Biol Test 2-A
The most abundant molecules in cell membranes are __________.
Phospholipids
Which of the following features explains why plant cells don't explode as a result of osmosis?
Plant cells have a cell wall that prevents the cell from absorbing too much water.
Which of the following enables a cell to acquire and concentrate a specific kind of molecule?
Receptor-mediated endocytosis
You observe a cell as it takes up certain molecules (Substance X). You notice that transport depends on the interaction of Substance X with a membrane protein. You conclude that the mode of cell uptake being demonstrated is __________.
Receptor-mediated endocytosis
Which of these is not a function of membrane proteins?
Reproduction
A nursing baby is able to obtain necessary proteins from its mother's milk. These molecules are able to enter the cells lining the baby's digestive tract through __________.
endocytosis (endo- in)
What is a concentration gradient?
A difference in the density of substances from one side of the structure to the other.
Which of the following would be least likely to diffuse through a cell membrane without the help of a transport protein?
A large hydrophilic molecule (which needs facilitated diffusion)
What is a difference between active transport (AT) and facilitated diffusion (FD)?
AT requires energy from ATP, and FD does not.
Which of the following statements concerning the plasma membrane is FALSE?
Cholesterol helps add a rigid framework, or scaffold, to the plasma membrane.
The movement of molecules from an area of higher concentration to an area of lower concentration is called __________.
Diffusion
You are given two substances to study, one large and one small. Given what you have learned about the movement of material across membranes, which of the following methods would you predict could be used by cells to transport the larger substance?
Exocytosis
The function of phospholipids is to __________.
Form cell membranes
Which of the following best describes the process of facilitated diffusion?
Movement of solutes across a membrane down their concentration gradients with the involvement of membrane proteins
Which of the following best describes the process of facilitated diffusion?
Movement of solutes across a membrane down their concentration gradients with the involvement of membrane proteins.
A plant cell is placed in a solution whose solute concentration is twice as great as the concentration of the cell cytoplasm. The cell membrane is selectively permeable, allowing water but not the solutes to pass through. What will happen to the cell?
The cell will shrivel because of osmosis.
In osmosis, water always moves toward the __________ solution—that is, toward the solution with the __________ solute concentration.
hypertonic; greater
If you are shipwrecked, it is not a good idea to drink seawater because it __________.
is a hypertonic solution and will make you thirstier.
The fluid-mosaic model was ultimately the best depiction of the cell membrane because __________.
it showed that the phospholipids and proteins within the layers were able to move
The maximum size of a cell is limited by __________.
its need for enough surface area for exchange with its environment
Red blood cells shrivel when placed in a 10% sucrose solution. When first placed in the solution, the solute concentration of the cells is __________ the concentration of the sucrose solution. After the cells shrivel, their solute concentration is __________ the concentration of the sucrose solution.
less than; equal to
In phospholipids, the "heads" are composed of __________ , whereas the "tails" are composed of __________.
phosphate; fatty acids
If phospholipids are dropped into water __________.
structures will form with the hydrophilic tails pointing outward and the hydrophobic heads pointing inward
To enter or leave a cell, substances must pass through __________.
the plasma membrane
