Botkin Environmental Science Earth as Living Planet 8th txtbk

6.2 Life and Global Chemical Cycles 111
6.2 Life and Global
Chemical Cycles
All living things are made up of chemical elements (see Appendix
D for a discussion of matter and energy), but of
the more than 103 known chemical elements, only 24 are
required by organisms (see Figure 6.8). These 24 are divided
into the macronutrients, elements required in large
amounts by all life, and micronutrients, elements required
either in small amounts by all life or in moderate amounts
by some forms of life and not at all by others. (Note: For
those of you unfamiliar with the basic chemistry of the elements,
we have included an introduction in Appendix E,
which you might want to read now before proceeding with
the rest of this chapter.)
The macronutrients in turn include the “big six” elements
that are the fundamental building blocks of life:
carbon, hydrogen, nitrogen, oxygen, phosphorus, and
sulfur. Each one plays a special role in organisms. Carbon
is the basic building block of organic compounds; along
with oxygen and hydrogen, carbon forms carbohydrates.
Nitrogen, along with these other three, makes proteins.
Phosphorus is the “energy element”—it occurs in compounds
called ATP and ADP, important in the transfer
and use of energy within cells.
Other macronutrients also play specific roles. Calcium,
for example, is the structure element, occurring
in bones and teeth of vertebrates, shells of shellfish, and
wood-forming cell walls of vegetation. Sodium and potassium
are important to nerve-signal transmission. Many
of the metals required by living things are necessary for
specific enzymes. (An enzyme is a complex organic compound
that acts as a catalyst—it causes or speeds up
chemical reactions, such as digestion.)
For any form of life to persist, chemical elements
must be available at the right times, in the right amounts,
and in the right concentrations. When this does not happen,
a chemical can become a limiting factor, preventing
the growth of an individual, a population, or a species, or
even causing its local extinction.
Chemical elements may also be toxic to some
life-forms and ecosystems. Mercury, for example, is toxic
even in low concentrations. Copper and some other
1
H
Hydrogen
3 4
Atomic number
Environmentally
important trace
elements
*
Ca
20
Name
Element reiatively abundant
in the Earth`s crust
Element symbol
Li Be
B C N O F Ne
Beryllium
Boron Carbon Nitrogen Oxygen Fluorine Neon
Calcium
13 14 15 16 17 18
* *
* *
Na Mg Al Si P S Cl Ar
Lithium
11 12
Sodium
Magnes
-ium
* * *
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn
19 20 21 22 23 24 25 26 27 28 29 30
Potassium
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn
Rubidium
Calcium
37 38 39
Strontium
55 56 57
Scandium
Yttrium
Titanium
40
Zirconium
72
Vanadium
41
73
Niobium
Chromium
42
74
Molybde
-num
Manganese
43
75
Technet
-ium
44
Iron
Ruthenium
76
Aluminum Silicon Phosphorus Sulfur Chlorine Argon
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po
45
Cobalt
Rhodium
77
46
Nickel
Palladium
78
47
79
Copper
Silver
48
80
Zinc
Cadmium
5 6
31
49
81
Indium
32 33
50
Tin
7 8
82 83 84
He
Ga Ge As Se Br Kr
Gallium Germanium Arsenic
Sb Te I Xe
Antimony
Selenium
Tellurium
Bromine
Iodine
2
10
34 35 36
51 52 53 54
9
85 86
At
Helium
Krypton
Xenon
Rn
Cesium
Barium
Lanthanum
Hafnium
Tantalum
Tungsten
Rhenium
Osmium
Iridium
Platinum
Gold
Mercury
Thallium
Lead Bismuth Polonium
Astatine
Radon
87 88 89
104 105 106 107 108 109
Fr Ra Ac
Francium Radium Actinium
Rf Db Sg Bh Hs Mt
Dubnium
Rutherfordium
Seaborgium
Bohrium Hassium Meitnerium
= Required for all life
= Required for some life-forms
58 59 60 61 62 63 64 65 66 67 68 69 70 71
Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Cerium
Thorium
Uranium
Np Pu Am Cm Bk Cf Es Fm Md No Lw
Samarium
Plutonium
Europium
Americium
Curium
Terbium
Berkelium
Holmium
90 91 92 93 94 95 96 97 98 99 100 101 102
Th Pa U
Erbium
Fermium
Thulium
Ytterbium
Nobellium
Lutetium
103
Praseodymium
Protactinium
Neodymium
Promethium
Neptunium
Gadolinium
Dysprosium
Californium
Einsteinium
Mendelevium
Lawrencium
= Moderately toxic: either slightly toxic to
all life or highly toxic to a few forms
= Highly toxic to all organisms, even in low concentrations
FIGURE 6.8 The Periodic Table of the Elements. The elements in green are required by all life; those in
hatched green are micronutrients—required in very small amounts by all life-forms or required by only some
forms of life. Those that are moderately toxic are in hatched red, and those that are highly toxic are solid red.