Chapter 5- Derived from the text

The principal force driving movement in diffusion is the __________. A. temperature B. particle size C. concentration gradient D. membrane surface area

A. Temperature

What problem is faced by organisms that live in fresh water? A. Their bodies tend to take in too much water. B. They have no way of controlling their tonicity. C. Only salt water poses problems for animals that live in it. D. Their bodies tend to lose too much water to their environment.

A. Their bodies tend to take in too much water

What is the primary function of carbohydrates attached to the exterior of cell membranes? A. identification of the cell B. flexibility of the membrane C. strengthening the membrane D. channels through membrane

A. identification of the cell

Which plasma membrane component can be either found on its surface or embedded in the membrane structure? A. protein B. cholesterol C. carbohydrate D. phospholipid

A. protein

5.4 Bulk Transport Summary

Active transport methods require the direct use of ATP to fuel the transport. Large particles, such as macromolecules, parts of cells, or whole cells, can be engulfed by other cells in a process called phagocytosis. In phagocytosis, a portion of the membrane invaginates and flows around the particle, eventually pinching off and leaving the particle entirely enclosed by an envelope of plasma membrane. Vesicle contents are broken down by the cell, with the particles either used as food or dispatched. Pinocytosis is a similar process on a smaller scale. The plasma membrane invaginates and pinches off, producing a small envelope of fluid from outside the cell. Pinocytosis imports substances that the cell needs from the extracellular fluid. The cell expels waste in a similar but reverse manner: it pushes a membranous vacuole to the plasma membrane, allowing the vacuole to fuse with the membrane and incorporate itself into the membrane structure, releasing its contents to the exterior.

Which transport mechanism can bring whole cells into a cell? A. pinocytosis B. phagocytosis C. facilitated transport D. primary active transport

B. phagocytosis

In what important way does receptor-mediated endocytosis differ from phagocytosis? A. It transports only small amounts of fluid. B. It does not involve the pinching off of membrane. C. It brings in only a specifically targeted substance. D. It brings substances into the cell, while phagocytosis removes substances.

C. It brings in only a specifically targeted substance.

How does the sodium-potassium pump make the interior of the cell negatively charged? A. by expelling anions B. by pulling in anions C. by expelling more cations than are taken in D. by taking in and expelling an equal number of cation

C. by expelling more cations than are taken in

What happens to the membrane of a vesicle after exocytosis? A. It leaves the cell. B. It is disassembled by the cell. C. It fuses with and becomes part of the plasma membrane. D. It is used again in another exocytosis event

C. it fuses with and becomes part of the plasma membrane`

Active transport must function continuously because __________. A. plasma membranes wear out B. not all membranes are amphiphilic C. facilitated transport opposes active transport D. diffusion is constantly moving solutes in opposite directions

D. diffusion is constantly moving solutes in opposite directions

Which characteristic of a phospholipid contributes to the fluidity of the membrane? A. its head B.cholesterol C. a saturated fatty acid tail D. double bonds in the fatty acid tail

D. double bonds in the fatty acid tail

What is the combination of an electrical gradient and a concentration gradient called? A. potential gradient B. electrical potential C. concentration potential D. electrochemical gradient

D. electrochemical gradient

Water moves via osmosis _________. A. throughout the cytoplasm B. from an area with a high concentration of other solutes to a lower one C. from an area with a high concentration of water to one of lower concentration D. from an area with a low concentration of water to one of higher concentration

D. from an area with a high concentration of water to one of lower concentration

Discuss why the following affect the rate of diffusion: molecular size, temperature, solution density, and the distance that must be traveled.

Heavy molecules move more slowly than lighter ones. It takes more energy in the medium to move them along. Increasing or decreasing temperature increases or decreases the energy in the medium, affecting molecular movement. The denser a solution is, the harder it is for molecules to move through it, causing diffusion to slow down due to friction. Living cells require a steady supply of nutrients and a steady rate of waste removal. If the distance these substances need to travel is too great, diffusion cannot move nutrients and waste materials efficiently to sustain life.

Why is it advantageous for the cell membrane to be fluid in nature?

In what important way does receptor-mediated endocytosis differ from phagocytosis? a. It transports only small amounts of fluid. b. It does not involve the pinching off of membrane. c. It brings in only a specifically targeted substance. d. It brings substances into the cell, while phagocytosis removes substances.

