M O V E M E N T A C R O S S C E L L M E M B R A N E S

Question 1

Cells are surrounded by a water solution that contains food molecules, gases, salts, and other
substances. This is the ________ for the cell.

Answer 1

external environment

Question 2

The cell’s outer surface of the
________ is in contact with this external environment, while the inner surface is in contact with the _____. Thus, the_______ controls what enters and leaves the cell.

Answer 2

plasma membrane
cytosol
plasma membrane

Question 3

Small molecules may pass through the membrane. However, the cell membrane is ________. That is, the membrane permits passage of some materials and does not permit
passage of others.

Answer 3

selectively permeable

Question 4

If no additional energy is required for substances to pass through the
membrane, the process is called ______.

Answer 4

passive transport

Question 5

______ is passive transport and is defined as the net movement of molecules from an area of
greater concentration to an area of lesser concentration.

Answer 5

Diffusion

Question 6

The molecules in a gas, a liquid, or a solid are in constant motion due to their _______

Answer 6

kinetic energy.

Question 7

_______ occurs when there is a difference in concentration from one region to another, or from one side of a membrane to another.
This unequal distribution of molecules is called a _________. When
the molecules become uniformly distributed, ________ exists.

Answer 7

Diffusion
concentration gradient.
dynamic equilibrium

Question 8

The equilibrium is______ because molecules continue to move, but there is no net change in concentration over time.

Answer 8

dynamic

Question 9

____ is a specific type of diffusion; it is
the movement of a solvent through a
differentially permeable membrane.

Answer 9

Osmosis

Question 10

In biology, we are concerned with water solutions. When water is mixed with other molecules, this mixture is called an _________

Answer 10

aqueous solution.

Question 11

Water is the ______
and the dissolved substances are the
____

Answer 11

solvent

solutes

Question 12

Since both the solute and solvent molecules take up space in the solution, the higher total
concentration of all solutes (______[Osm]) corresponds with a lower concentration of
water in that solution.

Answer 12

osmolarity

Question 13

If a membrane separating two solutions is impermeable to all solutes, but is permeable to the
water, the water will diffuse across the membrane according to its own concentration gradient.
If both of these solutions have the same osmolarity (i.e., they are ______), water will move
equally in both directions across the membrane and neither will gain water from the other (i.e.,
they are _____).

Answer 13

isosmotic

isotonic

Question 14

But if one solution has a higher
osmolarity (______) than the other, it has a lower water concentration and will therefore water will move
faster into the hyperosmotic solution from the hyposmotic
solution than water moving in the reverse direction.

Answer 14

hyperosmotic

Question 15

The attraction of water by osmosis is called ________.
In the situation descibed, the hyperosmotic solution has a
greater osmotic pressure (i.e., it is _____) and therefore pulls water from the hyposmotic solution with a
lower osmotic pressure (i.e., is ______).

Answer 15

osmotic pressure
hypertonic
hypotonic

Question 16

If however, cells are placed in hypertonic solution, water
will leave the cells faster than it enters and the cells will dehydrate and shrivel — a process called
_______.

Answer 16

crenation

Question 17

Conversely, if cells are placed in a hypotonic solution, water will move into the cell faster than it exits and the cells will swell as the cytosol is diluted. For cells with no cell walls, if
the osmotic pressure exceeds the tensile strength of the plasma membrane, the cells will swell
until they burst

Answer 17

(lysis).

Question 18

Erythrocytes contain _____, a soluble protein pigment.

Answer 18

hemoglobin

Question 19

Suspensions of intact red blood cells

thus appear ______ .The bursting of erythrocytes is called ______

Answer 19

cloudy red.

hemolysis.

Question 20

_____ carries a significantly lower health risk than working with human
blood. But there is always the remote possibility that any blood product may contain
a potential human pathogen.

Answer 20

Sheep blood

Question 21

A _______ is one of the defining features of a living cell.

Answer 21

selectively permeable barrier

Question 22

______ refers to the passive transport of substances across the phospholipid bilayer of the cell membrane without requiring a transport protein.

Answer 22

Simple diffusion

Question 23

if Solution A and Solution B have the same total concentration of
solutes, they also have the same concentration of water and are therefore ______(same
osmolarity).

Answer 23

isosmotic

Question 24

if these two isosmotic solutions are separated by a membrane
permeable to water but not permeable to the solutes, water would diffuse equally to and from
each solution and thus the two solutions are also _______

Answer 24

isotonic

Question 25

We will use three different alcohols:
\_\_\_\_\_\_\_\_
(Figure 1). They differ in size, having
1, 3 and 6 carbon atoms (and -OH
groups) respectively.

Answer 25

methanol, glycerol, and mannitol

Question 26

______is a chemical property that affects a molecule’s solubility. Remember that polar molecules
are more water soluble because water is itself a polar molecule. The uneven distribution of
electrons create some areas on a molecule that are more negative which are balanced by other
areas on a molecule that are more positive. The more negatively charged areas tend to associate
with the –H side of H2O, while the more positively charged areas tend to associate with the –OH
side of H2O.

Answer 26

Polarity

Question 27

One would predict then, the more polar or hydrophilic
a molecule, the _____ it will be
and the longer its hemolysis time.

Answer 27

less permeable