Chapter 7

Which of the following statements is most likely true of a protein that cotransports glucose and sodium ions into the intestinal cells of an animal?

A substance that blocks sodium ions from binding to the cotransport protein will also block the transport of glucose.

What property of dishwashing liquid (detergent) makes it useful to wash grease from pans?

Amphipathic nature

If a red blood cell is placed in a salt solution and bursts, what is the tonicity of the solution relative to the interior of the cell?

Hypotonic (The salt concentration in the solution is lower than it is in the cell, so water enters the cell, causing it to burst.)

Which of the following statements correctly describes osmosis?

In osmosis, water moves across a membrane from areas of lower solute concentration to areas of higher solute concentration.

Which of the following statements about diffusion is true?

It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.

How can a lipid be distinguished from a sugar?

Lipids are nonpolar molecules, whereas sugars are polar.

Which of the following particles could diffuse easily through a cell membrane?

Oxygen (O2) (Small nonpolar molecules such as oxygen can diffuse across cell membranes.)

What will happen to a red blood cell (RBC), which has an internal ion content of about 0.9%, if it is placed into a beaker of pure water?

The cell would swell because the water in the beaker is hypotonic relative to the cytoplasm of the RBC.

Which of the following factors does not affect membrane permeability?

The polarity of membrane phospholipids (Phospholipids contain both a polar head and a nonpolar hydrocarbon tail, both of which are necessary for their ability to form membrane bilayers.)

When a cell is in equilibrium with its environment, which of the following processes occurs for substances that can diffuse through the plasma membrane?

There is random movement of substances into and out of the cell.

True or false? Osmosis is a type of diffusion.

True (Osmosis is the diffusion of water across a selectively permeable membrane.)

True or false? The water-soluble portion of a phospholipid is the polar head, which generally consists of a glycerol molecule linked to a phosphate group.

True (The hydrophilic, or water-loving, portion of a phospholipid is the polar head, whereas the hydrophobic portion is the nonpolar tail.)

The force driving simple diffusion is ________, while the energy source for active transport is ________.

a concentration gradient; ATP hydrolysis

flaccid

a plant cell and its surroundings are isotonic, there is no net movement of water into the cell (call this limp)

turgid

a plant cell in a hypotonic solution swells until the wall opposes uptake; cell is now firm

Which of the following structures would decrease the electrochemical gradient across a membrane?

a potassium channel

Electrongenic Pump

a transport protein that generates voltage across a membrane; help store energy that can be used for cellular work (sodium-potassium pump)

proton pump

actively transports hydrogen ions out of the cell

Which of the following statements correctly describes the normal tonicity conditions for typical plant and animal cells? The animal cell is in _____.

an isotonic solution, and the plant cell is in a hypotonic solution

Which of the following molecules dramatically increases the rate of diffusion of water across cell membranes?

aquaporins

receptor-mediated endocytosis

binding of specific solutes to receptors triggers vesicle formation

According to the fluid mosaic model of cell membranes, phospholipids _____.

can move laterally along the plane of the membrane

Phagocytosis

cell engulfs a particle in a vacuole; cell eating

An animal cell lacking carbohydrates on the external surface of its plasma membrane would likely be impaired in which function?

cell-cell recognition

lysis

cells swell and burst

endocytosis

cells take in macromolecules by forming vesicles from the plasma membrane;

Which of the following types of molecules lack hydrophilic domains?

cholesterol

passive transport

diffusion of a substance across a membrane with no energy investment

osmosis

diffusion of water through a selectively permeable membrane

According to the fluid mosaic model of membrane structure, proteins of the membrane are mostly

embedded in a lipid bilayer.

Diffusion of ions across membranes through specific ion channels is driven by ________.

ion electrochemical gradients

According to the fluid mosaic model, a membrane ________.

is composed of a fluid bilayer of phospholipids with embedded amphipathic proteins

Celery stalks that are immersed in fresh water for several hours become stiff. Similar stalks left in a 0.15 M salt solution become limp. From this we can deduce that the fresh water_____.

is hypotonic and the salt solution is hypertonic to the cells of the celery stalks

A bacterium engulfed by a white blood cell through phagocytosis will be digested by enzymes contained in _____.

lysosomes

plasmolysis

membrane pulls away from the cell wall; causing the plant to wilt

Pinocytosis

molecules dissolved in droplets are taken up when extracellular fluid is "gulped" into tiny vesicles; cell drinking

When molecules move down their concentration gradient, they move from where they are ______ to where they are _______.

more concentrated; less concentrated

Cotransport

occurs when active transport of a solute indirectly drives transport of other substances

What name is given to the process by which water crosses a selectively permeable membrane?

osmosis

Diffusion across a biological membrane is called

passive transport

Facilitated diffusion is a type of _______.

passive transport (During facilitated diffusion, the cell is not expending energy to move the particles across the membrane; therefore, facilitated diffusion is a form of passive transport.)

Which of the following types of molecules are hydrophilic and therefore excluded from the hydrophobic portion of the phospholipid bilayer?

peripheral membrane proteins

White blood cells engulf bacteria using _____.

phagocytosis

facilitated diffusion

process of diffusion in which molecules pass across the membrane through cell membrane channels (uses transport proteins to speed up passive movement)

active transport

requires energy, usually in the form of ATP hydrolysis, to move substances against their concentration gradients

hypertonic

solute concentration is greater than that inside the cell; cell loses water

hypotonic

solute concentration is less than that inside the cell; cell gains water

isotonic

solute concentration is the same as that inside the cell; no net water movement across the plasma membrane

osmoregulation

the control of solute concentrations and water balance

bulk transport

the process by which large particles and macromolecules, polysaccharides and proteins, are transported through plasma membranes. Inc. exocytosis and endocytosis; requires energy

concentration gradient

the region along which the density of a chemical substance increases or decreases

diffusion

the tendency for molecules to spread out evenly into the available space; movement of molecules from an area of higher concentration to an area of lower concentration.

exocytosis

transport vesicles migrate to the membrane, fuse with it, and release their contents outside the cells