Which of the following statements regarding animal cell membrane is correct ?
- A.They are composed of phospholipids only.
- B.They are composed of proteins only.
- C.They are composed of phospholipids and proteins only.
- D.They are composed of phospholipids, proteins and cholesterol (lipid).
Correct answer
Explanation
The correct answer is D, phospholipids, proteins and cholesterol. The animal cell membrane is a phospholipid bilayer with proteins set in it and cholesterol between the lipid molecules.
The fluid mosaic model of Singer and Nicolson (1972) describes the membrane as a double layer of phospholipids, whose water-loving heads face outward and water-fearing tails face inward. Proteins float in this layer, some passing right through it as channels and carriers. Cholesterol sits among the phospholipid tails and keeps the membrane from becoming too fluid or too stiff as temperature changes; it is characteristic of animal membranes, while plant membranes have related sterols instead. Short carbohydrate chains are attached on the outer surface.
A is wrong because a membrane of phospholipids alone could not carry out transport or signalling.
B is wrong because proteins alone cannot form the bilayer that acts as the barrier.
C is wrong because it leaves out cholesterol, a key component of animal membranes.
Exam tip: fluid mosaic model, Singer and Nicolson 1972; cholesterol keeps animal membranes stable.
Practice Questions
View allWhich one of the following can charge an insulator?
- A.Current electricity
- B.Static electricity
- C.Magnetic field
- D.Gravitational field
Show answer
An insulator is charged by friction: rubbing transfers electrons from one surface to another, and because electrons cannot move through an insulator, the charge stays where it is as static electricity.
Read the full explanation →A glass prism splits white light into different colours. This phenomenon is called dispersion of light by prism. Which one of the following statements is correct?
- A.Red light will deviate the most and it is because of the reflection of light.
- B.Violet light will deviate the most and it is because of the refraction of light.
- C.Red light will deviate the most and it is because of the refraction of light.
- D.Violet light will deviate the most and it is because of the reflection of light.
Show answer
In glass, violet light has the shortest wavelength and the highest refractive index, so it bends the most; dispersion is a result of refraction.
Read the full explanation →A 5 N force is defined when a mass of 10 kg is accelerated with
- A.5.0 cm/s²
- B.0.5 m/s²
- C.0.5 cm/s²
- D.5.0 m/s²
Show answer
By Newton's second law, F = m × a, so a = F ÷ m = 5 N ÷ 10 kg = 0.5 m/s².
Read the full explanation →The breakdown of glucose in cytoplasm results in the formation of
- A.pyruvate and energy
- B.pyruvate and carbon dioxide
- C.pyruvate and oxygen
- D.pyruvate and nitrogen
Show answer
In the cytoplasm, glucose is split by glycolysis into two molecules of pyruvate, releasing a small amount of energy as ATP.
Read the full explanation →Which one of the following is the correct sequence in increasing complexity?
- A.Protein - Organism - Tissue - Organ
- B.Protein - Organ - Tissue - Organism
- C.Protein - Organism - Organ - Tissue
- D.Protein - Tissue - Organ - Organism
Show answer
Living things are built up level by level: molecules such as proteins form cells, cells form tissues, tissues form organs, organs form organ systems, and these together make an organism.
Read the full explanation →