Living organisms need to be able to take in matter and energy from their environment to grow and function. For example, the algae in the ocean can survive only because they are able to take the Sun’s energy and combine it with materials from the water around them to make the basic building blocks of their own tissues and to power their cellular activities. In turn, the algae are eaten by zooplankton, which are eaten by While one factor may be limiting at a given time, several
factors outside the optimum may combine to cause additional stress or even death. In particular, pollutants may act in a way that causes organisms to become more vulnerable to disease or drought. Such cases are examples of synergistic effects, or synergisms, which are defined as two or more factors inter- acting in a way that causes an effect much greater than one would anticipate from each of the two acting separately.
Habitat and Niche. Habitat refers to the kind of place—
defined by the plant community and the physical environment—
where a species is biologically adapted to live. For example, deciduous forests, swamps, and grassy fields are types of habi- tats. Different types of forests (for instance, coniferous versus tropical) provide markedly different habitats and support dif- ferent species of wildlife. Because some organisms operate on very small scales, we use the term microhabitat for things like puddles, spaces sheltered by rocks, and holes in tree trunks that might house their own small community (Figure 3–7).
Even when different species occupy the same habitat, competition may be slight or nonexistent because each spe- cies has its own niche. An ecological niche is the sum of all of the conditions and resources under which a species can live:
what and where it feeds, what it feeds on, where it finds shel- ter and nests, and how it responds to abiotic factors.
Rate of growth
Optimum
Celsius
temperature 8° 18° 28° 38°
Limit of tolerance
Limit of tolerance Death
occurs Death
occurs Increasing
stress Increasing
stress Range of tolerance
Optimal range Figure 3–6 Survival curve. for every factor
influencing growth, reproduction, and survival, there is an optimum level. above and below the optimum, stress increases until survival becomes impossible at the limits of tolerance.
The total range between the high and low lim- its is the range of tolerance.
UndErSTanding THE daTa 1. If you were growing bamboo in a green-
house, how would you expect its rate of growth to change if the temperature fell to 18°c?
2. What if the temperature rose to 40°c during a particularly hot day?
3.3 Matter in Living and Nonliving Systems 55 existing that has the characteristics of lead. A lead atom has a characteristic number of protons (positive particles), neutrons (neutral particles), and electrons (negative particles).
How can these relatively few building blocks make up the countless materials of our world, including the tissues of living things? Picture each kind of atom as a different-sized Lego® block. Like Legos, atoms can build a great variety of things. Also like Legos, natural materials can be taken apart into their separate constituent atoms, and the atoms can then be reassembled into different materials. All chemical reac- tions, whether occurring in a test tube, in the environment, or inside living things (and whether they occur very slowly or very quickly), involve rearrangements of atoms to form dif- ferent kinds of matter.
Atoms do not change during the disassembly and reas- sembly of different materials. A carbon atom will always remain a carbon atom. In chemical reactions, atoms are neither created nor destroyed. The same number and kind of different atoms exist before and after any reaction. This constancy of atoms is regarded as a fundamental natural law, the Law of Conservation of Matter. Nuclear reactions differ from the chemical reactions we are discussing and can result in the splitting of an atom of one element into multiple at- oms of another element. However, this is a very specific, rare instance and is not a chemical reaction. (Nuclear reactions will be discussed in Chapter 15.)
Now we turn our attention to the ways atoms are put together and how atoms are incorporated into organisms.
Molecules and Compounds. A molecule consists of two or more atoms (either the same kind or different kinds) bonded in a specific way. The properties of a material depend on the ex- act way in which atoms are bonded to form molecules as well as on the atoms themselves. A compound consists of two or more different kinds of atoms that are bonded. For example, the fundamental units of oxygen gas, which consist of two bonded oxygen atoms, are molecules (O2) but not compounds.
By contrast, when an oxygen atom binds with hydrogen atoms to create water, it is both a molecule and a compound (H2O).
On the chemical level, the cycle of growth, reproduction, death, and decay of organisms is a continuous process of us- ing various molecules and compounds from the environment (food), assembling them into living organisms (growth), dis- assembling them (decay), and repeating the process.
Four Spheres
During growth and decay, atoms move from the environ- ment into living things and then return to the environment. To picture this process, think of the environment as three open, nonliving systems, or “spheres,” interacting with the bio- sphere. The atmosphere is the thin layer of gases (including wa- ter vapor) separating Earth from outer space. The hydrosphere is water in all of its liquid and solid compartments: oceans, rivers, ice, and groundwater. The lithosphere is Earth’s crust, made up of rocks and minerals. Matter is constantly being exchanged within and between these four spheres, as shown in Figure 3–8 on the following page.
fish, which in turn are eaten by penguins. Both the penguins and their prey get from their food the energy and matter necessary to build their own tissues and to do the work they need to do in each of their cells. To understand this simple ecological relationship, we need to know some basic chem- istry and physics. Later, we will explore what happens to energy and matter as they move through the biosphere.
