HW: Chapter 5 : Biology

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

Active transport requires the expenditure of cellular energy, and facilitated diffusion does not.

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

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

Enzymes lower the overall energy input needed for a reaction to occur, Reactants cannot convert to products without an initial input of energy to start the reaction, By binding to reactant molecules, enzymes make it easier for the bonds in the molecules to break apart.

Why doesn't the antibiotic penicillin harm humans?

Human cells do not have cell walls.

Biologists use the fluid mosaic model to describe membrane structure. Which statements about the fluid mosaic structure of a membrane are correct? Select the three correct statements.

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, The diverse proteins found in and attached to membranes perform many important functions, 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.

Diffusion

a form of passive transport, molecules move across the plasma membrane by crossing the lipid bilayer.

Facilitated Diffusion

a form of passive transport. molecules move across the plasma membrane using a transport protein

Which of these is exhibiting kinetic energy?

a space station orbiting Earth

Exocytosis

a vesicle fuses with the plasma membrane and releases its contents into the extracellular fluid

An enzyme speeds up a reaction by lowering the

activation energy

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

active site

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

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

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

An enzyme is considered a ___ because it speeds up chemical reactions 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

A(n) ______which is often a vitamin, binds to an enzyme and plays a role in catalysis

coenzyme

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

High temperatures or changes in pH can _____ an enzyme, causing it to lose it shape and biological activity

denature

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

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

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

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

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

facilitated diffusion

Which of these are by-products of cellular respiration?

heat and water

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

hypertonic

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

hypertonic

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

hypotonic

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

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

isotonic

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

isotonic

In active transport,

molecules move across the plasma membrane against their concentration gradient

When molecules move down their concentration gradient, they move from where they are____to where they are____.

more concentrated; 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

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

osmosis

Diffusion across a membrane is called

passive transport

Chemical energy is a form of _____ energy.

potential

Which curve shows the course of the reaction in the presence of an enzyme--the black curve or the red curve? Which line represents the activation energy for that reaction--a, b, or c?

red curve; line b

Active Transport

requires energy from the cell. molecules move against their concentration gradient

In a catalyzed reaction, a reaction is often called a(n)

substrate

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

Endocytosis

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

You are working on a team that is designing a new drug. For this drug to work, it must enter the cytoplasm of specific target cells. 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

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

Water crosses the plasma membrane

through facilitated diffusion or diffusion.

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

water

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