Chapter 2-7 practice test

BI211

What is generally true about essential elements and living organisms?

Although all forms of life require iron, other elements are required only by certain species.

If you were told that concentrations of trace elements above what is required by organisms generally have no effect on those organisms, what would you say?

False. Elevated concentrations of some trace elements such as cobalt and chromium can be toxic.

How would you respond to this reasoning? Oxygen is not a greenhouse gas; therefore, gases containing oxygen—such as ozone, nitrous oxide, and carbon dioxide—are not greenhouse gases either.

False. Compounds can have emergent properties that are very different from those of the elements that form them.

There are __________ naturally occurring elements.

92

Which of the following is a trace element?

Copper

What are the four most abundant elements found in living systems?

Hydrogen, oxygen, nitrogen, and carbon

Which of the following has negligible mass?

Electron

Which of the following subatomic particles has appreciable mass but no charge?

Neutron

The number of protons in an uncharged atom __________.

equals the number of electrons

An element has eight protons, nine neutrons, and eight electrons. Its atomic number and atomic mass, respectively, are __________.

8 and 17

An uncharged atom of nitrogen (atomic number = 7) has __________.

seven protons and seven electrons

In which of the following will isotopes of an element always differ?

Atomic mass

A particular carbon isotope has an atomic number of 6 and an atomic mass of 14. The respective numbers of neutrons, protons, and electrons that this carbon isotope has are __________.

8, 6, and 6

Phosphorus-32 (radioactive) has __________ than phosphorus-35 (normal).

three fewer neutrons

The most common form of calcium has 20 protons, 20 neutrons, and 20 electrons. Which of the following elements would be an isotope of calcium?

An atom with 20 protons, 21 neutrons, and 20 electrons

Why are radioactive isotopes useful in scientific research?

Because they can be used as tracers to follow particular atoms and molecules through metabolic pathways

A neutral atom of chlorine has an atomic number of 17. It has __________ electrons in its third shell.

7

The chemical characteristics or reactivity of an element depend mostly on the __________.

number of electrons in its outermost shell

Some groups of chemical elements react similarly to one another. For example, the chemistries of sodium and of lithium are similar, as are the chemistries of chlorine and of iodine. These similarities in chemistry result when different elements have similar __________.

numbers of outer-shell electrons

How many electrons would be present in the valence shell of a sulfur atom (atomic number 16, mass number 32)?

Six electrons

For most atoms, when does the configuration of electrons make the atom unreactive?

When the atom has eight electrons in its outermost shell

An atom that normally has __________ in its outer shell would not tend to form chemical bonds with other atoms.

eight electrons

When one or more pairs of valence electrons are shared by two neutral atoms, what type of bond is formed?

A covalent bond

A covalent bond is likely to be polar if __________.

one of the atoms sharing electrons is much more electronegative than the other

When the proton number and electron number are unequal, the atom or molecule __________.

is an ion

Copper has an atomic number of 29 and a mass number of 64. What would result if an uncharged copper atom lost two electrons?

The atomic number would remain 29, the mass number would remain 64, and the atom would be a cation with a +2 charge.

The compound CaSO₄ ionizes into a calcium ion and a sulfate ion (SO₄). Calcium has two electrons in its outer shell. Upon ionization, what would you expect the charge on the sulfate ion to be?

–2

Ionic bonds form as a result of __________.

attraction between ions that have opposite charges

A hydrogen bond __________.

is a weak chemical bond

When do hydrogen bonds occur?

When partial opposite charges on molecules come close enough to attract each other

What is the role of van der Waals interactions in biological molecules?

Although they are weak bonds, van der Waals interactions help to reinforce the three-dimensional shapes of large molecules.

Which molecule has the shape of a completed tetrahedron?

Methane (CH₄)

Pharmaceutical researchers are often interested in blocking particular receptor proteins on cell surfaces. What chemical property of a molecule would be most important for this type of application?

The molecule's shape

Which statement is true about chemical reactions?

They involve the making and breaking of chemical bonds.

Which statement describes a reversible reaction that has reached chemical equilibrium?

The rate of the reverse reaction equals the rate of the forward reaction.

Cells are surrounded by water, with which they are mostly filled. Which of the following occurs as a result?

The temperature of living things tends to change relatively slowly.

Waste products produced by cell metabolism can be easily removed.