Basic Units of Matter
Matter is defined as anything that occupies space and has mass. This definition covers all solids, liquids, and gases as well as all living and nonliving things. Matter is composed of atoms—very small pieces—that are combined to form mol- ecules, which in turn can be combined into more complex structures.
Atoms. The basic building blocks of all matter are atoms.
Only 94 different kinds of atoms occur in nature, and these are known as the naturally occurring elements. Atoms are made up of protons, neutrons, and electrons, which in turn are made up of still smaller particles. For example, lead (Pb) is an element. An atom of lead is the smallest amount of lead Figure 3–7 Habitat and niche. for part of its life cycle, this species of damselfly lives in a pool of water trapped by a type of tropical plant;
the tiny pool is a microhabitat. The specific conditions required by the damselfly, such as the pool and the types of food it eats there or where it lays its eggs as an adult, are its niche.
56 CHAPTER 3 Basic Needs of Living Things
are normally stable, but under some circumstances, they react chemically to form new compounds. For example, ozone is produced from oxygen in the upper atmosphere (Chapter 18).
Plants take carbon dioxide in from the atmosphere, usu- ally through their leaves. Animals usually take oxygen in through some type of specialized organ such as a lung, but some, like earthworms, can simply absorb oxygen through their skin.
Hydrosphere. While the atmosphere is a major source of carbon and oxygen for organisms, the hydrosphere is the source of hydrogen. Each molecule of water consists of two hydrogen atoms bonded to an oxygen atom, so the chemical formula for water is H2O. A weak attraction known as hy- drogen bonding exists between water molecules.
Water is an important molecule for living things and usually needs to be available in liquid form. Water occurs in three different states. At temperatures below freezing, hydro- gen bonding holds the molecules in position with respect to one another, and the result is a solid crystal structure (ice or snow). At temperatures above freezing but below vaporiza- tion, hydrogen bonding still holds the molecules close but allows them to move past one another, producing the liquid state. Vaporization (evaporation) occurs as hydrogen bonds break and water molecules move into the air independently.
As temperatures are lowered again, all of these changes of state go in the reverse direction. Generally, water undergoes melting and evaporation, but sometimes water molecules leave snow or ice and go directly into the air. This process is sublimation (Figure 3–9). Moving from one state to another either releases or requires a great deal of energy. This is one reason why many animals sweat to cool off: changing from Biosphere
(Living systems)
Hydrosphere Atmosphere
Lithosphere
Figure 3–8 The four spheres of Earth’s environment. The bio- sphere is all of life on Earth. It depends on, and interacts with, the atmo- sphere (air), the hydrosphere (water), and the lithosphere (soil and rocks).
(Source: adapted from Geosystems, 5th ed., by robert W. christopherson, © 2005 Pearson Education, Inc.)
(b) HO H
Gas (water vapor)
Solid (ice)
Liquid (water) Sublimation
Deposition
Condensation Vaporization/
evaporation
Freezing Melting
(d) (c)
(+)
Water molecule(−) (a)
Figure 3–9 Water and its three states. (a) Water con- sists of molecules, each of which is formed when two hydro- gen atoms bond to an oxygen atom (h2o). (b) In water vapor, the molecules are separate and independent. (c) In liquid water, the weak attraction between water molecules known as hydrogen bonding gives the water its liquid property.
(d) at freezing temperatures, hydrogen bonding holds the molecules firmly, giving the solid state—ice.
Atmosphere. The lower atmosphere is a mixture of mol- ecules of three important gases—oxygen (O2), nitrogen (N2), and carbon dioxide (CO2)—along with water vapor and trace amounts of several other gases. The gases in the atmosphere
3.3 Matter in Living and Nonliving Systems 57
Organic Compounds
Your body, like that of the emperor penguin, is composed of relatively large chemical compounds in a number of broad cat- egories, such as proteins, carbohydrates (sugars and starches), lipids (fatty substances), and nucleic acids (DNA and RNA).
These compounds usually contain six key elements: carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), and sulfur (S). Living things need other elements as well, some- times in smaller, but no less important, amounts. Table 3–1 on the following page lists the elements in living organisms.
Unlike the relatively simple molecules that occur in the environment (such as CO2, H2O, and N2), the key chemi- cal elements in living organisms bond to form very large, complex molecules. The chemical compounds making up the the liquid to gas state requires heat and removes it from the
organism. Despite the changes of state, the water molecules themselves retain their basic chemical structure of two hy- drogen atoms bonded to an oxygen atom; only the relation- ship between the molecules changes.
