Question

1. 1a. Which of the following is not a possible function of membrane proteins?
   1. act as enzymes
   2. transport molecules or ions
   3. anchor the cytoskeleton
   4. help bind the membrane together

2. 1b. Which of these statements is not true of dynamic equilibria?
   1. As many solvent molecules move across the membrane in one direction as in the other.
   2. All random motion of molecules ceases once equilibrium is reached.
   3. All gradients have ceased to exist.
   4. Net diffusion is no longer occurring.

3. 1c. A tea strainer permitting the passage of tea solt1tion, but blocking the passage of tea leaves is
   1. isotonic permeability
   2. selective permeability
   3. active transport
   4. phagocytosis

4. 1d. All are examples of diffusion except
   1. dropping food coloring into a beaker of water
   2. the heart pumping blood through the arteries
   3. opening a perfume bottle
   4. placing a dye crystal on the surface of an agar plate

5. 1e. Why do plants sometimes wilt on a hot, dry day?
   1. Contractile vacuoles can no longer function.
   2. Water potential increases inside the cells.
   3. There is insufficient water to maintain turgor pressure.
   4. The cell wall becomes less rigid at higher temperatures.

6. 1f. Which of these substances would be located in the hydrophobic section of the cell membrane?

1. peripheral proteins
2. fatty acid tails
3. carbohydrate chains
4. phosphate heads

Answer 1

1a.Ans.(d) help bind the membrane together

Explaination: Membrane proteins can act as enzymes, transportation of molecules and ions across the membrane can take place through channel proteins as in case of facilitated diffusion, membrane proteins can directly bind to cytoskeleton providing structural rigidity of cells. Membrane proteins play no such role of binding membranes together.

1b.Ans.(b) all random motion of molecules ceases once equilibrium is reached.

Explaination: Even when equilibrium is reached, there is still movement of molecules across the membrane but the movement of molecules from one side to other side across the membrane are same from both sides maintaining a constant concentration of molecules or ions in both sides of the membrane.

1c. Ans.(b) selective permeability

Explaination: Selectively permeabale membrane allows only selected molecules or substances to pass through this membrane. Thus, selective permeability allows only specific molecules to pass through. Hence, in selective permeability tea solution is able to pass through but not tea leaves.

1d. Ans.(b) the heart pumping blood through the arteries.

Explaination: Diffusion is the process of movement of substances (ions or molecules) from its higher concentration to lower concentration. Pumping of blood is not diffusion. It involves the transfer of oxygenated blood to different body parts without depending on its concentration.

1e.Ans.(c) there is insufficient water to maintain turgor pressure

Explaination: Turgor pressure is the outward pressure given by liquid content in the cell to the membrane. If large amount of water is lost in hot dry day due to excessive transpiration, turgor pressure will be reduced, hence wilting takes place.

1f.Ans.(b) fatty acids tails

Explaination: Fatty acids are hydrophobic (water hating) molecules and hence it will be oriented inside of the cell membrane which is not in contact with water in the cytoplasm.