Download Chapter 4 - UNT-Biological Sciences

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Chemistry plays a central role in any environmental issue; it is crucial in understanding how pollutants and chemicals affect the
environment, and
in finding solutions to these problems. The chemical building blocks of all matter are elements, which are made up of atoms. Life on
Earth is enabled because of the chemical characteristics of water. Other molecules can join together to form long chains of repeated
molecules called polymers, which play key roles as the building blocks of life in the form of proteins, nucleic acids, and carbohydrates.
The organized complexity found in nature requires a constant input of energy. Although energy cannot be created or destroyed, it can
change in quality. Energy from the sun powers photosynthesis in plants, which converts water, carbon dioxide, and light energy into
glucose and water. Autotrophs make their own food for energy, while heterotrophs must consume food from outside sources. One of the
most debated topics in science is the origin and method of how life originated on Earth. Scientists have proposed several theories to
explain the origin of life. The theory of evolution by natural selection describes how organisms adapt to their environment and change
over time. Organisms that survive and reproduce pass genetic traits to their offspring, which enable them to better adapt to the
environment. Survival of the fittest refers to those organisms that best "fit" their particular environment.
Chapter 4 Outline
Bioremediation of the Exxon Valdez Oil Spill
In the largest oil spill in U.S. history, the tanker Exxon Valdez struck a reef in Alaska's Prince William Sound on March 24, 1989.
The Valdez spilled 11 million gallons of crude oil, killing hundreds of
thousands of seabirds, thousands of sea otters, hundreds of harbor seals, and countless fish.
The local economy suffered as hundreds of fishermen lost their jobs and tourism dropped..
Thousands of workers and volunteers tried to clean up the spill with: booms, skimmers, absorbent materials, and chemicals.
Scientists also tried bioremediation, which uses bacteria to biodegrade the oil, but the beaches lacked enough nitrogen and phosphorus,: so
scientists
applied a fertilizing solution, which helped the bacterial numbers increase. Because there were so many complicating factors involved in
the cleanup, experts do not agree on whether the bacteria actually helped clean up the spilled oil.
Chemistry and the Environment
The Exxon Valdez oil spill ignited scientific, economic, political, and social concerns.
The root of all the problems with the oil spill is the chemistry of the oil
itself: The chemical makeup of oil provides the characteristics that make it a potent pollutant.
Chemistry plays a central role in any environmental issue; it is crucial to understanding how pollutants and chemicals affect the
environment.
Atoms and elements are the chemical building blocks
An element is a fundamental type of matter that cannot be broken down into substances with other properties.
Although there are 92 naturally occurring elements, the most abundant elements are carbon, nitrogen, hydrogen, and oxygen.
Elements are composed of atoms, the smallest components of an element that keep the chemical properties of that element.
The nucleus of an atom is made up of positively charged particlesprotons-and neutral particles-neutrons.
Surrounding the nucleus are negatively charged particles called electrons. Usually, there are an equal number of protons and electrons, so
that the atom is neutral.
All atoms of a given element contain the same number of protons, but
not necessarily of neutrons.
Atoms of an element with different numbers of neutrons are called Isotopes
.
Although
masses. " isotopes of an element behave almost the same chemically, they have different physical properties because they have different
Atoms
that gain or lose electrons become ions, which are electrically j":,
,', c'
charged atoms or groups of atoms.
Atoms bond to form molecules and compounds i,; Atoms bonded together in chemical reactions are called molecules.
Molecules can be all the same element (e.g., 2 oxygens = O2) or they can
consist of different elements, in which case the molecule is called a com- ~: pound (e.g., water = H2O).
Atoms can be held together in different ways.
Covalent
bonds form between two uncharged atoms that may share electrons. This occurs when carbon and oxygen combine to form
carbon
dioxide.
Ionic bonds form between oppositely charged atoms, where an electrical attraction holds the atoms together.
In the case of ionic bonds, these associations are not called molecules, but are called ionic compounds or salts.
For example, the positively charged sodium (Na+) is attracted to the negatively charged chloride (CI-) to form NaCI, or common table
salt.
When elements, molecules, or compounds come together, but do not bond chemically, they form a mixture.
A homogeneous mixture of substances is called a solution, which is usually a liquid such as salt water or human blood.
The chemical structure of the water molecule facilitates life
, The
abundance of water is the main reason Earth can support life.
