1.1 Biology: The Science of Our Lives
Biology
literally means "the study of life". Biology is such a broad field,
covering the minute workings of chemical machines inside our cells, to broad
scale concepts of ecosystems and global climate change. Biologists study
intimate details of the human brain, the composition of our genes, and even the
functioning of our reproductive system. Biologists recently all but completed
the deciphering of the human genome, the sequence of deoxyribonucleic acid
(DNA) bases that may determine much of our innate capabilities and
predispositions to certain forms of behavior and illnesses. DNA sequences have
played major roles in criminal cases (O.J. Simpson, as well as the reversal of
death penalties for many wrongfully convicted individuals), as well as the
impeachment of President Clinton (the stain at least did not lie). We are
bombarded with headlines about possible health risks from favorite foods
(Chinese, Mexican, hamburgers, etc.) as well as the potential benefits of
eating other foods such as cooked tomatoes. Informercials tout the benefits of
metabolism-adjusting drugs for weight loss. Many Americans are turning to
herbal remedies to ease arthritis pain, improve memory, as well as improve our
moods.
Can a biology book give you the answers to these questions? No,
but it will enable you learn how to sift through the biases of investigators,
the press, and others in a quest to critically evaluate the question. To be
honest, five years after you are through with this class it is doubtful you
would remember all the details of meatbolism. However, you will know where to
look and maybe a little about the process of science that will allow you to
make an informed decision. Will you be a scientist? Yes, in a way. You may not
be formally trained as a science major, but you can think critically, solve
problems, and have some idea about what science can and cannoit do. I hope you
will be able to tell the shoe from the shinola.
1.2 Science and the Scientific Method
Science
is an objective, logical, and repeatable attempt to understand the principles
and forces operating in the natural universe. Science is from the Latin word, scientia,
to know. Good science is not dogmatic, but should be viewed as
an ongoing process of testing and evaluation. One of the hoped-for benefits of
students taking a biology course is that they will become more familiar with
the process of science.
Humans
seem innately interested in the world we live in. Young children drive their
parents batty with constant "why" questions. Science is a means to
get some of those whys answered. When we shop for groceries, we are conducting
a kind of scientific experiment. If you like Brand X of soup, and Brand Y is on
sale, perhaps you try Brand Y. If you like it you may buy it again, even when
it is not on sale. If you did not like Brand Y, then no sale will get you to
try it again.
In
order to conduct science, one must know the rules of the game (imagine playing Monopoly and
having to discover the rules as you play! Which is precisely what one does with
some computer or videogames (before buying the cheatbook). Thescientific method is to be used as a guide
that can be modified. In some sciences, such as taxonomy and certain types of geology,
laboratory experiments are not necessarily performed. Instead, after
formulating a hypothesis, additional observations and/or
collections are made from different localities.
Steps
in the scientific method commonly include:
1. Observation: defining the problem
you wish to explain.
2. Hypothesis: one or more falsifiable
explanations for the observation.
3. Experimentation: Controlled
attempts to test one or more hypotheses.
4. Conclusion: was the hypothesis
supported or not? After this step the hypothesis is either modified or
rejected, which causes a repeat of the steps above.
After
a hypothesis has been repeatedly tested, a hierarchy of scientific thought
develops. Hypothesis is the most common, with the lowest level of certainty. A theory is a hypothesis that has been
repeatedly tested with little modification, e.g. The Theory of Evolution. A Law
is one of the fundamental underlying principles of how the Universe is
organized, e.g. The Laws of Thermodynamics, Newton's Law of Gravity. Science
uses the word theory differently than it is used in the general population.
Theory to most people, in general nonscientific use, is an untested idea.
Scientists call this a hypothesis.
Scientific
experiments are also concerned with isolating the variables. A good science
experiment does not simultaneously test several variables, but rather a single
variable that can be measured against a control. Scientific controlled
experiments are situations where all factors are the same between two test
subjects, except for the single experimental variable.
Consider a commonly conducted science fair experiment. Sandy wants
to test the effect of gangsta rap music on pea plant growth. She plays loud rap
music 24 hours a day to a series of pea plants grown under light, and watered
every day. At the end of her experiment she concludes gangsta rap is conducive
to plant growth. Her teacher grades her project very low, citing the lack of a
control group for the experiment. Sandy returns to her experiment, but this
time she has a separate group of plants under the same conditions as the
rapping plants, but with soothing Led Zeppelin songs playing. She comes to the
same conclusion as before, but now has a basis for comparison. Her teacher
gives her project a better grade.
