Chapter 7

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

. the diffusion gradient in cell B is steeper ( As long as a metabolically active cell converts oxygen to water during cellular respiration shortly after it enters, diffusion into the cell will continue because the concentration gradient favors movement in that direction.)

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

1.0 M ( This solution is hypertonic to the plant cell. Water will leave the cell, and eventually the plasma membrane will pull away from the cell wall, resulting in plasmolysis.)

Green olives may be preserved in brine, which is a 30% salt solution. How does this method of preservation prevent microorganisms from growing in the olives

A 30% salt solution is hypertonic to the bacteria, so they lose too much water and undergo plasmolysis. ( If a cell is placed in a hypertonic solution, it will lose water to its environment, shrivel, and probably die.)

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. ( Active transport can move substances against the concentration gradient, but it requires energy in the form of ATP.)

Seawater is hypertonic to cytoplasm in vertebrate cells and in plant cells. 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.( Seawater will cause both cells to lose water.)

Which of the following statements about cotransport of solutes across a membrane is correct?

Cotransport proteins allow a single ATP-powered pump to drive the active transport of many different solutes. ( The electrochemical gradient created by a single ATP-dependent pump can drive the transport of many different solutes using cotransport proteins.)

Which of the following correctly describes a general property of all electrogenic pumps?

Electrogenic pumps create a voltage difference across the membrane. ( An electrogenic pump creates a net charge difference across a membrane (a membrane potential).)

Which statements about the sidedness of the plasma membrane is correct?

Every integral membrane protein has a specific orientation in the plasma membrane. The asymmetrical distribution of membrane proteins, lipids, and carbohydrates across the plasma membrane is determined as the membrane is being constructed. The two lipid layers may differ in specific lipid composition. Parts of proteins that are exposed on the cytoplasmic side of the endoplasmic reticulum are also exposed on the cytoplasmic side of the plasma membrane.

Which of these statements describes some aspect of facilitated diffusion?

Facilitated diffusion of solutes may occur through channel or transport proteins in the membrane. ( The passageways for facilitated diffusion may be either protein pores or carrier proteins)

Which of the following is FALSE in regard to facilitated diffusion?

Facilitated diffusion requires the hydrolysis of ATP. (Facilitated diffusion, like simple diffusion, needs only a concentration gradient—no energy input is required.)

Which of the following statements about diffusion is true?

It is a passive process. ( Diffusion is the tendency of molecules to spread out in the available space. A substance will diffuse from an area of higher concentration to an area of lower concentration without energy input)

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

Membrane carbohydrates function primarily in cell-cell recognition. ( Variations in carbohydrate structure distinguish one species from another, one individual from another, and even one cell type from another.)

Which of the following functions of membrane proteins is important in tissue formation during embryonic development in animals?

Membrane proteins with short sugar chains form identification tags that are recognized by other cells. ( Cell-cell recognition is an important function of membrane proteins, and this cell-cell recognition is important in tissue formation during embryogenesis.)

Which of the following is a major difference between prokaryotic and eukaryotic cells?

Most prokaryotic cells have no internal membranes; eukaryotic cells do.

A selectively permeable membrane separates two solutions. Water is able to pass through this membrane; however, sucrose (a disaccharide) and glucose (a monosaccharide) cannot pass. The membrane separates a 0.2-molar sucrose solution from a 0.2-molar glucose solution. With time, how will the solutions change?

Nothing will happen, because the two solutions are isotonic to one another.( Osmotic pressure is produced by the concentration of dissolved substances and is not influenced by the relative sizes of the solutes.)

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 solute molecules occurs down the concentration gradient of the molecule. ( Passive transport can occur in either direction, but the direction of net diffusion is down the concentration gradient of the solute.)

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.. ( Their structure allows some substances to penetrate easily and blocks others.)

Which of the following statements is true regarding potential energy?

Potential energy is the energy possessed by matter due to its location or structure.

The plasma membrane is referred to as a "fluid mosaic" structure. Which of the following statements about that model is true?

The fluid aspect of the membrane is due to the lateral and rotational movement of phospholipids, and embedded proteins account for the mosaic aspect.

Consider the transport of protons and sucrose into a plant cell by the sucrose-proton cotransport protein. Plant cells continuously produce a proton gradient by using the energy of ATP hydrolysis to pump protons out of the cell. Why, in the absence of sucrose, do protons not move back into the cell through the sucrose-proton cotransport protein?

