Cell Membrane: 19 MCQs with answers

Fluid mosaic model

The fluid mosaic model, proposed by Singer and Nicolson, describes the membrane as a fluid lipid bilayer with embedded proteins, which is the most widely accepted model.

To control the movement of substances in and out of the cell

The cell membrane is selectively permeable, regulating what enters and exits the cell, which is its primary function.

Phosphate head

The phosphate head is polar and charged, making it hydrophilic (water-loving), while the fatty acid tails are nonpolar and hydrophobic.

Osmosis

Osmosis is specifically the diffusion of water through a semipermeable membrane, driven by concentration gradients.

Active transport

Active transport moves substances against their concentration gradient, requiring ATP, unlike passive processes like diffusion and osmosis.

It allows only certain substances to pass through

Selective permeability means the membrane permits some molecules to cross while preventing others, based on size, charge, and solubility.

Cell signaling

The cell membrane participates in cell signaling through receptors, but protein synthesis, DNA replication, and ATP production occur in other organelles.

False

The membrane is selectively permeable, allowing some substances to pass while blocking others, not completely impermeable.

Phospholipids

Phospholipids, with their unsaturated fatty acid tails, create a fluid matrix. Cholesterol modulates fluidity but is not the primary contributor.

Integral proteins

Integral proteins are embedded within and often span the bilayer, while peripheral proteins are attached to the surface. Channel proteins are a type of integral protein, but not all integral proteins are channels.

Cell recognition and adhesion

Carbohydrates, often attached to proteins or lipids, form glycoproteins and glycolipids that function in cell-cell recognition and adhesion.

Energy production

Membrane proteins are involved in transport, signaling, and adhesion, but energy production occurs in mitochondria, not directly by membrane proteins.

It loses water and shrinks

In a hypertonic solution, the external solute concentration is higher, causing water to leave the cell, leading to shrinkage (crenation).

Cell recognition

Glycoproteins, with their carbohydrate chains, serve as recognition sites for other cells and molecules, crucial for immune responses and cell-cell interactions.

Oxygen (O2)

Small, nonpolar molecules like oxygen diffuse freely through the hydrophobic core of the bilayer, while ions and large polar molecules require transport proteins.

They are involved in cell signaling and support

Peripheral proteins are attached to the membrane surface and often function in signaling pathways or provide mechanical support, but they do not span the membrane.

It increases

Higher temperatures increase kinetic energy of phospholipids, making the membrane more fluid, until it may become too fluid and lose integrity.

False

Cholesterol is a component of animal cell membranes, not plant cell membranes, which typically contain other sterols.

It prevents the membrane from becoming too rigid

Cholesterol acts as a fluidity buffer: at low temperatures it prevents tight packing of fatty acids, maintaining fluidity; at high temperatures it restricts movement, reducing fluidity.