1.3 Theories Contributing to Modern Biology
Modern
biology is based on several great ideas, or theories:
1. The Cell Theory
2. The Theory of Evolution by Natural
Selection
3. Gene Theory
4. Homeostasis
Robert
Hooke (1635-1703), one of the first scientists to use a
microscope to examine pond water, cork and other things, referred to the
cavities he saw in cork as "cells", Latin for chambers. Mattias
Schleiden (in 1838) concluded all plant tissues consisted of cells. In 1839,
Theodore Schwann came to a similar conclusion for animal tissues. Rudolf
Virchow, in 1858, combined the two ideas and added that all cells come from
pre-existing cells, formulating the Cell Theory. Thus there is a chain-of-existence
extending from your cells back to the earliest cells, over 3.5 billion years
ago. The cell theory states that all organisms are composed of one or more cells,
and that those cells have arisen from pre-existing cells.
Figure 1.
James Watson (L) and Francis Crick (R), and the model they built of the
structure of deoxyribonucleic acid, DNA. While a model may seem a small
thing, their development of the DNA model fostered increased understanding of
how genes work.Image from the Internet.
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In
1953, American scientist James Watson and British scientist Francis Crick developed
the model for deoxyribonucleic acid (DNA), a chemical that had
(then) recently been deduced to be the physical carrier of inheritance. Crick
hypothesized the mechanism for DNA replication and further linked DNA to proteins, an idea since referred to as the
central dogma. Information from DNA "language" is converted into RNA (ribonucleic acid) "language"
and then to the "language" of proteins. The central dogma explains
the influence of heredity (DNA) on the organism (proteins).
Homeostasis
is the maintainence of a dynamic range of conditions within which the organism
can function. Temperature, pH, and energy are major components of this concept.
Theromodynamics is a field of study that covers the laws governingenergy transfers, and thus the basis for
life on earth. Two major laws are known: the conservation of matter and energy, andentropy. These will be discussed in more detail
in a later chapter. The universe is composed of two things: matter (atoms,
etc.) and energy.
These first three theories are very accepted by scientists and the
general public. The theory of evolution is well accepted by scientists and most
of the general public. However, it remains a lightening rod for school boards,
politicians, and television preachers. Much of this confusion results from what
the theory says and what it does not say.
1.4 Development of the Theory of Evolution
Modern
biology is based on several unifying themes, such as the cell theory, genetics
and inheritance, Francis Crick's central dogma of information flow, and Darwin
and Wallace's theory of evolution by natural selection. In this first unit we will
examine these themes and the nature of science.
The
Ancient Greek philosopher Anaxiamander (611-547 B.C.) and the Roman philosopher
Lucretius (99-55 B.C.) coined the concept that all living things were related
and that they had changed over time. The classical science of their time was
observational rather than experimental. Another ancient Greek philosopher, Aristotle developed his Scala
Naturae, or Ladder of Life, to explain his concept of the advancement of
living things from inanimate matter to plants, then animals and finally man.
This concept of man as the "crown of creation" still plagues modern
evolutionary biologists (See Gould, 1989, for a more detailed discussion).
Post-Aristotlean
"scientists" were constrained by the prevailing thought patterns of
the Middle Ages -- the inerrancy of the biblical book of Genesis and the
special creation of the world in a literal six days of the 24-hour variety.
Archbishop James Ussher of Ireland, in the late 1600's calculated the age of
the earth based on the geneologies from Adam and Eve listed in the biblical
book of Genesis. According to Ussher's calculations, the earth was formed on
October 22, 4004 B.C. These calculations were part of Ussher's book, History
of the World. The chronology he developed was taken as factual, and was
even printed in the front pages of bibles. Ussher's ideas were readily
accepted, in part because they posed no threat to the social order of the
times; comfortable ideas that would not upset the linked applecarts of church
and state.
Figure 2.
Archbishop James Ussher. Image from the Internet.
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Often
new ideas must "come out of left field", appearing as wild notions,
but in many cases prompting investigation which may later reveal the
"truth". Ussher's ideas were comfortable, the Bible was viewed as
correct, therefore the earth must be only 5000 years old.
