BIO311C PRACTICE QUESTIONS UNIT ONE

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

100 times more H+ - Each pH unit change represents a tenfold difference in the hydrogen ion concentration; thus 10 x 10 = 100.

A sodium atom has a mass number of 23. Its atomic number is 11. How many electrons does it have if it is not an ion?

11 - The number of electrons will equal the number of protons in an electrically neutral atom.

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 -By gaining two electrons from calcium, the sulfate ion now has a charge of −2 and calcium has a charge of +2.

Which functional group helps form all amino acids?

-NH2 - this is an amino group

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; 0.002 moles per L) solution?

0.092 g

What is the three-dimensional shape formed when a carbon atom is covalently bonded with four other atoms?

A tetrahedron with carbon in the center

What is ATP's role in the cell?

ATP stores the potential to react with water, thereby removing a phosphate group and releasing energy for cellular processes. - ATP releases energy during a hydrolysis reaction that removes a phosphate group.

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

All are properties related to hydrogen bonding - The extraordinary qualities of water are emergent properties resulting from hydrogen bonding.

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

All of the choices are correct: acts to moderate temperature, provides the surface tension that allows leaves to float on water, is called cohesion, keeps water moving through the vessels in a tree trunk

Which functional group increases the solubility of organic compounds in water?

All of the listed responses are correct: -SH, -COOH, -COH, -NH2 -- All of the functional groups are hydrophilic and thus increase the solubility of organic molecules in water.

Cells are surrounded by water, and cells themselves consist of about 70-95% water. Which choice best describes an emergent property of living things which derives from this fact?

All of the listed responses are correct: A variety of nutrient molecules is readily available as dissolved solutes, Waste products produced by cell metabolism can be easily removed, Dissolved substances can be easily transported within a cell or between cells in multicellular organisms, The temperature of living things tends to change relatively slowly.

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 and help hold membranes together. - Weak bonds are important in the three-dimensional structure of most large biological molecules, and they play a role in molecular interactions such as those between the hydrophobic parts of lipids in membranes

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

Because it is polar, water's oppositely charged ends are attracted to positively and negatively charged ions and molecules. Water molecules form a hydration shell around oppositely charged particles. - Polar water molecules surround the individual ions or charged molecules, separating and shielding the ions or molecules from one another.

Which molecule is a monosaccharide?

C6H12O6 - Monosaccharides have molecular formulas that are multiples of CH2O.

Which is an organic molecule?

CH4 - compounds containing carbon are said to be organic

Which element is always associated with organic chemistry?

Carbon - compounds containing carbon, except carbon dioxide, are organic compounds

High cholesterol levels are considered a major risk factor for heart disease. If it is so bad for humans, why does the body make cholesterol in the first place?

Cholesterol is the basis for many important molecules such as sex hormones. -

When a protein is denatured, why does it lose its functionality?

Denaturation breaks the weak bonds, such as hydrogen bonds and van der Waals interactions, that hold the protein in its three-dimensional shape. Without the proper shape, the protein cannot function. - Denaturation disrupts secondary, tertiary, and quaternary protein structure, causing the protein to lose its form, and thus its function.

Glucose and hexanoic acid each contain six carbon atoms, but they have completely different properties. Glucose is a nutrient found in food; hexanoic acid is poisonous. Their differences must be due to different __________.

Functional groups -Functional groups most commonly determine chemical properties such as the polarity and reactivity of molecules.

Which describes the dissociation of an acid?

HF → H+ + F− - Hydrofluoric acid (HF) dissociates into a hydrogen ion and a fluoride ion.

Why are cell membranes composed primarily of hydrophobic molecules?

In order to perform their function of separating the aqueous solutions outside of cells from the aqueous solutions inside of cells, cell membranes cannot be soluble in water. - If cell membranes were hydrophilic, they would break down and dissolve in the presence of water, rendering them useless as a barrier.

When the pH of a solution shifts from 7 to 3, how has the hydrogen ion concentration changed?

It has increased by 10,000 times. - Because the pH number is the negative log of the hydrogen ion concentration, a change from a pH of 7 to a pH of 3 increases the hydrogen ion concentration by 10,000 times. (7 − 3 = 4; 10^4 = 10,000.)

Generally, animals cannot break down the bonds between the glucose molecules in cellulose. How then do cows get nutrients by eating grass?

Microorganisms in their digestive tracts hydrolyze the cellulose to individual glucose units. - Cows have digestive chambers populated by microorganisms that can produce certain hydrolytic enzymes that cows cannot. The enzymes hydrolyze (digest) the cellulose polymer into glucose monomers.

Why would more carbon dioxide taken up by the oceans cause concern?

