46.​ Which of the following statements best explains the processes of passive and active transport?
AP
​ assive transport is the net movement of substances down a concentration gradient that requires
metabolic energy. Active transport is the movement of substances up a concentration gradient that does
not require energy.
B ​Passive transport is the net movement of substances down a concentration gradient that does not
require metabolic energy. Active transport is the movement of substances up a concentration gradient
that requires energy.
C ​Passive transport is the net movement of substances up a concentration gradient that requires
metabolic energy. Active transport is the movement of substances down a concentration gradient that
does not require metabolic energy.
D ​Passive transport is the net movement of substances up a concentration gradient that does not require
metabolic energy. Active transport is the movement of substances down a concentration gradient that
requires energy.
47. Which of the following statements best helps explain the reaction specificity of an enzyme?
A​ The free energy of the reactants is greater than the free energy of the products.
B ​The equilibrium constant of the reaction is much greater than 1.
C ​The shape and charge of the substrates are compatible with the active site of the enzyme.
D ​The concentration of the enzyme inside living cells is greater than the concentration of substrate.
48. A model of the plasma membrane showing several biological molecules, including a transmembrane
protein, is shown in Figure 1.
Figure 1. Phospholipid bilayer with transmembrane protein
Which statement best explains why correct protein folding is critical in the transmembrane protein shown
above?
A I​ nteractions of the hydrophobic and hydrophilic amino acids help to anchor the protein in the
membrane.
B ​Interactions of the peptide bonds of the protein with the membrane will affect the rate at which
substances can cross the membrane.
C ​Interactions of the protein and phospholipids increase membrane fluidity.
D ​Interactions of the quaternary structure of the protein will increase hydrogen bonding in the membrane
and make the membrane less fluid.