Structure and Function of Cell Membranes Reading Answers

Oct 31, 2025

Structure and Function of Cell Membranes Reading Answers consists of 13 questions and forms part of the evaluation framework for the IELTS General Reading test. Participants are given a time constraint of 20 minutes to finish the reading answers for the Structure and Function of Cell Membranes. This portion of the IELTS reading evaluation includes various types of questions, including labeling the diagram below, writing the correct letter, and choosing only one word from the passage for each answer.

Structure and Function of Cell Membranes Reading Answers provides a thorough examination of the cell membrane, which is made of a phospholipid bilayer, and acts as a protective barrier controlling the exchange of substances between the cell and its environment. Embedded proteins and cholesterol regulate transport, communication, and membrane fluidity, ensuring proper cell function. For further practice with similar reading evaluations, candidates can check the IELTS Reading Practice Test section.

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Structure and Function of Cell Membranes Reading Answers

(A)Human body is made up of millions of cells – little building blocks of life. Each cell contains many functional subunits (organelles) that enable its proper functioning and is protected from the external environment by a cell membrane. While structure and function of organelles are extensively covered in various biology courses, the importance of study of cell membranes is often underestimated. This article is dedicated to provide a short introduction into the basic structure and anatomy of a cell membrane.

(B)Cell membranes protect and organize cells. Most importantly they serve as barriers, discriminating the cell’s interior from the outer milieu. Because cells always exist in aqueous environment their membranes should be structured in such a way so they do not solve in water. This function is ideally carried by special chemical molecules – phospholipids. These molecules are constructed from two parts: tails made up of 2 molecules of fat that ‘avoid’ water and heads that have an affinity for water. For this specific behaviour the phospholipids’ tails are called hydrophobic (‘hydro’ means water and ‘phobia’ means fear) and heads are called hydrophilic (‘philos’ means love). When phospholipids are added to water they self-assemble into double-layered structures, shielding their hydrophobic portions from water and exposing their hydrophilic portions to the environment. This phospholipid bilayer may resemble a sandwich, where phospholipid heads are bread rolls and tails are the sandwich filling.

(C)In addition to lipids, membranes are loaded with proteins. They usually go through the lipid bilayer and are exposed to both aqueous environment and cell’s interior. In fact, proteins account for roughly half the mass of most cellular membranes. They make the membrane semi-permeable, which means that some molecules can diffuse across the lipid bilayer but others cannot. Small hydrophobic molecules and gases like oxygen and carbon dioxide cross membranes rapidly. Small polar molecules, such as water and ethanol, can also pass through membranes, but they do so more slowly. On the other hand, cell membranes restrict diffusion of highly charged molecules, such as ions, and large molecules, such as sugars and amino acids. The passage of these molecules relies on specific transport proteins embedded in the membranes.

(D)Membrane transport proteins are specific and selective for the molecules they move, and they often use energy to enhance passage. Also, these proteins transport some molecules against concentration gradient, which requires additional energy. The ability to maintain concentration differences and sometimes move materials against this is vital to cell health and maintenance. Thanks to membrane barriers and transport proteins, the cell can accumulate nutrients in higher concentrations than exist in the environment, and, conversely, dispose of waste products.

(E)Other membrane-embedded proteins have connection-related jobs. Large molecules from the extracellular environment, such as hormones or immune mediators, can bind to receptor proteins in the plasma membrane. Such binding causes a conformational change in the protein that transmits a signal to intracellular messenger molecules. Like transport proteins, receptor proteins are specific for the molecules they bind.

(F)Another important type of membrane’s component is cholesterol. Cholesterol accounts for about 20 percent of the lipids in animal cell plasma membranes. However, it is lacking in bacterial membranes and some plant membranes. The cholesterol molecules are embedded in between phospholipid molecules and help to regulate the fluidity and stiffness of membranes. To function properly, the membrane should be in fluid state. Cholesterol reduces membrane fluidity at moderate temperatures by reducing movement of phospholipids. But at low temperatures, it hinders solidification by disrupting the regular packing of phospholipids.

QUESTIONS 28-30

LABEL THE DIAGRAM BELOW.

WRITE NO MORE THAN ONE WORD FROM THE PASSAGE FOR EACH ANSWER. DO NOT WRITE THE ARTICLES.

WHICH ELEMENTS OF CELL MEMBRANE CORRESPOND TO THE NUMBERS IN THE DIAGRAM?

28. Answer: Transport protein

Supporting statement: “Membrane transport proteins are specific and selective for the molecules they move, and they often use energy to enhance passage.”

Keywords: Transport proteins, specific, selective, passage

Keyword Location: Paragraph D, lines 1–3

Explanation: The structure labeled 28 represents a transport protein, which spans the membrane and helps move molecules across it. These proteins control the entry and exit of substances, maintaining the cell’s internal balance by transporting materials, sometimes against the concentration gradient.

29. Answer: Cholesterol molecule

Supporting statement: “The cholesterol molecules are embedded in between phospholipid molecules and help to regulate the fluidity and stiffness of membranes.”

