mastering biology ch 5

Plasma membrane

B

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.

Which of these is exhibiting kinetic energy?

a space station orbiting Earth; Kinetic energy is energy of motion.

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.

Identify Structure D.

phospholipid bilayer of membrane; Phospholipids can be recognized by the presence of a head and two tails.

Transport protein

B

Plasma membrane

D

Which of these is ATP?

Figure C; three phosphates, adenin, and one ribose

Diffusion causes a net movement of molecules down their concentration gradient

D

What is the fate of the phosphate group that is removed when ATP is converted to ADP?

It is acquired by a reactant in an endergonic reaction; By acquiring the phosphate group the reactant acquires energy.

The reaction ADP + P --> ATP is a(n) _____ reaction.

endergonic; Energy has been acquired from the surroundings.

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

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

Which of the following is highest in chemical energy?

one molecule of glucose

Side with lower concentration of molecules

C

Structure B is a _____.

Transport Protein; The transport protein facilitates the movement of solute across the plasma membrane.

In cellular respiration, most energy is released and transferred to ATP when _____.

high-energy electrons "fall" to lower energy levels

In active transport,

molecules move across the plasma membrane against their concentration gradient.

You can recognize the process of pinocytosis when _____.

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

This cell is in a(n) _____ solution.

hypertonic; There is a greater concentration of solute outside the cell.

Kinetic energy is energy in motion. Potential energy is _____ energy.

stored

In cells, what is usually the immediate source of energy for an endergonic reaction?

ATP; The hydrolysis of ATP provides the energy needed for an endergonic reaction.

Antibiotics - for example, penicillin - cannot be used to treat viral infections, such as the common cold. Why?

Antibiotics inhibit enzymes that are essential to the survival of bacteria only, not enzymes important to humans; Antibiotics are designed specifically to fight bacterial infections. Many antibiotics, such as penicillin, inhibit a bacterial enzyme that is used to make protective cell walls. Neither animals nor viruses make such an enzyme and therefore are mostly unaffected by antibiotics.

In plant cells, carbon dioxide and water are joined to form carbohydrates. Plant cells can also break down carbohydrates such as glucose, releasing carbon dioxide, water, and energy. No one has ever observed such reactions between water and carbon dioxide outside of living cells. What allows simple molecules to assemble into more complex molecules, and also disassemble, in cells but not in other, nonbiological environments?

Cells couple energy-releasing reactions to energy-requiring reactions; One of the many things cells do well is the linking of metabolic reactions in ways that allow an energy-yielding reaction to be coupled to an energy-requiring reaction. ATP molecules are the key to energy coupling.

A(n) _____ reaction occurs spontaneously.

Exergonic; In exergonic reactions the products have less potential energy than the reactants

Which of these statements describes what occurs in facilitated diffusion?

Facilitated diffusion of solutes occurs through protein pores in the membrane; Protein pores are passageways for facilitated diffusion.

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.

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.

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.

exocytosis

figure 1

In this reaction _____.

the products have less potential energy than the reactants

What is energy coupling?

the use of energy released from an exergonic reaction to drive an endergonic reaction

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.

Energy is conserved. This means that in any system, _____.

total energy input equals total energy output

Side with higher concentration of molecules

A

Side with lower concentration of square molecules

A

Which statement best describes phagocytosis?

A cell engulfs a particle by wrapping pseudopodia around it and packaging it within a vacuole; After entry, the vacuole usually fuses with a lysosome, whose hydrolytic enzymes digest the contents of the vacuole.

Which of these is hydrophobic like the interior of the plasma membrane?

A; Lipid soluble molecules are hydrophobic.

Energy input from the cell

C

Side with higher concentration of square molecules

E

Frequently, transplanted organs are rejected by the recipient's body. How is this reaction related to plasma membranes?

Each person has a unique set of carbohydrate chains attached to his or her plasma membranes; When cells with unrecognized carbohydrate chains are placed in a person, his or her immune system attacks the foreign cells as though they were infectious agents.

Review the figure below of passive transport, then choose one of the following statements as being descriptive of this process.

Passive transport can transport molecules without the assistance of proteins from an area of high concentration to an area of lower concentration; Passive transport involves the vibration of molecules, which causes them to randomly move from areas where they are more concentrated to areas where they are less concentrated. It requires no energy or proteins to cross the membrane.

The hydrolysis of DNA into nucleotides constitutes an exergonic reaction. Yet, DNA is quite stable. Why is this the case?

The activation energy required to initiate this reaction is seldom reached; An input of energy, termed the activation energy, is required to initiate this reaction.