Both of he regular intravenous solutions administered in medicine, normal saline and lactated Ringer's solution, are isotonic. Why is this important?

Injection of isotonic solutions ensures that there will be no perturbation of the osmotic balance, and no water taken from tissues or added to them from the blood.

Why do ions have a difficult time getting through plasma membranes despite their small size?

Ions are charged,and consequently,they are hydrophilic and cannot associate with the lipid portion of the membrane.Ions must be transported by carrier proteins or ion channels

Where does the cell get energy for active transport processes?

The cell harvests energy from ATP produced by its own metabolism to power active transport processes, such as the activity of pumps.

5.3 Passive Transport Summary

The combined gradient that affects an ion includes its concentration gradient and its electrical gradient. A positive ion, for example, might tend to diffuse into a new area, down its concentration gradient, but if it is diffusing into an area of net positive charge, its diffusion will be hampered by its electrical gradient. When dealing with ions in aqueous solutions, a combination of the electrochemical and concentration gradients, rather than just the concentration gradient alone, must be considered. Living cells need certain substances that exist inside the cell in concentrations greater than they exist in the extracellular space. Moving substances up their electrochemical gradients requires energy from the cell. Active transport uses energy stored in ATP to fuel this transport. Active transport of small molecular- sized materials uses integral proteins in the cell membrane to move the materials: These proteins are analogous to pumps. Some pumps, which carry out primary active transport, couple directly with ATP to drive their action. In co-transport (or secondary active transport), energy from primary transport can be used to move another substance into the cell and up its concentration gradient.

Why do phospholipids tend to spontaneously orient themselves into something resembling a membrane?

The hydrophobic, nonpolar regions must align with each other in order for the structure to have minimal potential energy and, consequently, higher stability. The fatty acid tails of the phospholipids cannot mix with water, but the phosphate "head" of the molecule can. Thus, the head orients to water, and the tail to other lipids.

5.1 Components and Structure Summary

The modern understanding of the plasma membrane is referred to as the fluid mosaic model. The plasma membrane is composed of a bilayer of phospholipids, with their hydrophobic, fatty acid tails in contact with each other. The landscape of the membrane is studded with proteins, some of which span the membrane. Some of these proteins serve to transport materials into or out of the cell. Carbohydrates are attached to some of the proteins and lipids on the outward-facing surface of the membrane, forming complexes that function to identify the cell to other cells. The fluid nature of the membrane is due to temperature, the configuration of the fatty acid tails (some kinked by double bonds), the presence of cholesterol embedded in the membrane, and the mosaic nature of the proteins and protein-carbohydrate combinations, which are not firmly fixed in place. Plasma membranes enclose and define the borders of cells, but rather than being a static bag, they are dynamic and constantly in flux

5.2 Passive Transport Summary

The passive forms of transport, diffusion and osmosis, move materials of small molecular weight across membranes. Substances diffuse from areas of high concentration to areas of lower concentration, and this process continues until the substance is evenly distributed in a system. In solutions containing more than one substance, each type of molecule diffuses according to its own concentration gradient, independent of the diffusion of other substances. Many factors can affect the rate of diffusion, including concentration gradient, size of the particles that are diffusing, temperature of the system, and so on. In living systems, diffusion of substances into and out of cells is mediated by the plasma membrane. Some materials diffuse readily through the membrane, but others are hindered, and their passage is made possible by specialized proteins, such as channels and transporters. The chemistry of living things occurs in aqueous solutions, and balancing the concentrations of those solutions is an ongoing problem. In living systems, diffusion of some substances would be slow or difficult without membrane proteins that facilitate transport.

Why is it important that there are different types of proteins in plasma membranes for the transport of materials into and out of a cell?

The proteins allow a cell to select what compound will be transported, meeting the needs of the cell and not bringing in anything else.

How does the sodium-potassium pump contribute to the net negative charge of the interior of the cell?

The sodium-potassium pump forces out three (positive) Na+ ions for every two (positive) K+ ions it pumps in, thus the cell loses a positive charge at every cycle of the pump.

Why does water move through a membrane?

Water moves through a membrane in osmosis because there is a concentration gradient across the membrane of solute and solvent. The solute cannot effectively move to balance the concentration on both sides of the membrane,so water moves to achieve this balance.