Chapter 5 ppractice problems

The molecules in a solid lump of sugar do not move.

False

The movement of materials in solution

If a solute such as dye, is added to a solvent, such as water, the two combine to make a solution. Although the movement of the molecules is spontaneous and random, the net movement of dye is from areas of high concentration to low concentration. The net movement of water is from areas of high concentration to areas of low concentration. Eventually, the concentration of molecules reaches equilibrium, meaning there is roughly an equal concentration of molecules throughout the solution. This can be observed in image3 above.

Active transport

In contrast to passive transport, active transport requires energy for molecules to pass through cell membranes. This might occur when molecules need to move against a concentration gradient, as is the case of thyroid cells where iodine collects in large concentrations. This type of transport requires both chemical energy in the form of ATP and carrier proteins. Cells involved in this type of transport often have high numbers of mitochondria in order to facilitate this process.

Facilitated diffusion occurs

in either direction depending on the concentration gradient of the molecule.

Certain white blood cells engulf microorganisms and bring them in to digest them. This process is best described as

phagocytosis.

Osmosis can best be described as

the diffusion of water from areas where the water concentration is higher to areas where the water concentration is lower.

When sugar is mixed with water, equilibrium is reached when

the dissolved sugar molecules are evenly distributed throughout the solution.

Unlike simple diffusion, facilitated diffusion requires energy expenditure by the cell.

False

Exocytosis is a process by which cells

release substances from the cell via vesicles.

The sodium-potassium pump functions to pump

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

Facilitated diffusion is used to transport

sugars and amino acids.

The rate of diffusion is affected by which of the following?

temperature, the size of molecules, and steepness of the concentration gradient

Active transport can best be described as

the movement of molecules against their concentration gradient, from areas of lower concentration to areas of higher concentration.

Which of the following statements about receptor-mediated endocytosis is TRUE?

It involves coated pits.

If the contents of a beaker are hypotonic in relation to the interior of the cell, water will

enter the cell and lysis will occur.

If the contents of a beaker are hypertonic in relation to the interior of the cell, water will

exit the cell and crenation will occur.

If the contents of a beaker are isotonic in relation to the interior of the cell, water will

both enter and exit the cell at equal rates so no net loss or gain occurs.

What is the source of energy used to power the sodium-potassium pump?

breakdown of ATP

Facilitated diffusion requires

carrier proteins.

Simple diffusion is defined as the movement of

molecules from areas of higher concentration to areas of lower concentration.

Which of the following statements is true in regards to the order and location of the movement of ions in the sodium-potassium pump?

Three sodium ions leave the cell, and then two potassium ions enter the cell.

During one cycle, the sodium-potassium pump binds and moves

3 Na+ and 2 K+.

Diffusion and osmosis

Diffusion is the movement of molecules from regions of higher concentrations to regions of lower concentration until equilibrium is reached. For example, oxygen (O₂) diffuses from the air sacs into the capillaries of the lungs because there is a higher concentration of oxygen in the alveoli (air sacs) than the capillaries. Once all molecules are evenly distributed, their molecules continue to move about, but there is no net movement in any direction. Several factors influence the rate of diffusion and among these factors are temperature, pressure, electrical currents, and molecular size. For example, as temperature increases, the rate of diffusion increases. The diffusion of water across a differentially permeable membrane is called osmosis. For example, water will move from a lower salt solution to a higher salt solution when these two solutions are separated by a differentially permeable membrane.

Differences between endocytosis and exocytosis

Endocytosis is a way substances can enter a cell. During endocytosis, an intracellular vesicle forms to take in substances. Endocytosis occurs in several different ways. Phagocytosis occurs when substances to be transported into the cell are large. Digestion occurs when the resulting vacuole fuses with a lysosome. Pinocytosis occurs when a liquid or small molecule is transported into the cell through a vesicle. Receptor-mediated endocytosis is a form of pinocytosis where molecules first bind to specific receptor proteins, which migrate to or are already in a coated pit. Exocytosis is a way substances can exit a cell. During exocytosis, a vesicle fuses with the plasma membrane as secretion occurs. The Golgi apparatus often produces the vesicles that carry these cell products to the membrane.

Tonicity

In an isotonic solution in animal cells, there is no net movement of water. An animal cell in a hypotonic solution may lyse or burst open. An animal cell in a hypertonic solution will shrivel up or crenate. Plant cells react differently to osmotic changes due to the presence of the cell wall, a structure that animal cells lack. For a plant cell in a hypotonic solution, vacuoles fill with water, increasing turgor pressure. For a plant cell in a hypertonic solution, the cytoplasm shrinks, causing plasmolysis and decreasing turgor pressure.

Diffusion is one of the processes whereby materials are exchanged between a cell and its environment.

True

Facilitated diffusion requires a specific transporter for a specific molecule.

True

If the material the cell takes in is liquid, the process is termed pinocytosis.

True

Low-density lipoprotein is brought into the cell by receptor-mediated endocytosis.

True

The binding and release of sodium or potassium ions are due to conformational changes in the protein.

True

The sodium-potassium pump requires ATP in order to create a change in the shape of the carrier protein.

True

the movement of molecules against their concentration gradient, from areas of lower concentration to areas of higher concentration.

three sodium and two potassium ions.

Which of the following is responsible for determining which direction water will diffuse across the plasma membrane of cells?

tonicity