Chapter 3
Answers
1
QUICK-CHECK questions
Name the three elements found in all organic compounds.
The three elements found in all organic compounds are hydrogen (H), oxygen (O) and
carbon (C).
2
What is the difference between:
a
catabolism and anabolism?
Catabolism includes the chemical reactions in which compounds are broken down
to simpler substances; catabolic reactions release energy.
Anabolism includes the chemical reactions in which compounds are built up from
simpler substances: anabolic reactions require energy.
b
hydrophilic and hydrophobic substances?
Hydrophilic substances are substances that dissolve readily in water
Hydrophobic substances are substances that tend to be insoluble in water;
hydrophobic substances are said to be fat soluble.
3
Which is the stronger: a covalent bond or a hydrogen bond?
Covalent bonds that hold the atoms together in a molecule are far stronger than
hydrogen bonds.
4
Two proteins in a cell each contain the same number of amino acids and yet
have quite different functions. Explain.
The critical features that determine the function of a protein are the kinds of amino
acids present and the order (sequence) of these amino acids. While the two proteins in
question may have the same number of amino acids, the fact that they differ in their
function indicates that they differ in their constituent amino acids and in their amino
acid sequences.
5
Consider the carbohydrates glucose, starch, cellulose and glycogen. In what
ways are these compounds similar and in what ways are they different?
Glucose, starch, cellulose and glycogen are similar in that all are composed of one or
more glucose subunits. Starch, cellulose and glycogen are polymers.
Starch, cellulose and glycogen differ in the arrangement of the glucose subunits in
polymer (see figure 3.9).
6
Explain how the hydrophobic and hydrophilic parts of phospholipid molecules
influence the way they orientate in cell membranes.
Phospholipid molecules have a hydrophilic (water loving) portion and a hydrophobic
(water hating) portion. Cell membranes contain a double layer of phospholipids. In a
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Chapter 3: QUICK-CHECK answers
cell membrane, the hydrophilic portion of each phospholipid molecule is orientated to
the outside of the cell membrane so that it is exposed to the aqueous cytosol and the
aqueous contents of the nucleus. The hydrophobic portions of the phospholipid
molecules are orientated so that they form the inner portion of the plasma membrane
(see figure 3.11(b)).
7
In addition to C, H and O, which element is found in all proteins?
In addition to C, H and O, all proteins contain the element nitrogen (N).
8
Name, and give the function of, two minerals that the body requires in relatively
large amounts and two that it requires in trace amounts.
Minerals required in relatively large amounts in the human diet include calcium and
potassium.
Minerals required in trace amounts include cobalt and molybdenum.
(See table 3.4 for other examples.)
9
a
Name four foods that are a source of fat-soluble vitamins.
Foods that are a source of fat-soluble vitamins include butter, carrots, liver and
whole grains.
(See table 3.6 for other examples.)
b
Name four foods that are rich in water-soluble vitamins.
Foods that are rich in water-soluble vitamins include seafoods, meat, yeast, and
citrus fruits.
(See table 3.6 for other examples.)
10
What feature of enzymes controls which substrate they act on?
The feature of an enzyme that controls which substrate it can act on is the shape of
the active site of the enzyme molecule. Only compounds that include a region with a
shape complementary to the shape of the active site can be substrates of a specific
enzyme and so bind to the enzyme.
11
What is the difference between an autotroph and a heterotroph?
Autotrophs and heterotrophs differ in the manner in which they obtain the organic
matter that supplies the chemical energy for living. Autotrophs, such as plants, can
trap an external source of energy, typically sunlight, and use this energy to make
organic matter, such as sugars, from simple inorganic compounds. In contrast,
heterotrophs, such as animals and fungi, must ingest or absorb the organic matter that
is the source of chemical energy for living.
12
Where in a cell is light energy transformed to chemical energy?
Light is transformed to chemical energy by the chlorophyll present in the chloroplasts
of plant cells.
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Chapter 3: QUICK-CHECK answers
13
Name the inputs and outputs in photosynthesis.
Inputs to photosynthesis: sunlight, carbon dioxide and water
Outputs of photosynthesis: glucose and oxygen
14
Where in a cell does aerobic respiration occur?
Aerobic respiration occurs in the mitochondria of cells.
15
Name the inputs and outputs of:
a
aerobic respiration
Inputs: glucose and oxygen
Outputs: carbon dioxide, water and energy (ATP)
b
anaerobic respiration.
Input: glucose
Outputs: lactic acid, carbon dioxide and energy (ATP)
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