Geologists had for some time doubted the "truth" of a
5,000 year old earth. Leonardo
da Vinci (painter of the Last Supper, and the Mona
Lisa, architect and engineer) calculated the sedimentation rates in the Po
River of Italy. Da Vinci concluded it took 200,000 years to form some nearby
rock deposits. Galileo, convicted heretic for his contention that the Earth was
not the center of the Universe, studied fossils (evidence of past life) and
concluded that they were real and not inanimate artifacts. James Hutton, regarded as the Father of modern
geology, developed the Theory of Uniformitarianism, the basis of modern geology
and paleontology. According to Hutton's work, certain geological processes
operated in the past in much the same fashion as they do today, with minor
exceptions of rates, etc. Thus many geological structures and processes cannot
be explained if the earth was only a mere 5000 years old.
1.5 The Modern View of the Age of the Earth
Radiometric age assignments based on the rates of decay of
radioactive isotopes, not discovered until the late 19th
century, suggest the earth is over 4.5 billion years old. The Earth is thought
older than 4.5 billion years, with the oldest known rocks being 3.96 billion
years old. Geologic time divides into eons, eroas, and smaller units. An
overview of geologic time may be obtained at http://www.ucmp.berkeley.edu/help/timeform.html.
Figure
3. The geologic time scale, hilighting some of the firsts in the evolution of
life. One way to represent geological time. Note the break during the
precambrian. If the vertical scale was truly to scale the precambrian would
account for 7/8 of the graphic. This image is from http://www.clearlight.com/~mhieb/WVFossils/GeolTimeScale.html.
06. Development of the modern view of Evolution
Erasmus Darwin (1731-1802; grandfather of
Charles Darwin) a British physician and poet in the late 1700's, proposed that
life had changed over time, although he did not present a mechanism. Georges-Louis Leclerc, Comte de Buffon (pronounced
Bu-fone; 1707-1788) in the middle to late 1700's proposed that species could
change. This was a major break from earlier concepts that species were created
by a perfect creator and therefore could not change because they were perfect,
etc.
Swedish
botanist Carl Linne (more popularly known as Linneus, after the common practice of the day
which was to latinize names of learned men), attempted to pigeon-hole all known
species of his time (1753) into immutable categories. Many of these categories
are still used in biology, although the underlying thought concept is now evolution and not immutability of species.
Linnean hierarchical classification was based on the premise that the species was the smallest unit, and that each
species (or taxon) belonged to a higher category.
Kingdom Animalia
Phylum (Division is used for plants)
Chordata
Class Mammalia
Order Primates
Family Hominidae
Genus Homo
speciessapiens
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This
image is fromhttp://linnaeus.nrm.se/botany/fbo/welcome.html.en.
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Linneus
also developed the concept of binomial nomenclature, whereby scientists
speaking and writing different languages could communicate clearly. For example
Man in English is Hombre in Spanish, Mensch in
German, and Homo in Latin. Linneus settled on Latin, which was
the language of learned men at that time. If a scientist refers to Homo,
all scientists know what he or she means.
William
"Strata" Smith (1769-1839), employed by the English
coal mining industry, developed the first accurate geologic map of England. He
also, from his extensive travels, developed the Principle of Biological
Succession. This idea states that each period of Earth history has its own
unique assemblages of fossils. In essence Smith fathered the science of
stratigraphy, the correlation of rock layers based on (among other things)
their fossil contents. He also developed an idea that life had changed over
time, but did not overtly state that.
Abraham
Gottlob Werner and Baron Georges Cuvier (1769-1832) were among the foremost
proponents of catastrophism, the theory that the earth and
geological events had formed suddenly, as a result of some great catastrophe
(such as Noah's flood). This view was a comfortable one for the times and thus
was widely accepted. Cuvier eventually proposed that there had been several
creations that occurred after catastrophies. Louis Agassiz (1807-1873) proposed 50-80
catastrophies and creations.
Jean Baptiste de Lamarck (1744-1829)
developed one of the first theories on how species changed. He proposed theinheritance of acquired characteristics to
explain, among other things, the length of the giraffe neck. The Lamarckian
view is that modern giraffe's have long necks because their ancestors
progressively gained longer necks due to stretching to reach food higher and
higher in trees. According to the 19th century concept of use and disuse the
stretching of necks resulted in their development, which was somehow passed on
to their progeny. Today we realize that only bacteria are able to incorporate
non-genetic (nonheritable) traits. Lamarck's work was a theory that plainly
stated that life had changed over time and provided (albeit an erroneous)
mechanism of change.
Additional information about the biological thoughts of Lamarck is
available by clicking here.
