Cell Membrane: Structure, Function, and Transport

Which statement best defines the cell membrane?

• A rigid outer shell that provides structure only

• A flexible barrier that controls what enters and leaves the cell

• A storage site for water and nutrients

• A power source that produces energy for the cell

What is the main structural component of the cell membrane that forms a double layer?

• Protein filaments

• Cellulose sheets

• Phospholipid bilayer

• Sugar chains

Membrane proteins primarily function to:

• Provide genetic instructions

• Help transport substances and receive signals

• Store excess water

• Make cell walls rigid

Selective permeability of the cell membrane means it:

• Allows all substances to pass freely

• Blocks all substances from entering

• Allows some substances to pass while restricting others

• Only allows water to pass

Which process describes molecules like oxygen moving from an area of high concentration to an area of low concentration without energy use?

• Active transport

• Endocytosis

• Simple diffusion

• Exocytosis

Osmosis is best described as:

• The diffusion of any gas through the membrane

• The movement of water across the membrane to balance solute concentration

• The pumping of ions using energy

• The breakdown of large molecules

Why is osmosis important for cells?

• It ensures cells do not burst from too much water or shrink from too little water

• It produces energy for cellular activities

• It forms the cell wall

• It increases the rate of photosynthesis

Active transport differs from diffusion because active transport:

• Moves molecules down their concentration gradient without energy

• Moves molecules against their concentration gradient using energy

• Only moves water molecules

• Occurs only in plant cells

Which part of the membrane directly uses energy to move molecules across during active transport?

• Phospholipid tails

• Special protein pumps embedded in the membrane

• Carbohydrate chains on the surface

• Cholesterol molecules

A cell has a higher concentration of sodium ions outside than inside. Which transport method would move sodium into the cell against this gradient?

• Simple diffusion

• Osmosis

• Active transport using protein pumps

• Facilitated diffusion of water