A variety of nutrient molecules is readily available as dissolved solutes.

Water is a polar molecule. What does this statement mean?

That atoms in the molecule have partial charges as a result of unequal sharing of electrons in a covalent bond

The partial charges on a water molecule occur because of __________.

the unequal sharing of electrons between the hydrogen and the oxygen atoms of a water molecule

In a group of water molecules, hydrogen bonds form between which of the following?

The oxygen atom in one water molecule and a hydrogen atom in another water molecule

Which of the following accurately relates the emergent properties of water to the effects of global warming in the Arctic?

Ice floats because it is less dense than liquid water; floating ice insulates water below and provides a habitat for some species. The significant increase in Arctic air temperature over the past 50 years is causing a reduction in sea ice, compromising these beneficial effects of sea ice.

If water were not a polar molecule, how would the effects of climatic warming differ from those currently observed or predicted to occur in the future?

The effects would be drastically worse because the loss of the polar nature of water would greatly reduce its specific heat and its ability to moderate temperature.

The tendency of water molecules to stay close to each other as a result of hydrogen bonding __________.

is called cohesion, acts to moderate temperature, provides the surface tension that allows small animals to move across a water surface, and helps to keep water moving through the vessels in a tree trunk

What do cohesion, surface tension, and adhesion have in common with reference to water?

All are properties related to hydrogen bonding.

The ability of water molecules to form hydrogen bonds with other water molecules and water's ability to dissolve substances that have charges or partial charges are __________.

both caused by water's partial charges

The phenomenon responsible for maintaining the upward movement of water through vessels in a tree is __________.

cohesion

Adhesion is best described as which of the following?

The clinging of one substance to another substance

You can fill a glass of water to just slightly above the rim without the water spilling over the glass. What property of water best explains this phenomenon?

Surface tension

Which action would involve the greatest transfer of heat?

Condensing 5 g of steam to liquid water

Imagine that organisms consisted of 70–95% alcohol instead of 70–95% water. Alcohol's specific heat is about half that of water. How would living things be different?

Systems for temperature regulation would have to be much more efficient.

The amount of heat required to change the temperature of 1 g of any substance by 1°C is defined as __________.

the specific heat of that substance

The amount of heat required to convert 1 g of any substance from the liquid to the gaseous state is defined as __________.

the heat of vaporization of that substance

The reason that coastal climates are more moderate than inland climates primarily water's high __________.

specific heat

Sweating has a cooling effect because of water's high __________.

heat of vaporization

Water has __________ than other liquids such as ethanol, reflecting its capacity to absorb large amounts of heat.

a higher boiling point

Which of the following occurs because molecules of water are farther apart in ice than in liquid water?

Ice floats.

Water is a very versatile solvent because water molecules are __________. (

polar

How does the polarity of water contribute to its ability to dissolve so many substances?

Because it is polar, water's negatively charged oxygen atoms and positively charged hydrogen atoms are attracted to positively and negatively charged ions and molecules.

What are nonpolar molecules that cluster away from water molecules called?

Hydrophobic

A molecule that has all nonpolar covalent bonds would be __________.

hydrophobic

Why are cell membranes composed primarily of hydrophobic molecules?

In order to perform their function of separating the aqueous solutions outside cells from the aqueous solutions inside cells, cell membranes cannot be soluble in water.

Sucrose has a molecular mass of 342 daltons. To make a 2-molar (2 M) solution of sucrose, __________.

stir 342 g of sucrose in water to dissolve the sugar, and then add enough water to bring the total volume of the solution up to 0.5 L

A mole of ethyl alcohol weighs 46 g. How many grams of ethyl alcohol are needed to produce 1 L of a 2-millimolar (2 mM) solution?

0.092 g

An acid is __________.

a compound that donates hydrogen ions to a solution

Adding acid tends to __________ of a solution.

increase the hydrogen ion concentration and lower the pH

Which of the following dissociations is that of an acid?

HF → H⁺ + F^–

A glass of grapefruit juice, at pH 3, contains __________ H⁺ as a glass of tomato juice, at pH 4.

ten times as much

A solution at pH 6 contains __________ than the same amount of solution at pH 8.

