chp 3 composition of cells
DESCRIPTION
Chp 3 Composition of CellsTRANSCRIPT
3 Composition of cells
Figure 3.1 Footprints at a crime scene. No blood was visible to the naked eye but murder had occurred. The luminescence you see here is due to the reaction of minute traces of haemoglobin, a protein in blood, with a chemical called BLUESTAR ® FORENSIC. The chemical was sprayed because detectives suspected this was the scene of the crime. BLUESTAR ® FORENSIC is a recently developed
product and gives a better result than those obtained with Luminol, a chemical that has starred in many television shows about forensic investigations. In this chapter, we explore the major compounds of cells and the functions of those compounds, including their links with the biochemical reactions of photosynthesis and cellular respiration.
KEY KNOWLEDGEThis chapter is designed to enable students to:
• develop a knowledge and understanding of the composition of cells
• understand the relationship between the nature of various substances found in cells and the functions they perform in those cells
• understand the general role that enzymes play in cellular biochemical processes
• understand the inputs and outputs of the significant stages in the biochemical processes of photosynthesis and cellular respiration
• analyse and evaluate unfamiliar problem situations related to cells.
52 NATURE OF BIOLOGY BOOK 1
Symbol Element
C Carbon
H Hydrogen
N Nitrogen
O Oxygen
P Phosphorus
S Sulfur
Figure 3.2 The luminescence
indicates that an ‘invisible’ compound
has reacted with BLUESTAR ®
FORENSIC that was sprayed in this
area. Further testing proved the
compound was haemoglobin.
Cells reveal clues to a crimeDate: 5 May 2000. Place: Palo Alto, California, USA. A woman’s body lies at
the foot of the stairs leading from the kitchen to the basement of her home. Her
grief-stricken husband tells police that he arrived home to find his dead wife in
the basement near the foot of the stairs. The only blood visible is on the basement
floor, around the woman’s head. Upstairs, the kitchen is spotlessly clean. Appar-
ently, a tragic accident has caused the fatal head injuries to Kristine Fitzhugh,
wife of Kenneth Fitzhugh.
A post-mortem examination shows that the injuries Kristine suffered are not
those that would result from falling downstairs. Five days later, police return to
the Fitzhugh house. In the dark, they spray a chemical solution around the kitchen.
They take photographs which show glowing patches of bluish-green luminescence
on areas of the kitchen wallpaper, on a chair and a cabinet and on the floor leading
from the kitchen to the top of the basement stairs. The solution they sprayed is
known as Luminol (BLUESTAR® FORENSIC is a new product).
Luminol is a chemical that produces a short-lived bluish glow when it reacts
with the oxygen-carrying protein (haemoglobin) found in red blood cells.
Luminol can detect minute traces of blood, fresh or old, even at a dilution of one
part per million. Because of this extreme sensitivity, Luminol can reveal blood
traces even in a crime scene that has been wiped clean of any visible traces of
blood.
Luminol can also react with substances other than blood, for example, bleach.
Consequently, further tests are carried out in the Fitzhugh home which show
the substance in question is indeed blood. Samples taken from clothing in the
laundry basket and from between the kitchen floorboards are identified as blood,
and then more specifically as Kristine’s blood.
Kenneth Fitzhugh is charged with his wife’s murder. The prosecution asserts
that, during an argument in the kitchen, Kenneth Fitzhugh beat his wife,
inflicting fatal head injuries. He moved her body to the foot of the basement
stairs, arranging it to appear as if she had died as a result of a fall. He then
cleaned the blood from the kitchen and left the house. Kenneth Fitzhugh was
found guilty of his wife’s murder, due in part to his wife’s red blood cells and the
haemoglobin they contained.
In this chapter, we investigate the major groups of compounds that make up
cells and explore how some of these compounds are associated with processes
such as photosynthesis and cellular respiration.
Materials to build and fuel cellsWe have already mentioned some of the kinds of materials found in living cells
in chapter 2. The main groups of compounds found in cells are carbohydrates,
proteins, lipids and nucleic acids. These carbon-based compounds are called
organic compounds and all contain the elements carbon, hydrogen and oxygen.
Some also contain the elements nitrogen, phosphorus and sulfur. These elements
comprise the main elements in the human body. In addition to these compounds
we will also consider water, minerals and vitamins.
Water — essential for lifeWater is the most abundant compound in our bodies. About 50 per cent of an
average adult female is water. Males have less fat than females and have an
average water content of 60 per cent. Newborn babies are about 75 per cent
water.
COMPOSITION OF CELLS 53
Figure 3.3 The average distribution
of water for an average adult female in
three body regions
Intracellular water
(in cytosol)
60%Water
in plasma8%
Interstitial water(in tissue, the fluid
that surrounds cells)32%
Table 3.1 Typical water content
of some organisms
The average adult human body contains about 40 to 42 litres of water dis-
tributed across three interconnected compartments. The distribution of water in
these broad locations of the body, for an adult female, is shown in figure 3.3. As
indicated in table 3.1, a high water content is typical of living organisms.
OrganismAverage percentage
water by mass
human
adult male
adult female
newborn baby
60
50
75
bacterium 80
jellyfish 95
rat 67
mushroom 88
typical green plant 75
The water content in plants also varies. The raw
vegetables shown in figure 3.4 vary between 82 per cent
and 96 per cent water.
Metabolism goes well in waterMetabolism includes all the chemical reactions that occur
in an organism. It involves catabolism, the breakdown
of compounds to release energy and other compounds or
atoms, as well as anabolism, the synthesis of new com-
pounds from simpler ones. These reactions occur most
readily in solution. Water is the predominant solvent in
the body and, as many organic compounds dissolve in
water, metabolism occurs in a watery solution. Water
facilitates metabolism.
Water molecules stick togetherEach water molecule consists of a combination of a single oxygen atom with two
hydrogen atoms (see figure 3.5a). Each hydrogen atom is linked to the oxygen
atom by a strong covalent bond. Although a water molecule overall has a neutral
charge, the oxygen at the end of a covalent bond is slightly negative and the
Figure 3.4 Water content of the
raw vegetables shown here ranges
between 82 and 96 per cent. The value
will change for some on cooking.
54 NATURE OF BIOLOGY BOOK 1
Cl–
Cl–
Na+
Na+
Cl–
Cl–
Cl–
Cl–
Cl–
Cl–
Cl–
Cl–
Cl–
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
+ +–
+ +–
+ +–
+
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+ +–
+ +–
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hydrogen atoms are slightly positive areas. Individual molecules of water are
highly attracted to each other such that the negative oxygen of one molecule of
water is attracted to the positive hydrogen of another water molecule. In fact,
the oxygen of a water molecule attracts one hydrogen in each of two other water
molecules. Water molecules are said to be highly cohesive. They stick together,
held by so-called hydrogen bonds, which are weaker than covalent bonds (see
figure 3.5).
