The protoplasm of all cells is surrounded by one living cell membrane. It is also called plasma membrane or plasmalemma.
It was discovered by Swedish Botanist Carl Nagcli and C. Cramer in 1855.
J.Q. Plowe (1931) Give the name – Plasmalema.
Robertson – Unit Membrane
It is part of cytoplasm.
molecules of cytoplasm organized in a special pattern at the outer surface of cytoplasm form plasma membranes.
General Characters of Plasma membrane
It is 60A⁰ to 105A⁰ thick.
It is made up of Lipid and protein.
The lipid layer is bipolar, its internal part is called tail and outer part is called head. The tail is hydrophobic and the head is a hydrophilic part of the lipid.
The outer protein of plasma membrane can be easily removed but inner protein can not be removed.
It can be synthesized artificially.
It controls the molecule from outside of the cell.
It maintains ionic concentration inside and outside the cell. Thus it controls interaction among different cells.
It receives signals from outer environment and acts as communicator
In plants plasma membrane lies in between the cell wall and cytoplasm whereas in animal cells it is the outermost covering of the cell.
MCQs on Plasma Membrane with Answers and PYQs
1-10: Discovery and Structure of Plasma Membrane
Who first observed the plasma membrane?(NEET 2015) a) Robert Hooke b) Carl Nägeli and C. Cramer c) Robert Brown d) Overton Ans: (b) Carl Nägeli and C. Cramer
Who coined the term “Plasmalemma”?(CSIR-NET 2017) a) Overton b) J.Q. Plowe c) Singer and Nicolson d) Gorter and Grendel Ans: (b) J.Q. Plowe
Which scientist proposed the “Unit Membrane Model”?(GATE 2016) a) Robertson b) Overton c) Danielli and Davson d) Singer and Nicolson Ans: (a) Robertson
Which of the following is NOT a major component of the plasma membrane?(NEET 2019) a) Phospholipids b) Proteins c) Nucleic acids d) Carbohydrates Ans: (c) Nucleic acids
What is the approximate thickness of the plasma membrane?(CSIR-NET 2018) a) 5-10 Å b) 60-105 Å c) 500 Å d) 1000 Å Ans: (b) 60-105 Å
Which model best describes the plasma membrane?(NEET 2021) a) Sandwich Model b) Fluid Mosaic Model c) Unit Membrane Model d) Lipid Bilayer Model Ans: (b) Fluid Mosaic Model
Which scientist proposed the Fluid Mosaic Model?(CSIR-NET 2019) a) Robertson b) Singer and Nicolson c) Gorter and Grendel d) Danielli and Davson Ans: (b) Singer and Nicolson
What is the main function of cholesterol in the plasma membrane?(NEET 2022) a) Provides rigidity and stability b) Transports ions c) Acts as a receptor d) Forms channels Ans: (a) Provides rigidity and stability
What is the nature of the lipid bilayer in the plasma membrane?(GATE 2017) a) Hydrophilic b) Hydrophobic c) Amphipathic d) Non-polar Ans: (c) Amphipathic
Which of the following is a characteristic of integral proteins?(CSIR-NET 2020) a) Loosely attached to the membrane b) Can be removed easily c) Span the entire membrane d) Present only on the inner surface Ans: (c) Span the entire membrane
11-20: Transport Mechanisms
Which type of transport does NOT require ATP?(NEET 2018) a) Active transport b) Endocytosis c) Facilitated diffusion d) Exocytosis Ans: (c) Facilitated diffusion
Which process moves substances against a concentration gradient?(CSIR-NET 2019) a) Diffusion b) Osmosis c) Active transport d) Facilitated diffusion Ans: (c) Active transport
Which of the following is an example of passive transport?(GATE 2018) a) Sodium-potassium pump b) Phagocytosis c) Diffusion d) Exocytosis Ans: (c) Diffusion
Which protein helps in facilitated diffusion?(NEET 2020) a) Carrier protein b) DNA polymerase c) RNA polymerase d) Ribosome Ans: (a) Carrier protein
What is the movement of water across a semi-permeable membrane called?(NEET 2016) a) Diffusion b) Active transport c) Osmosis d) Endocytosis Ans: (c) Osmosis
Which ion pump is most commonly found in animal cells?(CSIR-NET 2022) a) Calcium pump b) Sodium-potassium pump c) Proton pump d) Chloride pump Ans: (b) Sodium-potassium pump
Endocytosis is the process by which cells(NEET 2019) a) Expel waste materials b) Take in external substances c) Transport ions across membranes d) Generate ATP Ans: (b) Take in external substances
What is exocytosis?(GATE 2021) a) The intake of large particles b) The breakdown of ATP c) The release of substances outside the cell d) The conversion of glucose to energy Ans: (c) The release of substances outside the cell
Which molecule can easily pass through the plasma membrane?(CSIR-NET 2017) a) Glucose b) Sodium ions c) Oxygen d) Proteins Ans: (c) Oxygen
Which transport mechanism requires ATP?(NEET 2022) a) Osmosis b) Facilitated diffusion c) Active transport d) Simple diffusion Ans: (c) Active transport
21-30: Membrane Proteins and Functions
Peripheral proteins in the plasma membrane are(NEET 2020) a) Embedded within the lipid bilayer b) Loosely attached to the surface c) Involved in lipid synthesis d) None of the above Ans: (b) Loosely attached to the surface
What is the function of glycoproteins in the plasma membrane?(CSIR-NET 2018) a) Transport molecules b) Act as receptors c) Provide structural support d) None of these Ans: (b) Act as receptors