Lithosphere. All the other elements that are required by liv- ing organisms, as well as the approximately 72 elements that they do not require, are found in the lithosphere, in the form of rock and soil minerals. A mineral is a naturally occurring solid, made by geologic processes; it is a hard, crystalline structure of a given chemical composition (Figure 3–10). Most rocks are made up of relatively small crystals of two or more minerals, and soil generally consists of particles of many dif- ferent minerals. Each mineral is made up of dense clusters of two or more kinds of atoms bonded by an attraction between positive and negative charges on the atoms (Appendix C).
Interactions. Air, water, and minerals interact with each other in a simple, but significant, manner. Gases from the air and ions (charged atoms) from minerals may dissolve in water. Therefore, natural water is inevitably a solution containing variable amounts of dissolved gases and miner- als. This solution is constantly subject to change because various processes may remove any dissolved substances in it or additional materials may dissolve in it. Molecules of water enter the air by evaporation and leave it again via condensation and precipitation (see the hydrologic cycle, Chapter 10). Thus, the amount of moisture in the air fluctu- ates constantly. Wind may carry dust or mineral particles, but the amount changes constantly because the particles gradually settle out from the air. These interactions are sum- marized in Figure 3–11. The materials in these three spheres interact with the biosphere as living organisms take materials from the spheres and use them to create complex molecules in their bodies. We will discuss the process of building these molecules next.
Figure 3–10 Minerals. minerals (hard, crystalline compounds) are composed of dense clusters of atoms of two or more elements. The at- oms of most elements gain or lose one or more electrons, becoming neg- ative (−) or positive (+) ions, and form a predictable pattern held closely together. This photograph is of a mineral, gypsum, in a mine in Texas.
O
– –
–
– –
– +
+ + + +
+
+ –
+ +
N NN
N N NN
N
NN OC
O OC
O OO
OO
O O
OO
O O O
Precipitation Evaporation
Mineral dissolving Crystallization
Air
Water
Dissolved minerals
Mineral
Dissolved gases
– + – + + – + –
– + – + – + + –
+ – – + + – + + – + + – – +
– – + –
– – + +
Figure 3–11 Interrelationship among air, water, and minerals.
minerals and gases dissolve in water, forming solutions. Water evaporates into air, causing humidity. These processes are all reversible: minerals in solution recrystallize, and water vapor in the air condenses to form liquid water.
58 CHAPTER 3 Basic Needs of Living Things
that contain carbon bonds, such as carbon dioxide, are still considered inorganic.
All plastics and countless other human-made com- pounds are also based on carbon bonding and are, chemically speaking, organic compounds. To resolve any confusion this may cause, the compounds making up living organisms are referred to as natural organic compounds and the human- made ones as synthetic organic compounds. The term organic can have a completely different meaning, such as in organic farming (Chapter 12).
tissues of living organisms are referred to as organic. Some of these molecules may contain millions of atoms. These molecules are constructed mainly from carbon atoms bonded into chains, with hydrogen and oxygen atoms attached.
Nitrogen, phosphorus, or sulfur may be present also, but the key common denominator is carbon–carbon and carbon–
hydrogen or carbon–oxygen bonds. Inorganic, then, refers to molecules or compounds with neither carbon–carbon nor carbon–hydrogen bonds. While this is the general rule, some exceptions occur; by convention, a few compounds
Table 3–1 Elements Found in Living Organisms and the Locations of Those Elements in the Environment Biologically Important Molecule or Ion
in Which the Element Occursa Location in the Environmentb
Element (Kind of Atom) Symbol Name Formula Atmosphere Hydrosphere Lithosphere
Carbon C Carbon dioxide CO2 X X X (CO3)
Hydrogen H Water H2O X (Water itself)
Atomic oxygen (required in respiration)
O Oxygen gas O2 X X
Molecular oxygen (required in photosynthesis)
O2 Water H2O (Water itself)
Nitrogen N Nitrogen gas
Ammonium ion Nitrate ion
N2 NH4+ NH3
X X
X X
Via fixation X X
Sulfur S Sulfate ion SO42− X X
Phosphorus P Phosphate ion PO43− X X
Potassium K Potassium ion K+ X X
Calcium Ca Calcium ion Ca2+ X X
Magnesium Mg Magnesium ion Mg2+ X X
Trace Elementsc
Iron Fe Iron ion Fe2+, Fe3+ X X
Manganese Mn Manganese ion Mn2+ X X
Boron B Boron ion B3+ X X
Zinc Zn Zinc ion Zn2+ X X
Copper Cu Copper ion Cu2+ X X
Molybdenum Mo Molybdenum ion Mo2+ X X
Chlorine Cl Chloride ion Cl− X X
Note: These elements are found in all living organisms—plants, animals, and microbes. Some organisms require certain elements in addition to the ones listed. For example, humans require sodium and iodine.
aA molecule is a chemical unit of two or more atoms that are bonded. An ion is a single atom or group of bonded atoms that has acquired a positive or negative charge as indicated.
bX means that element exists in the indicated sphere.
cOnly small or trace amounts of these elements are required.