In a water molecule, one oxygen atom is bonded to two hydrogen atoms with a special type of bond called a hydrogen bond.
Water has several properties that allow it to support life: (1) liquid water molecules stick together, which allows nutrients and wastes to
travel
through
change; it; (2) water molecules can absorb large amounts of heat without changing temperature, which helps stabilize systems against
(3) water molecules in ice are lighter than liquid water, so ice floats and prevents entire water bodies from freezing solid; and (4) water
can readily dissolve many solids.
Hydrogen ions determine acidity
In any aqueous solution, water molecules can separate into a positively charged hydrogen ion (H+) and a negatively charged hydroxide
ion (OH-).
On the pH scale, which quantifies the acidity of solutions, anything valued between 0 and 7 is acidic (it has more H+ ions), 7 is neutral,
and anything between 7 and 14 is considered basic (it has more OH- ions). The lower the number, the more acidic the substance, and the
higher the number, the more basic the substance is.
The pH of rain in some parts of the world is 4 or lower, which causes significant environmental concern.
Matter is composed of organic and inorganic compounds
Organic compounds contain carbon-to-carbon covalent bonds, with other elements such as hydrogen and oxygen joined to the molecule.
Crude oil and other petroleum products are made up of hydrocarbons, which contain mostly carbon and hydrogen.
!
In bioremediation, bacteria pull carbon atoms from hydrocarbons, which then unravel into hydrogen and carbon. '
Macromolecules are the building blocks of life
Organic molecules can join together to form long chains of repeated molecules called polymers.
Polymers in the form of proteins, nucleic acids? and carbohydrates are essential for life.
Lipids, also fundamental to life, are not polymers.
Proteins, nucleic acids, carbohydrates, and lipids are called macromolecules because of their large size.
Proteins are made up of combinations of 20 amino acids positioned in very convoluted forms.
Proteins serve many different functions, including tissue production, energy storage, immunity, and creation of enzymes (molecules that
promote chemical reactions).
Nucleic acids such as deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) carry the hereditary information that is passed from
parents to offspring.
The order of the nucleotides (bases) in DNA and RNA determines which amino acids are produced, which determines the protein made.
Genes are units of hereditary information located on strands of DNA that perform certain functions by producing specific proteins. J~
An entire DNA molecule is called a chromosome; different species have different shapes and numbers of chromosomes.
Carbohydrates are polymers containing carbon and water.
Simple carbohydrates (3-7 carbons long) are called sugars, or saccharides. Glucose, with 6 carbons, is one of the most common and
important sugars, and serves as a building block for complex sugars, called polysaccharides.
Plants store energy in starch (a polysaccharide), while animals eat plants to obtain the stored starch.
Carbohydrates are also used to build structures such as insect shells and cellulose in leaves, bark, and stems.
Lipids include fats, phospholipids, waxes, pigments, and steroids do not dissolve in water.
Animals use lipids in the form of fats for storing energy.
I. Rhospholipids have one water-repellant side and one water-attracting side, and when arranged in a double layer form the major part of
cell membranes.
Waxes can serve structural functions (e.g., beeswax), and steroids are used in cell membranes and hormones.
Organisms use cells to compartmentalize
Cells are the basic units of organization in living organisms.
Eukaryotes are multicellular organisms, while prokaryotes are much simpler organisms such as bacteria.
Eukaryotic cells contain organelles, which are internal structures that per- form specific functions.
Some organelles are ribosomes (which synthesize proteins) and mitrochondria (for energy extraction from sugars and fats). The nucleus of
eukaryotes houses the DNA.
; Prokaryotes lack organelles and a nucleus and are generally single-celled organisms.
Energy Fundamentals
Energy-anything that can change the position, physical composition, or temperature of matter-is used to organize matter into polymers,
build and maintain cellular structures, and provide power for survival and reproduction.
Potential energy (the energy of position) can become kinetic energy (the energy of motion).
Chemical energy is contained within the bonds between atoms; when molecules with high energy in their bonds are converted into
molecules with lower energy, energy is released by changing potential into kinetic energy.
The energy released allows motion, action, or heat.
Energy is always conserved.
The first law of thermodynamics states that energy can change from one
form to another, but it cannot be created or destroyed.
But energy changes in quality
The second law of thermodynamics states that energy changes from a more-ordered to a less-ordered state.
Entropy is the degree of disorder in a substance, system, or process; systems go toward greater entropy (disorder).
