HESI A2 Practice Test Biology

Correct Answer: A

Rationale: The correct answer is A: Carbohydrates, lipids, protein, and nucleic acids. These are considered the most important molecules in biology because they are essential for various biological functions. Carbohydrates provide energy, lipids are important for cell structure and energy storage, proteins are crucial for cell function and structure, and nucleic acids carry genetic information. Choices B, C, and D are incorrect because calcium, sulfur, and iron are important elements in biology but not considered the most important molecules for biological processes.

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: 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: D

Rationale: The correct answer is D: DNA. DNA is not directly involved in translation. Translation is the process of synthesizing proteins from mRNA using tRNA and ribosomes. DNA serves as the template for transcription, where mRNA is synthesized. Once mRNA is formed, it carries the genetic information from DNA to the ribosome for translation. tRNA brings in amino acids based on the codons on the mRNA, and the ribosome facilitates the assembly of amino acids into a polypeptide chain. Therefore, DNA is not directly involved in the actual process of translation, making it the correct answer.

Correct Answer: A

Rationale: The correct answer is A: Phospholipids. Phospholipids are essential components of the plasma membrane due to their amphipathic nature, with hydrophilic heads and hydrophobic tails. This structure allows phospholipids to form a lipid bilayer, creating a barrier that separates the internal and external environments of the cell. Steroids (B) are not a major component of the plasma membrane. Sugars (C) are found in glycoproteins and glycolipids on the membrane surface, but they are not the main structural component. Amino acids (D) are the building blocks of proteins, which can be membrane proteins, but they are not the key structural component of the membrane itself.