100 times more H⁺

Adding a base tends to __________ of a solution.

lower the hydrogen ion concentration and increase the pH

A substance that minimizes changes in the concentration of H⁺ and OH^– in a solution is a __________.

buffer

Why is the increasing amount of carbon dioxide being taken up by the oceans a cause for concern?

More carbon dioxide causes an increase in carbonic acid (H₂CO₃), which leads to a decrease in the concentration of carbonate ion (CO₃^2–).

The absorption of human-generated CO₂ by the oceans __________.

increases the hydrogen ion concentration in the oceans but decreases the carbonate ion concentration and threatens the livability of the oceans for organisms that produce calcium carbonate shells

What are the six most important chemical elements of life?

Carbon, nitrogen, oxygen, hydrogen, phosphate, sulfur

Using modern equipment, a former graduate student of Stanley Miller recently reanalyzed the sample results of volcano simulation experiments that Miller conducted along with his classic experiment described in the text. This reanalysis did which of the following?

Identified additional organic compounds that had not been found by Miller

Stanley Miller's experiments were significant because he demonstrated that __________.

a variety of simple organic compounds could be spontaneously synthesized from components in Earth's primitive atmosphere

Which of the following is an organic molecule?

CH₄

(Compounds containing carbon are said to be organic.)

What is the three-dimensional shape created by hybrid orbitals that are formed when a carbon atom is covalently bonded with four other atoms?

A tetrahedron with carbon in the center

A pharmaceutical company was forced to recall a pain reliever medication that had been linked to the fatalities of several hundred people. Analysis of the recalled drug revealed the presence of two isomers due to an asymmetrical carbon atom in the drug molecule. What can be hypothesized from this observation?

The isomers are enantiomers, with one having toxic effects on humans.

A straight-chain carbon compound constructed from __________ must contain at least one carbon-carbon double bond.

6 hydrogen atoms and 3 carbon atoms

What is the reason carbon atoms are the most versatile building blocks of the molecules used by living organisms?

Each carbon atom acts as an intersection point from which a molecule can branch off in up to four directions.

The carbon atom possesses __________ valence electron(s).

4

Which of the following are properties of hydrocarbons?

Hydrophobic, nonpolar, good source of stored energy

A molecule has one carbon-carbon double bond and four monovalent atoms or groups. How many different cis-trans isomers exist for this molecule?

Two

The two compounds
are related to each other by being __________.

hydrocarbons, isomers, organic compounds, and double-bonded compounds

Pharmaceutical companies are selling billions of dollars' worth of single-enantiomer drugs. Why might it be important to use only one form of an enantiomer?

One enantiomer may provide an effective treatment whereas the other may be ineffective or even toxic.

Which of the following functional groups is present in all amino acids?

—NH₂

Which of these is found in all amino acids?

both —COOH and —NH₂

Ethanol, propanol, and methanol are three simple alcohols. They can be grouped together because they __________.

share the same functional group: a hydroxyl

Which of the following molecules has a carboxyl functional group?

R—COOH

Which of the following functional groups increases the solubility of organic compounds in water?

—OH

—COH

—COOH

Which of the following examples best describes a unique functional property of the carboxyl group?

The covalent bond between oxygen and hydrogen is so polar that hydrogen ions tend to dissociate from oxygen reversibly.

Which of the following functional groups is associated with a release of energy when removed from the carbon skeleton with water?

Phosphate group

Which functional group would you predict is part of abscisic acid?

Carboxyl group

Which of the following groups is capable of hydrogen bonding with an oxygen atom on another functional group?

Amino group

Hydroxyl group

Carboxyl group

Which of these is a thiol?

None of the listed responses is correct.

What is ATP's importance in the cell?

ATP stores the potential to react with water, thereby removing a phosphate group and releasing energy for cellular processes.

What is the process by which monomers are linked together to form polymers?

Dehydration reaction

In a hydrolysis reaction, __________, and in this process, water is __________.

a polymer is broken up into its constituent monomers; consumed

The type of bond that forms to join monomers (such as sugars and amino acids) into polymers (such as starch and proteins) is a(n) __________ bond.

covalent

Generally, animals cannot digest (hydrolyze) the glyosidic linkages between the glucose molecules in cellulose. How then do cows get enough nutrients from eating grass?

Microorganisms in their digestive tracts hydrolyze the cellulose to individual glucose units.

In what polysaccharide form do plants store glucose to be available later as an energy source?

Starch