Cell Membrane Wall

8 MCQs9-step worked example

Source: NCERT Cell: Structure and FunctionPYQ coverage: NEET 2023, 2025Official key: NTA-verifiedLast updated: 25 Sep 2026

Cell Membrane Wall, explained for NEET

NEET setters swap "integral" and "peripheral" membrane proteins because both sound like vague descriptors rather than a precise rule. The rule is ease of extraction: peripheral proteins sit on the membrane surface; integral proteins are partially or totally buried in it (NCERT Class 11 Biology, Chapter 8, page 93). In the human red blood cell, the membrane is roughly 52% protein and 40% lipid — protein-rich, not lipid-dominated as students sometimes assume.

Singer and Nicolson's 1972 fluid mosaic model explains why: the quasi-fluid lipid bilayer lets proteins move laterally within it, so the membrane is a fluid "mosaic" of embedded proteins rather than a static wall (NCERT, page 94). That fluidity underlies membrane transport, and this is where the second common trap sits: direction. Passive transport — simple diffusion of neutral solutes, and osmosis of water — always runs from higher to lower concentration, needs no energy. Active transport runs the other way, from lower to higher concentration, and always costs ATP (e.g., the Na+/K+ pump). A NEET distractor that labels osmosis "active" because water is "moving somewhere" is testing whether you check direction and energy cost, not just recognise the word "transport."

The cell wall carries its own swap trap. Algae wall composition is cellulose, galactans, mannans, and calcium carbonate — a different list from other plants, whose wall is cellulose, hemicellulose, pectins, and proteins (NCERT, page 94). A young cell's primary wall can still grow; that capacity fades as the cell matures and a secondary wall forms on the inner, membrane-facing side, while the calcium-pectate middle lamella glues neighbouring cells together.

Watch out: "integral vs peripheral" is decided by extraction difficulty, not by size or charge; "passive vs active" is decided by direction and ATP use, not by whether something moves; and algal wall composition is never the general-plant list.

Can you answer these Cell Membrane Wall MCQs?

Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.

MCQ 1Easy RecallPractice

The fluid mosaic model of the plasma membrane, which describes lateral movement of proteins within the lipid bilayer, was proposed by which scientists?

Show answer and why every option is right or wrong

Answer: B. Singer and Nicolson proposed the fluid mosaic model in 1972, describing the quasi-fluid lipid bilayer that permits lateral protein movement (NCERT Class 11 Biology, Chapter 8, page 94).

Why A is wrong: A is wrong because Watson and Crick proposed the DNA double-helix structure, not the membrane model.

Why C is wrong: C is wrong because Schleiden and Schwann formulated cell theory, not the membrane model.

Why D is wrong: D is wrong because Robert Hooke coined the term 'cell' after observing cork; he did not propose a membrane model.

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MCQ 2Easy RecallPractice

In the human erythrocyte, the plasma membrane's approximate protein and lipid content is:

Show answer and why every option is right or wrong

Answer: A. NCERT states the human erythrocyte membrane has approximately 52% protein and 40% lipid (Class 11 Biology, Chapter 8, page 93).

Why B is wrong: B is wrong because it inverts the NCERT figures — lipid content is 40%, not 52%.

Why C is wrong: C is wrong because 70/30 is not the NCERT-stated ratio for the erythrocyte membrane.

Why D is wrong: D is wrong because 30/70 also inverts and overstates the lipid share against the NCERT figure.

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MCQ 3Easy RecallPractice

Membrane proteins are classified as integral or peripheral based on which criterion, per NCERT?

Show answer and why every option is right or wrong

Answer: C. NCERT classifies membrane proteins as integral or peripheral "depending on the ease of extraction" (Class 11 Biology, Chapter 8, page 93).

Why A is wrong: A is wrong because molecular weight is not the stated classification basis — a heavy protein can still be peripheral.

Why B is wrong: B is wrong because a carbohydrate side chain marks a glycoprotein, a separate classification from integral/peripheral.

Why D is wrong: D is wrong because electric charge is not the criterion NCERT gives for this classification.

