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71 Cards in this Set

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the intermingling of substances by the natural movement of their particles.

Concentration Gradient

A region along which the density of a chemical substance increases or decreases. Cells often maintain concentration gradients of ions across their membranes. When a concentration gradient exists, substances tend to move from where they are more concentrated to where they are less concentrated.

Passive transport

The diffusion of a substance across a biological membrane, with no expenditure of energy.

Selective Permeability

A property of biological membranes that allows some substances to cross more easily than others and blocks the passage of other substances.

Fluid Mosaic Model

The currently accepted model of cell membrane structure, depicting the membrane as a mosaic of diverse protein molecules embedded in a fluid bilayer of phospholipid molecules.


The diffusion of free water across a selectively permeable membrane.


The ability of a solution surrounding a cell to cause that cell to gain or lose water.


Referring to a solution that, when surrounding a cell, cause no net movement of water into or out of the cell.


Referring to a solution that, when surrounding a cell, will cause the cell to take up water.


Referring to a solution that, when surrounding a cell, will cause the cell to lose water.


The homeostatic maintenance of solute concentrations and water balance by a cell or organism.

facilitated diffusion

The passage of a substance through a specific transport protein across a biological membrane down its concentration gradient.


A transport protein in the plasma membrane of an animal, plant, or microorganism cell that facilitates the diffusion of water across the membrane (osmosis).

active transport

The movement of a substance across a biological membrane against its concentration gradient, aided by the specific transport p[roteins and requiring an input of energy (often as ATP).


The movement of materials out of a cell by the fusion of vesicles with the plasma membrane.


Cellular uptake of molecules or particles via formation of new vesicles from the plasma membrane.


Cellular "eating"; a type of endocyrosis in which a cell engulfs macromolecules, other cells, or particles into its cytoplasm.

receptor-mediated endocytosis

The movement of specific molecules into a cell by the infolding of vesicles containing proteins with receptor sites specific to the molecules being taken in.


Cellular uptake of molecules or particles via formation of new vesicles from the plasma membrane.


The capacity to cause change, especially to perform work.

kinetic energy

The energy associated with the motion of objects. Moving matter does work by imparting motion to other matter.

thermal energy

Kinetic energy due to the random motion of atoms and molecules; energy in its most random form.


Thermal energy in transfer from one body of matter to another.

potential energy

The energy that matter possesses because of its location or spatial arrangement. Water behind a dam possesses potential energy; so do chemical bonds.

chemical energy

Energy available in molecules for release in a chemical reaction; a form of potential energy.


The study of energy transformation that occurs in a collection of matter.

first law of thermodynamics

The principles of conservation of energy. Energy can be transferred or transformed, but it cannot be created or destroyed.


A measure of disorder, or randomness. See second law of thermodynamics.

second law of thermodynamics

Every energy conversion reduces the order of the universe, increasing its entropy.

cellular respiration

The aerobic harvesting of energy from food molecules.

exergonic reaction

An energy-releasing chemical reaction in which the reactants contain more potential energy than the products.

endergonic reaction

An energy-requiring chemical reaction, which yields products with more potential energy than the reactants.


The totality of an organism's chemical reactions.

metabolic pathway

A series of chemical reactions that either builds a complex molecules or breaks down a complex molecule into simpler compounds.

energy coupling

in cellular metabolism, the use of energy released from an exergonic reaction to drive an endergonic reaction.


The transfer of a phosphate group, usually from ATP, to a molecule Nearly all cellular work depends on ATP energizing other molecules by phosphorylation.


Adenosine Triphosphate, the main energy source for cells. ATP releases energy when its phosphate bonds are hydrolized.

activation energy

The amount of energy that reactants must absorb before a chemical reaction will start.


A macromolecules, usually a protein, that serves as a biological catalyst, changing the rate of a chemical reaction without being consumed by the reaction.


A specific substance (reactant) on which an enzyme acts. Each enzyme reacognizes only the specific substrate or substrates of the reaction it catalysis.

active site

The part of an enzyme where a substrate molecule attaches; typically a pocket or groove on the enzymes surface.

induced fit

The change in shape of the active site of an enzyme, caused by entry of the substrate so that it binds the substrate snugly.


A nonprotein molecule or ion that is required for the proper functioning on an enzyme.


An organic molecule serving as a cofactor. Most vitamins function as coenzymes in important metabolic reactions.

competitive inhibitor

A substance that reduces the activity of an enzyme by entering the active site in place of the substrate. A competitive inhibitor's structure mimics the shape of the substrate.

noncompetitive inhibitor

A substance that reduces the activity of an enzyme without entering an active site. By binding elsewhere on the enzyme, a noncompetitive inhibitor changes the shape of the enzyme so that it can no longer accept its substrate.

feedback inhibition

A method of metabolic control in which a product of a metabolic pathway acts as an inhibitor of an enzyme within that pathway.

In the origin of a cell, why would the formation of a simple lipid bilayer memberane not be sufficient? What else would have to be part of such a membrane?

