in protein synthesis within the cell.

Correct Answer: B

Rationale: The correct answer is B: Mitochondrion. Mitochondria are known as the powerhouse of the cell due to their role in producing ATP through cellular respiration. This process involves the breakdown of glucose to generate energy in the form of ATP. Mitochondria contain specialized structures such as the inner mitochondrial membrane and ATP synthase that are essential for ATP production. Explanation of why other choices are incorrect: A: Nucleus - The nucleus is responsible for storing genetic material and controlling cell activities but not for ATP production. C: Chloroplast - Chloroplasts are found in plant cells and are responsible for photosynthesis to produce glucose, not ATP. D: Lysosome - Lysosomes are involved in the digestion and recycling of cellular waste, not ATP production.

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: C

Rationale: The correct answer is C: Supply electrons in the light reactions. In photosynthesis, water molecules are split during the light reactions of photosynthesis, releasing electrons that are used to drive the electron transport chain. This process generates ATP and NADPH, which are essential for the synthesis of glucose in the Calvin cycle. Water does not combine with carbon dioxide (A), absorb light energy (B), or transport hydrogen ions in the dark reactions (D) during photosynthesis.