Cell Membrane and Membrane Transport Flashcards
The substances in cell membranes that form a barrier to the movement of materials across the membrane are
lipids
The _____ portion of the cell membrane is responsible for the isolating function of the membrane, whereas the _____ portion regulates exchange and communication with the environment.
lipid; protein
Plasma membranes are best described as a
double layer of phospholipids with hydrophobic tails oriented toward one another.
The hydrophobic tails of a phospholipid bilayer are oriented toward the
interior of the plasma membrane (i.e. toward one another)
Which of the following would NOT be found in a membrane?
Cellulose
The net movement of molecules from a high concentration to a low concentration is best described by which of the following?
simple diffusion
For diffusion to occur, there must be
a gradient
The bacterium Vibrio cholera releases a toxin that blocks a channel protein in the membranes of cells that line the intestine. This toxin prevents the movement of sodium ions from the inside of the intestine into cells. If the sodium ions could not move into the cells, how would this affect the movement of water between the inside of the intestine and the cells?
Water would leave the cells and enter the intestines by osmosis.
Which of the following is an energy-requiring mode of transport that brings substances into a cell?
Receptor-mediated endocytosis
In reference to diffusion, “passive” really means
no energy required
Carbon dioxide crosses the plasma membrane by simple diffusion. The rate at which carbon dioxide enters the cell is determined by the
concentration of carbon dioxide on each side of the membrane
What is active transport
movement of molecules into or out of a cell against a concentration gradient
When substances move through a plasma membrane and down gradients of concentration, this is called
passive transport
To say that a cell is “selectively permeable” means
only certain molecules can pass through.
Molecules that permeate a plasma membrane by facilitated diffusion
require the aid of transport proteins
Which of the following occurs as an enzyme produced by a cell is secreted from the cell?
exocytosis
molecules assisted by carrier proteins may cross a selectively permeable membrane by
facilitated diffusion
If red blood cells are taken from the body and placed in a hypertonic solution, what happens to the cells?
The cells shrivel up because water leaves them.
Osmosis moves water from a region of
low solute concentration off to a region of high solute concentration.
The cytoplasm of a certain cell, such as a neuron, already has a high concentration of K+ ions. How can K+ ions continue to enter the cell?
active transport
The process in which white blood cells engulf bacteria is termed
phagocytosis
Cells use exocytosis to
release substances from the cell.
T/F Carrier molecules in the plasma membrane are required only for active transport
False
