Plasma Membrane Practice Questions
20 free Plasma Membrane practice questions for the NCERT Biology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
The detailed structure of the cell membrane was studied only after the advent of the electron microscope in the:
- A 1950s
- B 1930s
- C 1970s
- D 1990s
Correct answer: 1950s
Significant progress in understanding membrane structure was made in the 1950s following the development of the electron microscope. This allowed scientists to observe the bilayer arrangement that was previously only hypothesized.
The cell membrane is mainly composed of which two primary organic molecules?
- A Lipids and Proteins
- B Carbohydrates and Nucleic acids
- C Proteins and ATP
- D Lipids and Cellulose
Correct answer: Lipids and Proteins
Chemical studies, especially on human red blood cells, enabled scientists to deduce that the plasma membrane is primarily composed of lipids and proteins. Carbohydrates are also present but in smaller proportions.
In the lipid bilayer of the plasma membrane, the lipids are arranged with their:
- A Polar heads towards the inner side and hydrophobic tails towards the outside
- B Polar heads towards the outer side and hydrophobic tails towards the inside
- C Both heads and tails towards the outside
- D Both heads and tails towards the inside
Correct answer: Polar heads towards the outer side and hydrophobic tails towards the inside
The amphipathic lipids arrange themselves so that the hydrophilic polar heads face the aqueous environment on both sides. The hydrophobic hydrocarbon tails are protected in the interior of the membrane.
The lipid component of the membrane mainly consists of:
- A Triglycerides only
- B Phosphoglycerides
- C Cholesterol only
- D Glycolipids only
Correct answer: Phosphoglycerides
The most abundant lipids in the cell membrane are phospholipids, specifically phosphoglycerides. These molecules provide the basic fluid structure of the membrane.
According to the biochemical investigation of the human erythrocyte membrane, the percentage of protein and lipid is approximately:
- A 40% protein and 60% lipid
- B 52% protein and 40% lipid
- C 20% protein and 80% lipid
- D 70% protein and 30% lipid
Correct answer: 52% protein and 40% lipid
In human red blood cells, the membrane has approximately 52 percent protein and 40 percent lipids. The ratio of protein to lipid varies considerably in different cell types.
Membrane proteins are classified as peripheral or integral based on their:
- A Size and weight
- B Ease of extraction
- C Color under the microscope
- D Function in the cell
Correct answer: Ease of extraction
Peripheral proteins lie on the surface of the membrane and are easily removed. Integral proteins are partially or totally buried in the membrane and require detergents for extraction.
The widely accepted 'Fluid Mosaic Model' of the cell membrane was proposed by:
- A Schleiden and Schwann
- B Singer and Nicolson
- C Watson and Crick
- D Robert Brown
Correct answer: Singer and Nicolson
In 1972, S.J. Singer and G.L. Nicolson proposed the fluid mosaic model. This model describes the membrane as a quasi-fluid structure where proteins float in a mosaic of lipids.
The 'quasi-fluid nature' of lipids in the membrane enables:
- A Rigidity of the cell
- B Lateral movement of proteins within the bilayer
- C Permanent attachment of all proteins to the bilayer
- D Complete impermeability to water
Correct answer: Lateral movement of proteins within the bilayer
The lipid bilayer behaves as a two-dimensional fluid, so phospholipids and most embedded proteins diffuse sideways within the plane of the membrane instead of being locked in place. That lateral mobility is what allows receptors to cluster, transporters to redistribute and membranes to fuse during vesicle traffic, and it is why the structure is described by the fluid mosaic model rather than as a rigid sheet.
The fluid nature of the membrane is important from the point of view of functions such as:
- A DNA replication, repair, and transcription
- B Protein synthesis and folding
- C Energy production, cellular storage, and ATP synthesis
- D Cell growth, secretion, endocytosis, and division
Correct answer: Cell growth, secretion, endocytosis, and division
Membrane fluidity allows lipids and proteins to rearrange dynamically, which is essential for cell growth, secretion of substances, endocytosis (engulfing materials), and the physical separation of cells during division. A rigid, non-fluid membrane could not support these dynamic, shape-changing processes.
