NAS2 Part 5 Review

What is metabolism?

The sum total of all chemical reactions that occur to maintain an organism’s health and life.

How do anabolic and catabolic chemical reactions differ?

Anabolic reactions build larger molecules from smaller molecules or atoms; catabolic reactions break larger molecules into smaller molecules or atoms.

A reaction joins small components to form a larger molecule. Is it anabolic or catabolic?

Anabolic.

A reaction breaks bonds in a large molecule and releases smaller components. Is it anabolic or catabolic?

Catabolic.

What two things are exchanged or transformed during both anabolic and catabolic reactions?

Matter and energy.

Why must reacting particles collide with sufficient precision and force?

So old chemical bonds can be broken and new chemical bonds can form.

What is kinetic energy?

The energy matter possesses because of its motion.

What is potential energy?

The energy of position or structure—the energy matter possesses because of the arrangement of its components.

How does kinetic energy differ from potential energy?

Kinetic energy is associated with motion; potential energy is stored because of position or structure.

A brick is lifted and placed on a wall. Which energy forms are illustrated?

Kinetic energy is used while lifting and placing the brick; once positioned, the wall stores potential energy.

A wall collapses and its bricks fall. What energy conversion occurs?

Stored potential energy is converted into kinetic energy.

What is chemical energy?

A form of potential energy stored in chemical bonds.

True or false: Forming chemical bonds releases chemical energy, and breaking bonds requires chemical energy to be stored.

False. In the textbook’s treatment, energy is invested when bonds form and stored in them; energy is released when those bonds break.

What happens to energy during chemical reactions according to conservation of energy?

Energy is not created or destroyed; it is converted from one form to another.

How can food from an energy bar eventually help muscles move?

The body breaks down and rearranges food molecules, and muscle cells convert their chemical energy into kinetic and mechanical energy.

What is an exergonic reaction?

A chemical reaction that releases more energy than it absorbs.

What is an endergonic reaction?

A chemical reaction that absorbs more energy than it releases.

How do exergonic and endergonic reactions differ in net energy exchange?

Exergonic reactions have a net release of energy; endergonic reactions require a net input of energy.

Why is the catabolism of food considered exergonic?

It releases some of the chemical energy stored in food, including energy transferred to fuel molecules and released as heat.

What energy does the product of an endergonic reaction store?

The chemical energy originally present in its components plus the energy supplied to drive the reaction.

Where does the energy for many endergonic reactions in the body come from?

From exergonic reactions; energy-releasing reactions can provide the input needed for energy-absorbing reactions.

Does “exergonic” mean that a reaction releases all of its stored energy?

No. It means the reaction releases more energy than it absorbs; some energy may remain stored or be transferred to other molecules.

What four forms of energy are especially important in human functioning?

Chemical, mechanical, radiant, and electrical energy.

What is mechanical energy?

Energy stored in physical systems that directly powers the movement of matter.

Which form of energy directly powers a muscle moving a limb or lifting an object?

Mechanical energy.

What is radiant energy?

Energy emitted and transmitted as waves rather than as matter.

What is the electromagnetic spectrum?

The full range of radiant-energy wavelengths, from long radio waves and microwaves to short gamma waves.

Why is one portion of the electromagnetic spectrum called visible light?

It contains the wavelengths the human eye can detect as colors from red to violet.

How does the body use ultraviolet radiant energy from sunlight?

It uses ultraviolet energy to convert a compound in skin cells into vitamin D.

What is electrical energy in the context of human functioning?

Energy associated with moving charged particles that contributes to voltage changes in cells.

How do electrolytes support nerve and muscle function?

Electrolytes in cells and body fluids contribute to voltage changes that help transmit nerve and muscle impulses.

Distinguish chemical, mechanical, radiant, and electrical energy.

Chemical energy is stored in bonds; mechanical energy powers movement; radiant energy travels as waves; electrical energy arises from moving charges and voltage changes.

What is a reactant?

One or more substances that enter into a chemical reaction.

What is a product?