Water is a
versatile solventWater is the predominant solvent in
living organisms. Its versatility as a
solvent is due to the cohesive nature
of the molecule that we examined
in the previous section. Substances
that dissolve readily in water are
called hydrophilic or polar. Sub-
stances that tend to be insoluble in
water are called hydrophobic or
non-polar. How would you classify
fats?
How do substances dissolve in
water? A substance such as sodium
chloride (salt, NaCl) dissociates
into its parts — positively charged
sodium ions and negatively charged
chloride ions — when it comes
into contact with water molecules.
This occurs because the positive
sodium ions are attracted by the
negative oxygen and the negative
chloride ions are attracted by the
positive hydrogen of water. These
attractions are sufficient to break
the bonds between sodium and
chloride. A ring of water mol-
ecules surrounds each sodium and
chloride atom and they remain in
solution (see figure 3.6).
Table 3.2 Water content in tissues
Tissue Percentage
blood (red cell) 60
blood (plasma) 92
muscle 75
cartilage 70
Figure 3.5 Each water molecule
is made of a single oxygen atom
combined with two hydrogen atoms.
(a) The hydrogen atoms are joined
to the oxygen with covalent bonds.
(b) Water molecules are attracted to
each other and hydrogen bonds form
between them. Hydrogen bonds are
shown as broken lines in the diagram.
Figure 3.6 A grain of salt contains many sodium chloride
molecules. When salt is placed in water, salt molecules dissociate
because of the attraction of sodium and chloride to different parts
of the water molecules. A ring of water molecules surrounds each
sodium and chloride atom and they remain in solution.
= oxygen
= hydrogen
(a) (b)
COMPOSITION OF CELLS 55
Other chemicals
70% 18% 4% 3% 2% 2% 1.1% 0.25%
Pro
tein
s
Inorg
anic
ions
and s
mall m
ole
cule
s
Phosp
holipid
s
Oth
er
lipid
s
Poly
sacchari
des
RN
A
DN
A
Wate
r
70%Water
30%Other chemicals
Figure 3.7 The graphs show the percentage of total cell weight of major chemicals in a
typical human cell.
Carbohydrates, proteins, lipids and nucleic acids are organic compounds.
Metabolism refers to all the chemical reactions that occur in a living
organism.
Water is the predominant solvent in living organisms.
Water molecules are highly cohesive because of the attraction between
hydrogen and oxygen atoms.
Substances vary in their ability to dissolve in water.
•
•
•
•
•
KEY IDEAS
QUICK-CHECK
1 Name the three elements found in all organic compounds.
2 What is the difference between:
a catabolism and anabolism?
b hydrophilic and hydrophobic substances?
3 Which is the stronger: a covalent bond or a hydrogen bond?
Water is the major component of cellsWater is by far the main component of living human cells. Although the per-
centage of water in different cells may vary (see table 3.2, page 54), 70 per
cent is a reasonable average for us to consider. In such a human cell, the
percentage of major chemicals are as outlined in figure 3.7.
56 NATURE OF BIOLOGY BOOK 1
Organic compoundsOrganic molecules are often large molecules made of smaller sub-units that are
bonded together in various ways. Compounds formed in this way are called
polymers. The sub-units are called monomers. We can classify molecules on the
basis of the kind of sub-unit they contain. Some examples are shown in figure 3.8.
The kinds of organic molecules we will consider are carbohydrates, proteins,
lipids, and nucleic acids. We will examine the basic unit of structure of each,
how the basic units combine to form the complex molecules, where each kind
of molecule is found in a cell and the function of the molecules. We will also
examine minerals and vitamins and their importance in cells.
Carbohydrates — energy-richThe basic unit of carbohydrates is a sugar molecule also called a monosaccharide.
The most common monosaccharide is glucose and units of glucose combine in
different ways to form different kinds of polysaccharides. Carbohydrates con-
taining one or two sugar units are sometimes called simple; those containing
many sugar units are called complex carbohydrates or polysaccharides. Starch,
cellulose and glycogen are all polysaccharides composed entirely of glucose mol-
ecules and yet their properties are very different. The difference in property relates
to the way in which the glucose molecules are linked together (see table 3.3).
Type Example Function Structure
monosaccharides glucose energy source in plant
and animal cell
disaccharides sucrose form of carbohydrate
for transport in plants
polysaccharides starch
glycogen
cellulose
form of energy storage
in plants
form of energy storage
in animals
structural carbohydrate
in plant cell walls
Figure 3.8 The four main groups of
organic molecules in cells. Note the
monomers that make up the polymers
of each group.
Table 3.3 Basic structure and
function of various groups of
carbohydrates
building blocks of the cell larger units of the cell
Sugars
MONOMERS:
Polysaccharides
POLYMERS:
Fatty acids Fats, lipids, membranes
Amino acids Proteins
Nucleotides Nucleic acids
COMPOSITION OF CELLS 57
Starch
Glycogen
CellulosemoleculesCellulosemolecules
Microfibril
Primary cell wall
Secondary cell wall
Liver
Chloroplast
Carbohydrates are important in plants as structural material. The firm
outer covering of insects and spiders is also a polysaccharide — chitin.
Cellulose is the most abundant organic compound on Earth. Carbohydrates
are also stored and used as a source of energy for plant and animal cells (see
figure 3.9).
Cells require energy all the time. Energy is used for movement, for making
new material for growth and repair, for maintaining internal conditions within
a narrow range and for detecting and responding to environmental changes.
When glucose is broken down in cells to smaller products during cellular res-
piration, the chemical energy present in the glucose is released. A portion of
this energy is harvested and captured in ATP molecules (discussed further on
pages 69–70).
Proteins
Proteins are large molecules built of sub-units called amino acids (figure 3.10a).
Note that all amino acids and hence proteins contain nitrogen as well as carbon,
hydrogen and oxygen. Some proteins also contain sulfur.
There are 20 naturally occurring amino acids (refer to appendix B) and each
amino acid has one part of its molecule different from other amino acids (figure
3.10a and b). Two amino acids join together when a peptide bond forms between
them (figure 3.10c). When a number of amino acids join in this way, a poly-
peptide is formed (figure 3.10d). Each type of protein has its own particular
sequence of amino acids. Polypeptide chains become folded in different ways
depending on their function.
Figure 3.9 Carbohydrates are made of sugar units. Note the
structure, location and function of each of the carbohydrates. What are
the similarities and differences between each of the polysaccharides?
