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AP®BiologyCollege BoardExam QuestionsUnit 2: Cell Structure & FunctionCell Membranes & Transport

Cell Membranes & Transport (College Board AP® Biology)

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Cell Membranes & Transport

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Cell Membranes & Transport

1
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Cell membranes consist of a structural framework of different molecules that can flow around the surface of the cell within the membrane.

Diagram of a cell membrane showing lipid bilayer, proteins, and carbohydrate chains, labelled from 1 to 5, illustrating membrane composition.
Figure 1. Diagram of the cell membrane

Which of the following predicts the effect on the membrane of increasing the proportion of molecule 1?

  • The fluidity of the membrane would decrease.

  • The fluidity of the membrane would increase.

  • The fluidity of the membrane would remain the same.

  • The membrane would rupture.

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2
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Proteins in the cell surface membranes of mouse cells and human cells were labelled with coloured dyes, with a different colour for human and mouse proteins.

When a cell from each species is fused together, the different-coloured labels are first found in different regions of the hybrid cell’s cell surface membrane. After 40 minutes, the labels are evenly distributed around the entire cell surface membrane. This is shown in the diagram below; the viewpoint is looking down onto the surface of the membrane.

Diagram showing sections of human and mouse membranes with proteins merging into a fused membrane. Phospholipid heads are depicted as circles.
Figure 1. Diagram of sections of human and mouse membranes

Which of the following explains this observation?

  • Groups of protein and phospholipid molecules in the cell surface membrane are attached to each other and move together.

  • Only protein molecules in the outer layer of the cell surface membrane can move freely between phospholipid molecules

  • All protein molecules in the cell surface membrane are fixed to structures within the cell, but phospholipid molecules move freely between them

  • Protein molecules in the outer layer of the cell surface membrane and those which span the bilayer can move freely between phospholipid molecules

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3
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The structure of a molecule affects its ability to pass through the plasma membrane. Membrane proteins are required for facilitated diffusion across the plasma membrane. Which of the following is not true of membrane proteins?

  • Charged ions, including Na+ and K+, require channel proteins to move through the membrane.

  • Membrane proteins are necessary for active transport.

  • Large quantities of water pass through aquaporins.

  • Membrane proteins are in a fixed position within the plasma membrane.

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41 mark

Students were investigating osmosis in the plant cells of carrots.

Step 1: The student cut five cylinders of carrot using a cork borer to the same length

Step 2: The student placed the cylinders in five increasing concentrations of sucrose solution

Step 3: The student recorded the masses of the carrot cylinders after 24 hours

The student's results are shown in the graph in Figure 1.

Graph showing a curve of percentage change in mass versus sucrose concentration (M), ranging from +5% at 0M to -7% at 1M, on a grid background.

Which of the following conclusions is supported by the results in the graph?

  • The solution is isotonic to the carrot at 0 (M) because there is a net movement of water into the carrot by osmosis.

  • The solution is isotonic to the carrot at 2.2 (M) because there is no net movement of water into the carrot by osmosis.

  • The solution is isotonic to the carrot at 1 (M) because there is a net movement of water out of the carrot by osmosis.

  • The solution is not isotonic to the carrot during the student's experiment.

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51 mark

Osmoregulation maintains water balance and allows organisms to control their internal solute composition/water potential. Protists maintain osmoregulation by pumping water out of the cell using an organelle called contractile vacuoles (CVs)

Scientists investigated protists living in a body of water 200m inland from a coastal region. The table gives the data collected by the scientists to calculate the solute potential.

C

R

T

2

0.12 M

0.00831 kJ mol-1 K-1

12 oC

Which of the following is the solute potential of the body of water?

  • 0.568 (MPa)

  • -0.568 (MPa)

  • 0.024 (MPa)

  • -0.024 (MPa)

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