Lisa Gani - 000446298
Chemistry of Life Practice Questions
1.
Organisms are composed of atoms, elements, compounds and molecules.
Define each term and provide an example of each.
Term
Definition
Example
the smallest unit of matter that still
retains the properties of an element.
C- Carbon
a substance that cannot be broken
down to other substances by
ordinary chemical means.
gold, copper, carbon, and
oxygen
Atom
Element
Compound
a substance consisting of two or more table salt (sodium chloride,
different
NaCl)
elements combined in a fixed ratio.
Two or more atoms held together by
covalent bonds
Molecule
a covalent bond connects
two hydrogen atoms in a
molecule of the gas H2.
2. What are isotopes and radioactive isotopes? How are radioactive isotopes dangerous?
Explain how radioactive isotopes have valuable medical applications.
Isotopes : atoms of the same elements that differ in the number of neutrons
Radioactive isotopes : one in which the nucleus decays spontaneously, giving off
particles and energy.
Uncontrolled exposure to them can harm living organisms by damaging molecules,
especially DNA and cause cancer. The particles and energy thrown off by radioactive
atoms can break chemical bonds and also cause abnormal bonds to form.
Radioactive isotopes are an essential part of medical diagnostic procedures. In combination
with imaging devices which register the gamma rays emitted from within, they can be used
for imaging to study the dynamic processes taking place in various parts of the body.
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3. There are 3 important types of chemical bonds discussed in the assigned readings.
Complete the chart below.
Chemical bond
Ionic bond
Covalent bond
Hydrogen bond
Definition
A chemical bond resulting from the
attraction between oppositely charges
ions
A type of strong chemical bond in which
two atoms are share one or more pair of
valence electrons
A type of weak chemical bond formed
when the slightly positive hydrogen atom
of polar covalent bond in one molecule is
attracted to the slightly negative atom of
polar covalent bond in another molecule
or in another region of the same
molecule
Example
NaCl
H2
H2O
4. Explain the role of hydrogen bonds and why each of the following are important to
biology.
a. Cohesive properties of water
Hydrogen bonds between molecules of liquid water last for only a few trillionths of a
second, yet at any instant, many molecules are hydrogen-bonded to others. Water
flows freely but water molecules do not separate from each other.
b. Water’s ability to moderate temperature
Heat must be absorbed in order to break hydrogen bonds, and heat is released when
hydrogen bonds form. To raise the temperature of water, heat energy must first disrupt
hydrogen bonds before water molecules can move faster. Thus, water absorbs a large
amount of heat while warming up only a few degrees. Conversely, when water cools,
more hydrogen bonds form, and a considerable amount of heat is released.
c. Ice floating on the surface of a lake
As water freezes, each molecule forms stable hydrogen bonds with its neighbors,
holding them at “arm’s length” and creating a three-dimensional crystal. In The ice
crystal has fewer molecules than an equal volume of liquid water. Therefore, ice is less
dense and floats on top of liquid water.
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5. What property of water makes it the universal solvent? Explain.
Due to its polarity and ability to form hydrogen bonds, water facilitates chemical
reaction, inside and outside living organism. Water can dissolve many different kinds of
molecules, most chemicals. Water dissolves more substances than any other solvent. As
the solvent inside all cells, in blood, and in plant sap, water dissolves an enormous variety
of solutes necessary for life.
6. What is pH? What is the difference between an acid, a base and something that is neutral?
Give an example of each.
pH is a measure of hydrogen ion concentration equal to -log H+ and ranging in value from
0-14
Acid : A compound that donates hydrogen ions to solutions hydrochloric acid (HCl), the
acid in the gastric juice in your stomach. In solution, HCl dissociates completely into H and
Cl.
Base : a compound that accepts hydrogen ions and removes them from solution sodium
hydroxide (NaOH), do this by donating OH; the OH combines with H to form H2O, thus
reducing the H concentration.
Neutral : Pure water and aqueous solutions that are neither acidic nor basic. The pH of the
solution inside most living cells is close to 7.
7. What are buffers? How do they work? Why is this important in living systems?
Buffers : substances that minimize changes in pH, keep them within normal limits.
They work by accepting H ions when it is in excess and donating H ions when it is
depleted.
It is important in living systems because a slight change in pH can be harmful because the
chemical processes of the cell are very sensitive to the concentrations of hydrogen and
hydroxide ions.
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