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MCQ 4Direct ApplicationPractice

A membrane protein is found partially buried within the phospholipid bilayer, requiring the bilayer to be disrupted before it can be extracted. Based on ease of extraction, this protein is:

Show answer and why every option is right or wrong

Answer: D. NCERT states integral proteins are "partially or totally buried in the membrane," matching a protein that needs the bilayer disrupted for extraction (Class 11 Biology, Chapter 8, page 93).

Why A is wrong: A is wrong because it reverses the rule: peripheral proteins lie on the surface, not buried within the bilayer — the swap trap this question tests.

Why B is wrong: B is wrong because cholesterol is a lipid component of the membrane, not a protein.

Why C is wrong: C is wrong because phospholipids are the bilayer's structural lipid, not the protein being classified here.

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MCQ 5Direct ApplicationPractice

Which statement correctly describes active transport across the plasma membrane, as in the Na+/K+ pump?

Show answer and why every option is right or wrong

Answer: A. NCERT defines active transport as movement of ions/molecules from lower to higher concentration, an energy-dependent process using ATP, exemplified by the Na+/K+ pump (Class 11 Biology, Chapter 8, page 94).

Why B is wrong: B is wrong because it describes passive transport (simple diffusion), which needs no energy and moves the opposite direction to active transport.

Why C is wrong: C is wrong because this describes osmosis, a passive process, not the energy-dependent active transport the stem asks about.

Why D is wrong: D is wrong because this describes simple diffusion of neutral solutes along the gradient, not active transport against it.

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MCQ 6Concept TrapPractice

A student observes water crossing a cell's plasma membrane from a region of higher water concentration to lower water concentration, with no ATP consumed. Which classification correctly fits this observation?

Show answer and why every option is right or wrong

Answer: C. NCERT names movement of water by diffusion, from higher to lower concentration, osmosis — a passive process (Class 11 Biology, Chapter 8, page 94); the stem's "no ATP consumed" detail confirms it.

Why A is wrong: A is wrong because it labels a passive, no-ATP process as active — the direction-and-energy trap NEET setters use for osmosis.

Why B is wrong: B is wrong because water is a neutral molecule undergoing simple diffusion (osmosis), not a charged ion needing a carrier.

Why D is wrong: D is wrong because active transport is defined by NCERT as always ATP-dependent; 'active but no ATP' contradicts the definition itself.

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MCQ 7Direct ApplicationPractice

Which list correctly gives the composition of the algal cell wall, as distinct from the cell wall of other plants?

Show answer and why every option is right or wrong

Answer: B. NCERT states algal cell walls are made of cellulose, galactans, mannans and minerals like calcium carbonate (Class 11 Biology, Chapter 8, page 94).

Why A is wrong: A is wrong because this is the composition NCERT gives for the cell wall of OTHER plants, not algae — the exact list-swap this question tests.

Why C is wrong: C is wrong because chitin, glucan and mannoproteins are not the algal wall composition NCERT states on this page.

Why D is wrong: D is wrong because peptidoglycan and teichoic acid are not part of the NCERT algal wall list here.

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MCQ 8CalculationPractice

A young plant cell's primary wall is capable of growth. As the cell matures, which sequence of events does NCERT describe?

Show answer and why every option is right or wrong

Answer: D. NCERT states the primary wall is capable of growth in a young cell, and this capacity "gradually diminishes as the cell matures," while the secondary wall forms "on the inner (towards membrane) side" (Class 11 Biology, Chapter 8, page 94).

Why A is wrong: A is wrong because it reverses the sequence: the primary wall exists and grows first, before any secondary wall forms.

Why B is wrong: B is wrong because NCERT describes the middle lamella as the calcium-pectate layer holding neighbouring cells together, not a layer that dissolves away.

Why C is wrong: C is wrong because the primary wall's growth capacity diminishes with maturity as the secondary wall forms — it does not thicken forever unchecked.