07. Darwinian evolution
Charles
Darwin, former divinity student and former medical student, secured (through
the intercession of his geology professor) an unpaid position as ship's
naturalist on the British exploratory vessel H.M.S. Beagle. The voyage would
provide Darwin a unique opportunity to study adaptation and gather a great deal of proof
he would later incorporate into his theory of evolution. On his return to
England in 1836, Darwin began (with the assistance of numerous specialists) to
catalog his collections and ponder the seeming "fit" of organisms to
their mode of existence. He eventually settled on four main points of a radical
new hypothesis:
1. Adaptation: all organisms adapt to
their environments.
2. Variation: all organisms are
variable in their traits.
3. Over-reproduction: all organisms
tend to reproduce beyond their environment's capacity to support them (this is
based on the work of Thomas Malthus, who studied how populations of
organisms tended to grow geometrically until they encountered a limit on their
population size).
4. Since not all organisms are equally
well adapted to their environment, some will survive and reproduce better than
others -- this is known as natural selection. Sometimes this is also
referred to as "survival of the fittest". In reality this merely
deals with the reproductive success of the organisms, not solely their relative
strength or speed.
Figure 4.
Charles Darwin (right) and Alfred Wallace (left), the co-developers of the
theory of evolution by means of natural selection. Image of Charles
Darwin fromhttp://zebu.uoregon.edu/~js/glossary/darwinism.html.Image
of A.R. Wallace (right) is modified fromhttp://www.prs.k12.nj.us/schools/phs/science_Dept/APBio/Natural_Selection.html.
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Unlike
the upper-class Darwin, Alfred Russel Wallace (1823-1913) came from
a different social class. Wallace spent many years in South America, publishing
salvaged notes in Travels on the Amazon and Rio Negro in 1853.
In 1854, Wallace left England to study the natural history of Indonesia, where
he contracted malaria. During a fever Wallace managed to write down his ideas
on natural selection.
In
1858, Darwin received a letter from Wallace, in which Darwin's
as-yet-unpublished theory of evolution and adaptation was precisely detailed.
Darwin arranged for Wallace's letter to be read at a scientific meeting, along
with a synopsis of his own ideas. To be correct, we need to mention that both
Darwin and Wallace developed the theory, although Darwin's major work was not
published until 1859 (the book On the Origin of Species by Means of Natural Selection,
considered by many as one of the most influential books written [follow the
hyperlink to view an online version]). While there have been some changes to
the theory since 1859, most notably the incorporation of genetics and DNA into
what is termed the "Modern Synthesis" during the 1940's, most
scientists today acknowledge evolution as the guiding theory for modern
biology.
Recent revisions of biology curricula stressed the need for
underlying themes. Evolution serves as such a universal theme. An excellent
site devoted to Darwin's thoughts and work is available by clicking here. At that same site is a timeline showing many of the events
mentioned above in their historical contexts.
1.8 The Diversity of Life
Evolutionary
theory and the cell theory provide us with a basis for the interrelation of all
living things. We also utilize Linneus' hierarchical classification system,
adopting (generally) five kingdoms of living organisms. Viruses, as discussed later, are not considered
living. Click here for a table summarizing the five
kingdoms. Recent studies suggest that there might be a sixth Kingdom, the
Archaea.
Figure 5. A
simple phylogenetic representation of three domains of life" Archaea,
Bacteria (Eubacteria), and Eukaryota (all eukaryotic groups: Protista,
Plantae, Fungi, and Animalia). Image from Purves et al., Life:
The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com)
and WH Freeman (www.whfreeman.com),
used with permission.
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Table 1. The
Five Kingdoms.
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Monera, the most primitive kingdom, contain
living organisms remarkably similar to ancient fossils. Organisms in this group
lack membrane-bound organelles associated with higher forms of
life. Such organisms are known as prokaryotes. Bacteria (technically the Eubacteria) and blue-green bacteria (sometimes
called blue-green algae, or cyanobacteria) are the major forms of life in
this kingdom. The most primitive group, the archaebacteria, are today restricted to marginal
habitats such as hot springs or areas of low oxygen concentration.
Figure 6.
Representative photosynthetic cyanobacteria: Oscillatoria (left)
and Nostoc (right). The left image is cropped
from gopher://wiscinfo.wisc.edu:2070/I9/.image/.bot/.130/Cyanobacteria/Oscillatoria_130.
The right image is cropped fromgopher://wiscinfo.wisc.edu:2070/I9/.image/.bot/.130/Cyanobacteria/Nostoc_130.