One or more substances produced by a chemical reaction.

In a chemical equation written left to right, where are reactants and products usually shown?

Reactants are on the left of the arrow; products are on the right.

What does the law of conservation of mass state?

Matter cannot be created or destroyed in a chemical reaction.

Why must every type and number of atom present in the reactants also appear in the products?

Because chemical reactions rearrange matter but do not create or destroy it.

Can a product contain an element that was absent from all reactants?

No. Products cannot contain matter that was not present in the reactants.

What does a chemical equation represent?

How reactants are transformed into products during a chemical reaction.

What does the arrow in a chemical equation indicate?

The direction in which the chemical reaction proceeds.

In N + 3H → NH₃, identify the reactants and product.

Nitrogen and three hydrogen atoms are the reactants; ammonia is the product.

What process is represented by NH₃ → N + 3H?

The decomposition of ammonia into nitrogen and hydrogen components.

What is a synthesis reaction?

A chemical reaction that joins components that were previously separate.

What is the general equation for a synthesis reaction?

A + B → AB.

Why is N + 3H → NH₃ a synthesis reaction?

Separate nitrogen and hydrogen reactants join to form the larger product ammonia.

How is energy involved in the textbook’s example of an anabolic synthesis reaction?

The reaction requires energy, which is then stored in the bonds of the product.

What is a decomposition reaction?

A chemical reaction that breaks a larger substance into its constituent parts.

What is the general equation for a decomposition reaction?

AB → A + B.

What generally happens to stored potential energy when a compound is decomposed in the textbook’s example?

Potential energy stored in its bonds is released.

Compare synthesis and decomposition reactions.

Synthesis joins smaller components to form a larger product; decomposition breaks a larger reactant into smaller products.

What is an exchange reaction?

A reaction in which decomposition and synthesis both occur: some bonds break while new bonds form.

What is the simplest general form of an exchange reaction presented in the section?

A + BC → AB + C.

In A + BC → AB + C, which bond changes occur?

B separates from C, and A bonds with B.

Give either complex general form of an exchange reaction shown in the section.

AB + CD → AC + BD, or AB + CD → AD + BC.

How is chemical energy handled in an exchange reaction?

Energy may be absorbed, stored, and released as bonds are broken and formed.

How can you identify synthesis, decomposition, and exchange reactions from their patterns?

Synthesis combines parts into one product; decomposition splits one reactant into parts; exchange breaks and forms bonds so partners are rearranged.

What three fundamental reaction types are illustrated in Figure 2.12?

Synthesis, decomposition, and exchange reactions.

Visualize letter groups as molecules. If two separate letter groups join into one word-like group, which reaction type is shown?

A synthesis reaction.

Visualize one word-like group separating into smaller letter groups. Which reaction type is shown?

A decomposition reaction.

Visualize letter groups exchanging partners to create new groups. Which reaction type is shown?

An exchange reaction.

Under the right conditions, in how many directions can a chemical reaction theoretically proceed?

Either direction.

How is a reversible chemical reaction indicated in an equation?

With a double arrow.

What reverse reaction corresponds to A + BC → AB + C?

AB + C → A + BC.

Why do many reactions in the human body proceed predictably in one direction even though reactions can theoretically be reversible?

The favored direction is usually the path of least resistance; the alternate direction generally requires more energy.

What four major categories of factors influencing reaction rate are emphasized for human functioning?

Properties of the reactants, temperature, concentration and pressure, and enzymes or other catalysts.

Why does chewing food help chemical digestion?

Chewing increases the food’s surface area, giving digestive chemicals easier access to reactant particles.

How does greater reactant surface area affect reaction rate?

It generally increases reaction rate by allowing reactant particles to interact more readily.

Why do gases generally react faster than liquids or solids?

Gas particles already have more space between them, so less energy is needed to separate them and allow interactions.

Why are reactions involving smaller molecules generally expected to proceed faster than reactions involving larger molecules?

Smaller molecules usually have fewer total bonds to rearrange or break.

