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Study questions for the biology praxis




Anything that takes up space and has mass.


Any substance that cannot be broken
down to any other substance by chemical


A substance consisting of two or more
different elements combined in a fixed ratio.

essential element

A chemical element required
for an organism to survive, grow, and reproduce.

trace element

An element indispensable for life
but required in extremely minute amounts.

Explain how table salt has emergent properties.

Table salt (sodium chloride) is made up of sodium and chlorine. We are able to eat the compound, showing that it has different properties from those of a metal (sodium) and a poisonous gas (chlorine).

Is a trace element an essential element?

Yes, because an organism requires trace elements, even though only in small amounts

In humans, iron is a trace element required for the
proper functioning of hemoglobin, the molecule that
carries oxygen in red blood cells. What might be the
effects of an iron deficiency?

A person with an iron deficiency will probably show fatigue and other effects of a low oxygen level in the blood. (The condition is called anemia and can also result from too
few red blood cells or abnormal hemoglobin.)

Review the discussion of natural selection in Chapter 1 (pp. 14-16) and explain how natural selection might have played a role in the evolution
of species that are tolerant of serpentine soils.

Variant ancestral plants that could tolerate the toxic elements could grow and reproduce in serpentine soils. (Plants that were well adapted to nonserpentine soils would not be expected to survive in serpentine areas.) The offspring of the variants would also vary, with those most capable of thriving under serpentine conditions growing best and reproducing most. Over many generations, this probably led to the serpentineadapted species we see today.


The smallest unit of matter that retains the properties of an element.


A subatomic particle having no electrical charge (electrically neutral), with a mass of about 1.7 1024 g, found in the nucleus of an atom.


A subatomic particle with a single positive electrical charge, with a mass of about 1.7 1024 g, found in the nucleus
of an atom.


A subatomic particle with a single negative electrical charge and a mass about 1/2,000 that of a neutron or proton. One or more electrons move around the nucleus of an atom.

atomic nucleus

An atom's dense central core, containing protons and neutrons.


A measure of mass for atoms and subatomic particles; the same as the atomic mass unit, or amu.

atomic number

the number protons in an atom

mass number

the sum of protons and neutrons in the nucleus of an atom

atomic mass

The total mass of an atom, which is the mass in grams of 1 mole of the atom.


One of several atomic forms of an element, each with the same number of protons but a different number of neutrons,
thus differing in atomic mass.

radioactive isotopes

is one which the nucleus decays spontaneously giving off particles of energy


The capacity to cause change, especially to do work (to move matter against an opposing force).

Potential energy

the energy that matter possesses because of its location or structure.

Notes: the more distant an electron is from the nucleus, the greater its potential energy.


electron shells

An energy level of electrons at a characteristic average distance from the nucleus of an atom.

valence electrons

An electron in the outermost electron shell.

valence shell

The outermost energy shell of an atom, containing the valence electrons involved in the chemical reactions of that atom.


the three dimensional space where an electron is found 90% of the time.

A lithium atom has 3 protons and 4 neutrons. What
is its atomic mass in daltons?


A nitrogen atom has 7 protons, and the most common isotope of nitrogen has 7 neutrons. A radioactive isotope of nitrogen has 8 neutrons. Write the atomic number and mass number of this radioactive nitrogen as a chemical symbol with a subscript and superscript.

15/7 N

How many electrons does fluorine have? How many
electron shells? Name the orbitals that are occupied.
How many electrons are needed to fill the valence

9 electrons; two electron shells; 1s, 2s, 2p (three orbitals); 1 electron
is needed to fill the valence shell.

if two or more elements are in the same row, what do they have in common? If two or more elements are in the same column, what do they have in common?

The elements in a row all have the same number of electron shells. In a column, all the elements have the same number
of electrons in their valence shells.