The movement of protons through the cotransport protein cannot occur unless sucrose moves at the same time. ( The obligate coupling of proton movement to sucrose movement prevents the energy of the proton gradient from being lost if sucrose is not present.)

How do membrane phospholipids interact with water?

The polar heads interact with water; the nonpolar tails do not.

Active transport requires an input of energy and can also generate voltages across membranes. Based on this information, which of the following statements is true?

The sodium-potassium pump hydrolyzes ATP and results in a net positive change outside the cell membrane ( This is how the sodium-potassium pump generates voltage across the cell membrane.)

Glucose can be moved into cells via an active transport mechanism when the concentration of glucose inside the cell is higher than the concentration of glucose outside of the cell. This active transport mechanism moves glucose and sodium into the cell at the same time. The glucose moves up its gradient and the sodium moves down its gradient. Which of the following statements about this mechanism is accurate?

To pump glucose up its concentration gradient, sodium moves down its concentration gradient, and the distribution of sodium ions across the membrane forms an electrochemical gradient that drives this mechanism. ( The movement of sodium down its gradient drives glucose up its gradient, and because sodium is at different concentrations on either side of the membrane and as sodium has a +1 charge, an electrochemical gradient also exists.)

A single plant cell is placed in an isotonic solution. Salt is then added to the solution. Which of the following would occur as a result of the salt addition?

Water would leave the cell by osmosis, causing the volume of the cytoplasm to decrease. ( The added salt makes the solution hypertonic compared to the cell. Water will leave the cell by osmosis.)

The concentration of solutes in a red blood cell is about 2%, but red blood cells contain almost no sucrose or urea. Sucrose cannot pass through the membrane, but water and urea can. Osmosis would cause red blood cells to shrink the most when immersed in which of the following solutions

a hypertonic sucrose solution ( When a cell is placed in a hypertonic environment, water will leave the cell, causing it to shrink.)

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 ( The combination of being polar and large means that this molecule will be the slowest one from the choices to move across the membrane.)

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

carbon dioxide ( Hydrophobic molecules, such as hydrocarbons, carbon dioxide, and oxygen, can dissolve in the membrane and cross it with ease.)

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 ( Endocytosis is the procedure that cells use to import large molecules across their plasma membrane.)

Which of the following is NOT a function of membrane proteins?

energy, carbon, and nitrogen storage ( Proteins are not present in biological membranes to act as stores of energy, carbon, and nitrogen.)

Which of the following processes and organelles account for the replacement of lipids and proteins lost from the plasma membrane?

exocytosis and smooth ER and rough ER ( In exocytosis, vesicles derived from the endomembrane system fuse with the plasma membrane, thus increasing the number of phospholipids in the plasma membrane and increasing its surface area. The smooth ER is largely responsible for production of lipids destined for the membrane, and the rough ER produces proteins destined for the plasma membrane.)

A cell has a membrane potential of -100 mV (more negative inside than outside) and has 1,000 times more calcium ions outside the cell than inside. Which of the following best describes a mechanism by which Ca2+ enters the cell

facilitated diffusion of Ca2+ into the cell down its electrochemical gradient ( Both the electrical and chemical (concentration) gradients contribute the energy to move Ca2+ into the cells by facilitated diffusion as long as there is a channel or carrier that is specific for Ca2+.)

Consider the currently accepted fluid mosaic model of the plasma membrane. Where in the plasma membrane would cholesterol most likely be found?

in the interior of the membrane ( The steroid cholesterol, wedged between phospholipid molecules in the plasma membranes of animals, helps stabilize the membrane.)

Hydrophobic substances like salad oil are

nonpolar molecules that repel water molecules.

Consider the currently accepted fluid mosaic model of the plasma membrane. Where in the membrane would carbohydrates most likely be found?

on the outside (external) surface of the membrane ( Membrane carbohydrates are covalently bonded to lipids or proteins and extend out from the external side of the plasma membrane as a means of cell identification.)

Which of the following pairs correctly matches a membrane transport process to its primary function?

pinocytosis: the uptake of water and small solutes into the cell by formation of vesicles at the plasma membrane ( Pinocytosis is the uptake of liquid and the solutes dissolved in the liquid)

Which of the following enables a cell to pick up and concentrate a specific kind of molecule?

receptor-mediated endocytosis ( In receptor-mediated endocytosis, only a specific molecule, called a ligand, can bind to the receptor. Without receptor binding occurring first, endocytosis does not proceed)