Facilitated diffusion across a biological membrane requires ______ and moves a substance ______ its concentration gradient.
transport proteins . . . down
A balloon permeable to water but not to glucose contains a 10% glucose solution. A beaker contains a 5% glucose solution. Which of the following is true?
The solution in the balloon is hypertonic relative to the solution in the beaker.
When two solutions that differ in solute concentration are placed on either side of a selectively permeable membrane, and osmosis is allowed to take place, the water will ______.
exhibit a net movement to the side with lower water concentration
A cell that neither gains nor loses water when it is immersed in a solution is ______.
isotonic to its environment
Some protozoans have special organelles called contractile vacuoles that continually eliminate excess water from the cell. The presence of these organelles tells you that the environment ______.
is hypotonic to the protozoan
Which of the following processes could result in the net movement of a substance into a cell, if the substance is more concentrated in the cell than in the surroundings?
Active transport ______.
can move solutes against their concentration gradient
uses ATP as an energy source
can involve the transport of ions
requires the cell to expend energy