working cell

Which of the following substances would have the most trouble crossing a biological membrane by diffusing through the lipid bilayer?

Na+

The fluid mosaic model describes the plasma membrane as consisting of

diverse proteins embedded in a phospholipid bilayer.

A molecule moves down its concentration gradient using a transport protein in the plasma membrane. This is an example of

facilitated diffusion

The molecules responsible for membrane transport are

protein

Most of the functions of a cell membrane, including transport and enzymatic function, are performed by

proteins

If placed in tap water, an animal cell will undergo lysis, whereas a plant cell will not. What accounts for this difference?

the relative inelasticity and strength of the plant cell wall

Water crosses the plasma membrane

through facilitated diffusion or diffusion.

Facilitated diffusion across a biological membrane requires ________ and moves a substance ________ its concentration gradient.

transport proteins . . . down

In an oil-based, nonpolar environment, phospholipds would arrange themselves so that they _____.

would stay together but in a reverse orientation, with their tails projecting outward

In active transport,

molecules move across the plasma membrane against their concentration gradient.

Diffusion does not require the cell to expend ATP. Therefore, diffusion is considered a type of

passive transport

Which of the following is an accurate comparison of active transport and facilitated diffusion?

Active transport moves solutes against their concentration gradient; facilitated diffusion moves substances down their concentration gradient.

he eukaryotic cell has multiple membrane-enclosed compartments. This evolutionary innovation provides what advantage to the cell?

The different membrane-enclosed spaces allow different parts of the cell to perform specific functions.

The sodium-potassium pump uses energy from ATP to move sodium ions out of the cell, and potassium ions into the cell. This is an example of

active transport

Which of the following processes can move a solute against its concentration gradient?

active transport

Small, nonpolar, hydrophobic molecules such as fatty acids

easily pass through a membrane's lipid bilayer.

The plasma membrane forms a pocket that pinches inward, forming a vesicle that contains material from outside the cell. This describes the process of

endocytosis

When two aqueous solutions that differ in solute concentration are placed on either side of a semipermeable membrane and osmosis is allowed to take place, the water will

exhibit a net movement to the side with lower free water concentration.

A cell that neither gains nor loses water when it is immersed in a solution must be

isotonic to its environment.

All cells are enclosed by a plasma membrane that is similar in ________ and ________.

structure . . . function

Which of the following statements is true among all types of passive transport?

the concentration gradient is the driving force

Osmosis is often viewed incorrectly as a process driven directly by differences in solute concentration across a selectively permeable membrane. What really drives osmosis?

the difference in water concentration across a selectively permeable membrane

What controls the direction of a molecule, such as oxygen, involved in passive transport?

the direction of the oxygen concentration gradient

Plasma membranes are selectively permeable. This means that

the plasma membrane allows some substances to enter or leave a cell more easily than others.