One of the most important functions of the plasma membrane is the transport of molecules. It is described as:
- A Impermeable
- B Freely permeable
- C Selectively permeable
- D Semi-permeable only to water
Correct answer: Selectively permeable
The membrane is selectively permeable because it allows only certain molecules to pass through while restricting others. This allows the cell to maintain a specific internal environment.
Movement of neutral solutes across the membrane along the concentration gradient without the requirement of energy is called:
- A Active transport
- B Endocytosis
- C Osmosis
- D Simple diffusion
Correct answer: Simple diffusion
Simple diffusion is a form of passive transport where molecules move from higher concentration to lower concentration. No metabolic energy (ATP) is consumed during this process.
The movement of water by diffusion across a selectively permeable membrane is specifically called:
- A Active transport
- B Facilitated diffusion
- C Osmotic process
- D Pinocytosis
Correct answer: Osmotic process
Osmosis is the passive movement of water molecules from a region of high water concentration to a region of low water concentration. It is a critical process for maintaining cell turgor.
Polar molecules cannot pass through the non-polar lipid bilayer easily. They require _______ to facilitate their transport.
- A ATP only
- B Cholesterol
- C Carbohydrate chains
- D Carrier proteins
Correct answer: Carrier proteins
Because the interior of the membrane is hydrophobic, polar or hydrophilic molecules require specific membrane carrier proteins to cross. This process is known as facilitated diffusion.
Which of the following is an example of active transport across the cell membrane?
- A Movement of oxygen into the cell
- B Movement of water via osmosis
- C Sodium-Potassium pump using ATP
- D Diffusion of glucose along the gradient
Correct answer: Sodium-Potassium pump using ATP
The Sodium-Potassium pump uses ATP to move ions against their concentration gradients. This is a classic example of active transport, which is essential for maintaining nerve and muscle function.
Active transport is characterized by the movement of molecules:
- A From higher to lower concentration using energy
- B From higher to lower concentration without energy
- C From lower to higher concentration without energy
- D From lower to higher concentration using energy
Correct answer: From lower to higher concentration using energy
Active transport requires the expenditure of ATP because it moves substances 'uphill' against their concentration gradient. This is often performed by specific pumps in the membrane.
Cholesterol is found in the plasma membrane and serves to:
- A Act as a specific catalytic membrane enzyme
- B Transport ions across the membrane
- C Store genetic information
- D Provide stability and regulate fluidity
Correct answer: Provide stability and regulate fluidity
Cholesterol molecules are tucked between the phospholipids in animal cell membranes. They help maintain the structural integrity of the membrane and keep it from becoming too fluid or too rigid.
The 'mosaic' part of the fluid mosaic model refers to the:
- A Continuous layer of lipids
- B Arrangement of the water molecules
- C Presence of the cell wall
- D Random distribution of proteins
Correct answer: Random distribution of proteins
The term 'mosaic' refers to the various proteins that are embedded in or attached to the phospholipid bilayer. These proteins are distributed somewhat like tiles in a mosaic pattern.
The tail of the phospholipid molecule is:
- A Hydrophilic and composed only of fully saturated hydrocarbons
- B Polar and attracted to water
- C Hydrophobic, made of saturated or unsaturated hydrocarbons
- D Always found on the outer surface of the membrane
Correct answer: Hydrophobic, made of saturated or unsaturated hydrocarbons
The fatty acid tails are hydrophobic (water-fearing) and avoid contact with water by pointing toward the center of the bilayer. This ensures that the aqueous environments of the cell are separated.
Which component of the membrane is often involved in cell-to-cell recognition?
- A Phospholipids
- B Integral membrane proteins only
- C Glycoproteins and glycolipids
- D Cholesterol
Correct answer: Glycoproteins and glycolipids
Short chains of sugars (carbohydrates) often attach to proteins (glycoproteins) or lipids (glycolipids) on the outer surface. These act as molecular 'ID tags' for cell recognition and signaling.
The membrane fluidity can be increased by increasing the proportion of:
- A Unsaturated fatty acids in lipids
- B Saturated fatty acids only in lipids
- C Integral proteins
- D Peripheral proteins
Correct answer: Unsaturated fatty acids in lipids
Unsaturated fatty acids have 'kinks' in their tails that prevent them from packing tightly together. This increases the space between molecules, making the membrane more fluid.