BIOL 112 CH 7

Which of the following statements about diffusion is true?

It is a passive process.

Which of the following statements concerning carbohydrates associated with the plasma membrane is correct?

Membrane carbohydrates function primarily in cell-cell recognition.

All molecules have energy that causes thermal motion. One result of thermal motion is diffusion: the tendency of substances to spread out evenly in the available space. Although the motion of each individual molecule is random, there can be directional motion of an entire population of molecules. Consider a chamber containing two different types of dye molecules, purple and orange. The chamber is divided into two compartments (A and B) by a membrane that is permeable to both types of dye. Initially (left image), the concentration of the orange dye is greater on side A, and the concentration of the purple dye is greater on side B. With time, the dye molecules diffuse to a final, equilibrium state (right image) where they are evenly distributed throughout the chamber.

Orange dye moves independently of purple dye - always Concentration gradients exist that drive diffusion of both dyes - only before equilibrium is reached There is a net movement of orange dye from side A to side B - only before equilibrium is reached Purple dye moves only from side B to side A - never There is no net movement of purple dye - only at equilibrium

Which of the following statements about passive transport is correct?

Passive transport permits the solute to move in either direction, but the net movement of the population of solute molecules occurs down the concentration gradient of the molecule.

Which of the following statements about the role of phospholipids in the structure and function of biological membranes is correct?

Phospholipids form a selectively permeable structure.

How does the "fluid mosaic model" describe the structure of the plasma membrane?

Proteins in the membrane contribute to the mosaic quality of the membrane while the lateral and rotational movements of phospholipids contribute to its fluidity.

Red blood cells contain approximately a 2% concentration of solutes. A red blood cell is placed into a solution that contains a 4% concentration of solutes to which the cell is not permeable. What will happen to the red blood cell?

The cell will decrease in size as water flows out of it.

Which of the following statements correctly describe(s) the driving forces for diffusion of Na+ and K+ ions through their respective channels? Select all that apply.

The diffusion of Na+ ions into the cell is facilitated by the Na+ concentration gradient across the plasma membrane The diffusion of K+ ions out of the cell is impeded by the electrical gradient across the plasma membrane The electrochemical gradient is larger for Na+ than for K+

A cell is placed into a solution and the cell shrinks. Which of the following is true regarding the solution?

The solution is hypertonic.

Which of the following is correct regarding peripheral proteins?

These proteins are found only on the surface of the plasma membrane.

Which of the following is correct regarding integral proteins?

These proteins exhibit both hydrophilic and hydrophobic properties.

If you are going to bake potatoes, and your potatoes are soft and dehydrated, they can be soaked in __________ to make them more firm before baking.

a hypotonic solution such as tap water

Which of the following would be least likely to diffuse through a plasma membrane without the help of a transport protein?

a large polar molecule

A cell that neither gains nor loses water while sitting in a solution is probably sitting in

an isotonic environment.

In facilitated diffusion, __________ proteins provide openings in the plasma membrane for substances to flow through without changing structure, and __________ proteins allow passage of substances through the plasma membrane after undergoing a subtle change in shape.

channel; carrier

A nursing infant is able to obtain disease-fighting antibodies, which are large protein molecules, from its mother's milk. These molecules probably enter the cells lining the baby's digestive tract via which process?

endocytosis

Sort the phrases into the appropriate bins depending on whether they describe exocytosis, endocytosis, or both. exocytosis endocytosis both

exocytosis- requires fusion of vesicles with the plasma membrane, secretes large molecules out of the cell, and increases the surface area of the plasma membrane endocytosis- forms vesicles from inward folding of the plasma membrane, and decreases the surface area of the plasma membrane both- requires cellular energy, transported substances never physically cross the plasma membrane

Paramecium is a genus of protists that lives in water. It has organelles called contractile vacuoles that continually eliminate the excess water gained through osmosis. Knowing that Paramecia gain water through osmosis, we can deduce that they normally live in

freshwater lakes and ponds.

(last flashcard) Some solutes pass readily through the lipid bilayer of a cell membrane, whereas others pass through much more slowly, or not at all. Small nonpolar (hydrophobic) molecules, such as dissolved gases (O2, CO2, N2) and small lipids, can pass directly through the membrane. They do so by interacting directly with the hydrophobic interior of the lipid bilayer. Very small polar molecules such as water and glycerol can pass directly through the membrane, but much more slowly than small nonpolar molecules. The mechanism that permits small polar molecules to cross the hydrophobic interior of the lipid bilayer is not completely understood, but it must involve the molecules squeezing between the hydrophobic tails of the lipids that make up the bilayer. Polar molecules such as glucose and sucrose have very limited permeability. Large molecules such as proteins cannot pass through the lipid bilayer. Ions and charged molecules of any size are essentially impermeable to the lipid bilayer because they are much more soluble in water than in the interior of the membrane.

hydrophobic (nonpolar) molecules (O2, CO2, and N2) goes through the phospholipid bilayer small, uncharged polar molecules (H2O, urea, and glycerol) goes through the phospholipid bilayer large, uncharged polar molecules (glucose and sucrose) do not go through the bilayer ions (Cl-, K+, and Na+) do not go through the bilayer

A human cell placed into a hypertonic solution is likely to

lose water by osmosis.