58 NATURE OF BIOLOGY BOOK 1
Short chains of carbohydrate molecules attach to protein
Phospholipids form bilayer of plasma membrane
Glycerol (b) (a)
Fatty acid
Triglyceride
Cell membrane Cytoplasm
Fat storage
Adipose cell
Nucleus Protein
Proteins may be structural, for example in cell membranes (see figure 3.11)
or the protein filaments within a cell (refer to figure 2.24, page 41). The hae-
moglobin of red blood cells is protein. The enzymes that take part in all the
metabolic processes of every living cell are also proteins. Some hormones are
proteins.
Figure 3.10 Proteins are large
molecules made from amino acid
sub-units.
Figure 3.11 (a) Fats are important
energy stores, particularly in adipose cells.
(b) Phospholipids are an important component of
cell membranes. Note the carbohydrate molecule
attached to the protein in the cell membrane.
(b) Pool of amino acids
(d) Polypeptide chain of amino acids
Peptide bond(c) Dipeptides
(a) Generalised structure of an amino acidR = variable group
H3N+
C C
R
H
O
O
COMPOSITION OF CELLS 59
ODD FACT
Animals would have to carry twice as much
carbohydrate, compared with a weight of fat, to have the same
energy store.
LipidsLipid is the general term for fats, oils and waxes. They have little affinity for water. Fats and waxes are generally solid at room temperature and oils are liquid. A fat molecule is made of two kinds of molecules, fatty acids and glycerol. Triglycerides (figure 3.11a, page 58) are a common form of fats. These fats have a single glycerol molecule to which three fatty acid molecules are attached. The fatty acid molecules may be the same or different and lack affinity for water. Hence, fats also have little or no attraction for water and are insoluble in it. Fats and other compounds insoluble in water are called hydrophobic. Phospholipids, another kind of fat, have two fatty acids attached to a glycerol. They also have a phosphate group attached to the glycerol and other small groups attached to the phosphate to make different kinds of phospholipids. Phospho-lipids are a major component of cell membranes (see figure 3.11b). On a weight basis, fat stores twice as much energy as the same weight of polysaccharide so fats are important energy stores in cells, particularly animal
cells because animals carry their energy store around with them. Plants are able
to rely more heavily on polysaccharide energy storage.
Nucleic acidsThere are two kinds of nucleic acid. One is deoxyribonucleic acid (DNA) that
is located in chromosomes in the nucleus of eukaryotic cells. It is the genetic
material that contains hereditary information and is transmitted from generation
to generation. The second kind is ribonucleic acid (RNA) that is formed against
DNA which acts as the template.
Deoxyribonucleic acidThe genetic material deoxyribonucleic acid (DNA) is a polymer of nucleotides.
Each nucleotide unit has a sugar (deoxyribose) part, a phosphate part and an
N-containing base. The sugar and phosphate parts are the same in each nucleo-
tide. There are four different kinds of nucleotides because four different kinds
of N-containing bases are involved. The four different N-containing bases are
adenine, thymine, cytosine and guanine and the four different nucleotides are
denoted by the letters A, T, C and G because of the kind of base each contains
(figure 3.12).
P
S T
A
T
S
P
S
P
S G
P
S
P
C
(a) (b) (c)
Nucleotide
Nucleotidesjoin toform chain
P
P
P
P
A
G
C
P
T
P
P
P
A T
G
C
5'
3'
3'5'
Complementarypairing ofnucleotide basesof two chains to form a DNA doublehelix (DNA molecule)
Figure 3.12 Deoxyribonucleic acid
is made from nucleotide sub-units.
Each DNA molecule is made of two
complementary chains of nucleotides.
60 NATURE OF BIOLOGY BOOK 1
DNA double helix
Each DNA moleculecombines with protein to form a chromosome.
Chromosome700 nm
2 nm
3.4 nm
0.34 nm
Chromosomesin cell nucleus Each
chromosomecontains one DNA molecule.
(a) (b) (c)
Examine figure 3.12 (page 59). The nucleotide sub-units (a) are assembled
together to form a chain (b) in which the sugar of one nucleotide is bonded with
the phosphate of the next nucleotide in the chain. Each DNA molecule contains
two chains (c) that bond with each other because the bases in one chain pair with
the bases in another. The base pairs between the two strands, namely A with T,
and C with G, are said to be complementary base pairs.
Now examine figure 3.13. The two chains form a double-helical molecule of
DNA (a) that combines with certain proteins to form a chromosome (b). These
chromosomes reside in the nucleus of a cell (c) and the DNA they contain carries
genetic instructions that control all functions of the cell.
Figure 3.14 The four
nucleotide sub-units, uracil,
adenine, guanine and cytosine,
from which the three RNAs
are constructed.
QUICK-CHECK
4 Two proteins in a cell each contain the same number of amino acids and
yet have quite different functions. Explain.
5 Consider the carbohydrates glucose, starch, cellulose and glycogen.
In what ways are these compounds similar and in what ways are they
different?
6 Explain how the hydrophobic and hydrophilic parts of phospholipid
molecules influence the way they orientate in cell membranes.
7 In addition to C, H and O, which element is found in all proteins?
The major compounds that make up living cells are different kinds of
carbohydrates, lipids, proteins and nucleic acids.
Each major compound has a specific role. Some exist only in either plant
or animal cells; others play an important role in both.
•
•
KEY IDEAS
Figure 3.13 In eukaryotic cells,
each DNA molecule combines with
proteins to form a chromosome.
Ribonucleic acidRibonucleic acid (RNA) is also a polymer of nucleotides. It differs from DNA
in that it is an unpaired chain of nucleotide bases and exists in three different
forms. RNA is constructed from four different bases, three of which — adenine,
guanine and cytosine — are identical to those in DNA. The fourth nucleotide is
uracil that is capable of pairing with A (figure 3.14). The three different forms of RNA are:
messenger RNA (mRNA), formed against DNA as a template. mRNA carries the genetic message to the ribosomes where the message is translated into a particular protein.ribosomal RNA (rRNA) which, together with particular proteins, makes the ribosomes found in cytosoltransfer RNA (tRNA), molecules that carry amino acids to ribosomes where
they are used to construct proteins.
The strand of nucleotides in each of the RNAs is folded in a different way.
•
•
•
A
U
S
P
S
P
S G
P
S
P
C
COMPOSITION OF CELLS 61
MineralsMinerals are inorganic ions required by both animal and plant cells. In humans,
minerals make up about six per cent of the body (see table 3.4). Some, for
example calcium and phosphorus, are present in relatively large amounts. Others,
for example cobalt and molybdenum, are present only in trace amounts.
