The Cell Membrane — Drills · Grade 10 Science

Chapter: Cells, Membranes & Exchange

What these drills covers

By the end of The Cell Membrane you should be able to:

6 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: phospholipid, hydrophilic, hydrophobic, phospholipid bilayer, fluid mosaic model, selective permeability, membrane protein.

Problem 1

In a cell membrane, the phospholipid tails face
  1. outward toward the watery surroundings
  2. inward, away from water, forming the membrane's interior
  3. toward the nucleus
  4. in random directions
Answer and explanation

inward, away from water, forming the membrane's interior

The nonpolar tails are excluded from water and cluster inward; the polar heads face the watery cytoplasm and exterior.

Problem 2

Which substance crosses a phospholipid bilayer most readily without help?
  1. A sodium ion
  2. A glucose molecule
  3. Oxygen
  4. A protein
Answer and explanation

Oxygen

Small nonpolar molecules such as oxygen and carbon dioxide dissolve in the nonpolar interior and cross freely. Ions and large polar molecules require transport proteins.

Problem 3

The term "fluid mosaic" refers to the fact that
  1. membranes are rigid sheets of protein
  2. lipids and proteins move laterally within a patterned bilayer
  3. membranes dissolve in water
  4. all membrane proteins are identical
Answer and explanation

lipids and proteins move laterally within a patterned bilayer

The bilayer behaves as a two-dimensional fluid in which embedded proteins and lipids drift, giving a mosaic that is not fixed in place.

Problem 4

A membrane is about 8 nm thick. How many such membranes stacked together would span 1 µm?
Answer and explanation

125

1 µm = 1,000 nm, and 1,000 / 8 = 125 membranes.

Problem 5

Explain why the membrane is described as selectively permeable rather than simply permeable or impermeable.
Answer and explanation

Some substances cross freely, some cross only through specific proteins, and some do not cross at all. Small nonpolar molecules such as oxygen dissolve in the bilayer's interior and pass; ions and polar molecules such as glucose need channels or carriers; large molecules are excluded unless the cell uses vesicles. The membrane therefore selects by size, charge, and polarity rather than admitting or blocking everything.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 6

Name three functions of membrane proteins besides transport, and say what each contributes.
Answer and explanation

Receptor proteins bind signalling molecules and trigger a response inside the cell, so the cell can react to its surroundings. Recognition proteins and attached carbohydrates mark the cell's identity, which the immune system reads. Enzymes anchored in the membrane catalyse reactions at the surface, and anchoring proteins attach the membrane to the cytoskeleton or to neighbouring cells, maintaining shape and tissue structure.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

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