Which one of the following statements is correct about the cell membrane?
- A.It is made up of cellulose.
- B.It is a permeable structure for all substances.
- C.It is flexible and enables the cell to engulf many materials.
- D.It does not allow diffusion of gases like oxygen and carbon dioxide.
Correct answer
Explanation
The correct answer is C. The cell membrane is flexible, and this lets a cell fold it around food and other material and take it in.
The cell (plasma) membrane is a thin layer of lipids and proteins that surrounds every cell. Because it is flexible, cells such as Amoeba and white blood cells can engulf particles by endocytosis, forming a food vacuole. The membrane is selectively permeable: it lets some substances through freely, controls others and keeps some out, which is how the cell keeps its inner conditions steady.
A is wrong: cellulose makes the cell wall of plants, which lies outside the membrane.
B is wrong: the membrane is selectively permeable, not open to all substances.
D is wrong: oxygen and carbon dioxide are small molecules that diffuse freely across it.
Exam tip: cell wall is made of cellulose and is rigid; cell membrane is made of lipids and proteins and is flexible and selectively permeable.
Practice Questions
View allWhich of the following properties is true for a tooth paste?
- A.It is acidic
- B.It is neutral
- C.It is basic
- D.It is made up of Calcium phosphate, the material of tooth enamel
Show answer
Toothpaste is mildly basic so that it can neutralise the acid that causes tooth decay. Bacteria in the mouth break down sugar and food particles left on the teeth and produce acids.
Read the full explanation →A stainless steel chamber contains Ar gas at a temperature T and pressure P. The total number of Ar atoms in the chamber is n. Now Ar gas in the chamber is replaced by CO₂ gas and the total number of CO₂ molecules in the chamber is n/2 at the same temperature T. The pressure in the chamber now is P'. Which one of the following relations holds true? (Both the gases behave as ideal gases)
- A.P' = P
- B.P' = 2P
- C.P' = P/2
- D.P' = P/4
Show answer
For an ideal gas in a fixed volume at a fixed temperature, pressure is proportional to the number of molecules, so half the molecules give half the pressure.
Read the full explanation →In which of the following pairs are the ions isoelectronic?
- A.Mg²⁺, Ar
- B.Na⁺, O²⁻
- C.Al³⁺, Cl⁻
- D.K⁺, Ne
Show answer
Both have 10 electrons, the same number as a neon atom, so they are isoelectronic. Isoelectronic species have the same number of electrons.
Read the full explanation →A solid disc and a solid sphere have the same mass and same radius. Which one has the higher moment of inertia about its centre of mass?
- A.The disc
- B.The sphere
- C.Both have the same moment of inertia
- D.The information provided is not sufficient to answer the question
Show answer
About an axis through the centre, a solid disc has I = ½MR² while a solid sphere has I = ⅖MR², and ½ is larger than ⅖.
Read the full explanation →Numerically two thermometers, one in Fahrenheit scale and another in Celsius scale shall read same at
- A.−40°
- B.0°
- C.−273°
- D.100°
Show answer
At this one temperature the Celsius and Fahrenheit scales show the same number. The two scales are linked by F = (9/5)C + 32.
Read the full explanation →