How does the inherent reactivity of an element affect reaction rate?

Highly reactive elements participate in reactions more readily and usually faster than less reactive or stable elements.

Compare hydrogen and helium in terms of expected chemical reactivity.

Hydrogen is highly reactive and commonly participates in faster reactions; stable helium is unlikely to react.

True or false: Larger molecules usually react faster because they contain more bonds.

False. Larger molecules usually react more slowly because more bonds are involved; smaller molecules generally react faster.

How does increasing temperature usually affect the rate of a chemical reaction?

It increases the reaction rate.

Why does a higher temperature usually speed a reaction?

Thermal energy increases particle kinetic energy, so particles move faster, collide more often, and are more likely to react.

True or false: Higher temperature slows reactions because particles become farther apart.

False. Higher temperature increases particle motion and collision likelihood, generally speeding reactions.

What is concentration in the discussion of reaction rate?

The number of particles present within a given space.

How does increasing reactant concentration affect reaction rate?

It increases the chance that particles will collide, generally increasing reaction rate.

How can decreasing the volume of a space speed a reaction involving particles?

It increases pressure and particle concentration, making collisions more likely.

One hundred particles are moved into a container half the original volume. What happens to their concentration and collision likelihood?

The concentration doubles, and collisions become more likely.

Does increasing pressure speed a reaction by creating new reactant particles?

No. It packs the existing particles into less space, increasing collision frequency.

What is a catalyst?

A substance that increases the rate of a chemical reaction without itself undergoing change.

How do catalysts increase the probability of a reaction?

They promote effective collisions and make it more likely that valence-shell electrons will interact.

True or false: A catalyst is consumed and permanently changed during the reaction it speeds up.

False. A catalyst increases reaction rate without itself undergoing change.

Why can the body not rely only on high temperature to accelerate life-sustaining reactions?

Very high heat can damage cells and be life-threatening, while normal body temperature alone is too low to drive many reactions fast enough.

What is an enzyme?

A biological catalyst composed of protein or RNA.

What are the most important catalysts in the human body?

Enzymes.

What is activation energy?

The threshold level of energy required to break bonds in the reactants so a reaction can begin.

How do enzymes speed chemical reactions?

They lower the activation energy that must be invested for the reaction to begin.

Do enzymes eliminate the need for activation energy?

No. They lower the activation energy required; they do not reduce it to zero.

What is the central message of Figure 2.13?

An enzyme lowers the activation-energy barrier, so less energy input is needed for the reaction to begin.

On an energy-versus-reaction-progress graph, how does the curve with an enzyme compare with the curve without an enzyme?

The enzyme-assisted curve has a lower peak, representing lower activation energy.

If two reaction diagrams have the same start and end points but different peak heights, which one represents enzyme action?

The diagram with the lower peak.

Give an important physiological role of enzymes mentioned in the section.

They assist with breaking down food and converting it to usable energy.

How common is enzyme facilitation in the body’s chemistry?

Most chemical reactions in the body are facilitated by enzymes.

How is a catalyst different from an energy source for a reaction?

A catalyst lowers the activation-energy barrier and is not consumed; an energy source supplies energy that the reaction may absorb or transform.

Which changes would all tend to speed a reaction: crushing a solid, warming it, increasing reactant concentration, and adding an enzyme?

All four: they increase surface area, particle motion, collision frequency, or lower activation energy.

A reaction remains slow at normal body temperature even though reactants are present. What missing factor is especially likely in a biological system?

An appropriate enzyme or other catalyst may be absent.

According to the chapter review, what must occur before old chemical bonds break and new bonds form?

An initial energy investment must fuel collisions among atoms, ions, or molecules.

Summarize the energy pattern of the three fundamental reaction types.

Synthesis requires energy to form bonds; decomposition breaks bonds and releases energy; exchange reactions both break and form bonds, exchanging energy.

Which reaction-rate factors are named in the chapter review?

Properties of reactants, temperature, concentration and pressure, and the presence or absence of a catalyst.