what function does cholesterol a phospholipid serve within the cell membrane

HESI RN

Biology Practice Test

1. What function does cholesterol, a phospholipid, serve within the cell membrane?

A. It builds up fats to make the structure more flexible
B. It allows protein channels to form
C. It makes the structure very rigid and impermeable
D. It stabilizes the membrane structure

Correct answer: D

Rationale: Cholesterol helps to maintain the fluidity and stability of the cell membrane by fitting between the phospholipid molecules. Choice A is incorrect because cholesterol does not build up fats in the cell membrane. Choice B is incorrect as protein channels are formed by proteins, not cholesterol. Choice C is incorrect as cholesterol actually helps regulate the fluidity of the membrane, making it less rigid and more permeable.

2. DNA and RNA are both subunits of which biological molecule?

A. Nucleic acids
B. Proteins
C. Carbohydrates
D. Lipids

Correct answer: A

Rationale: The correct answer is A: Nucleic acids. DNA and RNA are both types of nucleic acids, which are fundamental biological molecules responsible for storing and transmitting genetic information. Choice B, Proteins, are not subunits of DNA and RNA but are composed of amino acids. Carbohydrates, choice C, are another type of biological molecule involved in energy storage and structural support, not subunits of DNA and RNA. Lipids, choice D, are a diverse group of molecules that include fats, oils, and steroids, but they are not subunits of DNA and RNA.

3. Which organelle has the ability to hydrolyze fats, nucleic acids, proteins, and sugars?

A. Chloroplasts
B. Mitochondria
C. Lysosomes
D. Ribosomes

Correct answer: C

Rationale: The correct answer is C, Lysosomes. Lysosomes contain hydrolytic enzymes that are capable of breaking down various biomolecules such as fats, nucleic acids, proteins, and sugars. This organelle acts as the 'digestive system' of the cell. Choices A, B, and D are incorrect because chloroplasts are involved in photosynthesis, mitochondria are responsible for energy production, and ribosomes are responsible for protein synthesis, not the hydrolysis of biomolecules.

4. Why does ice have the capability of floating on water?

A. It has a higher viscosity
B. It has a different chemical composition
C. It has a high specific heat
D. It forms a lattice when freezing

Correct answer: D

Rationale: The correct answer is D. Ice forms a lattice structure when it freezes, which makes it less dense than liquid water, allowing it to float. Choice A is incorrect because viscosity refers to a fluid's resistance to flow and is not related to ice floating. Choice B is incorrect as ice and liquid water have the same chemical composition (H2O). Choice C is incorrect because the high specific heat of water is not the reason why ice floats.

5. Which of the following is a lipid that is a membrane component and a precursor to significant hormones?

A. Nucleic acids
B. Proteins
C. Carbohydrates
D. Steroids

Correct answer: D

Rationale: The correct answer is D, Steroids. Steroids are a type of lipid that function as essential components of cell membranes and serve as precursors for significant hormones like estrogen and testosterone. Nucleic acids (choice A) are not lipids but are molecules like DNA and RNA that store genetic information. Proteins (choice B) and carbohydrates (choice C) are biomolecules but are not lipids and do not serve as precursors for hormones or membrane components.