All cells have voltages across their membranes. This voltage is called a(n) __________ and is often maintained by __________.

membrane potential; electrogenic pumps

Which of the following molecules are most abundant in the plasma membrane?

phospholipids

Which of the following cell structures exhibits selective permeability between a cell and its external environment?

plasma membrane

Some solutes are able to pass directly through the lipid bilayer of a plasma membrane, whereas other solutes require a transport protein or other mechanism to cross between the inside and the outside of a cell. The fact that the plasma membrane is permeable to some solutes but not others is what is referred to as selective permeability. Which of the following molecules can cross the lipid bilayer of a membrane directly, without a transport protein or other mechanism?

proteins ions oxygen sucrose carbon dioxide water lipids oxygen, carbon dioxide, water, and lipids

Which of the following structural arrangements of the components in biological membranes facilitates the cell membrane's property of selective permeability?

proteins embedded in two layers of phospholipids

When a person is dehydrated, his or her IV fluids

should be isotonic, because either a hypertonic or hypotonic IV would damage red blood cells.

A human cell placed in a hypotonic environment would

take up water through osmosis.

Many bacteria and fungi have a difficult time surviving on our food if the food is very salty. The best explanation for this is

that the salt in the food creates a hypertonic environment for the bacteria and fungi.

The plasma membrane exhibits selective permeability. This means that __________.

the plasma membrane allows some substances to flow through it more easily than others

The sodium-potassium pump __________.

transports sodium ions out of the cell and transports potassium ions into the cell

All cells contain ion pumps that use the energy of ATP hydrolysis to pump ions across the plasma membrane. These pumps create an electrochemical gradient across the plasma membrane that is used to power other processes at the plasma membrane, including some transport processes. In animal cells, the main ion pump is the sodium-potassium pump.

-

both channels and carriers

- provide a hydrophilic path across the membrane - transport solutes down a concentration or electrochemical gradient - are integral membrane proteins

--

--

only in carriers

-undergo a change in shape to transport solutes across the membrane -transport primarily small polar organic molecules

The internal solute concentration of a plant cell is about 0.8M. To demonstrate plasmolysis, it would be necessary to suspend the cell in what solution?

1.0M

Which of the following plant cells would exhibit the most turgor pressure?

A cell placed in a hypotonic solution

Which of the following substances would be most likely to pass through the plasma membrane without the help of a transport protein?

A nonpolar molecule, such as a hydrocarbon

Which of the following is a correct difference between active transport and facilitated diffusion?

Active transport requires energy from ATP, and facilitated diffusion does not.

only in channels

Allow water molecules and small ions to flow quickly across the membrane. Provide a continuous path across the membrane.

How does cholesterol affect membrane fluidity?

At body temperature, it makes the membrane less fluid.

Cells A and B are the same size, shape, and temperature, but cell A is metabolically less active than cell B; cell B is actively converting oxygen to water in cellular respiration. Oxygen will diffuse more rapidly into cell __________ because __________.

B; the diffusion gradient in cell B is steeper

Why is energy required for active transport?

Because it moves solutes against their concentration gradient

If a red blood cell and a plant cell were placed in seawater, what would happen to the two types of cells?

Both cells would lose water; the red blood cell would shrivel, and the plant plasma membrane would pull away from the cell wall.

Which of the following molecules is most likely to passively diffuse across the plasma membrane?

Carbon Dioxide

What function do carbohydrates fulfill in the plasma membrane?

Cell-to-cell recognition

Which of the following processes and organelle(s) accounts for the replacement of lipids and proteins lost from the plasma membrane?

Exocytosis and smooth and rough ER

Which of these statements describes some aspect of facilitated diffusion?

Facilitated diffusion of solutes may occur through channel or transport proteins in the membrane.

Use targets of Group 1 to indicate the relative concentration of glucose inside and outside the cell. Use targets of Group 2 to indicate the direction that Na+ ions and glucose move through the cotransporter. Use targets of Group 3 to complete the sentences on the right, indicating how Na+ ions and glucose move through the cotransporter relative to their electrochemical and concentration gradients.

In cotransport, the energy required to move one solute against its concentration or electrochemical gradient is provided by an ion moving into the cell down its electrochemical gradient. The ion that moves into the cell down its gradient is usually the same ion that is pumped out of the cell by an active transport pump: for example, Na+ in animal cells using the sodium-potassium pump, or H+ in plants and prokaryotes using the proton pump. In the case of the glucose-sodium cotransporter in animals, Na+ moves back into the cell down its electrochemical gradient, providing the energy for glucose to move into the cell against its concentration gradient. The energy for glucose transport into the cell is supplied indirectly by the sodium-potassium pump's hydrolysis of ATP, and directly by the Na+ electrochemical gradient created by the pump.