Which type of protein extends through the entire plasma membrane?(GATE 2019) a) Peripheral proteins b) Integral proteins c) Carrier proteins d) Receptor proteins Ans: (b) Integral proteins
Which of the following statements about membrane proteins is FALSE?(NEET 2021) a) They help in transport of substances b) They can act as enzymes c) They are only present on the outer surface d) Some act as receptors Ans: (c) They are only present on the outer surface
Which of the following is NOT a function of the plasma membrane?(CSIR-NET 2016) a) Selective permeability b) ATP production c) Cell signaling d) Structural support Ans: (b) ATP production
Which enzyme is involved in the sodium-potassium pump?(GATE 2022) a) ATP synthase b) Na⁺/K⁺ ATPase c) Catalase d) DNA polymerase Ans: (b) Na⁺/K⁺ ATPase
Which structure in the plasma membrane is responsible for cell recognition?(NEET 2017) a) Phospholipids b) Cholesterol c) Glycoproteins d) Integral proteins Ans: (c) Glycoproteins
What role do cholesterol molecules play in animal cell membranes?(CSIR-NET 2015) a) Provide energy b) Maintain fluidity c) Act as receptors d) Assist in protein synthesis Ans: (b) Maintain fluidity
Which of the following acts as a cell-to-cell recognition site?(GATE 2020) a) Phospholipids b) Glycoproteins c) Channel proteins d) Cholesterol Ans: (b) Glycoproteins
What type of protein is mainly responsible for transport across the plasma membrane?(NEET 2018) a) Receptor proteins b) Channel proteins c) Structural proteins d) Peripheral proteins Ans: (b) Channel proteins
31-40: Membrane Fluidity and Cell Signaling
Membrane fluidity increases with(CSIR-NET 2020) a) Increased cholesterol content b) Increased saturation of fatty acids c) Increased temperature d) Decreased temperature Ans: (c) Increased temperature
Which type of molecules can easily pass through the plasma membrane?(NEET 2019) a) Large uncharged molecules b) Small nonpolar molecules c) Charged ions d) Proteins Ans: (b) Small nonpolar molecules
The fluidity of the plasma membrane is maintained by(CSIR-NET 2018) a) Saturated fatty acids b) Cholesterol c) Integral proteins d) ATP molecules Ans: (b) Cholesterol
Which type of transport does not require a carrier protein?(GATE 2017) a) Facilitated diffusion b) Active transport c) Simple diffusion d) Endocytosis Ans: (c) Simple diffusion
Which organelle is responsible for modifying and packaging plasma membrane proteins?(NEET 2016) a) Mitochondria b) Golgi apparatus c) Lysosome d) Ribosome Ans: (b) Golgi apparatus
Which of the following best describes exocytosis?(CSIR-NET 2019) a) Movement of ions across the membrane b) Transport of large molecules outside the cell c) Diffusion of gases through the membrane d) Endocytosis of liquids Ans: (b) Transport of large molecules outside the cell
Which of the following is an example of cell signaling?(NEET 2021) a) Active transport b) Hormone binding to a receptor c) Protein synthesis d) Osmosis Ans: (b) Hormone binding to a receptor
G-protein coupled receptors (GPCRs) are involved in(GATE 2022) a) Passive diffusion b) Signal transduction c) DNA replication d) Endocytosis Ans: (b) Signal transduction
Which component of the plasma membrane helps in the recognition of pathogens?(CSIR-NET 2017) a) Cholesterol b) Glycoproteins c) Phospholipids d) Lipid rafts Ans: (b) Glycoproteins
Which molecule is primarily responsible for the semi-permeability of the plasma membrane?(NEET 2020) a) Proteins b) Carbohydrates c) Phospholipids d) Cholesterol Ans: (c) Phospholipids
41-50: Advanced Concepts & Applications
The plasma membrane is most permeable to(CSIR-NET 2021) a) Ions b) Large proteins c) Small lipophilic molecules d) Polysaccharides Ans: (c) Small lipophilic molecules
What is the main function of tight junctions?(NEET 2017) a) Transport of molecules b) Connecting adjacent cells c) Allowing ion exchange d) Providing mechanical strength Ans: (b) Connecting adjacent cells
Lipid rafts are enriched with(CSIR-NET 2018) a) Phospholipids b) Cholesterol and sphingolipids c) Integral proteins d) Nucleotides Ans: (b) Cholesterol and sphingolipids
Which of the following molecules require ATP for transport?(GATE 2021) a) Oxygen b) Water c) Sodium ions d) Carbon dioxide Ans: (c) Sodium ions
Which type of transport allows large molecules to enter the cell?(NEET 2022) a) Passive diffusion b) Facilitated diffusion c) Endocytosis d) Osmosis Ans: (c) Endocytosis
The plasma membrane is best described as(CSIR-NET 2016) a) Rigid b) Selectively permeable c) Impermeable d) Static Ans: (b) Selectively permeable
Which macromolecule plays a key role in plasma membrane recognition?(NEET 2019) a) Lipids b) Carbohydrates c) Proteins d) RNA Ans: (b) Carbohydrates
Which of the following processes decreases membrane fluidity?(GATE 2018) a) Increased temperature b) Increased cholesterol c) Increased unsaturated fatty acids d) Presence of peripheral proteins Ans: (b) Increased cholesterol
The main structural component of the plasma membrane is(NEET 2020) a) DNA b) RNA c) Phospholipids d) ATP Ans: (c) Phospholipids
Which scientist proposed the phospholipid bilayer model?(CSIR-NET 2015) a) Gorter and Grendel b) Singer and Nicolson c) Robertson d) Overton Ans: (a) Gorter and Grendel