More carbon dioxide causes an increase in carbonic acid (H2CO3), which leads to a decrease in the concentration of carbonate ion (CO32−). - As seawater becomes more acidic, carbonate ion concentration decreases. The decrease in the availability of carbonate ion makes it more difficult for marine organisms to secrete calcium carbonate shells.

To what does the term "polypeptide" refer?

None of the listed responses is correct. - A polypeptide is a chain of amino acids that have been linked together by dehydration reactions.

Which of these is a thiol?

None of the listed responses is correct: -SH, -COOH, -OH, -NH2 -- A thiol is a molecule containing a sulfhydryl functional group.

Which true comparing phospholipids and triacylglycerols (fats and oils)?

Phospholipid molecules have a distinctly polar "head" and a distinctly nonpolar "tail," whereas triacylglycerols are predominantly nonpolar. - Triacylglycerols consist of three (nonpolar) fatty acid tails attached to a glycerol molecule. Phospholipids have two fatty acid tails and a hydrophilic head containing a negatively charged phosphate group.

Nutritionally, saturated triacylglycerols are considered to be less healthful than unsaturated triacylglycerols. What is the chemical difference between them?

Saturated triacylglycerols have more hydrogen atoms than unsaturated triacylglycerols. - Saturated triacylglycerols are saturated with hydrogen atoms.

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

Six hydrogen and three carbon - there must be a carbon-carbon double bond for this molecule to exist

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. - In order for living things to inhabit a wide range of environments, temperature regulation would need to be more efficient for a fluid with a lower specific heat.

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 loss or gain of electrons does not influence the atomic number (number of protons) or the mass number (number of protons plus neutrons) of an atom.

If water were not a polar molecule, how would the effects of warming climate be different?

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. - A loss of the polar nature of water would equate to a loss in the ability to form hydrogen bonds. Breaking hydrogen bonds absorbs energy, which accounts for water's high specific heat and its ability to influence and moderate climate.

Amylase is an enzyme that breaks down starch. Why can't the same enzyme break down cellulose?

The monosaccharide monomers in cellulose are bonded together differently than in starch. - The glucose monomers in cellulose are bonded in a beta glycosidic linkage, whereas those in starch have an alpha glycosidic linkage. The enzyme amylase is specific for the alpha glycosidic linkage.

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

The rate of the reverse reaction equals the rate of the forward reaction. - This is the definition of chemical equilibrium.

Which of the following statements is true about chemical reactions?

They involve the making and breaking of chemical bonds, leading to changes in the composition of matter.

If a small droplet of triacylglycerol molecules is suspended in water, they form a ball with no particular orientation. But if a droplet of phospholipid molecules is put in water, all the molecules point outward toward the water, because phospholipids have __________.

a charged end and a noncharged end - The hydrocarbon tails of phospholipids are hydrophobic and are excluded from water. The negatively charged phosphate group and its attachments form a hydrophilic head that is attracted to water.

An acid is __________.

a compound that donates hydrogen ions to a solution - An acid donates hydrogen ions to a solution.

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

a covalent bond - Covalent bonds are formed between atoms that share one or more pairs of valence electrons.

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

a polymer is broken up into its constituent monomers ... consumed - The meaning of "hydrolysis" is "to break with water."

Manufacturers make vegetable oils solid or semisolid at room temperature by __________.

adding hydrogen atoms to the double bonds in the fatty acid hydrocarbon chains - The phrase "hydrogenated vegetable oils" found on food labels means that unsaturated fats have been synthetically converted to saturated fats by the addition of hydrogen.

Although the structures of the functional groups that critical to life vary, they share one thing in common: they __________.

all are hydrophilic and increase the organic compound's water solubility - all are hydrophilic and increase the organic compound's water solubility

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

all share the same functional group: a hydroxyl -Alcohols are distinguished by the presence of the hydroxyl (−OH) functional group.

When two atoms are so unequal in their attraction for valence electrons that the more electronegative atom strips an electron completely away from its partner, the two resulting oppositely charged atoms (or molecules)____________.

are ions - When the proton number and electron number are unequal, the atom or molecule has a net positive (cation) or negative charge (anion).

Lipids differ from other large biological molecules in that they __________.

are not truly polymers - Lipids are not all made of the same type of monomer. Their association as a group (fats, phospholipids, and steroids) is related to their solubility behavior.

Ionic bonds form as a result of __________.

attraction between ions that have opposite charges - Oppositely charged ions attract each other electrically, forming an ionic bond.

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 - Two molecules of water are held together by a hydrogen bond formed between the slight positive charge of the hydrogen and the slight negative charge of the oxygen. Water is a very versatile solvent, a quality traced to the polarity of the water molecule.

Which of these is found in all amino acids?

both −COOH and −NH2 -For a compound to be an amino acid, it must contain at least one carboxyl functional group and one amino functional group. In addition, it may contain one or more of the other functional groups.