Chemical Bonds

An attraction between two atoms, resulting from a sharing of outer-shell electrons or the presence of opposite charges
on the atoms. The bonded atoms gain complete outer electron shells.


two or more atoms held together by covalent bonds

single bond

A single covalent bond; the sharing of a pair of valence electrons by two atoms.

double bond

A double covalent bond; the sharing of two pairs of valence electrons by two atoms.


the attraction of a particular atom for the electrons of a covalent bond

nonpolar covalent bond

A type of covalent bond in which electrons are shared equally between two atoms of similar electronegativity.

polar covalent bond

A covalent bond between atoms that differ in electronegativity. The shared electrons are pulled closer to the more
electronegative atom, making it slightly negative and the other atom slightly positive.


a charged atom


positive charged atom


a negatively charged atom

ionic bond

A chemical bond resulting from the attraction between oppositely charged ions.

ionic compounds or salts

compounds formed by ionic bonds

van der waals

A weak attractive force between atoms or nonpolar molecules caused by an instantaneous dipole moment of one atom or molecule that induces a similar temporary dipole moment in adjacent atoms or molecules.

hydrogen bond

A type of weak chemical bond that is formed when the slightly positive hydrogen atom of a polar covalent bond in one molecule is attracted to the slightly negative atom of a polar covalent bond in another molecule or in another region of
the same molecule.

Why does the structure H-C=C-H fail to make
sense chemically?

Each carbon atom has only three covalent bonds instead of the required four.

What holds the atoms together in a crystal of magnesium
chloride (MgCl2)?

The attraction between oppositely charged ions, forming ionic bonds

If you were a pharmaceutical researcher,
why would you want to learn the three-dimensional
shapes of naturally occurring signaling molecules?

If you could synthesize molecules that mimic these shapes, you might be able to treat diseases or conditions caused by the inability of affected individuals to synthesize such molecules.


starting materials


ending materials after a chemical reaction

chemical equilibrium

In a chemical reaction, the state in which the rate of the forward reaction equals the rate of the reverse reaction, so
that the relative concentrations of the reactants and products do not change with time.

Consider the reaction between hydrogen and oxygen that forms water, shown with ball-and-stick models on page 42. Study Figure 2.12 and draw the Lewis dot structures representing this reaction.

Which type of chemical reaction occurs faster at equilibrium,
the formation of products from reactants or
reactants from products?

At equilibrium, the forward and reverse reactions occur at the same rate.

Write an equation that uses the products
of photosynthesis as reactants and the reactants of
photosynthesis as products. Add energy as another
product. This new equation describes a process that
occurs in your cells. Describe this equation in words.
How does this equation relate to breathing?

C6H12O6 6 O2 S 6 CO2 6 H2O Energy. Glucose and oxygen react to form carbon dioxide and water, releasing energy. We breathe in oxygen because we need it for this reaction to occur, and we breathe out carbon dioxide because
it is a by-product of this reaction.

In the term trace element, the adjective trace means that
a. the element is required in very small amounts.
b. the element can be used as a label to trace atoms through
an organism's metabolism.
c. the element is very rare on Earth.
d. the element enhances health but is not essential for the organism's
long-term survival.
e. the element passes rapidly through the organism.

a. the element is required in very small amounts.

In what way does the need for iodine or iron in your diet differ
from your need for calcium or phosphorus?

Iodine (part of a thyroid hormone) and iron (part of hemoglobin in blood) are both trace elements, required in minute quantities. Calcium and phosphorus (components
of bones and teeth) are needed by the body in much greater quantities.

Draw the electron distribution diagrams for neon
(10Ne) and argon (18Ar). Use these diagrams to explain why these
elements are chemically unreactive.

Both neon and argon have completed valence shells, containing 8 electrons. They do not have unpaired electrons that could participate in chemical bonds.

In terms of electron sharing between atoms, compare nonpolar
covalent bonds, polar covalent bonds, and the formation of ions.

Electrons are shared equally between the two atoms in a nonpolar covalent bond. In a polar covalent bond, the electrons are drawn closer to the more electronegative
atom. In the formation of ions, an electron is completely transferred from one atom to a much more electronegative atom.

What would happen to the concentration of products if more
reactants were added to a reaction that was in chemical equilibrium?
How would this addition affect the equilibrium?

The concentration of products
would increase as the added reactants were converted to products. Eventually, an
equilibrium would again be reached in which the forward and reverse reactions
were proceeding at the same rate and the relative concentrations of reactants and
products returned to where they were before the addition of more reactants

Compared with 31P, the radioactive isotope 32P has
a. a different atomic number. d. one more electron.
b. a different charge. e. one more neutron.
c. one more proton.


