Keystone Test Biology: Cell Processes/Transport 5

Question 1

Which term describes the state when the concentration of solutes is equal on both sides of a semipermeable membrane and net movement of water stops?

Accepted Answer

Dynamic equilibrium

Answer

Dynamic equilibrium is reached when concentrations are equal on both sides, so molecules continue moving but there is no net change in concentration.

Question 2

Which of the following is the DIRECT energy source used by the sodium-potassium pump to move ions against their gradient?

Accepted Answer

ATP

Answer

The sodium-potassium pump is an ATPase enzyme that directly hydrolyzes ATP to ADP + Pi to power the conformational changes that transport ions.

Question 3

A student observes that a wilted plant becomes firm after being watered. Which process BEST explains this recovery?

Accepted Answer

Water entering cells by osmosis, increasing turgor pressure

Answer

Water moves by osmosis from the soil (lower solute concentration) into plant cells (higher solute concentration), restoring turgor pressure and making the plant firm.

Question 4

Which molecule is the primary reactant (starting material) in glycolysis?

Accepted Answer

Glucose

Answer

Glycolysis begins with a 6-carbon glucose molecule that is split into two 3-carbon pyruvate molecules through a series of enzyme-catalyzed reactions.

Question 5

Why can small nonpolar molecules like O2 and CO2 cross the cell membrane without assistance while charged ions cannot?

Accepted Answer

The phospholipid bilayer's hydrophobic core repels charged/polar molecules but allows nonpolar ones to pass

Answer

The hydrophobic fatty acid tails in the phospholipid bilayer allow nonpolar molecules to dissolve through but create a barrier for polar molecules and ions.

Keystone Test Practice Test

Keystone Test Practice Test

Keystone Test Biology: Cell Processes/Transport 5