Biology Test 2, Chapter 5

Front 1

Diffusion

Back 1

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

Front 2

Concentration Gradient

Back 2

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.

Front 3

Passive transport

Back 3

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

Front 4

Selective Permeability

Back 4

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

Front 5

Fluid Mosaic Model

Back 5

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.

Front 6

Osmosis

Back 6

The diffusion of free water across a selectively permeable membrane.

Front 7

Tonicity

Back 7

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

Front 8

Isotonic

Back 8

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

Front 9

Hypotonic

Back 9

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

Front 10

Hypertonic

Back 10

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

Front 11

osmoregulation

Back 11

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

Front 12

facilitated diffusion

Back 12

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

Front 13

aquaporin

Back 13

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

Front 14

active transport

Back 14

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).

Front 15

exocytosis

Back 15

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

Front 16

endocytosis

Back 16

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

Front 17

phagocytosis

Back 17

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

Front 18

receptor-mediated endocytosis

Back 18

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.

Front 19

endocytosis

Back 19

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

Front 20

energy

Back 20

The capacity to cause change, especially to perform work.

Front 21

kinetic energy

Back 21

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

Front 22

thermal energy

Back 22

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

Front 23

heat

Back 23

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

Front 24

potential energy

Back 24

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

Front 25

chemical energy

Back 25

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

Front 26

thermodynamics

Back 26

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

Front 27

first law of thermodynamics

Back 27

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

Front 28

entropy

Back 28

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

Front 29

second law of thermodynamics

Back 29

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

Front 30

cellular respiration

Back 30

The aerobic harvesting of energy from food molecules.

Front 31

exergonic reaction

Back 31

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

Front 32

endergonic reaction

Back 32

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

Front 33

metabolism

Back 33

The totality of an organism's chemical reactions.

Front 34

metabolic pathway

Back 34

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

Front 35

energy coupling

Back 35

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

Front 36

phosphorylation

Back 36

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

Front 37

ATP

Back 37

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

Front 38

activation energy

Back 38

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

Front 39

enzymes

Back 39

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

Front 40

substrate

Back 40

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

Front 41

active site

Back 41

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

Front 42

induced fit

Back 42

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

Front 43

cofactors

Back 43

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

Front 44

coenzyme

Back 44

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

Front 45

competitive inhibitor

Back 45

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.

Front 46

noncompetitive inhibitor

Back 46

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.

Front 47

feedback inhibition

Back 47

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

Front 48

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?

Back 48

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

Front 49

Why is diffusion across a membrane called passive transport?

Back 49

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

Front 50

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.

Back 50

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

Front 51

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

Back 51

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.

Front 52

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

Back 52

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

Front 53

Why are aquaporins important in kidney cells?

Back 53

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

Front 54

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

Back 54

outside; active transport moves calcium against its concentration gradient.

Front 55

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

Back 55

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

Front 56

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

Back 56

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.

Front 57

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?

Back 57

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

Front 58

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

Back 58

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

Front 59

Explain how an enzyme speeds up a specific reaction.

Back 59

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.

Front 60

What determines whether enzyme inhibition is reversible or irreversible?

Back 60

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.

Front 61

Explain an advantage of feedback inhibition to a cell.

Back 61

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

Front 62

Which best describes the structure of a cell membrane?

Back 62

proteins embedded in a bilayer of phospholipids.

Front 63

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

Back 63

become turgid, burst.

Front 64

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?

Back 64

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

Front 65

The synthesis of ATP from ADP and...

Back 65

stores energy in a form that can drive cellular work.

Front 66

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

Back 66

transport proteins/down

Front 67

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

Back 67

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.

Front 68

Relate the laws of thermodynamics to living organisms.

Back 68

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.

Front 69

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

Back 69

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.

Front 70

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

Back 70

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.

Front 71

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

Back 71

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).