GB1 Reviewer (Cell Membrane, Transport Mechanisms, Biomolecules)

The plasma membrane contains proteins that assist in transporting substances. What are these proteins called?

• Enzymes

• Lipids

• Transport proteins

• Structural proteins

Answer explanation

The proteins that assist in transporting substances across the plasma membrane are called transport proteins. They facilitate the movement of molecules in and out of the cell, making them essential for cellular function.

Which process involves the movement of water molecules across a semipermeable membrane?

• Diffusion

• Osmosis

• Active transport

• Facilitated diffusion

Answer explanation

Osmosis is the process that specifically refers to the movement of water molecules across a semipermeable membrane, distinguishing it from diffusion, active transport, and facilitated diffusion, which involve other substances.

Which of the following statements correctly describes the phospholipid bilayer?

• The heads are hydrophobic, and the tails are hydrophilic

• The heads are hydrophilic, and the tails are hydrophobic

• Both heads and tails are hydrophobic

• Both heads and tails are hydrophilic

Answer explanation

The phospholipid bilayer consists of hydrophilic (water-attracting) heads that face outward and hydrophobic (water-repelling) tails that face inward, creating a barrier. Thus, the correct statement is: The heads are hydrophilic, and the tails are hydrophobic.

Which of the following best describes active transport?

• Requires energy and moves substances against the concentration gradient

• Does not require energy and moves substances along the concentration gradient

• Only moves water molecules

• Moves substances in random directions without energy

Answer explanation

Active transport requires energy to move substances against their concentration gradient, meaning it moves molecules from an area of lower concentration to an area of higher concentration, unlike passive transport.

Which molecule cannot easily pass through the plasma membrane without the aid of transport proteins?

• Oxygen

• Carbon dioxide

• Glucose

• Water

Answer explanation

Glucose is a large polar molecule and cannot easily pass through the plasma membrane, which is hydrophobic. It requires transport proteins, such as glucose transporters, to facilitate its movement across the membrane.

The sodium-potassium pump moves ions across the membrane. What type of transport protein is this?

• Uniporter

• Symporter

• Antiporter

• Aquaporin

Answer explanation

The sodium-potassium pump is an antiporter because it moves sodium ions out of the cell while bringing potassium ions in, functioning in opposite directions across the membrane.

David notices that his skin becomes wrinkled after soaking in a bathtub for too long. What process is responsible for this change?

• Diffusion

• Osmosis

• Active transport

• Facilitated diffusion

Answer explanation

Osmosis is the process where water moves across a semipermeable membrane. When David's skin is soaked, water enters the skin cells, causing them to swell and wrinkle due to the loss of moisture from the outer layer.

When you sprinkle salt on a snail, it shrinks because:

• Water moves out of the snail’s cells by osmosis.

• The salt enters the snail’s cells by diffusion.

• The snail produces more waste as a response to the salt.

• The salt blocks oxygen uptake by the snail.

Answer explanation

When salt is sprinkled on a snail, it creates a hypertonic environment. Water moves out of the snail's cells by osmosis to balance the concentration, causing the snail to shrink.

What would happen to a red blood cell placed in a solution that is hypertonic?

• Swell

• Shrink

• Remain the same

• Undergo active transport

Answer explanation

A red blood cell placed in a hypertonic solution will lose water to the surrounding solution, causing it to shrink. This occurs because the concentration of solutes outside the cell is higher than inside, leading to osmosis.

Maria places a slice of apple in distilled water. After several hours, the apple slice becomes more firm. What best explains this result?

• The distilled water caused the apple to absorb more solute.

• The distilled water is hypertonic to the apple, causing it to lose water.

• The distilled water is hypotonic to the apple, causing water to enter the cells.

• The distilled water diffused into the air, making the apple firmer.

Answer explanation

The distilled water is hypotonic to the apple, meaning it has a lower concentration of solutes. This causes water to move into the apple cells, making the apple slice firmer as it absorbs water.