What happens to the chemical energy that is extracted from molecules by cellular activities but that is not used for cellular work?

The energy contributes to the entropy of the system; The second law of thermodynamics states that in any energy transformation, the overall disorder of the universe increases. Most often, this disorder comes in the form of thermal molecular motion (heat), which is a form of energy that is not lost but cannot be harnessed for work.

The concentration of solutes in a red blood cell is about 2%. 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; Water moves by osmosis from the hypotonic environment, the cell interior, to the hypertonic environment.

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 movement of atoms, ions, or molecules from a region of higher concentration to regions of lower concentration is called _____.

diffusion; Diffusion is the tendency of molecules to spread out in the available space. A substance will diffuse from an area of high concentration to an area of lower concentration.

This graph illustrates a(n) _____ reaction.

endergonic; The products contain more potential energy than the reactants.

Which of these reactions requires a net input of energy from its surroundings?

endergonic; The products of endergonic reactions have more potential energy than the reactants.

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

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.

Select the INCORRECT association.

exergonic ... uphill; Exergonic reactions release energy.

The reaction A --> B + C + heat is released in a(n) _____ reaction.

exergonic; Energy has been released

The energy for an endergonic reaction comes from a(n) _____ reaction.

exergonic; The energy released by an exergonic reaction can be used to drive an endergonic reaction.

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.

endocytosis

figure 2

What condition might result from an excess of aquaporins?

fluid retention in pregnant women; Aquaporins transport water. An excess of aquaporins during pregnancy can result in fluid retention.

Identify Structure A.

glycoprotein; Structure A is composed of both a carbohydrate and a protein.

Which of these are by-products of cellular respiration?

heat and water

In this reaction _____.

heat has been released to the environment; The potential energy of the products is less than that of the reactants.

In the process of osmosis, water displays a net movement from an area of __________ water concentration to an area of __________ water concentration.

higher ... lower; Water displays a net movement down its concentration gradient. Movement down a concentration gradient is a characteristic of passive transport.

What type of reaction breaks the bonds that join the phosphate groups in an ATP molecule?

hydrolysis; Hydrolysis involves breaking bonds with the addition of water.

You know that this cell is in a(n) _____ solution because it _____.

hypertonic solution ... lost water; A cell will lose water when placed in a hypertonic solution.

You know that this cell is in a(n) _____ solution because the cell _____.

hypotonic ... swelled; A cell will gain water when placed in a hypotonic solution.

Endocytosis moves materials _____ a cell via _____.

into ... membranous vesicles; The prefix "endo-" means "inward."

Light is _____ energy, which is converted into _____ energy by plants.

kinetic ... chemical; Light is kinetic energy, and molecules possess chemical energy. Chemical energy refers to the potential energy that can be released during chemical reactions.

When molecules move down their concentration gradient, they move from where they are __________ to where they are __________

more concentrated; less concentrated

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

osmosis; Osmosis is the passive transport of water.

The plasma membrane is selectively permeable. Which of the following can pass freely through the membrane with no assistance?

oxygen and carbon dioxide; Oxygen and carbon dioxide, as well as other small, hydrophobic molecules, can move freely across the membrane.

Diffusion across a biological membrane is called __________

passive transport

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.

Chemical energy is a form of _____ energy.

potential; Chemical energy is a form of stored energy.

Overall, membranes seem to have a great deal in common, but on closer inspection it is revealed that membranes of different cells have unique properties. What is the primary component of membranes that gives membranes cell-specific properties?

proteins; There is a large variety of proteins, and it is differences in these widely varying molecules that give a particular membrane its unique properties.

The lipids in a cell membrane are arranged _____.

so that the nonpolar parts of two lipids point toward each other; A phospholipid bilayer can exist as a stable boundary between two aqueous compartments because the molecular arrangement shelters the hydrophobic tails of the phospholipids from water while exposing the hydrophilic heads to water.

Structure A is a _____.

solute; A solute is crossing the plasma membrane.

What is the function of Structure E?

stabilization of the phospholipids; Cholesterol helps to stabilize the structure of the plasma membrane.

The first law of thermodynamics _____.

states that energy is neither created nor destroyed; The first law of thermodynamics states that energy can be transformed but can be neither created nor destroyed.

For an enzyme to catalyze a reaction there must be a specific fit between the __________ and the enzyme's __________.

substrate ... active site; The shapes of these two components are complementary.

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.

Structure A in the figure is a(n) _____.

transport protein; The protein is allowing solute molecules to enter the cell.

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; Correct. The hydrophilic heads would orient themselves so that they are in contact with the aqueous surroundings, forming water bubbles, with the hydrophobic tails oriented toward each other.