Mineral Percentage Mineral Percentage
calcium 2.0 copper 0.000 15
potassium 1.0 iodine 0.000 04
phosphorus 1.0 manganese 0.000 03
sulfur 0.25 cobalt trace
sodium 0.15 molybdenum trace
chloride 0.15 fluoride trace
magnesium 0.05 selenium trace
iron 0.005 chromium trace
zinc 0.002
Minerals play a role in metabolic processes of cells and are incorporated into
many structures produced by cells. For example, animal body structures such as
bone and teeth have significant mineral content in the form of calcium. The cell
walls of plants contain minerals such as silicon and boron and rely on calcium
for their middle lamella. Minerals also contribute to cell manufacture of many
hormones, enzymes and vitamins.
Plants and animals cannot manufacture minerals. Animals must obtain their
minerals from their diet; plants generally obtain theirs from the soil. Table 3.5
shows a sample of minerals important for plants and animals.
Mineral nutrient
FUNCTIONS
Animals Plants
Calcium Bones and teeth, transmission of
nerve impulses, enzyme reactions
Middle lamella of cell
walls, enzyme reactions
Potassium Osmotic balance of cells,
transmission of nerve impulses
Establishing cell turgor,
co-factor for many
enzyme reactions
Sodium Osmotic balance of cells,
transmission of nerve impulses
Substitutes for potassium
in some functions
Phosphorus Metabolism of fat, protein and
carbohydrate, cellular respiration
Cellular respiration
Iron Cytochromes — needed by all
cells for respiration
Cytochromes — involved
in photosynthesis,
nitrogen fixation and
cellular respiration
ODD FACT
Some metals, for example mercury,
cadmium and lead, are extremely toxic to cells even in
very small doses. Lead was once a common ingredient of paint. It is now banned from general
use in paints because of deaths associated with its ingestion.
Table 3.4 Percentages of minerals
in the body mass of humans
Table 3.5 A sample of minerals
important for animal and plant
processes
62 NATURE OF BIOLOGY BOOK 1
Although some minerals are required in relatively small amounts, they are still
vital for normal healthy functioning of cells. For example, copper is an essential
mineral for cellular respiration. A deficiency of copper supply to cells results in a
significant deficiency of production of energy-rich ATP. Some babies are unable
to supply sufficient copper to their cells and this has a fatal effect. Read about
Professor Julian Mercer and his work on copper deficiency in babies.
BIOLOGIST AT WORK
Professor Julian Mercer — Molecular geneticist
Professor Julian Mercer is a Research Scientist and
Director of the Centre for Cellular and Molecular
Biology, School of Biological and Chemical Sciences,
Deakin University in Melbourne. Julian writes:
From my school days I was always interested in chem-
istry. After school I completed a BSc majoring in
biology and chemistry at the Australian National Uni-
versity. After completing my honours year in organic
chemistry, I decided that the biological sciences were
more interesting to me than pure chemistry, and the
developing field of molecular biology was particularly
exciting. At the time, the mechanisms of protein syn-
thesis on the ribosome were still being worked out, and
I undertook a PhD to work in this area in the Biochem-
istry department at the University of Adelaide. My PhD
involved a lot of organic synthesis; I was making the
end of transfer RNA to see if it would work in peptide
bond formation.
After completing a PhD, a young scientist needs
to find a laboratory to continue postdoctoral research
training. I chose to return to the Australian National
University because I had an offer of a Fellowship to
work on mRNA isolation, which moved me closer to
molecular biology than chemistry.
After three years in Canberra, I moved to the Lab-
oratory of Molecular Biology in Cambridge, UK, for
another two years postdoctoral work. What an exciting
place to work in! The Laboratory of Molecular Biology
was, and still is, an amazing place. At the time I was
there, five Nobel Prize winners were working in the
same building. These included Francis Crick who, with
James Watson, successfully worked out the structure
of DNA. It was truly awe-inspiring to meet and talk
with these famous scientists — people who had laid
the foundations of molecular biology. One of the won-
derful aspects of science is the opportunity to meet and
work with extraordinary people from all cultures, and
also to live and work in other countries. You realise that
science is an international culture, one that overcomes
many of the cultural barriers that may arise in other
aspects of life.
I completed my conversion into a molecular geneticist
when I joined Professor David Danks in the Genetics
Research Unit (which later became the Murdoch Insti-
tute) at the Children’s Hospital in Melbourne. The field
was just entering the era of cloning disease genes and
I undertook projects aimed at cloning the gene affected
in PKU and the gene affected in the X-linked copper
disorder, Menkes disease. I did not know then, but my
investigation of Menkes disease would occupy me for
more than twenty years.
Figure 3.15 Professor Julian Mercer in his laboratory
It is not widely known that copper is an essential
element, and an adequate supply of this metal is vital
for normal development. Copper forms part of many
important enzymes. Perhaps the most important is
cytochrome c oxidase which is involved in aerobic
respiration in mitochondria. Babies with Menkes
disease cannot supply enough copper to cytochrome
c oxidase and this impairs their ability to form ATP. The
deficient ATP production has a catastrophic effect on
COMPOSITION OF CELLS 63
brain development (the brain is a big user of ATP) and
boys with Menkes disease usually die within 3 years.
Fortunately the disease is rare.
Menkes disease is an X-linked condition found in
about 1/100 000 boys born; very few girls are known to
have had the condition. Affected children have a range
of other abnormalities that can be related to copper
deficiency:
reduced hair pigmentation because tyrosinase, which
is part of the pathway that makes the dark pigment
melanin, needs copper
Figure 3.16 Copper deficiency in sheep causes ‘steely wool’, as
in this sample. The white banding in the black wool of this sheep
is due to the lack of copper that results in reduced tyrosinase and
hence reduced pigment.
•
weak artery walls leading to aneurisms and weak
bones, because copper is needed for an enzyme that
helps in connective tissue formation
unusual hair, which tends to be a bit like steel wool in
texture and is an important diagnostic feature.
Interestingly, Professor Danks discovered that Menkes
disease was caused by copper deficiency because he was
aware of Australian research that showed copper defi-
ciency in sheep causes ‘steely wool’ (see figure 3.16),
very like the unusual hair in boys with Menkes disease.
We worked for many years to try to find the gene
affected in this disease, but had success only when a rare
female was diagnosed with Menkes disease. Her condi-
tion arose as a result of a genetic accident at a very early
stage of her development. A portion of one chromosome
broke away and became inserted into the Menkes gene,
disrupting the normal function of that gene. If we could
find the location at which the piece had been inserted
— that is, the breakpoint in the X-chromosome — we
could locate the position of the Menkes gene. After much
work we were successful. The rare female was a chance
event that we were able to use to our advantage.
Chance events over the years have provided scientists
with opportunities for insights about situations that have
long puzzled them. The isolation of the Menkes gene
was an international race between four laboratories.
Eventually three succeeded and the three papers were
published together, so each laboratory received credit
for their discovery. The fourth laboratory isolated the
wrong gene.
