71 terms

Biology Chapter 5: Membrane Transport

In active transport,
molecules move across the plasma membrane against their concentration gradient.
A molecule moves down its concentration gradient using a transport protein in the plasma membrane. This is an example of
facilitated diffusion
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.
The plasma membrane forms a pocket that pinches inward, forming a vesicle that contains material from outside the cell. This describes the process of

In endocytosis, the plasma membrane forms a pocket that pinches inward, forming a vesicle that contains material from outside the cell.
Energy is conserved. This means that in any system, _____.
total energy input equals total energy output
Kinetic energy is energy in motion. Potential energy is _____ energy.
Which of the following is highest in chemical energy?
one molecule of Glucose
In cellular respiration, most energy is released and transferred to ATP when _____.
high-energy electrons "fall" to lower energy levels
An enzyme is considered a _________ because it speeds up a chemical reaction without being used up.
In catalyzed reaction, a reactant is often called a _________.
An enzyme is specific because of the shape its ______ ____ matches only particular reactants.
active site
An enzyme peeds up reactions by lowering the __________ ______.
activation energy
The _______ ___ between an active site and its substrate often strains bonds and helps the reaction proceed.
induced fit
A ________, which is often a vitamin, binds to an enzyme and plays role in catalysis.
High temperatures or changes in pH can ________ an enzyme, causing it to lose its shape and biological activity.
In oil-based liquids, phospholipids are arranged so that their _____ face outward and their _____ are orientated inward.
hydrophobic tails ... hydrophilic heads

This arrangement shelters the hydrophilic heads of the phospholipids from the oil while exposing the hydrophobic tails to the oil. This is seen in oil-based solutions.
The movement of molecules from an area of higher concentration to an area of lower concentration is called _____.
When water moves toward the solution with the _____ solute concentration, the solution is _____.
greater ... hypertonic
Reactions can be exergonic or endergonic. Which of these reactions is endergonic?
protein synthesis
During enzymatic reactions, substrates are converted to products. A property of enzymes that facilitates this reaction is that they are catalysts and therefore _____.
change the rate of a reaction without being consumed by the reaction.

This permits enzyme molecules to be used repeatedly.
The eukaryotic cell has multiple membrane-enclosed compartments. This evolutionary innovation provides what advantage to the cell?
The different membrane-enclosed spaces allow different parts of the cell to perform specific functions.

The membranes that surround organelles make it possible to construct very different chemical environments within and on the surface of each of these organelles.
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?

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 fluid mosaic model describes the plasma membrane as consisting of
diverse proteins embedded in a phospholipid bilayer.
Plasma membranes are selectively permeable. This means that
the plasma membrane allows some substances to enter or leave a cell more easily than others.
All cells are enclosed by a plasma membrane that is similar in ________ and ________.
structure . . . function
What controls the direction of a molecule, such as oxygen, involved in passive transport?
the direction of the oxygen concentration gradient.

The direction material moves in passive transport is determined solely by the material's concentration gradient, with material diffusing from regions of higher concentration to regions of lower concentration.
Oxygen crosses a plasma membrane by
passive transport.
Diffusion does not require the cell to expend ATP. Therefore, diffusion is considered a type of
passive transport.
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.
When two aqueous solutions that differ in solute concentration are placed on either side of a semipermeable membrane and osmosis is allowed to take place, the water will
exhibit a net movement to the side with lower free water concentration.
You are adrift in the Atlantic Ocean, and, being thirsty, drink the surrounding seawater. As a result,
you dehydrate yourself.
Facilitated diffusion across a biological membrane requires ________ and moves a substance ________ its concentration gradient.
transport proteins . . . down
What substance is transported by aquaporins?

Aquaporins are a newly discovered class of transport proteins that transport water in cells with very high water permeability needs.
Which of the following processes can move a solute against its concentration gradient?
active transport
A vesicle inside the cell fuses with the plasma membrane and releases its contents outside the cell.
A form of passive transport. Molecules move across the plasma membrane using a transport protein.
Facilitated Diffusion
The plasma membrane forms a pocket that pinches inward, forming a vesicle that contains materia from outside the cell.
A form of passive transport. Molecules move across the plasma membrane by crossing the lipid bilayer.
Requires energy from the cell. Molecules move against their concentration gradient.
Active Transport
Certain cells that line the stomach synthesize a digestive enzyme and secrete it into the stomach. This enzyme is a protein. Which of the following processes could be responsible for its secretion?
The process of a white blood cell engulfing a bacterium is
Light is _____ energy, which is converted by plants into molecules, which possess _____ energy.
kinetic ... chemical
Kinetic energy differs from chemical energy in that
kinetic energy is the energy of a moving object, whereas chemical energy is the potential energy of molecules.
According to ________, energy cannot be created or destroyed.
the first law of thermodynamics
Which of the following energy transfers is impossible in living systems?
heat to light energy
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.
Which of the following processes is endergonic?
the synthesis of glucose from carbon dioxide and water
What is the basic difference between exergonic and endergonic reactions?
Exergonic reactions release energy; endergonic reactions absorb it.
When a cell uses chemical energy to perform work, it uses the energy released from a(n) ________ reaction to drive a(n) ________ reaction.
exergonic . . . endergonic
Which part of the ATP molecule breaks free of the rest when an ATP molecule is used for energy?
one phosphate group.
Which of the following statements about the ATP molecule is true?
It releases energy when one phosphate group leaves ATP.
Anything that prevents ATP formation will most likely
result in cell death.
The energy required to initiate an exergonic reaction is called
the activation energy.
Most of a cell's enzymes are
When an enzyme catalyzes a reaction,
it lowers the activation energy of the reaction.
Substrates bind to an enzyme's ________ site.
The active site of an enzyme is
the region of an enzyme that attaches to a substrate.
Which of the following statements regarding enzyme function is false?
Enzymes are used up when they catalyze a chemical reaction, so must be synthesized for each new chemical reaction.
Heating inactivates enzymes by
changing the enzyme's three-dimensional shape.
How does inhibition of an enzyme-catalyzed reaction by a competitive inhibitor differ from inhibition by a noncompetitive inhibitor?
Competitive inhibitors bind to the active site of the enzyme; noncompetitive inhibitors bind to a different site.
Bacterial production of the enzymes needed for the synthesis of the amino acid tryptophan declines with increasing levels of tryptophan and increases as tryptophan levels decline. This is an example of
feedback inhibition.
Which of the following statements is true about passive transport?
Passive transport requires no expenditure of cellular energy.
The diffusion of water across a selectively permeable membrane is called _____.
Seawater is dangerous to drink because _____.
seawater is hypertonic to your body tissues and drinking it will cause you to lose water by osmosis
Which of the following terms specifically refers to the intake of very large particles by cells?
Energy is _____.
the capacity to perform work
According to the second law of thermodynamics, which of the following is true?
The ordering of one system depends on the disordering of another.
The first law of thermodynamics _____.
states that energy is neither created nor destroyed
The phosphorylation of ADP to form ATP is an _____ reaction that _____ energy.
endergonic ... requires an input of
Energy can be classified as either potential or kinetic. Which of the following is an example of kinetic energy?
a running child