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

buffer - Buffers are substances that minimize changes in the concentration of hydrogen ions and hydroxide ions in a solution; therefore, buffers maintain a relatively constant pH.

Which component of a tossed salad will pass through the human digestive tract and be digested least?

cellulose (in the lettuce) - Cellulose contains glycosidic linkages that cannot be broken by human digestive enzymes.

Which of these is a polymer?

cellulose, a plant cell wall component - The polysaccharide cellulose is a major component of plant cell walls. It is a polymer composed of many glucose monomers joined together by glycosidic linkages.

At a conference, the speaker's grand finale was sautéing mealworms (insect larvae) in butter and serving them to the audience. They were crunchy (like popcorn hulls) because their exoskeletons contain the polysaccharide __________.

chitin - Chitin is the structural polysaccharide found in arthropod exoskeletons.

Which action would involve the greatest transfer of heat?

condensing 5 g of steam to liquid water - This would release about 2,900 calories (580 calories per gram, times 5 grams).

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 - Monomers are joined together by a dehydration reaction in which two molecules are covalently bonded to each other through the loss of a water molecule.

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

dehydration reactions - When monomers are linked together to form a more complex polymer, a water molecule is removed by dehydration reactions.

Carbon atoms are the most versatile building blocks of the molecules used by living organisms because __________.

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

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

eight electrons - Eight electrons will leave no unpaired electrons in the valence shell. In this configuration atoms are chemically unreactive or inert.

Carbohydrates are used in our bodies mainly for __________.

energy storage - Simple sugar molecules, stored in polysaccharides such as glycogen in animals and starch in plants, are a major energy source for cellular work.

Some lipids are formed when fatty acids are linked to glycerol. These subunits are linked together by __________.

ester linkages - In making a fat, each of the three fatty acid molecules is bonded to a glycerol by an ester linkage type of covalent bond.

Which carbohydrate molecule has the lowest molecular weight?

glucose - Glucose is a monosaccharide.

A polysaccharide that is used for storing energy in human muscle and liver cells is __________.

glycogen - Humans and other vertebrates store glucose as a polysaccharide called glycogen in their liver and muscles.

The subunits (monomers) in cellulose are linked together by __________.

glycosidic linkages - The glucose monomers of cellulose are linked together by a specific type of covalent bond known as a glycosidic linkage.

Hydrophilic substances, unlike hydrophobic substances, __________.

have charges and/or partial charges to which water molecules can adhere - Hydrophilic substances are water-loving and have an affinity for water. There is an unequal sharing of electrons resulting in a polar molecule, or there is the gain or loss of an electron(s) resulting in the formation of negatively and positively charged ions.

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

heat of vaporization - Water's high heat of vaporization results in evaporative cooling because when water evaporates, the surface of the water cools down.

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

hydrophobic - For example, the hydrophobic behavior of oil molecules results from a prevalence of nonpolar covalent bonds. Nonpolar molecules do not have an affinity for water or other polar molecules.

Nonpolar molecules that cluster away from water molecules are called __________ molecules

hydrophobic - Substances that are nonionic and nonpolar repel water.

What is the term for compounds that do not mix with water?

hydrophobic -Hydrophobic compounds are those that are insoluble in water.

The fatty acid tails of a phospholipid are __________ because they __________ .

hydrophobic ... have no charges to which water molecules can adhere - Phospholipid tails, which consist of nonpolar hydrocarbon chains, are hydrophobic.

Which is a property of hydrocarbons?

hydrophobic, nonpolar, good source of stored energy - Because they are nonpolar, hydrocarbons are hydrophobic. They also provide energy in the forms of things such as fossil fuels and fats.

Because molecules of water are farther apart in ice than in liquid water, __________.

ice floats on liquid water - Because water molecules in ice are farther apart than in liquid water, ice is less dense, and therefore, it floats.

Adding acid tends to __________ of a solution.

increase the hydrogen ion concentration and lower the pH - Because pH is a negative log, its value is inversely proportional to the hydrogen ion concentration.

A hydrogen bond __________.

is a weak chemical bond - Hydrogen bonds are weak chemical bonds that are very important in the chemistry of life

The sex hormones estrogen, progesterone, and testosterone belong to which class of molecules?

lipids - Steroids, such as estrogen, progesterone, and testosterone, are lipids based on their insolubility in water. The molecules are characterized by a carbon skeleton consisting of four fused rings of carbon atoms.

Adding a base tends to __________ of a solution.

lower the hydrogen ion concentration and increase the pH - A substance that reduces the hydrogen ion concentration is a base. Reducing the hydrogen ion concentration increases the pH.