•
•
VitaminsVitamins are a group of organic compounds that occur in minute quantities in
food. Although the requirement for vitamins may vary from animal to animal,
they are unable to make them and hence require vitamins in their diets. Although
it was known for centuries that certain diseases could be ‘cured’ by the addition
of a range of fresh foods to the diet, vitamins were not discovered and extracted
from food until early in the twentieth century.
When vitamins were first discovered, their chemical structures were unknown.
This resulted in the use of a series of letters — A, B, and so on — to designate
different vitamins. Now, the chemical structures are known and vitamins tend to
be called by their chemical names.
Vitamins can be divided on the basis of their chemical nature into two groups:
fat-soluble and water-soluble vitamins. Refer to table 3.6 (page 64) for more
information about vitamins.
Vitamins are essential for many of the chemical reactions that occur in cells.
The water-soluble vitamins, except for vitamin C, are components of co-enzymes.
Co-enzymes are small molecules necessary for the normal functioning of many
of the enzyme-controlled reactions within cells. The function of fat-soluble
enzymes is not as well understood as that of water-soluble ones but it is known
that they have an important role in blood coagulation, bone structure and vision
(see the information on ‘Enzyme function and specificity’ on page 65).
ODD FACT
The name of thewater-soluble vitamin folic
acid is derived from folium, Latin for ‘leaf’, and is found in green
plants, fresh fruit, yeast and liver. The active co-enzyme form of folic acid is tetrahydrofolate.
64 NATURE OF BIOLOGY BOOK 1
Vitamin Source Required for Recommended daily intake
Fat-soluble vitamins
A retinol
fish-liver oils, butter and margarine, green and yellow vegetables, carrots, yellow-fleshed fruits, tomatoes, egg yolk, liver and kidneys, whole milk
epithelial tissues — skin, linings of nose, mouth, digestive and urinary tracts; vision in dim light — forms visual purple in retina of eye
infants and children 250–750 µg; adults 750 µg; lactating women 1200 µg
D calciferol
liver, eggs, and can be made by the body
stimulates absorption of calcium and phosphorus in bone and teeth formation
5–10 µg; children and pregnant women have greatest need because of bone growth
E tocopherols
wheatgerm, butter and margarine, bread, green leafy vegetables, whole-grain products
prevents damage to cell membranes; protects fats and vitamin A from destruction by oxidation
10–15 mg
K phytomenadione
green vegetables, tomatoes, cabbage, cauliflower, potatoes, cereal, eggs
formation of prothrombin, essential for blood clotting
children 15–100 mg; adults 70–100 mg
Water-soluble vitamins
B1 thiamine
seafood, meat, whole-grain products the release of chemical energy from carbohydrate
children 0.5–1.2 mg; women 0.6–0.8 mg; men 0.8–1.1 mg
B2 riboflavin
meat, eggs, green vegetables, mushrooms, whole-grain products, pasta
protein metabolism; helps maintain healthy skin and eyes; growth of new body tissue
children 0.5–1.2 mg; women 0.8–1.0 mg;men 1.0–1.4 mg
B3 niacin
leafy vegetables, whole-grain products, peanut butter, potatoes, tuna, eggs
enzyme systems that convert carbohydrates, proteins and fats into energy; aids synthesis of hormones
children 9–20 mg; women 10–13 mg; men 14–18 mg
B6 pyridoxine
yeast, wheat germ, cereals, liver, meat, soya beans, peanuts, egg yolk
many enzyme reactions and for development of red blood cells
adolescents 1–2.2 mg; adults 1–1.5 mg; lactating women 1.6–2.2 mg
B12 cyanocobalamin
liver, meat, eggs, oysters, sardines development of red and white blood cells; also involved in metabolism
adults 2 µg; pregnant and lactating women 3–3.5 µg
folate liver, kidneys, yeast, mushrooms, leafy green vegetables
reduction of neural tube defects; development of red blood cells and metabolism of protein; linked with vitamin B12
adults 200 µg; pregnant women 400 µg; lactating women 300 µg
biotin liver, meat, fish, yeast, egg yolk, milk, smaller amounts in grains and vegetables
metabolism of fat and protein; growth and function of nerve cells
children 65–200 µg; adults 100–200 µg
pantothenic acid liver, meat, fish, egg yolk, yeast, cereals, peanuts and vegetables; also found in ‘royal jelly’ (fed to the queen bee) but this is most expensive and not in any way a source superior to others
metabolism of carbohydrate, fat and protein
estimated 5–10 mg
C ascorbic acid
citrus and other fruits, tomatoes, leafy vegetables, potatoes, rosehips
connective tissues, bones, teeth; promotes wound healing and absorption of iron
children 30–50 mg; adults 30 mg; pregnant and lactating women 60 mg
Note: In an attempt to set a standard for an adequate diet for groups of the population, health authorities introduced a scheme of recom-
mended dietary intakes (RDI). These recommendations are often quoted now in labelling of nutrients on foods, but it is important to realise
that an RDI does not necessarily equal the requirement of a particular individual.
Variation exists in the amount of nutrients required by different individuals. Variation is due to a number of factors including genetic
factors, body size, activity level and state of health. An RDI value should satisfy the requirements of 95 per cent of the population but some
people require less than the RDI and others require more. A person with a varied and well-balanced diet will receive adequate amounts of
vitamins and minerals.
Table 3.6 Vitamins — their source and functions
COMPOSITION OF CELLS 65
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.
9 a Name four foods that are a source of fat-soluble vitamins.
b Name four foods that are rich in water-soluble vitamins.
10 What feature of enzymes controls which substrate they act on?
QUICK-CHECK
The body requires a number of minerals, some in relatively large amounts,
others in trace amounts.
Minerals play a role in metabolic processes of cells and are incorporated
into many structures produced by cells.
Copper is an essential mineral for cellular respiration.
Vitamins are a group of organic compounds and are essential for many of
the chemical reactions that occur in cells.
Vitamins can be divided on the basis of their chemical nature into two
groups: fat-soluble and water-soluble vitamins.
Each enzyme acts on only one kind of substrate.
•
•
•
•
•
•
KEY IDEAS
ENZYME FUNCTION AND SPECIFICITY
Enzymes are protein molecules that increase the rate
of the reactions that occur in living organisms. Without
enzymes, metabolism would be so slow at body temper-
ature and pH that insufficient energy would be available
to maintain life. Many enzymes are intracellular; they
are used within cells that produce them. Others (for
example, the digestive enzymes) are extracellular. They
are secreted by cells and act outside those cells.
The compound being acted on by an enzyme is called
a substrate. The compounds obtained as a result of the
enzyme action are called the products. Enzymes are
highly specific in their action; each enzyme acts on only
one kind of substrate. This is because the shape of one
enzyme matches that of one substrate at a particular
region known as the active site of the enzyme, as shown
in figure 3.17.
