Unit 2 FRQ (Intercellular Transport)

AP Bio Unit 2 FRQ: Intercellular Transport

Explore the Mechanisms of Material Transport in Cells

👋 Welcome to the AP Bio Unit 2 FRQ (Intercellular Transport).
These questions are longer, so grab a pen and paper or open up a blank page on your computer to jot down your answers. After you finish, you can check your responses with the Unit 2 FRQ (Intercellular Transport) Answers.

⏱ Time Management Tip: Remember, you will have 6 free-response questions on the AP Biology exam, and you’ll have 90 minutes to complete all of them. This means you should allocate about 15 minutes per FRQ.

🤔 Need a quick refresher? Check out the Unit 2 Overview for key concepts about cell structure, function, and transport mechanisms.

😩 Feeling stuck? Consult the Unit 2 Resources for more help!

Scenario

Living cells require the movement of various materials across their membranes to maintain proper cellular functions. These materials may include ions, molecules, and proteins, which can move across membranes through various transport mechanisms depending on their structure and properties.

Questions

(a) Sodium and potassium ions are both necessary for life and constantly move across cellular membranes. Identify the transport method that both sodium and potassium use together to move across membranes.

Response Guide:

• Transport Method: Sodium-Potassium Pump (Na+/K+ pump)
  • Sodium and potassium ions are transported through an active transport mechanism known as the sodium-potassium pump. This pump actively moves 3 sodium ions out of the cell and 2 potassium ions in, against their respective concentration gradients. This process requires ATP to fuel the conformational changes in the pump.

(b) A bulk amount of protein is created in a cell’s endomembrane system and needs to evacuate the cell. Explain the method the bulk substance should use to exit the cell.

Response Guide:

• Method for Protein Exit: Exocytosis
  • The bulk amount of protein that is produced in the endoplasmic reticulum and processed in the Golgi apparatus will leave the cell through a process called exocytosis. In exocytosis, vesicles containing the protein bud off from the Golgi and fuse with the plasma membrane, releasing their contents outside the cell. This process allows cells to secrete large quantities of substances, such as enzymes, hormones, or waste materials, in a controlled manner.

(c) Design an experiment to test which molecules can pass through the membrane via simple diffusion.

The molecules you will test are: Water, Glucose, Salt (Na+), and Carbon dioxide.

Response Guide:

Experimental Design:

• Objective: Determine which molecules (Water, Glucose, Salt, and Carbon Dioxide) can pass through a semi-permeable membrane via simple diffusion.

• Materials Needed:

  • Dialysis tubing (acts as a model of a semi-permeable membrane)
  • Beakers filled with water
  • Solutions of each molecule: water (H₂O), glucose, salt (NaCl), and carbon dioxide (CO₂)
  • Indicator solutions to detect the presence of the molecules (e.g., Benedict’s solution for glucose, pH indicators for ions)
  • Measuring instruments (pipettes, graduated cylinders)

• Procedure:

  1. Prepare four dialysis tubes and fill each with a separate solution: Water, Glucose, Salt, and Carbon Dioxide.
  2. Seal each tube tightly and place them into separate beakers filled with pure water.
  3. Allow the setup to sit for a specific amount of time (e.g., 30 minutes).
  4. Observe and measure the change in concentration of molecules both inside and outside the dialysis tubing. Use appropriate indicators to test for the presence of each molecule.

• Expected Results:

  • Water and Carbon Dioxide are expected to pass through the dialysis tubing via simple diffusion, as they are small and nonpolar (in the case of CO₂) or can pass through special aquaporins (in the case of H₂O).
  • Glucose (a larger polar molecule) and Salt (Na+) (an ion) are not expected to pass through the dialysis tubing via simple diffusion, as they typically require transport proteins or channels to cross the membrane.

• Data Analysis:

  • Compare the concentrations of each molecule inside and outside the dialysis tubing.
  • If a molecule passes through the tubing, its concentration inside and outside will equalize over time.

• Conclusion:

  • The experiment will confirm that water and carbon dioxide can diffuse through a semi-permeable membrane without assistance, while glucose and salt ions cannot pass through via simple diffusion due to their size and polarity.

Summary of Key Concepts:

1. Sodium-Potassium Pump: Sodium and potassium ions are moved by an active transport mechanism that helps maintain the electrochemical gradient across the cell membrane.
2. Exocytosis: Proteins produced by the cell are exported using vesicles that fuse with the cell membrane and release their content outside.
3. Diffusion Experiment: The ability of different molecules to pass through a semi-permeable membrane can be tested by using dialysis tubing as a model and measuring molecule movement over time.