The reactivity of an atom arises from
a. the average distance of the outermost electron shell from
the nucleus.
b. the existence of unpaired electrons in the valence shell.
c. the sum of the potential energies of all the electron shells.
d. the potential energy of the valence shell.
e. the energy difference between the s and p orbitals.


Which statement is true of all atoms that are anions?
a. The atom has more electrons than protons.
b. The atom has more protons than electrons.
c. The atom has fewer protons than does a neutral atom of
the same element.
d. The atom has more neutrons than protons.
e. The net charge is 1.


Which of the following statements correctly describes any
chemical reaction that has reached equilibrium?
a. The concentrations of products and reactants are equal.
b. The reaction is now irreversible.
c. Both forward and reverse reactions have halted.
d. The rates of the forward and reverse reactions are equal.
e. No reactants remain.


We can represent atoms by listing the number of protons,
neutrons, and electrons—for example, 2p, 2n0, 2e for helium.
Which of the following represents the 18O isotope of
a. 6p, 8n0, 6e d. 7p, 2n0, 9e
b. 8p, 10n0, 8e e. 10p, 8n0, 9e
c. 9p, 9n0, 9e


The atomic number of sulfur is 16. Sulfur combines with hydrogen
by covalent bonding to form a compound, hydrogen
sulfide. Based on the number of valence electrons in a sulfur
atom, predict the molecular formula of the compound.
a. HS b. HS2 c. H2S d. H3S2 e. H4S


What coefficients must be placed in the following blanks so
that all atoms are accounted for in the products?
C6H12O6 S _____ C2H6O _____ CO2
a. 1; 2 b. 3; 1 c. 1; 3 d. 1; 1 e. 2; 2


polar covalent bonds

A covalent bond between atoms that differ in electronegativity. The shared electrons are pulled closer to the more electronegative atom, making it slightly negative
and the other atom slightly positive.

polar molecule

the overall charge is unevenly distributed.

What is electronegativity, and how does it affect interactions between water molecules?

Electronegativity is the attraction of an atom for the electrons of a covalent bond. Because oxygen is more electronegative than hydrogen, the oxygen atom in H2O pulls electrons toward itself, resulting in a partial negative charge on the
oxygen atom and partial positive charges on the hydrogen atoms. Atoms in neighboring water molecules with opposite partial charges are attracted to each other, forming a hydrogen bond.

What would be the effect on the properties of the water molecule if oxygen and hydrogen had equal electronegativity?

The covalent bonds of water molecules would not be polar, and water molecules would not form hydrogen bonds with each other.


The linking together of like molecules, often by hydrogen bonds.


The clinging of one substance to another, such as water to plant cell walls by means of hydrogen bonds.

surface tension

A measure of how difficult it is to stretch or break the surface of a liquid. Water has a high surface tension because of the
hydrogen bonding of surface molecules.

kinetic energy

the motion of energy


A muscular pump that uses metabolic energy to elevate the hydrostatic pressure of the circulatory fluid (blood or hemolymph). The fluid then flows down a pressure gradient
through the body and eventually returns to the heart.


is a measure of heat intensity that represents the average kinetic energy of the molecules, regardless of volume.

Note: heat passes from the warmer to the cooler object until the two are the same temperature.


Celsius Scale

A temperature scale (°C) equal to 5/9(°F - 32) that measures the freezing point of water at 0°C and the boiling point of water at 100°C.


A thousand calories; the amount of heat energy required to raise the temperature of 1 kg of water by 1°C.


A unit of energy: 1 J 0.239 cal;
1 cal 4.184 J.

specific heat

The amount of heat that must be absorbed or lost for 1 g of a substance to change its temperature by 1°C.

heat of vaporization

is the quantity of heat of liquid must absorb for 1g of it to be converted from the liquid to the gaseous state

evaporation cooling

The process in which the surface of an object becomes cooler during evaporation, a result of the molecules with the
greatest kinetic energy changing from the liquid to the gaseous state.


A liquid that is a homogeneous mixture
of two or more substances.


A substance that is dissolved in a solution.