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How do you solve a Cell Membrane Wall question? A worked example

1
Given
The human erythrocyte plasma membrane is approximately 52% protein and 40% lipid (NCERT Class 11 Biology, Chapter 8, page 93). This membrane must both let water cross to balance osmotic pressure and keep Na+ and K+ ion concentrations unequal across itself.
2
Required
Explain why the erythrocyte membrane relies on passive osmosis for water balance while its Na+/K+ pump actively maintains ion gradients against the concentration gradient — despite being the same protein-rich membrane.
3
Concept
NCERT's transport rule is defined by direction and energy, not by the molecule involved: passive transport (simple diffusion of neutral solutes, and osmosis of water) always runs from higher to lower concentration and needs no ATP; active transport always runs from lower to higher concentration and always needs ATP (Class 11 Biology, Chapter 8, page 94).
4
Formula
No numeric formula applies; the governing rule is qualitative: direction of movement (high→low = passive; low→high = active) plus energy requirement (no ATP = passive; ATP = active) together fix the classification.
5
Substitution
Apply the rule to water: water moves from the side of higher water concentration to lower, so it is classified as osmosis — passive, no ATP needed. Apply the same rule to Na+/K+: the pump moves these ions from lower to higher concentration on each side, which the direction rule alone classifies as active.
6
Calculation
There is no arithmetic here — the "calculation" is applying the direction-plus-energy test to each case separately, since the membrane's high protein content (52%) does not by itself decide which transport type applies; the Na+/K+ pump is one specific integral protein among that 52%, while water crosses independently of any single carrier.
7
Final answer
The erythrocyte membrane uses osmosis for water because water moves down its own concentration gradient — no energy is needed regardless of how protein-rich the membrane is. It uses the ATP-dependent Na+/K+ pump for ions because maintaining unequal Na+/K+ concentrations means moving ions against their gradient, which the direction rule always classifies as active transport.
8
Common trap
Students see "protein-rich membrane" and "pump" together and assume all membrane transport in that cell must be active. The membrane's protein content sets which carrier proteins exist; it does not decide whether a given crossing is passive or active — direction and ATP use decide that, transport by transport (the trap tested in MCQ 5 and MCQ 6).
9
Similar NEET-style question
A plant root-hair cell absorbs water from soil (higher water concentration outside) while separately pumping K+ ions from the soil solution (lower K+ concentration outside) into the cell against the gradient. Classify each process. (Answer: water uptake is osmosis — water moves from higher to lower concentration, so it is passive and needs no ATP; K+ uptake against its gradient — from lower outside concentration to higher inside concentration — is active transport and requires ATP, by the same direction-plus-energy rule applied in Step 5.)

What to remember before solving Cell Membrane Wall questions

Definition

Fluid mosaic model

An improved model of the cell membrane structure was proposed by Singer and Nicolson (1972), widely accepted as the fluid mosaic model. According to this model, the quasi-fluid nature of the lipid enables lateral movement of proteins within the overall bilayer, and this ability to move within the membrane is measured as its fluidity. The fluid nature of the membrane is also important for functions such as cell growth, formation of intercellular junctions, secretion, endocytosis and cell division.

-- NCERT Class 11 Biology, Ch. 8, p. 94

Definition

Cell wall structure and composition

A non-living rigid structure called the cell wall forms an outer covering for the plasma membrane of fungi and plants. The cell wall gives shape to the cell, protects it from mechanical damage and infection, helps in cell-to-cell interaction, and provides a barrier to undesirable macromolecules. Algae have a cell wall made of cellulose, galactans, mannans and minerals like calcium carbonate, while in other plants it consists of cellulose, hemicellulose, pectins and proteins.

-- NCERT Class 11 Biology, Ch. 8, p. 94

Key Fact

Cell Membrane composition

The detailed structure of the cell membrane was studied only after the electron microscope arrived in the 1950s; chemical studies on human RBC membranes helped scientists deduce its structure. Studies showed the cell membrane is mainly composed of lipids and proteins. The major lipids are phospholipids arranged in a bilayer, with polar heads toward the outer sides and hydrophobic tails toward the inner part, protecting the nonpolar tail of saturated hydrocarbons from the aqueous environment. The membrane also contains cholesterol. Biochemical investigation later revealed the membrane also possesses protein and carbohydrate. The protein:lipid ratio varies considerably between cell types; in humans the erythrocyte membrane has approximately 52 percent protein and 40 percent lipids. Depending on ease of extraction, membrane proteins are classified as integral or peripheral: peripheral proteins lie on the membrane surface while integral proteins are partially or totally buried in the membrane.

