Understanding Cell Transport Mechanisms

What is the primary function of the cell membrane in cell transport?

• To produce energy for the cell

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

• To store genetic information

• To synthesize proteins

Answer explanation

The primary function of the cell membrane is to control the movement of substances in and out of the cell, acting as a selective barrier that regulates what enters and exits, thus maintaining homeostasis.

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DOK Level 1: Recall

Which of the following is an example of passive transport?

• Endocytosis

• Exocytosis

• Diffusion

• Sodium-potassium pump

Answer explanation

Diffusion is a type of passive transport where molecules move from an area of higher concentration to an area of lower concentration without the use of energy. In contrast, endocytosis, exocytosis, and the sodium-potassium pump require energy.

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DOK Level 1: Recall

Explain how concentration gradients affect the process of diffusion.

• They create a barrier that prevents diffusion.

• They cause molecules to move from areas of low concentration to high concentration.

• They drive the movement of molecules from areas of high concentration to low concentration.

• They have no effect on diffusion.

Answer explanation

Concentration gradients drive diffusion by causing molecules to move from areas of high concentration to low concentration, seeking to equalize the concentration on both sides.

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DOK Level 2: Skill/Concept

Describe the process of osmosis in living cells.

• Movement of water molecules from a region of low solute concentration to high solute concentration through a semi-permeable membrane.

• Movement of solute molecules from a region of high concentration to low concentration.

• Active transport of water molecules using ATP.

• Movement of water molecules from a region of high solute concentration to low solute concentration.

Answer explanation

Osmosis is the movement of water molecules from a region of low solute concentration to high solute concentration through a semi-permeable membrane, allowing cells to maintain balance and proper function.

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DOK Level 2: Skill/Concept

What happens to a cell placed in a hypertonic solution?

• The cell will swell and burst.

• The cell will remain the same size.

• The cell will shrink.

• The cell will become isotonic.

Answer explanation

In a hypertonic solution, the concentration of solutes outside the cell is higher than inside. Water moves out of the cell to balance the solute concentrations, causing the cell to shrink.

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DOK Level 1: Recall

Which of the following processes requires ATP?

• Osmosis

• Facilitated diffusion

• Active transport

• Simple diffusion

Answer explanation

Active transport requires ATP because it moves substances against their concentration gradient, which is an energy-consuming process. In contrast, osmosis, facilitated diffusion, and simple diffusion do not require ATP.

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DOK Level 1: Recall

How does ATP provide energy for active transport processes?

• By breaking down into ADP and releasing energy.

• By forming bonds with other molecules.

• By storing energy in the form of glucose.

• By converting into water and carbon dioxide.

Answer explanation

ATP provides energy for active transport by breaking down into ADP and releasing energy. This process is essential for moving substances against their concentration gradient, which is a key function of active transport.

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DOK Level 2: Skill/Concept

Compare and contrast diffusion and active transport.

• Both require energy and move substances against the concentration gradient.

• Diffusion requires energy, while active transport does not.

• Diffusion moves substances down the concentration gradient without energy, while active transport moves substances against the gradient using energy.

• Both processes move substances down the concentration gradient without energy.

Answer explanation

Diffusion is a passive process that moves substances down their concentration gradient without energy, while active transport requires energy to move substances against their gradient.

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DOK Level 3: Strategic Thinking

What is the role of protein channels in facilitated diffusion?

• They provide energy for the transport process.

• They act as pumps to move substances against the concentration gradient.

• They provide a pathway for specific molecules to pass through the cell membrane.

• They store molecules for later use.

Answer explanation

Protein channels facilitate diffusion by providing a specific pathway for certain molecules to cross the cell membrane, allowing them to move down their concentration gradient without the need for energy.

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DOK Level 2: Skill/Concept

Predict the effect of placing a plant cell in an isotonic solution.

• The cell will become turgid.

• The cell will lose water and become plasmolyzed.

• The cell will gain water and burst.

• The cell will remain the same size.

Answer explanation

In an isotonic solution, the concentration of solutes is equal inside and outside the plant cell. Therefore, there is no net movement of water, and the cell will remain the same size.

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DOK Level 3: Strategic Thinking