1.3 and 1.4 Membrane structure and function

Which property of phospholipid molecules helps them to form bilayers in water?

• Phosphate properties

• Polar properties

• Amphipathic properties

• Lipid properties

Which of the following is characteristic of proteins found in cell membranes?

• They are found in a range of positions and have different structures adapted to their specific function.

• The are found in a range of positions, with the same structure, but each with a different function.

• They are found in a range of positions with different structures, but they all serve the same function.

• They are found in the same position, but have different structures and functions.

What is the role of cholesterol in mammalian cell membranes?

• It increases membrane fluidity and permeability to some solutes.

• It reduces membrane fluidity but has no effect on permeability.

• It increases membrane fluidity but has no effect on permeability.

• It reduces membrane fluidity and permeability to some solutes.

This diagram show an image of the membranes of two adjacent cells. Parallel dark lines are clearly seen on both membranes.

In electron micrography, heavy metal stains are often used to enhance contrast. The stains absorb the beam electrons or scatter part of it. DNA and Proteins often show as dark areas because these molecules can attach to the stain.

Which of the following statements explains how this type of image led to the proposal of the Davson-Danielli model of membranes?

• Dark lines are layers of protein which surround the phospholipid bilayer.

• The lines indicate a spiral protein structure forming part of the membrane.

• The extracellular layer is made of protein and the membrane's phospholipids show as pale.

• Dark lines are layers of phospholipid with protein in between.

The extraordinary illustration shown below is of a ribosome attached to a membrane.

The ribosome is synthesizing a protein within the membrane.

What is the most likely function of this membrane protein?

• An enzyme

• A protein channel.

• An antibody.

• An oxygen carrying molecule.

Using the fluidity of membranes, cells can take in large particles and release substances outside the cell as secretions. What are the names of these two processes?

• Exocytosis moves things into cells and endocytosis moves things out of the cell.

• Endocytosis moves things into cells and exocytosis moves things out of the cell.

• Cell apoptosis moves things into cells, and exocytosis moves things out of the cell.

• Endocytosis moves things into cells and endosymbiosis moves things out of the cell.

This box contains skin tissue waiting for a skin grafting operation.

What is special about the solution inside the box which surrounds the tissue?

• The solution has the same osmolarity as the cells in the tissue.

• The solution is made of cytoplasm from cells in the tissue.

• The solution is hypertonic compared to the tissue.

• The solution is hypotonic compared to the tissue.

The four cells shown below have each been surrounded by a solution for 1 hour.

Which cells have been in a hypotonic solution and which have been in a hypertonic solutions?

• Cells 2 & 3 have been in hypotonic solutions and 1 & 4 have been in hypertonic solutions

• Cells 1 & 2 have been in hypotonic solutions and 3 & 4 have been in hypertonic solutions.

• Cells 1, 2 & 3 have been in hypotonic solutions and Cell 4 has been in a hypertonic solution.

• Cells 3 & 4 have been in hypotonic solutions and 1 & 2 have been in hypertonic solutions.

The table of results below shows the % plasmolysis of a sample of cells at different concentrations of salt.

Which of the following is the best estimate of the molarity of the cytoplasm of these cells?

• 0.5M

• 1.2 M

• 0.3 M

• 0.8M

The arrow points to a component of the membrane that is best described as a

• sugar floating in lipids.

• protein floating in lipids.

• lipid floating in proteins.

• lipid floating in sugars.