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Protista were the first of the eukaryotic kingdoms, these organisms and all
others have membrane-bound organelles, which allow for compartmentalization and
dedication of specific areas for specific functions. The chief importance of
Protista is their role as a stem group for the remaining Kingdoms: Plants,
Animals, and Fungi. Major groups within the Protista include the algae, euglenoids, ciliates, protozoa, and flagellates.
Figure 7. Scanning
electron micrographs of diatoms (Protista).There are two basic types of
diatoms: bilaterally symmetrical (left) and radially symmetrical (right). Images
are fromhttp://WWW.bgsu.edu/departments/biology/algae/index.html.
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Figure 8.
Light micrographs of some protistans. The images are Copyright 1994 by
Charles J. O'Kelly and Tim Littlejohn, used by permission from:http://megasun.bch.umontreal.ca/protists/gallery.html.
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Fungi are almost entirely multicellular (with yeast, Saccharomyces
cerviseae, being a prominent unicellular fungus),heterotrophic (deriving their energy from
another organism, whether alive or dead), and usually having some cells with
two nuclei (multinucleate, as opposed to the more common one,
or uninucleate) per cell. Ecologically this kingdom
is important (along with certain bacteria) as decomposers and recyclers of
nutrients. Economically, the Fungi provide us with food (mushrooms; Bleu
cheese/Roquefort cheese; baking and brewing), antibiotics (the first of the wonder drugs,
penicillin, was isolated from a fungus Penicillium), and crop parasites (doing several billion dollars per
year of damage).
Figure 9.
Examples of fungi. The images are fromhttp://www.cinenet.net/users/velosa/thumbnails.html.
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Plantae (click here for more information about the Plantae)
include multicelled organisms that are all autotrophic (capable of making their own
food by the process of photosynthesis, the conversion of sunlight energy
into chemical energy). Ecologically, this kingdom is generally (along with
photosynthetic organisms in Monera and Protista) termed the producers, and rest at the base of all food webs. A food web is an ecological concept to
trace energy flow through an ecosystem. Economically, this kingdom is
unparalleled, with agriculture providing billions of dollars to the economy (as
well as the foundation of "civilization"). Food, building materials,
paper, drugs (both legal and illegal), and roses, are plants or plant-derived
products.
Figure 10. Examples
of plants. The left image of species of Equisetum is
cropped and reduced fromgopher://wiscinfo.wisc.edu:2070/I9/.image/.bot/.130/Fern_Allies/Sphenophyta/Equisetum/E._arvense_and_E._laevigatum_KS.
The center image of Iris, is reduced and cropped fromgopher://wiscinfo.wisc.edu:2070/I9/.image/.bot/.401/Flowering_Plants/Monocots/Iridaceae/Iris/Iris_pumula_habit.
The right image of Pereskia (Cactaceae) is reduced fromgopher://wiscinfo.wisc.edu:2070/I9/.image/.bot/.401/Flowering_Plants/Dicots/Cactaceae/Pereskia/Pereskia_leafy_stem_RK.
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| Animalia consists entirely of multicelluar heterotrophs that are all capable (at some point during their life history) of mobility. Ecologically, this kingdom occupies the level of consumers, which can be subdivided into herbivore (eaters of plants) and carnivores (eaters of other animals). Humans, along with some other organisms, are omnivores (capable of functioning as herbivores or carnivores). Economically, animals provide meat, hides, beasts of burden, pleasure (pets), transportation, and scents (as used in some perfumes). |
Figure 11.
Examples of animals. The left image of a jellyfish is fromhttp://www.smoky.org/~mtyler/bio/coelenterata.html.
The center image of a tree frog is fromhttp://frog.simplenet.com/froggy/images/wild28.gif.
The right image of the chimpanzee is fromhttp://www.selu.com/~bio/PrimateGallery/art/Copyright_Free02.html.
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09. Characteristics of living things
Living
things have a variety of common characteristics.
- Organization. Living things exhibit a high
level of organization, with multicellular organisms being subdivided into
cells, and cells into organelles, and organelles into molecules, etc.
- Homeostasis. Homeostasis is the
maintenance of a constant (yet also dynamic) internal environment in terms
of temperature, pH, water concentrations, etc. Much of our own metabolic
energy goes toward keeping within our own homeostatic limits. If you run a
high fever for long enough, the increased temperature will damage certain
organs and impair your proper functioning. Swallowing of common household
chemicals, many of which are outside the pH(acid/base) levels we can tolerate, will
likewise negatively impact the human body's homeostatic regime. Muscular
activity generates heat as a waste product. This heat is removed from our
bodies by sweating. Some of this heat is used by warm-blooded animals,
mammals and birds, to maintain their internal temperatures.
