Cell Membrane Dynamics and Transport Mechanisms

Dr. Mark Todorovic explains how the characteristics of substances affect their movement through cell membranes. The lipid bilayer of cells allows small, non-charged substances like water and gases to pass through, while large or charged substances like ions and glucose require protein channels. Diffusion occurs when substances move from high to low concentration without energy, but active transport requires ATP to move substances against the concentration gradient.

What is the primary function of the lipid bilayer in a cell?

• To produce proteins for the cell

• To store energy for the cell

• To separate the cell's internal and external environments

• To transport nutrients into the cell

Which of the following substances can freely pass through the lipid bilayer?

• Sodium ions

• Water

• Proteins

• Glucose

Why can't ions freely pass through the phospholipid bilayer?

• They are charged

• They are too small

• They are not soluble in water

• They are too large

What is the role of protein channels in the cell membrane?

• To produce energy for the cell

• To synthesize lipids

• To store genetic information

• To act as doorways for specific substances

In the classroom analogy, what does the open door represent?

• A lipid bilayer

• An open protein channel

• An active transport mechanism

• A closed protein channel

What happens when a protein channel is closed?

• The cell membrane becomes impermeable

• Diffusion occurs more rapidly

• Diffusion cannot occur

• Active transport is initiated

What is required for a substance to move against its concentration gradient?

• Energy in the form of ATP

• A smaller molecule size

• A higher temperature

• A larger concentration gradient

What is the role of ATP in active transport?

• To close protein channels

• To provide energy for moving substances against their gradient

• To open protein channels

• To increase the concentration gradient

Which of the following is an example of a substance that requires active transport to enter a cell?

• Glucose

• Carbon dioxide

• Oxygen

• Water

What is the main difference between diffusion and active transport?

• Diffusion requires energy, active transport does not

• Active transport requires energy, diffusion does not

• Active transport moves substances with their gradient, diffusion does not

• Diffusion moves substances against their gradient, active transport does not