An enzyme is named for the substrate it associates
with. The enzyme maltase acts on the disaccharide
maltose. Lipase acts on lipid, and amylase on amylose.
Note the -ase endings in the name of most enzymes. The
few exceptions include trypsin and pepsin.
Although enzymes participate in reactions, they are
not used up in the reactions and are available for reuse.
The rate of an enzyme reaction is influenced by pH,
temperature, enzyme concentration and substrate con-
centration. Why do you think the activity of an enzyme
is destroyed at high temperatures?
Many enzymes require the presence of other factors
before they act. If the factor is an organic molecule
(for example a vitamin), it is called a coenzyme. Some
poisons, for example cyanide and arsenic, block the
active sites of enzymes and hence interfere with cell
metabolism.
Figure 3.17 Representation showing that each enzyme reacts
with only one kind of substrate. This is because the active site of
an enzyme matches the shape of a particular substrate and the
two are able to come closer together. This matching of shapes is
often called the ‘lock and key’ theory of enzyme action.
Active
site
Enzyme Possible substrates Only one substrate
fits the active site
Enzyme Substrate Enzyme–substrate
complex
Enzyme Products
66 NATURE OF BIOLOGY BOOK 1
Autotrophs are also called
producers and heterotrophs are
called consumers.
Figure 3.18 The inputs and outputs
of the process of photosynthesis
Producers at work: photosynthesisHow do carbohydrates originate? Using the energy of sunlight, plants, algae
and some protists (such as phytoplankton) can make organic molecules, such as
sugars, by photosynthesis. Organisms with this ability are termed autotrophic.
Other organisms, such as animals and fungi, that depend, directly or indirectly,
on the organic compounds produced by producers are called heterotrophic.
Photosynthesis is the process in which light energy is transformed into
chemical energy stored in sugars. In a typical producer, such as a terrestrial
flowering plant, the complex series of reactions in photosynthesis can be sum-
marised as follows:
In fact, the complete balanced equation for photosynthesis is
6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O light
This is often simplified to:
6CO2 + 6H2O C6H12O6 + 6O2
light
showing net consumption of water only.
The general word equation for photosynthesis is the summary for a chain of
biochemical reactions, as we will see later. One way of summarising the inputs
and outputs of photosynthesis is shown in figure 3.18.
In fact, the details of the chemical reactions that make up photosynthesis are
more complex than the equation shown here. You will be introduced to more
information about the chemistry of photosynthesis as you progress through your
biology studies. For now, we will explore where photosynthesis occurs and how
different wavelengths of light can influence the process.
Light
+
Carbon dioxide
+
Water
Glucose
+
Oxygen
INPUTS OUTPUTS
carbon dioxide + water glucose + oxygen
chlorophyll
carbon dioxide + water glucose + oxygen
chlorophyll
ELight
COMPOSITION OF CELLS 67
Porp
hyri
n r
ing
CH3 in chlorophyll
in chlorophyll
a
CHO b
C N
CH3
CH3
CH3
CH3
CH3
C
C
C
C
C
C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
C
H
CH
CH H
O C O
CH2
CH2
C
CC
H
H
H3C
C
C
HC
C
C
C CH3
CH2CH3
N C
CH
N C
Mg
C N
HC
C
CC
C
C
C
C
CH H
CH2
C O
C O
OCH3
H3
Chloroplasts: where the action is!The cytoplasm of cells in the leaf tissue where photosynthesis occurs contains
specialised organelles, known as chloroplasts. Each chloroplast has an outer
membrane and folded inner membranes joined to form stacks of flattened discs,
know as grana (singular = granum) (see figures 2.20 (page 37) and 3.19).
The enzymes needed for the reactions in photosynthesis are located inside the
chloroplasts, with some located in the grana membranes and some in solution in
the stroma.
Light-trapping pigmentsRadiant energy from the sun includes a range of wavelengths:
visible light, in the range from about 0.4 to 0.7 µm
infra-red (IR), with wavelengths greater than 0.7 µm
ultraviolet light (UV), with wavelengths shorter than 0.4 µm.
Various pigments can trap light energy. The major light-trapping pigments
are green chlorophylls (see figure 3.20) located on the grana membranes. Other
kinds of light-trapping pigments, known as accessory pigments, are also found
in the chloroplasts of various organisms (see table 3.7).
Table 3.7 Occurrence of various light-trapping pigments in plants and algae
Pigment Organisms where found
chlorophyll a all plants and all algae
chlorophyll b all plants and green algae
chlorophyll c brown algae and phytoplankton
chlorophyll d red algae
carotenoids all plants and green algae
phycobilins red algae
Carotenoids are red, orange and yellow pigments that are normally masked by
the green chlorophylls. In temperate climates in early autumn, deciduous trees
begin to withdraw the chlorophyll from their leaves, exposing the carotenoids and
other pigments that are normally hidden (see figure 3.21). Phycobilins are blue-
green (phycocyanin) and red (phycoerythrin) water-soluble pigments.
•
•
•Figure 3.20 Molecular structure of
chlorophyll a
(a) Air spaces
(b) Stroma Granum
Chloroplasts in cell
Stoma (pore) Lower epidermis
Upper epidermis
Figure 3.19 (a) Features of a leaf
(b) Internal structure of chloroplast showing
many layers of membranes, the grana, and
stroma, the fluid part
Figure 3.21 Deciduous leaves in
early autumn
68 NATURE OF BIOLOGY BOOK 1
The various pigments trap light energy of different wavelengths (see figure
3.22). Consequently, the presence of accessory pigments extends the range of
light wavelengths that can be absorbed by a plant and converted to chemical
energy. Light energy absorbed by accessory pigments must be transferred to
chlorophyll a before it can be converted into chemical energy. If the accessory
pigments were removed from a plant cell, what would you predict would happen
to the rate of photosynthesis?
Photosynthesis is most efficient in light of red and blue wavelengths. These
wavelengths do not penetrate very far below the surface of water. In deeper
waters most of the light wavelengths available are blue-green, which accessory
pigments can absorb. The phycobilins, in particular, contribute to photosynthesis
in deeper waters and these are found in seaweeds (see figure 3.23). Seaweeds
that have colour when brought to the surface of the water often look black when
looked at in water. Can you determine why this is so? Think about absorption and
reflection of different wavelengths of light.
Figure 3.22 Absorption of light
of various wavelengths for different
plant pigments. Which pigment
absorbs yellow light best? What
wavelengths of light (colours) are
best absorbed by chlorophylls?