- Adaptation. Living things are suited to
their mode of existence. Charles Darwin began the recognition of the
marvellous adaptations all life has that allow those organisms to exist in
their environment.
- Reproduction and heredity. Since all cells come from
existing cells, they must have some way of reproducing, whether that
involves asexual (no recombination of genetic
material) or sexual (recombination of genetic material).
Most living things use the chemical DNA (deoxyribonucleic acid) as the
physical carrier of inheritance and the genetic information. Some
organisms, such as retroviruses (of which HIV is a member), use RNA (ribonucleic
acid) as the carrier. The variation that Darwin and Wallace recognized as
the wellspring of evolution and adaptation, is greatly increased by sexual
reproduction.
- Growth and development. Even single-celled organisms
grow. When first formed by cell division, they are small, and must grow
and develop into mature cells. Multicellular organisms pass through a more
complicated process of differentiation and organogenesis (because they
have so many more cells to develop).
- Energy acquisition and release. One view of life is that it
is a struggle to acquire energy (from sunlight, inorganic chemicals, or
another organism), and release it in the process of forming ATP (adenosine triphosphate).
- Detection and response to stimuli (both internal and
external).
Interactions. Living things interact with their
environment as well as each other. Organisms obtain raw materials and energy
from the environment or another organism. The various types of symbioses (organismal interactions with each
other) are examples of this.
10. Levels of Organization
Biosphere: The sum of all living things taken in
conjunction with their environment. In essence, where life occurs, from the
upper reaches of the atmosphere to the top few meters of soil, to the bottoms
of the oceans. We divide the earth intoatmosphere (air), lithosphere (earth), hydrosphere (water), and biosphere (life).
Ecosystem:
The relationships of a smaller groups of organisms with each other and their
environment. Scientists often speak of the interrelatedness of living things.
Since, according to Darwin's theory, organisms adapt to their environment, they
must also adapt to other organisms in that environment. We can discuss the flow
of energy through an ecosystem from photosynthetic autotrophs to herbivores to
carnivores.
Community: The relationships between groups of
different species. For example, the desert communities consist of rabbits,
coyotes, snakes, birds, mice and such plants as sahuaro cactus (Carnegia
gigantea), Ocotillo, creosote bush, etc. Community structure can be
disturbed by such things as fire, human activity, and over-population.
Species:
Groups of similar individuals who tend to mate and produce viable, fertile
offspring. We often find species described not by their reproduction (a
biological species) but rather by their form (anatomical or form species).
Populations: Groups of similar individuals who
tend to mate with each other in a limited geographic area. This can be as
simple as a field of flowers, which is separated from another field by a hill
or other area where none of these flowers occur.
Individuals:
One or more cells characterized by a unique arrangement of DNA
"information". These can be unicellular or multicellular. The
multicellular individual exhibits specialization of cell types and division of
labor into tissues, organs, and organ systems.
Organ System: (in multicellular organisms). A
group of cells, tissues, and organs that perform a specific major function. For
example: the cardiovascular system functions in
circulation of blood.
Organ: (in multicellular organisms). A group of
cells or tissues performing an overall function. For example: the heart is an organ that pumps blood within
the cardiovascular system.
Tissue: (in multicellular organisms). A group of
cells performing a specific function. For example heart muscle tissue is found in the heart
and its unique contraction properties aid the heart's functioning as a pump. .
Cell: The fundamental unit of living things. Each cell has some
sort of hereditary material (either DNA or more rarely RNA), energy acquiring
chemicals, structures, etc. Living things, by definition, must have the
metabolic chemicals plus a nucleic acid hereditary information molecule.
Organelle:
A subunit of a cell, an organelle is involved in a specific subcellular
function, for example the ribosome (the site of protein synthesis) or mitochondrion (the site of ATP generation in
eukaryotes).
Molecules, atoms, and subatomic particles: The fundamental
functional levels of biochemistry.
Figure 12.
Organization levels of life, in a graphic format. Images from Purves et
al., Life: The Science of Biology, 4th Edition, by Sinauer
Associates (www.sinauer.com)
and WH Freeman (www.whfreeman.com),
used with permission.
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