3.2.3 Transport across cell membranes Questions

Specification route: 3.2.3
Question bank: 24 questions
Course stage: AS / Year 12

Sample questions

QUESTION 1 · 3.2.3 · LEVEL 2

What role does cholesterol play in cell membranes?

It restricts the movement of other molecules making up the membrane.
It acts as a primary channel for active transport.
It facilitates the diffusion of water molecules (osmosis).
It identifies the cell to the immune system as an antigen.

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It helps regulate the fluidity of the phospholipid bilayer.

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Answer: It restricts the movement of other molecules making up the membrane.

Cholesterol may also be present in cell membranes where it restricts the movement of other molecules making up the membrane.

QUESTION 2 · 3.2.3 · LEVEL 2

Which ions are absorbed by cells lining the mammalian ileum via co-transport with glucose?

Sodium ions ($Na^{+}$)
Potassium ions ($K^{+}$)
Hydrogen ions ($H^{+}$)
Calcium ions ($Ca^{2+}$)

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This ion creates the concentration gradient necessary to pull glucose into the cell.

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Answer: Sodium ions ($Na^{+}$)

Co-transport is illustrated by the absorption of sodium ions and glucose by cells lining the mammalian ileum.

QUESTION 3 · 3.2.3 · LEVEL 2

Which structural adaptation would most effectively increase the rate of transport across a cell membrane?

An increase in the number of protein channels and carrier molecules.
An increase in the amount of cholesterol in the phospholipid bilayer.
A decrease in the surface area of the internal membranes.
The complete removal of glycoproteins from the fluid-mosaic model.

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More pathways allow more molecules to cross simultaneously.

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Answer: An increase in the number of protein channels and carrier molecules.

Cells may be adapted for rapid transport across their internal or external membranes by an increase in surface area of, or by an increase in the number of protein channels and carrier molecules in, their membranes.

QUESTION 4 · 3.2.3 · LEVEL 1

Which process of movement across cell membranes specifically requires the hydrolysis of ATP?

Active transport
Osmosis
Facilitated diffusion
Simple diffusion

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This process moves substances against their concentration gradient.

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Answer: Active transport

Movement across membranes occurs by: simple diffusion; facilitated diffusion; osmosis; active transport. Active transport uniquely requires energy from ATP to pump molecules against the gradient.

QUESTION 5 · 3.2.3 · LEVEL 2

In the fluid-mosaic model of membrane structure, what does 'mosaic' refer to?

The varied arrangement of proteins, glycoproteins, and glycolipids embedded throughout the phospholipid bilayer.
The continuous lateral movement of phospholipid molecules within the membrane.
The rigid, crystalline structure formed by cholesterol molecules locking the membrane in place.
The alternating layers of water and lipid that construct the boundary of the cell.

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Think of a piece of art made of many different, scattered pieces.

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Answer: The varied arrangement of proteins, glycoproteins, and glycolipids embedded throughout the phospholipid bilayer.

The arrangement and any movement of phospholipids, proteins, glycoproteins and glycolipids in the fluid-mosaic model of membrane structure. 'Mosaic' describes the diverse pattern of embedded proteins.

QUESTION 6 · 3.2.3 · LEVEL 3

A student states that facilitated diffusion requires ATP. Why is this incorrect?

Facilitated diffusion is a passive process where molecules move down their concentration gradient via channel or carrier proteins.
Facilitated diffusion only transports non-polar molecules directly through the phospholipid bilayer.
Facilitated diffusion involves the movement of water molecules specifically, which never requires ATP.
Facilitated diffusion actively pumps molecules against their concentration gradient using kinetic energy.

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The word 'facilitated' means helped by a protein, but 'diffusion' always implies passive movement.

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Answer: Facilitated diffusion is a passive process where molecules move down their concentration gradient via channel or carrier proteins.

Movement across membranes occurs by: simple diffusion; facilitated diffusion; osmosis; active transport. Facilitated diffusion relies on existing kinetic energy to move substances down a gradient, unlike active transport.

QUESTION 7 · 3.2.3 · LEVEL 2

Which statement correctly defines osmosis?

The net movement of water molecules from an area of higher water potential to an area of lower water potential through a partially permeable membrane.
The active transport of water molecules against their water potential gradient using ATP.
The movement of solute ions from an area of high concentration to an area of low concentration.
The diffusion of water molecules through fully permeable murein cell walls.

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Water potential is the measure of the tendency of water to move; pure water is 0, and adding solutes makes it negative.

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Answer: The net movement of water molecules from an area of higher water potential to an area of lower water potential through a partially permeable membrane.

Movement across membranes occurs by... osmosis. Osmosis specifically refers to the passive movement of water along its water potential gradient.

QUESTION 8 · 3.2.3 · LEVEL 4

During the co-transport of glucose in the mammalian ileum, what directly provides the energy to move glucose against its concentration gradient into the epithelial cell?

The diffusion of sodium ions ($Na^{+}$) down their concentration gradient into the epithelial cell.
The direct hydrolysis of ATP by the glucose carrier protein.
The active pumping of potassium ions ($K^{+}$) out of the epithelial cell.
The simple diffusion of water molecules pulling glucose through the membrane.

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Co-transport is a form of secondary active transport; the gradient of one ion 'drags' another molecule with it.

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Answer: The diffusion of sodium ions ($Na^{+}$) down their concentration gradient into the epithelial cell.

Co-transport (illustrated by the absorption of sodium ions and glucose by cells lining the mammalian ileum). Sodium ions move down their gradient (created by a separate active pump), co-transporting glucose against its gradient.

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