The membrane would need empedded proteins that could regulate the movement of substances into and out of the cell.

Why is diffusion across a membrane called passive transport?

The cell does not expend energy to transport substances that are diffusing down their concentration gradient.

Indicate the direction of net water movement between two solution - a .5% sucrose solution and a 2% sucrose solution--separated by a membrane not permeable to sucrose.

From the .5% sucrose solution (lower solute concentration) to the 2% sucrose solution (higher solute concentration)

Explain the function of the contractile vacuoles in a freshwater paramecium in terms of what you have learned about water balance in cells.

The pond water in which Paramecium lives is hypotonic to the cell. The contractile vacuoles expel the water that constantly enters the cell by osmosis.

How do transport proteins contribute to a membrane's selective permeability.

Because they are specific for the solutes they transport, the numbers and kinds of transport proteins affect a membrane's permeability to various solutes.

Why are aquaporins important in kidney cells?

Kidney cells must reabsorb a large amount of water when producing urine.

Cells actively transport Ca2+ out of the cell. Is calcium more concentrated inside or outside of the cell? Explain

outside; active transport moves calcium against its concentration gradient.

As a cell grows, its plasma membrane expands. Does this involve endocytosis or exocytosis? Explain.

Exocytosis: when a transport vesicle fuses with the plasma membrane, its contents are released and the vesicle membrane adds to the plasma membrane.

How does the second law of thermodynamics explain the diffusion of a solute across a membrane?

Diffusion across a membrane results in equal concentrations of solute, which is a more disordered arrangement (higher entropy) than a high concentration on one side and a low concentration on the other.

Cellular respiration is an exergonic process. Remembering that energy must be conserved, what do you think becomes of the energy extracted from food during this process?

some of it is stored in ATP molecules; the rest is released as heat.

Explain how ATP transfers energy from exergonic to endergonic processes in the cell.

Exergonic processes phosphorylate ADP to form ATP. ATP transfers energy to endergonic processes by phosphorylating other molecules.

Explain how an enzyme speeds up a specific reaction.

An enzyme lowers the activation energy needed for a reaction when its specific substrate enters its active site. With an induced fit, the enzyme strains bonds that need to break or position substrates in the orientation that aids the conversion of reactants to products.

What determines whether enzyme inhibition is reversible or irreversible?

If the inhibitor binds to the enzyme with covalent bonds the inhibition is usually irreversible. When weak chemical interactions bind inhibitor and enzyme, the inhibition is reversible.

Explain an advantage of feedback inhibition to a cell.

It prevents the cell from wasting valuable resources by synthesizing more of a product than is needed.

Which best describes the structure of a cell membrane?

proteins embedded in a bilayer of phospholipids.

A plant cell placed in distilled water will_______; an animal cell placed in disyilled water will________.

become turgid, burst.

The sodium concentration in a cell is 10 times less than the concentration in the surrounding fluid. How can the cell move sodium out of the cell?

active transport. only active transport can move a concentration against its gradient.

The synthesis of ATP from ADP and...

stores energy in a form that can drive cellular work.

Facilitated diffusion across a membrane requires ______ and moves a solute _________its concentration gradient.

transport proteins/down

Why is the barrier of the activation energy beneficial for cells? Explain how enzymes lower activation energy.

Energy is stored in the chemical bonds of a cell's organic molecules. The activation energy barrier prevents those molecules from spontaneously breaking down and releasing that energy. When a substrate fits into an enzyme's active site with an induced fit, its bonds may be strained and thus easier to break, or the active site may orient two substrates in such a way that facilitates the reaction.

Relate the laws of thermodynamics to living organisms.

Energy is neither created nor destroyed but can be transferred and transformed. Plants transform the energy of sunlight into chemical energy stored in organic molecules. Almost all organisms rely on the products of photosynthesis for the source of their energy. In every energy transfer or transformation, disorder increases as some energy is lost to random motion of thermal energy and released as heat.

How do the components and structure of cell membranes relate to the functions of membranes?

Cell membranes are composed of diverse proteins suspended in a fluid phospholipid bilayer. The hydrophilic heads of the phospholipids face the aqueous environment on both sides of the membrane and the fatty acid tails cluster in the hydrophobic center of the membrane. The membrane forms a selectively permeable boundary between cells and their surroundings (or between organelles and the cytosol). the proteins perform the many functions of membranes, such as enzyme action, transport attachment, and signaling.

Sometimes inhibitors can be harmful to a cell; often they are beneficial. Explain.

Inhibitors that are toxins or poison irreversibly key cellular enzymes. Inhibitors that are designed as drugs are beneficial, such as when they interfere with the enzymes of bacterial or viral invaders or cancer cells. Cells use feedback inhibition of enzymes in metabolic pathways as important mechanisms that conserve resources.

What are the main types of cellular work? How does ATP provide the energy for this work?

The work of cells falls into three main categories: chemical, transport, and mechanical. ATP provides the energy for cellular work by transferring a phosphate group to a substrate (chemical) or to a protein (transport and mechanical).