The dissolving agent of a solution. Water is the most versatile solvent known.

aqueous solution

A solution in which water is the solvent.

hydration shell

the sphere of water molecules around each dissolved ion


water loving


water hating


A mixture made up of a liquid and particles
that (because of their large size) remain
suspended rather than dissolved in that liquid.

molecular mass

the sum of the massess of all the atoms in a moleucle


6.02 x 10^23


the number of moles of solute per liter of solution

hydrogen ion


hydroxide ioin


hydronium ion



a substance that increased the hydorgen ion concentration of a solution


a substance that reduces the hydrogen ion concentration of a solution


the negative logarithm of the hydrogen ion concentration


is a substance that minimizes changes in the concentrations of H+ and OH- in a solution

ocean acidification

Decreasing pH of ocean waters due to absorption of excess atmospheric CO2 from the burning of fossil fuels.

Acid precipitation

rain, snow or fog with a pH lower than 5.2

Describe how properties of water contribute to the
upward movement of water in a tree.

Hydrogen bonds hold neighboring water molecules together. This cohesion
helps the chain of water molecules move upward against gravity in waterconducting
cells as water evaporates from the leaves. Adhesion between water
molecules and the walls of the water-conducting cells also helps counter gravity.

Explain the saying "It's not the heat; it's the

High humidity hampers cooling by suppressing the evaporation of sweat.

How can the freezing of water crack boulders?

As water freezes, it expands because water molecules move farther apart in forming ice crystals. When there is water in a crevice of a boulder, expansion due to freezing may crack the boulder.

The concentration of the appetite-regulating hormone
ghrelin is about 1.3 1010M in a fasting person. How
many molecules of ghrelin are in 1 L of blood?

A liter of blood would contain 7.8 1013
molecules of ghrelin (1.3 1010 moles per liter 6.02 1023 molecules per mole).

A water strider (which can walk on water)
has legs that are coated with a hydrophobic substance.
What might be the benefit? What would
happen if the substance were hydrophilic?

The hydrophobic substance repels water, perhaps helping to keep the ends of the legs from becoming coated with water and breaking through the surface. If the legs were coated with a hydrophilic substance, water would be drawn up them, possibly making it more difficult for the water strider to walk on water.

Compared with a basic solution at pH 9, the same
volume of an acidic solution at pH 4 has ____ times
as many hydrogen ions (H).

105, or 100,000

HCl is a strong acid that dissociates in water:
HCl S H Cl. What is the pH of 0.01 M HCl?

H] 0.01 M 102M, so pH 2

Acetic acid (CH3COOH) can be a buffer, similar to
carbonic acid. Write the dissociation reaction, identifying
the acid, base, H acceptor, and H donor.

CH3COOH S CH3COO H. CH3COOH is the acid (the H donor), and CH3COO is the base (the H acceptor).

Given a liter of pure water and a liter solution
of acetic acid, what would happen to the pH if you
added 0.01 mol of a strong acid to each? Use the reaction equation from question 3 to explain the result.

The pH of the water should decrease from 7 to about
2; the pH of the acetic acid solution will decrease only a small amount, because
the reaction shown for question 3 will shift to the left, with CH3COO accepting
the influx of H and becoming CH3COOH molecules.

Describe how different types of solutes dissolve in water. Explain
the difference between a solution and a colloid.

Ions dissolve in water when polar water molecules form a hydration shell around them. Polar molecules dissolve as water molecules form hydrogen bonds with them and surround them. Solutions are homogeneous mixtures of solute and solvent. Colloids form when particles that are too large to dissolve remain suspended in a liquid.

Explain how increasing amounts of CO2 dissolving in the ocean
leads to ocean acidification. How does this change in pH affect
carbonate ion concentration and the rate of calcification?

CO2 reacts with H2O to form carbonic acid (H2CO3),
which dissociates into H and bicarbonate (HCO3
). Although the carbonic
acid-bicarbonate reaction is a buffering system, adding CO2 drives the reaction to
the right, releasing more H and lowering pH. The excess protons combine with
2 to form bicarbonate, lowering the concentration of carbonate available for
the formation of calcium carbonate (calcification) by corals.

Many mammals control their body temperature by sweating.
Which property of water is most directly responsible for the
ability of sweat to lower body temperature?
a. water's change in density when it condenses
b. water's ability to dissolve molecules in the air
c. the release of heat by the formation of hydrogen bonds
d. the absorption of heat by the breaking of hydrogen bonds
e. water's high surface tension


The bonds that are broken when water vaporizes are
a. ionic bonds.
b. hydrogen bonds between water molecules.
c. covalent bonds between atoms within water molecules.
d. polar covalent bonds.
e. nonpolar covalent bonds.