Petroleum and high-voltage electricity are considered high-quality energy, because they contain concentrated forms of easily releasable energy.
Sunlight is a low-quality energy source because the energy is spread out and hard to harness.
As energy is transferred, much of it is lost due to inefficiency in the conversion.
To counteract disorder, living organisms must find some way to' consume
energy.
Light energy from the sun powers most living systems
The sun is the original source of energy for most organisms.
Photosynthesis produces food for plants and animals
The sun provides energy to autotrophs (also called primary producers),
which are organisms that can use this energy to produce their own food. Autotrophs (e.g., green plants) use photosynthesis to turn carbon
dioxide and water into sugars and oxygen (which is released into the environment).
The light-dependent portion of photosynthesis uses sunlight to split water into hydrogen, oxygen, and high-energy molecules that are used
to run the second set of reactions, called the dark reactions.
In the dark reaction, carbon dioxide is broken down into carbon and oxygen, and the carbons are linked together into the sugar known as
glucose.
Cellular respiration releases chemical energy
Cellular respiration splits a glucose molecule into water and carbon dioxide and also releases energy, which can form chemical bonds or
do other work.
Cellular respiration is the opposite of photosynthesis.
Heterotrophs, including most animals, consume other organisms to obtain their energy.
Tidal and geothermal forces also provide energy to Earth's systems Earth obtains energy from sources other than the sun.
A weak source of energy is the gravitational pull of the moon, which causes tides in the oceans.
Radiation from the center of Earth consists of a gradual release of high- energy rays or particles, which heat the inside of the planet and
may explode from volcanoes or as hot water emerging from geysers. Heat from deep within the planet is called geothermal energy.
Hydrothermal vent communities utilize chemical energy instead of light energy Hydrothermal vents occur in the deep, cold depths of the ocean
and re- lease jets of geothermally heated water.
Entire communities of organisms live within these hydrothermal vents
and obtain their energy not from the sun, but through chemosynthesis,
which uses the chemical energy contained in organic molecules, particularly hydrogen sulfide.
The end product of chemosynthesis is similar to photosynthesis (sugar, oxygen, and water), with additional sulfates.
The Origin of Life on Earth
,
How and where life originated on Earth is an intensely debated question.
Early Earth was a hostile place
Earth formed about 4.5 million years ago, and during its early years it was an extremely hostile place.
It was bombarded with space debris, and had severe volcanic and tectonic activity; any life that started was probably killed off.
The fossil record has revealed to us much about the history of life Simple bacteria were present on Earth over 3 billion years ago.
When organisms die, their organic matter may be replaced by minerals and preserved, leaving behind a fossil, an imprint in stone of the
dead orgarnsms.
Scientists use the fossil record to gain knowledge about the history of past life on Earth.
The fossil record shows five major conclusions: (1) the vast majority of
organisms that have ever lived are now extinct; (2) earlier types of organ- isms changed, or evolved, over time; (3) the overall number of
species has increased through time; (4) there have been several episodes of mass extinction; and (5) past organisms were simpler than
current ones.
Present-day organisms and their genes can also help us decipher the history of life
Biologists use present-day organisms to gain knowledge about past organ- isms in Earth's history.
Branching diagrams show relationships among organisms.
There are three major branches to the tree of life: bacteria, archaea (single-celled prokaryotes), and eukaryotes.
.
The air was very different on early Earth
Other scientists use geological evidence to determine Earth's early conditions.
Scientists have concluded that oceans appeared very early, ultraviolet radiation was very intense, asteroids and comets may have brought
water, and atmospheric oxygen was present in very low levels until photosynthesis by microbes occurred.
; Scientists
believe the early atmosphere contained mainly carbon dioxide,
nitrogen, and carbon monoxide.
Several theories have been proposed to explain life's origin
Most scientists agree that inorganic chemicals became linked into small molecules and formed organic compounds.
These compounds became able to reproduce themselves, while others grouped and became early proto-cells.
The debate on the beginning of life centers around the specific details of
this process. "
Primordial soup: the heterotrophic hypothesis One hypothesis suggests that carbon dioxide, oxygen, and nitrogen dissolved in shallow waters, forming
simple amino acids, which gave rise to more complex organic compounds.
This view of life is termed "heterotrophic" because the first life forms
used organic compounds from the environment as an energy source. "
""
In the lab, an electrical current passed through hydrogen, water vapor, ammonia, and methane produced amino acids and other organic
compounds.