Which molecule has the shape of a completed tetrahedron?

methane (CH4) - The nucleus of the carbon atom is at the center of the tetrahedron, with its four covalent bonds radiating to the hydrogen nuclei at the corners of the tetrahedron.

A covalent bond is likely to be polar if __________.

one of the atoms sharing electrons is much more electronegative - If one atom is more electronegative than the other, electrons of the bond will not be shared equally, resulting in a polar covalent bond. For example, oxygen is more elctronegatvie than hydrogen, so shared electrons are pulled more toward oxygen.

Most of water's unique features (for example, its versatility as a solvent, ability to moderate temperature, and cohesive behavior) result from the fact that __________.

oxygen attracts electrons more than hydrogen does - Because oxygen is more electronegative than hydrogen, water molecules are polar and form hydrogen bonds that give water its extraordinary properties.

The lipids that form the main structural component of cell membranes are __________.

phospholipids - Phospholipids have a hydrophilic head and two hydrophobic tails. This permits the phospholipids to be arranged in a bilayer, or double layer, which forms a boundary between the cell and its external environment.

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

polar - Because molecules of polar solvents have a positive and a negative pole, polar solvents are excellent solvents for ions and for other polar materials.

Cellulose is a __________ made of many __________.

polymer ... glucose molecules - Cellulose is a polysaccharide and therefore a polymer, constructed from many monosaccharide glucose monomers.

Which list ranks molecules by size in their correct order?

protein, sucrose, glucose, water - largest to smallest

Adhesion is best described as __________.

the clinging of one substance to another substance - Adhesion is the attraction of one substance to another.

A polar covalent bond is a bond that __________.

the electrons of the bond are not shared equally - Polar covalent bonds share electrons unequally, so that one part of the molecule has a partial negative region and one part a partial positive region.

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 - Heat of vaporization is the quantity of heat a liquid must absorb for 1 g of it to be converted from the liquid to the gaseous state.

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?

the molecule's shape - The molecule would have to have the correct shape to bind to the receptor protein and block it.

In a 1-4 glycosidic linkage, __________.

the number 1 carbon in one monosaccharide is bound to the number 4 carbon in another monosaccharide - Glycosidic linkages, the covalent bonds that link simple sugars, are named according to the carbon atoms they join.

Water is a polar molecule. This means that __________.

the opposite ends of the molecule have opposite electrical charges - In the case of water, the oxygen is slightly negative and the hydrogen atoms are slightly positive.

In a group of water molecules, hydrogen bonds form between __________.

the oxygen atom in one water molecule and a hydrogen atom in another water molecule - The slightly negatively charged region of an oxygen atom of one water molecule is attracted to the slightly positively charged region of a hydrogen atom of another water molecule.

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 specific heat of a substance is defined as the amount of heat that must be absorbed or lost to change the temperature of 1 g of that substance by 1°C.

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 - Because oxygen is more electronegative than hydrogen, electrons of the polar bond spend more time closer to the oxygen atom, resulting in a slight negative charge on the oxygen atom and slight positive charges on the hydrogen atoms.

Some substances, such as oil and gasoline, will not dissolve in water because __________.

their molecules have no charges or partial charges to which water molecules can adhere - The hydrophobic behavior of oil and gasoline molecules results from a prevalence of nonpolar covalent bonds between carbon and hydrogen.

One characteristic shared by sucrose, lactose, and maltose is that __________.

they are all disaccharides - A disaccharide consists of two monosaccharides joined together by a glycosidic linkage.

Hydrophobic molecules are __________ water.

unable to interact with - Substances that are nonionic and nonpolar have not way to interact with it and this stand apart from it.

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

specific heat - Because of its high specific heat, water's temperature will change less when it absorbs or loses a given amount of heat. Thus, the oceans can absorb and store a huge amount of heat and release it later when the temperature of the air has dropped.

In what polysaccharide do plants store glucose?

starch - Starch is a glucose storage polymer in plants.

The polysaccharide that you are most likely to have eaten recently is __________.

starch - Starch is a storage polysaccharide found especially in certain plant tissues.

Sucrose has a molecular mass of 342 daltons. To make a 2 molar (2 M; 2 moles per L) 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

Carbohydrates can function in which of the following ways?

structural support and energy storage - Carbohydrates function as both storage molecules (starch, glycogen) and as structural support molecules (cellulose).

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

surface tension - Water has a greater surface tension, a measure of how difficult it is to break the surface of a liquid, than most other liquids.

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

ten times as much - The pH scale is a base-10 logarithmic scale. The change from any pH value to the next smaller value represents a tenfold increase in the hydrogen ion concentration.

The overall three-dimensional shape of a single polypeptide is called the __________.

tertiary structure - The tertiary structure is determined by hydrogen bonds, hydrophobic R groups, ionic bonds between R groups, van der Waals interactions, and disulfide bridges.