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The fluid mosaic model describes membranes as fluid because ___________.
the phospholipids and proteins move from place to place within the bilayer
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Which of the following types of molecules must pass through membranes via the aqueous pores formed by membrane proteins?
small charged ions such as Na+ and Ca++
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Diffusion is the movement of molecules from __________.
an area of higher concentration of that type of molecule to an area of lower concentration
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In osmosis, water diffuses from the side of the membrane with a higher concentration of water to the side with a lower concentration of water. What determines the concentration of water in a solution?
the amount of molecules other than water dissolved in the solution
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Which of the following processes does a cell use to take up molecules against their concentration gradient?
Both the c and d are correct.
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What is the difference between active transport and passive transport?
- Active transport requires energy and can move substances against their concentration gradient. Passive transport does
- not require energy and can move substances only down their concentration gradient.
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Of the following list of substances that can enter a cell, match the order with the correct mechanism by which they would enter cells: oxygen, water, sodium ions, potassium ions, bacterium. (Note that sodium ions are more concentrated outside cells than inside; potassium ions are more concentrated inside cells than outside.)
simple diffusion, osmosis, facilitated diffusion, active transport, endocytosis
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Imagine that you are studying cell structure in various organisms in your biology lab. Your instructor gives you a microscope slide showing two types of cells that have been suspended in pure water. One type of cell swells up until it
bursts. The other cell maintains its shape throughout the experiment. Suggest an explanation for these observations; assume that both cells were alive at the start of the experiment. Assume also that the concentration of water inside both types of cells is similar.
The cell that remained intact had a contractile vacuole for pumping out the excess water that entered the cell via osmosis.
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The concentration of sodium ions is lower in the cytoplasm of a heart muscle cell than it is in the extracellular fluid. By what mechanism does the cell maintain this difference?
active transport
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When placed in a certain sucrose solution, the volume of a cell decreases; therefore, the sucrose solution is __________ to the cell contents.
hypertonic
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Choose the substance that will diffuse most rapidly across the plasma membrane.
oxygen
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Facilitated diffusion requires __________.
a membrane transport protein and a concentration gradient
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During endocytosis, the contents of the endocytic vesicle __________.
enter the cell
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Which of the following transport processes require(s) energy?
endocytosis
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Membrane fluidity within a phospholipid bilayer is based upon __________.
interactions among nonpolar (hydrophobic) lipid tails
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Recognition proteins function to __________.
permit the cells of the immune system to distinguish between pathogens such as bacteria and cells of your own body
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The point at which a substance is evenly dispersed within a fluid __________.
Both the first and third answers are correct.
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Substances are able to cross the lipid bilayer of a cell at different rates that are unique for each substance. Which of the
following characteristics would favor the simple diffusion of a
substance across a cell membrane?
small molecule size
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The term tonicity describes the solute concentration of the extracellular fluid relative to the solute concentration of the aqueous solution known as cytoplasm. In which direction would water flow according to the principles of osmosis if a cell were placed in a hypertonic solution?
Water would flow out of the cell, leaving the cell shriveled and wrinkled.
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Certain microorganisms have a high percentage of unsaturated fatty acids in their membrane. Because of this, these organisms __________.
are able to withstand low temperatures because their embranes do not solidify as rapidly
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A hormone circulating in the bloodstream would most likely bind to __________.
a receptor protein
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Many metabolic poisons work by inhibiting ATP production. Which type of transport would be most affected?
active transport
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The antifungal drug nystatin combines with sterols in the plasma membrane of the fungal cell to disrupt the membrane and kill the cell. What other cell types might also be affected by nystatin?
animal cells
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When a drop of food coloring is placed in a glass of water, the spreading out of the molecules of food dye is caused by __________.
the random movement of molecules
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Two types of connections between cells called "gap junctions" and "plasmodesmata" are specialized to __________.
permit the passage of substances (e.g., ions) between cells through small passageways that directly link the cytoplasm of one cell to the cytoplasm of another cell
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All cells are surrounded by a thin __________.
plasma membrane
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The __________ consists of all of the internal contents of a cell, except the nucleus in eukaryotic cells.
cytoplasm
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Substances move from high to low concentration by a process called __________.
diffusion
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During __________, energy is used to move substances against their concentration gradient.
active transport
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If a cell is placed in a __________ solution, there will be net water movement out of the cell.
hypertonic
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The type of cell connection that makes the adjacent cells leakproof is a __________.
tight junction
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Label the indicated parts of the cell membrane.
- A phospholipid bilayer
- B cholesterol
- C carbohydrate
- D protein filaments
- E glycoprotein
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This is a diagram of one phospholipid from the cell membrane. Label the individual parts.
- A hydrophilic head
- B hydrophobic tail
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Match the steps in the process of diffusion with the sequence of images below:
- A A drop of dye is placed in water.
- B Dye molecules diffuse into the water, and water molecules diffuse into the dye.
- C Both dye molecules and water molecules are evenly dispersed.
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Blood cells are used to demonstrate osmosis, since they show obvious shape changes in various solutions. Label the solution
to which each of the following blood cells is reacting.
- A isotonic solution
- B hypertonic solution
- C hypotonic solution
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Identify the structures of a typical plant cell as seen in the image below.
- A primary cell wall
- B secondary cell wall
- C cell membrane
- D cytoplasm
- E middle lamella
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Active transport through the plasma membrane occurs
through the action of:
membrane proteins
-
The following is a characteristic of a plasma membrane:
all of the above
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If an animal cell is placed into a solution whose concentration
of dissolved substances is higher than that inside the
cell,
both (1) and (4) are correct
-
Small, nonpolar hydrophobic molecules such as fatty acids
pass readily through a membrane’s lipid bilayer
-
Which of the following would be least likely to diffuse
through a lipid bilayer?
sodium ions
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Which of the following processes causes substances to
move across membranes without the expenditure of cellular
energy?
diffusion
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