,
Seeds from space: the heterotrophic extraterrestrial hypothesis Some scientists believe that bacteria on meteorites from space crashed into
Earth and began the process of life.
This "panspermia" hypothesis has been supported with evidence that
some meteorites that have crashed to Earth contain high concentrations of amino acids.
Life from the depths: the chemoautotrophic hypothesis This hypothesis proposes that life began in the scalding-hot deep-sea vents.
In this hypothesis, organisms were autotrophic and created their own food from the abundant sulfur present in the vents.
Organic polymers had to develop the ability to self-replicate
In order for life to develop, organisms had to be able to self-replicate.
Scientists think the first self-replicating molecule was RNA, because it can act as both an enzyme and an information carrier.
In the lab, when short chains of RNA and amino acids are combined in a flask, the amino acids can line up along the RNA and form a
copy. Cell precursors were another crucial step
Another key step in the origin of life was the formation of cells.
Simple unicellular organisms may have been formed when abiotically pro- duced polymers joined by chance.
The Theory of Evolution and Natural Selection
Life began evolving as soon as it began, and has resulted in more than 1.5 million species currently on Earth.
To understand ecology, a central part of environmental studies, one must understand the evolutionary process: how organisms adapt to
their environments and change over time.
Biological evolution is the genetically based change in the appearance, function, and/or behavior of organisms through natural selection.
Although the theory of evolution is well supported scientifically, many
,
people remain unconvinced of its validity.
Darwin and Wallace proposed the concept of natural selection
In 1858, Charles Darwin and Alfred Russell Wallace simultaneously pro- posed the concept of natural selection as a mechanism for
evolution. Darwin and Wallace postulated that organisms face a constant struggle to survive and reproduce, and those individuals that had
offspring with some sort of edge over others would survive and reproduce.
Furthermore, the characteristics that gave some individuals an edge might be inherited by their offspring, so those characteristics wo~ld
become more prevalent in future generations.
Scientists at that time knew that traits were inherited, but they did not know of Gregor Mendel's (called "the father of genetics") work that
showed a genetic basis for inheritance.
Mendel's work provided further support for evolutionary theory.
Natural selection shapes organisms and organismal diversity
Natural selection offers a powerful, yet simple, explanation for the patterns seen in nature.
The idea of natural selection follows a straightforward premise that individuals of the same species vary in their characteristics.
Variation in the genetic makeup of individuals, as well as the environment and the interaction between genes and the environment, means
that certain individuals of a species will be better suited to the environment than will other individuals.
Those better suited to their environment will survive and have more offspring.
Such characteristics are passed from parent to offspring, and eventually
the species will evolve to possess those characteristics that lead to a better fit with that environment.
The fittest individuals are those that are best suited to their environment by being stronger or faster, or better able to avoid competition or
use new resource.
Fitness refers to two things: (1) the likelihood that an individual will have offspring, and (2) the number of offspring that individual has
during its lifetime.
A trait that increases fitness is termed adaptation, whereas a maladaptive trait reduces fitness.
Adaptation is a moving target
As the environment changes over time, what was an adaptive trait may become maladaptive.
Other individuals that might previously have had less chance of survival may, in the new environment, have a higher chance of survival
and reproduction.
" Because
the environment is constantly changing, there will never be a species perfectly adapted to its environment. '
Evidence of natural selection is all around us
Both in the natural world and in labs, the results of natural selection have been demonstrated.
Artificial selection, which is natural selection conducted by humans, is evident in the breeding of domestic animals and provides the best
evidence that a trait can spread throughout a population. '
.
'
Selection can operate in different ways
Natural and artificial selection can come in three forms: directional, stabilizing, and disruptive selection.
Directional selection drives a feature in one direction: For example, high water pressure selects for thick shells in oysters; thin shells
would not be selected for at all.
Stabilizing selection promotes intermediate traits; extreme traits are not selected for.
For example, very thick crab shells would waste resources, too-thin shells would break, and medium shells are just right.
Disruptive selection favors more than one extreme trait; for example, a
very small individual may easily hide, and a very large individual would
be too large to eat, but a medium-sized individual would be preyed upon.
DNA is the source of heritability and variation
For a trait to be heritable (passed on from one generation to the next), it must be found in the DNA within the genes.
Natural selection occurs because DNA replication is not perfect; mutations are accidental changes in DNA.
Certain chemicals and radiation can cause genetic mutations.