Chapter 5 homework Bio 107

Cells A and B are the same size and shape, but cell A is metabolically quiet and cell B is actively consuming oxygen. Oxygen will diffuse more quickly into cell _____ because _____.

B ... the diffusion gradient there is steeper: As long as a metabolically active cell consumes oxygen as it enters, diffusion into the cell will continue because the concentration gradient favors movement in that direction.

What name is given to the process by which water crosses a selectively permeable membrane?

Osmosis: is the passive transport of water

Which statements about the fluid mosaic structure of a membrane are correct?

The diverse proteins found in and attached to membranes perform many important functions. The framework of a membrane is a bilayer of phospholipids with their hydrophilic heads facing the aqueous environment inside and outside of the cell and their hydrophobic tails clustered in the center. Because membranes are fluid, membrane proteins and phospholipids can drift about in the membrane.

Lactase is essential for digesting lactose in milk. This enzyme is specific for this sugar. Why?

There is a precise compatibility between the active site and the lactose molecule : The three-dimensional characteristics of the molecule provide for a precise interaction with the active site.

In this diagram of the plasma membranes of two adjoining cells, identify the protein indicated by the white arrow, including its function

a receptor protein that binds with a signaling molecule and relays the message into the cell by activating other molecules inside the cell

Which of these is exhibiting kinetic energy?

a space station orbiting Earth

An enzyme speeds up reactions by lowering the - -.

activation energy

An enzyme is specific because the shape of its - - matches only particular reactants.

active site

Utah's Great Salt Lake has an average salinity seven times higher than that of the oceans. Very few multicellular organisms live in this harsh environment. An example is the brine shrimp, which must devote a large portion of its metabolic energy to osmoregulation. These brine shrimp must _____.

actively pump water back into their cells to counter its loss due to osmosis: A cell (in this case, cells within the body of a brine shrimp) will experience a net output of water in a hypertonic environment. For cells to prevent shriveling, they must actively recapture water from their surroundings.

Why doesn't the antibiotic penicillin harm humans?

Human cells dont have cell walls

When in solution, a molecule that moves slowly across an artificial membrane moves rapidly across a plasma membrane. This molecule rapidly enters the cell regardless of whether its concentration is higher inside or outside the cell. Using this information, which transport mechanism is most likely to be responsible for the movement of the molecule across a plasma membrane?

active transport: Some transport proteins can move molecules against their concentration gradient in a process called active transport.

An enzyme is considered a(n)- because it speeds up a chemical reaction without being used up.

catalyst

In your body, what process converts the chemical energy found in glucose into the chemical energy found in ATP?

cellular respiration: This is the name given to the process by which the body converts food energy to energy stored in ATP.

Which of these are by-products of cellular respiration?

heat and water : These are the by-products of cellular respiration.

There is a net diffusion of water out of an animal cell when it is placed in a(n) _____________ solution.

hypertonic

The ideal osmotic environment for a plant cell is a(n) _____________ environment.

hypotonic

The - - between an active site and its substrate often strains bonds and helps the reaction proceed.

induced fit

In active transport,

molecules move across the plasma membrane against their concentration gradient.

In a catalyzed reaction, a reactant is often called a(n) -.

substrate

Aquaporins are proteins that facilitate the transport of __________ across the membrane.

water: Aquaporins are a newly discovered class of transport proteins that transport water in cells with very high water permeability needs

A plant cell placed in a(n) ___________ solution will lose water and plasmolyze

hypertonic

An animal cell placed in a(n)____________ solution will gain water, swell, and possibly burst.

hypotonic

A plant cell surrounded by a(n) ________ solution will be flaccid (limp).

isotonic

Water crosses the plasma membrane

through facilitated diffusion or diffusion:Water can cross the plasma membrane through the process of facilitated diffusion. However, water molecules can also cross the lipid bilayer directly.

The sodium-potassium pump uses energy from ATP to move sodium ions out of the cell, and potassium ions into the cell. This is an example of

Active transport:The sodium-potassium pump moves ions across the plasma membrane against their concentration gradients. This requires energy and is an example of active transport.

Endocytosis moves materials _____ a cell via ____

into ... membranous vesicles: endo means into

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 __________.

endocytosis:Endocytosis is the procedure that cells use to import large molecules across their membranes. Review Figure 5.9 in the textbook.