Which of the following is a hydrophobic material?
a. paper d. sugar
b. table salt e. pasta
c. wax


We can be sure that a mole of table sugar and a mole of
vitamin C are equal in their
a. mass in daltons. d. number of atoms.
b. mass in grams. e. number of molecules.
c. volume.


Measurements show that the pH of a particular lake is 4.0.
What is the hydrogen ion concentration of the lake?
a. 4.0 M b. 1010 M c. 104 M d. 104 M e. 4%


What is the hydroxide ion concentration of the lake described
in question 5?
a. 1010 M b. 104 M c. 107 M d. 1014M e. 10 M


A slice of pizza has 500 kcal. If we could burn the pizza and
use all the heat to warm a 50-L container of cold water, what
would be the approximate increase in the temperature of the
water? (Note: A liter of cold water weighs about 1 kg.)
a. 50°C b. 5°C c. 1°C d. 100°C e. 10°C


How many grams of acetic acid (C2H4O2) would you use to
make 10 L of a 0.1 M aqueous solution of acetic acid? (Note:
The atomic masses, in daltons, are approximately 12 for
carbon, 1 for hydrogen, and 16 for oxygen.)


Draw the hydration shells that form around a
potassium ion and a chloride ion when potassium chloride (KCl) dissolves in water. Label the positive, negative, and partial charges on the atoms.

What do global warming (see
Chapter 1, p. 6) and ocean acidification have in common?

Both global warming and ocean acidification are caused by increasing levels of carbon dioxide in the atmosphere, the result of burning fossil fuels.

In agricultural areas, farmers pay close attention to the weather forecast. Right before a predicted overnight freeze, farmers spray water on crops to protect the plants. Use the properties of water to explain how this method works. Be sure to mention
why hydrogen bonds are responsible for this phenomenon.

Due to intermolecular hydrogen bonds, water has a high specific heat (the amount of heat required to increase the temperature of water by 1°C). When water is heated, much of the heat is absorbed in breaking hydrogen bonds before the water molecules increase their motion and the temperature increases. Conversely, when water is cooled, many H bonds are formed, which releases a significant
amount of heat. This release of heat can provide some protection against freezing of the plants' leaves, thus protecting the cells from damage.

Organic Chemistry

Branch of Chemistry that specializes in carbon compounds


The belief in a life force outside the jurisdiction of physical and chemical laws


the view that physical and chemical laws govern all natural phenomena, including the processes of life

In 1953, Stanley Miller, a graduate student of Harold Urey's at the University of Chicago, helped bring the
abiotic (nonliving) synthesis of organic compounds into the context of evolution. From his results, Miller concluded that complex organic molecules could arise spontaneously under conditions thought to have existed on the early Earth. Miller also performed experiments designed to mimic volcanic
conditions, with roughly similar results.






Ethene (ethylene



organic molecules consisting of only carbon and hydrogen


variation in the architecture of organic molecules

Structural isomers

One of several compounds
that have the same molecular formula but
differ in the covalent arrangements of their

cis-trans isomers

One of several compounds that have the same molecular formula and covalent bonds between atoms but differ in the spatial arrangements of their atoms owing to the inflexibility of double bonds; formerly called a geometric isomer.


One of two compounds that are mirror images of each other
and that differ in shape due to the presence of an asymmetric carbon.

Functional groups

the chemical groups affect molecular function by being directly involved in chemical reactions


-OH, , Alchols


CO, Ketones and Aldehydes


COOH, carboylic acids


NH2, Amines


SH, Thiols


OP3, Organic phosphates


CH3, Methylated compounds

adenosine triphospate

An adenine-containing nucleoside
triphosphate that releases free energy when its
phosphate bonds are hydrolyzed. This energy
is used to drive endergonic reactions in cells.

Why was Wöhler astonished to find he had made urea?

Prior to Wöhler's experiment, the prevailing view was that only living organisms could synthesize "organic" compounds. Wöhler made urea, an organic compound, without the involvement of living organisms.

When Miller tried his experiment without
the electrical discharge, no organic compounds
were found. What might explain this result?

The spark provided energy needed for the inorganic molecules in the atmosphere to react with each other.

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