Keywords: Cholesterol, phospholipid, fluidity, stiffness

Keyword Location: Paragraph F, lines 2–4

Explanation: The structure labeled 29 indicates a cholesterol molecule, located between phospholipid tails. Cholesterol stabilizes the membrane, reducing fluidity at moderate temperatures and preventing solidification at low temperatures, ensuring the membrane stays functional.

30. Answer: Receptor protein

Supporting statement: “Large molecules from the extracellular environment, such as hormones or immune mediators, can bind to receptor proteins in the plasma membrane.”

Keywords: Receptor proteins, hormones, binding, plasma membrane

Keyword Location: Paragraph E, lines 1–3

Explanation: The structure labeled 30 shows a receptor protein that binds to signaling molecules from outside the cell. This interaction triggers internal cellular responses, allowing communication between the cell and its external environment.

QUESTIONS 31-35

WHICH PARAGRAPH CONTAINS THE FOLLOWING INFORMATION?

WRITE THE CORRECT LETTER, A-F, IN BOXES 31-35 ON YOUR ANSWER SHEET.

31. Specific proteins transport nutrients from the external environment against the concentration gradient.

Answer: D

Supporting statement: “These proteins transport some molecules against concentration gradient, which requires additional energy.”

Keywords: transport proteins, against concentration gradient, energy

Keyword Location: Paragraph D, line 2

Explanation: Paragraph D explains that specific membrane transport proteins move molecules against their concentration gradient, which fits the statement perfectly.

32. The barrier function of cell membranes is supported by a bilayer of phospholipids.

Answer: B

Supporting statement: “When phospholipids are added to water they self-assemble into double-layered structures… This phospholipid bilayer may resemble a sandwich…”

Keywords: phospholipid bilayer, barrier, double-layer

Keyword Location: Paragraph B, lines 8–10

Explanation: Paragraph B describes how phospholipids form a bilayer that acts as the cell membrane’s barrier function.

33. The level of membrane fluidity is regulated by cholesterol molecules.

Answer: F

Supporting statement: “The cholesterol molecules are embedded in between phospholipid molecules and help to regulate the fluidity and stiffness of membranes.”

Keywords: cholesterol, regulate fluidity, stiffness

Keyword Location: Paragraph F, line 4

Explanation: Paragraph F specifically mentions the regulatory role of cholesterol in controlling the membrane’s fluidity and stiffness.

34. The importance of cell membranes are often underestimated.

Answer: A

Supporting statement: “The importance of study of cell membranes is often underestimated.”

Keywords: importance, underestimated, cell membranes

Keyword Location: Paragraph A, line 4

Explanation: Paragraph A directly states that the importance of studying cell membranes is often undervalued, matching the question exactly.

35. Proteins make the membrane semi-permeable.

Answer: C

Supporting statement: “They make the membrane semi-permeable, which means that some molecules can diffuse across the lipid bilayer but others cannot.”

Keywords: proteins, semi-permeable, diffuse

Keyword Location: Paragraph C, line 3

Explanation: The paragraph explains that proteins make membranes semi-permeable, allowing selective diffusion of molecules.

QUESTIONS 36-40

CHOOSE ONLY ONE WORD FROM THE PASSAGE FOR EACH ANSWER.

Cell membranes protect cells and organize their activities. The first main function of cell membrane - barrier function is carried by phospholipids. These molecules don't solve in water and, thus, are ideal for cells that always exist in 36....................

Answer: aqueous

Supporting statement: “Because cells always exist in aqueous environment…”

Keywords: exist in, environment

Keyword Location: Paragraph B, line 2

Explanation: The text specifies that cells live in an aqueous environment, referring to water-based surroundings.

Environment. In addition to lipids, membranes are loaded with 37.........

Answer: proteins

Supporting statement: “In addition to lipids, membranes are loaded with proteins.”

Keywords: membranes loaded with, proteins

Keyword Location: Paragraph C, line 1

Explanation: The passage directly mentions proteins as additional membrane components besides lipids.

That makes the membrane 38……………

Answer: semi-permeable

Supporting statement: “They make the membrane semi-permeable, which means that some molecules can diffuse across the lipid bilayer but others cannot.”

Keywords: make the membrane, semi-permeable

Keyword Location: Paragraph C, line 3

Explanation: The text clearly defines the term “semi-permeable” in relation to membrane function.

Which means that some molecules can diffuse across the lipid bilayer but others-cannot. One of the most important types of membrane proteins are 39..............

Answer: transport

Supporting statement: “One of the most important types of membrane proteins are transport proteins and receptor proteins.”

Keywords: important types, transport proteins

Keyword Location: Paragraph D, line 1

Explanation: The correct word is “transport,” describing one of the two main types of membrane proteins.

Proteins and receptor proteins. The last type of membrane elements are cholesterol molecules, which are embedded in place of 40…………… Molecules and help to regulate the stiffness of membranes.

Answer: phospholipid

Supporting statement: “The cholesterol molecules are embedded in between phospholipid molecules…”

Keywords: embedded between, phospholipid molecules

Keyword Location: Paragraph F, line 4

Explanation: Cholesterol molecules are placed among phospholipid molecules, as mentioned in Paragraph F.

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