MB Chapter 5

function cholesterol in PM

Stabilize the structure of the plasma membrane.

The concentration of solutes in a red blood cell is about 2%. Sucrose cannot pass through the membrane, but water and urea can. Osmosis would cause red blood cells to shrink the most when immersed in which of the following solutions?

a hypertonic sucrose solution Water moves by osmosis from the hypotonic environment, the cell interior, to the hypertonic environment.

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. The sodium-potassium pump moves ions across the plasma membrane against their concentration gradients. This requires energy and is an example of active transport.

Phagocytosis is to eating as pinocytosis is to

drinking.

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

facilitated diffusion. In facilitated diffusion, molecules use a transport protein to move across the plasma membrane. There is a net movement of molecules down the concentration gradient -- that is, there is a net movement of molecules from where they are more concentrated to where they are less concentrated.

Identify Structure A.

glycoprotein Structure A is composed of both a carbohydrate and a protein.

The cholesterol associated with animal cell membranes

helps to keep phospholipids from being too close to one another.

Endocytosis moves materials _____ a cell via _____.

into ... membranous vesicles The prefix "endo-" means "inward."

the engulfing of large particles.

phagocytosis

The process of a white blood cell engulfing a bacterium is

phagocytosis.

receptor-mediated endocytosis

A receptor protein is involved in this process.

Which of the following is a difference between active transport and facilitated diffusion? - Facilitated diffusion involves transport proteins, and active transport does not. - Facilitated diffusion can move solutes against a concentration gradient, and active transport cannot. - Active transport requires the expenditure of cellular energy, and facilitated diffusion does not. - Active transport involves transport proteins, and facilitated diffusion does not.

Active transport requires the expenditure of cellular energy, and facilitated diffusion does not. Active transport can move substances against the concentration gradient, but it requires energy, usually in the form of ATP.

Which of the following statements regarding diffusion is false? -Diffusion occurs when particles spread from areas where they are less concentrated to areas where they are more concentrated. - Diffusion requires no input of energy into the system. -Diffusion occurs even after equilibrium is reached and no net change is apparent. -Diffusion is a result of the thermal energy of atoms and molecules.

Diffusion occurs when particles spread from areas where they are less concentrated to areas where they are more concentrated.

Fluidity of an animal cell plasma membrane is enhanced by __________.

cholesterol molecules At low temperatures, cholesterol hinders solidification of the membrane because it prevents the close packing of phospholipids.

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. In endocytosis, the plasma membrane forms a pocket that pinches inward, forming a vesicle that contains material from outside the cell.

A membranous vesicle is fusing with the plasma membrane and releasing its contents into the extracellular fluid.

exocytosis

This process is referred to as _____.

facilitated diffusion Diffusion is occurring via a transport protein.

There is a net diffusion of water out of an animal cell when it is placed in a(n) ___________ solution.

hypertonic

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.

A white blood cell engulfing a bacterium is an example of _____.

phagocytosis Phagocytosis occurs when a cell engulfs a large particle.

You know that this process is _____ because _____.

pinocytosis ... the cell is engulfing extracellular fluid Pinocytosis is "cell drinking."

The lipids in a cell membrane are arranged _____.

so that the non polar parts of two lipids point toward each other A phospholipid bilayer can exist as a stable boundary between two aqueous compartments because the molecular arrangement shelters the hydrophobic tails of the phospholipids from water while exposing the hydrophilic heads to water.

what are the particles called who want to enter the cell

the particles the want to enter the membrane are the solutes

Water crosses the plasma membrane

through facilitated diffusion or diffusion. Water can cross the plasma membrane through the process of facilitated diffusion. However, water molecules can also cross the lipid bilayer directly.