Figure 3.23 Different algae: (a) green seaweed, Caulerpa remotifolia, found at depths of up to 10 metres (b) brown seaweed,
Macrocyctis pyrifera, also found at depths of up to 10 metres (c) red seaweed, Callophyllis lambertii, found at depths of up to 35 metres
ODD FACT
Trees that lose their leaves during one short
period of the year are said to be deciduous. In contrast, Australian native trees drop
leaves in small numbers over the entire year. Because these trees do not become leafless, they are
termed evergreens.
80
60
40
20
0.4 0.5 0.6 0.7
Wavelength ( m)
Rela
tive a
bsorp
tion (
%)
Chlorophyll a
Chlorophyll b
Carotenoids
Phycoerythrin Phycocyanin
Violet Blue Green RedViolet Blue Green Yellow Red
Gamma rays X-rays Ultraviolet Microwaves Radio waves
Visible light in
electromagnetic spectrum
Infra-red
(a) (b) (c)
COMPOSITION OF CELLS 69
Accessing energy: cellular respirationAll living organisms require energy to maintain life. The energy required to
maintain cellular functions is in the form of adenosine triphosphate (ATP) (see
figure 3.24). Where does this ATP come from? As we saw on pages 29 and 32,
ATP is formed when energy is released during cellular respiration of glucose,
a carbohydrate.
Figure 3.24 Energy is necessary for life. ATP, a high-energy compound, is a major source of
energy for many functions in the human body, some of which are outlined here.
The transfer of chemical energy from glucose to ATP occurs through a coupling
of chemical reactions (see figure 3.25).
The process of energy transfer from glucose to ATP is not 100 per cent
efficient. Some of the chemical energy is converted to and ‘lost’ as heat energy.
In general, the energy transfers in cellular respiration are 40 per cent efficient
— about 40 per cent of the chemical energy present in glucose is transferred
Muscle
contraction
Nervous
tissue
Digestive
system
Excretory
system
New tissue and
structure production
Manufacturing
chemicals
heart
muscle
skeletal
muscle
muscle
in gut migration of
vesiclesconduction
of impulses
transmitter
substances
blood
proteins
secretion
of enzymes
active
secretion of
ions
active
reabsorption
of water
active
transport across
membranes
nails
hair
blood
skin
antibodies
enzymes
hormones
diaphragm
peristalsis
wound tissue
ATP
Figure 3.25 Energy released
from reactions involving glucose is
transferred to the energy-requiring
process of ATP production. Is the
process 100% efficient?
(Pi � inorganic phosphate;
ADP � adenosine diphosphate)
OutIn
Breakdown
products
CO2, H2O
ATP
ADP + Pi
High
energy level
Low
energy levelHeat energy
E
Chemical
Glucose
70 NATURE OF BIOLOGY BOOK 1
Like all living tissue, fruit and vegetables carry out
cellular respiration and produce some heat energy. The
higher the rate of respiration, the more heat energy is
produced and the greater the chance that deterioration
of the plant material will occur. The rate of respiration
varies in different produce (see table 3.8).
Respiration rates depend on the storage tempera-
ture and the stage of ripeness of the plant material. For
example, broccoli at 20°C respires nearly 15 times faster
than broccoli at 0°C. Produce that is highly perishable
generally has a high respiration rate and a high rate of
heat evolution. Unless this heat is removed, the tem-
perature of the produce increases resulting in an even
higher rate of respiration, greater release of heat energy
and more rapid deterioration.
Several techniques are used to slow respiration rate
and prevent deterioration:
cooling of fruit and vegetables after harvesting and
transport to markets in refrigerated trucks
keeping the produce in a confined space in an atmos-
phere with reduced oxygen and increased carbon
dioxide. The reduced oxygen results in a slower
rate of aerobic respiration and lower heat produc-
tion. However, the level of gases must be carefully
controlled because too little oxygen can cause anaer-
obic respiration or fermentation which can also ruin
produce.
•
•
coating the surface of produce, such as apples and
bananas, with wax. This coating lengthens shelf life
by slowing the intake of oxygen and the escape of
carbon dioxide.
Table 3.8 Examples of approximate
respiration rates (watts/tonne)
Fruit or vegetable
Respiration rate
storage at 0°C
broccoli 212
lettuce 72
celery 61
peaches 23
cabbage 15
plums 6
storage at 2°C
asparagus 155
storage at 14°C
bananas
(ripening)
111
bananas
(green)
40
•
CELLULAR RESPIRATION IN FRUIT AND VEGETABLES
Figure 3.26 The living
cells in fruit and vegetables
respire.
to ATP and the remaining 60 per cent appears as heat energy. So, living cells
produce heat. The box below describes how heat production from respiring fruit
and vegetables contributes to their deterioration.
Cells cannot use heat energy to drive energy-requiring activities, such as
muscle contraction or transport against a concentration gradient. However, in
mammals and birds, the heat energy released from cellular respiration is trapped
by insulating layers of fat, fur or feathers and is the internal source of the heat
needed to maintain their core body temperatures within narrow ranges.
When cellular respiration involves the use of oxygen, the term aerobic
respiration or aerobic cellular respiration is used and the overall equation is:
Aerobic respiration of glucose generally yields 36 molecules of ATP per molecule
of glucose.
In some tissues, respiration occurs without the involvement of oxygen and is
referred to as anaerobic respiration. Anaerobic respiration is far less efficient
than aerobic respiration in converting the energy in glucose into energy in ATP
yielding just 2 ATP molecules per molecule of glucose. The end products of
anaerobic respiration in human muscle are lactic acid and carbon dioxide.
E
C6H
12O
6 + 6O
2
glucose carbon dioxide wateroxygen
ADP + Piin the form
of ATP
6CO2 + 6H
2O
ODD FACT
The end productsof anaerobic respiration in
yeast are the alcohol ethanol and carbon dioxide.
ODD FACT
Built-in electric blanket! Brown
fat tissue is found in young mammals and in adult mammals of species that hibernate. Brown
fat is metabolised and the energy released appears as heat energy, not as chemical energy
in the form of ATP.
COMPOSITION OF CELLS 71
Levels of biological organisationIn chapter 2 (pages 42–46), we introduced you to the various levels of organ-
isation of cells. Figure 3.27 shows how the molecules and compounds we have
discussed in this chapter fit in the organisation of cells and of the living world.
The progression of complexity from subatomic to atomic extends into molecules
and compounds, then to cells that become functional entities, capable of sus-
taining life and being the basic building block of all living organisms.
11 What is the difference between an autotroph and a heterotroph?12 Where in a cell is light energy transformed to chemical energy?13 Name the inputs and outputs in photosynthesis.14 Where in a cell does aerobic respiration occur?15 Name the inputs and outputs of (a) aerobic respiration; (b) anaerobic
respiration.
QUICK-CHECK
Photosynthesis is the process of converting light energy to chemical energy stored in sugars. Organisms that can make organic molecules by photosynthesis are called autotrophs and include all plants, algae and some bacteria.Adenosine triphosphate (ATP) is formed when energy is released during cellular respiration of glucose, a carbohydrate.