Azidothymidine (AZT) is an antiretroviral drug used in the treatment of HIV. It shares a structural similarity to a nucleotide. What might be the mode of action for this drug?

competitive inhibition: AZT and the nucleotide compete for the active binding site. When AZT binds to an enzyme known as reverse transcriptase, it blocks the replication of the genetic material of HIV.

The ideal osmotic environment for an animal cell is a(n) ___________ environment.

isotonic

When molecules move down their concentration gradient, they move from where they are ___________ to where they are ______________.

more concentrated, less concentrated

Facilitated diffusion is a type of _____.

passive transport:During facilitated diffusion, the cell is not expending energy to move the particles across the membrane; therefore, facilitated diffusion is a form of passive transport.

A white blood cell engulfing a bacterium is an example of _____.

phagocytosis: Phagocytosis occurs when a cell engulfs a large particle.

In the figure below, working from the inside out, what would be the order of components observed?

water, hydrophilic head, hydrophobic tail, hydrophobic tail, hydrophilic head, water

"Conservation of energy" refers to the fact that _____.

energy cannot be created or destroyed but can be converted from one form to another

Osmosis is often viewed incorrectly as a process driven directly by differences in solute concentration across a selectively permeable membrane. What really drives osmosis?

the difference in water concentration across a selectively permeable membrane: The driving force for osmosis is water's concentration gradient across a selectively permeable membrane. Differences in solute concentration across a membrane create water concentration differences, but solute concentration differences do not directly drive osmosis.

Which of the following would be a factor that determines whether the molecule selectively enters the target cells?

the similarity of the drug molecule to other molecules that are transported into the target cells

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

Active transport moves solutes against their concentration gradient; facilitated diffusion moves substances down their concentration gradient: Active transport can move substances against the concentration gradient, but it requires energy, usually in the form of ATP.

Use the graph and your knowledge of enzymes to identify the three true statements about enzymes.

For a chemical reaction to begin, chemical bonds in the reactant molecules must be broken. This process requires that the molecules absorb energy from their surroundings. The energy that must be invested to start a reaction is called activation energy because it activates the reactants and triggers the chemical reaction. Enzymes enable metabolism to occur by reducing the amount of activation energy required to break the bonds of reactant molecules.

Taq polymerase is an enzyme isolated from the organism Thermophilus aquaticus. This organism has been found living in the hot springs of Yellowstone National Park. This enzyme is used to copy human DNA from crime scenes. Most reactions are performed at ranges similar to those of the human body; however, what considerations should be made for optimum use of this enzyme?

The temperature should be raised : These enzymes are not denatured by high heat and work more efficiently at temperatures of around 70-75°C. If the temperature is not increased, then the reaction will occur at a much slower rate.

The plasma membrane forms a pocket that pinches inward, forming a vesicle that contains material from outside the cell. This describes the process of

endocytosis:In endocytosis, the plasma membrane forms a pocket that pinches inward, forming a vesicle that contains material from outside the cell.

A molecule moves down its concentration gradient using a transport protein in the plasma membrane. This is an example of

facilitated diffusion:In facilitated diffusion, molecules use a transport protein to move across the plasma membrane. There is a net movement of molecules down the concentration gradient -- that is, there is a net movement of molecules from where they are more concentrated to where they are less concentrated.

The synthesis of an amino acid follows this pathway: precursor A > intermediate B > amino acid C. Each reaction is catalyzed by a different enzyme. This metabolic pathway is controlled by feedback inhibition with amino acid C inhibiting the conversion of precursor A to intermediate B. Amino acid C acts as a _____ of the first enzyme in the pathway.

noncompetitive inhibitor: In this form of feedback inhibition, the end product of the pathway inhibits an early-acting enzyme. Because the product of the pathway and the substrate of the early-acting enzyme are very different in structure, competitive inhibition is unlikely as this involves binding of an inhibitor to the active site. Much more plausible is noncompetitive inhibition in which the inhibitor binds to a site on the enzyme that is different from the active site.

Chemical energy is a form of _____ energy.

potential: chemical energy is stored energy

You can recognize the process of pinocytosis when _____.

the cell is engulfing extracellular fluid: Pinocytosis is "cell drinking."