-- NCERT Class 11 Biology, Ch. 8, p. 93

Key Fact

Passive transport across the membrane

One of the most important functions of the plasma membrane is transport of molecules across it; the membrane is selectively permeable to some molecules on either side. Many molecules move briefly across the membrane without any requirement of energy, called passive transport. Neutral solutes may move by simple diffusion along the concentration gradient, i.e., from higher concentration to lower. Water may also move across the membrane from higher to lower concentration; movement of water by diffusion is called osmosis. Because polar molecules cannot pass through the nonpolar lipid bilayer, they require a carrier protein of the membrane to facilitate their transport across it.

-- NCERT Class 11 Biology, Ch. 8, p. 94

Key Fact

Active transport across the membrane

A few ions or molecules are transported across the membrane against their concentration gradient, i.e., from lower to higher concentration. Such transport is an energy dependent process, in which ATP is utilised, and is called active transport, e.g., the Na+/K+ Pump.

-- NCERT Class 11 Biology, Ch. 8, p. 94

Key Fact

Primary wall, secondary wall and middle lamella

The cell wall of a young plant cell, the primary wall, is capable of growth, which gradually diminishes as the cell matures, and the secondary wall is formed on the inner (towards membrane) side of the cell. The middle lamella is a layer mainly of calcium pectate which holds or glues the different neighbouring cells together. The cell wall and middle lamellae may be traversed by plasmodesmata, which connect the cytoplasm of neighbouring cells.

-- NCERT Class 11 Biology, Ch. 8, p. 94

Where do students lose marks on Cell Membrane Wall?

These are the exact patterns that cause wrong answers in NEET. Each trap includes when it triggers and how to avoid it.

Trap

Integral vs peripheral membrane protein

Category: Similar Terms

Students swap integral and peripheral membrane proteins because both terms sound like generic descriptors rather than a precise ease-of-extraction classification.

When it triggers

A NEET question describes a membrane protein 'partially or totally buried in the membrane' and asks whether it is integral or peripheral, or the reverse describing a surface-lying protein.

How to avoid

Per C11_BIO_08_FACT_11, peripheral proteins lie on the surface of the membrane while integral proteins are partially or totally buried in the membrane; the classification is based on ease of extraction.

Trap

Diffusion direction confused with active transport direction

Category: Similar Terms

Students forget that passive transport (diffusion, osmosis) always moves from higher to lower concentration, while only active transport moves a substance from lower to higher concentration using ATP.

When it triggers

A NEET question gives a concentration gradient and a transport type and asks whether ATP is required, or asks students to identify which direction defines active transport.

How to avoid

Per C11_BIO_08_FACT_13 and C11_BIO_08_FACT_14, passive transport (simple diffusion, osmosis) moves molecules from higher to lower concentration without energy, whereas active transport moves ions/molecules from lower to higher concentration and is energy dependent, using ATP (e.g., Na+/K+ Pump).

Mistake

Students mark osmosis (movement of water by diffusion, higher to lower concentration) as an active, energy-requiring process.

Root cause: concept gap

Correction

Per C11_BIO_08_FACT_13, water moves across the membrane from higher to lower concentration by diffusion, called osmosis, which is passive and needs no energy; only transport against the gradient (C11_BIO_08_FACT_14) is active and ATP-dependent.

Wrong option pattern

labels osmosis/simple diffusion as ATP-dependent active transport

Mistake

Students assign cellulose, hemicellulose, pectins and proteins (the composition for other plants) to algal cell walls, or vice versa, instead of the algae-specific list.

Root cause: term confusion

Correction

Per C11_BIO_08_DEF_15, algal cell walls are made of cellulose, galactans, mannans and minerals like calcium carbonate, while cell walls of other plants consist of cellulose, hemicellulose, pectins and proteins; the two lists are distinct.

Wrong option pattern

swaps the algae wall list with the general plant wall list

More in Cell: Structure and Function: 10 exam traps and mistakes · 1 formula · 1 question pattern from its other lessons.