•
•
•
KEY IDEAS
ECOSYSTEM
Dynamic systemof organismsinteracting witheach other andtheir environment
MOLECULES
Two or more atoms bonded together
ORGANELLES
and CYTOPLASM
Components from which cells are constructed
CELL
The smallest unit that is itself alive
MULTICELLULAR
ORGANISM
Individual composedof many specialised cells
POPULATION
Group of organismsof the same species in the same area
COMMUNITY
Populations oforganisms livingtogether in the same habitat
BIOSPHERE
Entire surface of the earth and its organisms
Ability toperform simplebiologicalfunctions
Capacity toperform complexbiologicalfunctions
Higher biologicalproperties e.g. sight, emotion,intelligence
Social order;evolution
Species interaction(predation,parasitism,mutualism, etc.)
LIFE
Unique phenomena that emerge as complexity increases
SUBATOMIC PARTICLES
Protons, neutrons,and electrons
ATOMS
Smallest unit of a substance that retains the properties of that substance
Figure 3.27 Levels of
biological organisation. As each
level increases, structural
complexity increases and unique
phenomena may emerge.
BIOCHALLENGE
72 NATURE OF BIOLOGY BOOK 1
1 2
3
4
Many compounds contain the element carbon, symbol C. For
example, the formula for the mineral calcite is CaCO3.
Explain whether you would classify calcite as an organic
compound.
Mammalian tissue cells live in a moist environment of tissue
fluid. This fluid contains many different materials in solution.
Would you expect these materials to be monomers or
polymers?
The temperature at which an enzyme is most efficient is the
temperature at which the rate of a reaction involving the enzyme
is at its highest point. It is reasonable to assume that this
temperature is close to the body temperature of an organism.
Scientists investigated the rates of reaction of three enzymes
over a range of temperatures. The enzymes were taken from the
following warm-body organisms:
• Arctic gull, body temperature 34°C
• human, body temperature 37°C
• western pewee bird, body temperature 44.8°C.
The results for two of the enzymes investigated are given in the
following graph.
a From which organism is enzyme B likely to have come?
b If the results from the third enzyme were plotted, where would
you expect them to be in relation to the two results already on
the graph?
Examine the illustrations above. Which of the structures is:
a an amino acid?
b a lipid polymer?
c a carbohydrate monomer?
d an amino acid polymer?
e a nucleic acid polymer?
f a carbohydrate polymer?
A B C D
E F G H
Temperature °C
Enzyme A Enzyme B
17 21 25 29 33 37 41 45 49
Rate of
enzyme
reaction
COMPOSITION OF CELLS 73
CHAPTER REVIEW
accessory pigments
active site
adenine
aerobic cellular
respiration
aerobic respiration
amino acids
anabolism
anaerobic respiration
autotrophic
bonds
carbohydrates
catabolism
cellular respiration
cellulose
chemical energy
chitin
chlorophylls
chloroplasts
coenzyme
cohesive
complex carbohydrates
covalent bond
cytosine
deoxyribonucleic acid
(DNA)
enzymes
fatty acids
glucose
glycerol
glycogen
grana
guanine
heterotrophic
hydrogen bonds
hydrophilic
hydrophobic
light energy
lipids
metabolism
minerals
monomers
monosaccharide
non-polar
nucleic acids
organic compounds
phospholipids
photosynthesis
polar
polymers
polysaccharides
proteins
ribonucleic acid
(RNA)
starch
stroma
substrate
thymine
triglycerides
vitamins
Key words
Questions
1 Making connections between concepts ³�Prepare a concept map, using key
words and phrases from the list above. You may use any additional concepts
that you wish.
2 Understanding scientific terminology ³ Many vitamins are called
coenzymes. What is the function of such vitamins?
3 Applying understanding to new contexts ³ When phospholipids
are added to water, they aggregate
(come together) as shown in figure
3.28. Explain why the molecules
come together in this way.
4 Interpreting and communicating ideas ³ Discuss the validity of each
of the following statements.
a The source of oxygen used in
aerobic respiration is the same for
plants and animals.
b All nucleic acids are identical.
c All enzymes act in the same way
because they are all made of
proteins.
CROSSWORD
Figure 3.28
74 NATURE OF BIOLOGY BOOK 1
5 Making connections between concepts ³ The diagram in figure 3.29 is
sometimes called the ‘biology energy wheel’. Process A is photosynthesis.
a Name process B.
b Name the input element X.
c Name the output product at Y.
d In what form must energy be before it can be used for metabolic processes
in a cell?
6 Analysing information and making connections ³ All living cells in
humans are close to a blood supply that delivers oxygen that is then avail-
able for aerobic cellular respiration. Skeletal muscle is also capable of
carrying out anaerobic respiration and does so at certain times.
a What is the advantage of skeletal muscle being able to carry out anaerobic
respiration as well as aerobic respiration?
b Describe the conditions that individuals might be under when their
skeletal muscles engage in anaerobic respiration.
7 Application of concepts ³ Fruit and vegetables are sometimes transported
over very long distances between grower and consumer. For many products,
refrigerated transport is essential. Why is such transport needed to ensure
that the produce is in good order on its arrival at markets?
8 Analysing and evaluating information ³ Suggest explanations for the
following observations.
a It is cheaper to keep a large pot plant alive than a small dog.
b A greengrocer found that his refrigerator costs were greater when he
stored broccoli in his cold room than when he stored the same amount of
cabbages.
9 Analysing and evaluating information ³ Discuss the validity of each of
the following statements.
a A tissue contains groups of cells where each group has quite a different
function.
b Delivery mechanisms are important if a group of small cells is to operate
more effectively than one large cell.
c The surface-area-to-volume ratio of a cell influences the rate at which
substances can enter or exit the cell.
10 Using the web ³ Go to www.jaconline.com.au/natureofbiology/natbiol1-3e
and click on the ‘Photosynthesis’ weblink for this chapter. Select ‘Center
for Study of Early Events in Photosynthesis’ from the given list. Read ‘The
Power of Green’ and examine the drawing on the page.
a The drawing on the page implies some similarity between photosynthesis
in a plant and the water wheel of a mill. Explain what similarity you think
the artist was indicating in the drawing.
b Select ‘Educational Resources’ from the index bar. Then select ‘What
is photosynthesis?’ Select ‘Introduction to Photosynthesis and its
Applications’ and read the section headed ‘Basics’.
i Why do we see most leaves as the colour green?
ii Suggest why wavelengths of light below 330 nm are likely to damage
cells.
Eradiant
E
X
Process B
Process A
Energy formetabolicprocesses
carbon dioxide + waterY
Figure 3.29