HESI A2 Practice Test Biology

Correct Answer: A

Rationale: The correct answer is A: Mitochondrion and chloroplast. Mitochondria are known as the powerhouse of the cell, producing energy in the form of ATP through cellular respiration. Chloroplasts are responsible for photosynthesis in plant cells, converting sunlight into energy. Nucleus is not involved in energy production but contains genetic material. Lysosomes are involved in digestion and waste removal, not energy production. Therefore, A is correct as both mitochondria and chloroplasts play crucial roles in generating cell energy.

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: B

Rationale: The correct answer is B: Cell membrane. The cell membrane is a selectively permeable barrier that protects the cell, regulates communication with the external environment, and allows substances to enter and exit the cell. It is composed of a phospholipid bilayer with embedded proteins that facilitate transport and signaling. The other choices are incorrect because: A: Nucleus - The nucleus houses the cell's genetic material and is responsible for controlling cell activities, but it does not directly contribute to protection or substance passage. C: Endoplasmic reticulum - The ER is involved in protein synthesis and lipid metabolism, but it does not have a primary role in protection or communication. D: Cytoplasm - The cytoplasm is the fluid-filled region of the cell where organelles are suspended, but it does not play a direct role in protection or communication at the cell's boundary.

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: During the S phase of the cell cycle, chromosomes are duplicated. This process involves the replication of DNA to ensure that each daughter cell receives an identical copy of the genetic material. This is crucial for cell division and passing on genetic information accurately. Cell growth occurs in the G1 phase, DNA synthesis occurs in the S phase, and DNA destruction does not occur during any phase of the cell cycle. Therefore, the correct answer is A because it specifically describes the key event that occurs during the S phase.