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The Scientific Method
During the early years of Microbiology, a controversy over the Theory of Spontaneous Generation
led, in part, to the development of the Scientific Method. Historically, it was believed that microbial
life came about spontaneously from inanimate objects. Aristotle compiled work from previous
naturalists, and wrote about his theory. At the time, the theory made sense; as one could see
maggots and mold appearing on rotting meat. The theory remained intact until the seventeen
hundreds, when the evolving field of Microbiology began testing these ideas. While a series of
scientists do receive credit for testing Spontaneous Generation (Francisco Redi), it was Louis Pasteur
who settled the issue. Mr. Pasteur’s work was well organized, detailed and followed a logical
sequence testing both the validity of Spontaneous Generation and explaining the process of
Fermentation. This systematic approach has evolved into the Scientific Method.
There are two approaches to the Scientific Method. The two approaches are equally valid, their
ultimately validity is based on the experimental designs. The inductive method is used most
frequently in modern experimental science.
• Inductive – facts and observations analysis are made before the Hypothesis is developed.
This Hypothesis is truly based on previous observation.
• Deductive – a Hypothesis is developed first, then tested by the experiment.
Using the example set by Louis Pasteur, we now follow the steps listed below.
1) Observation – individuals notice details centering around a problem. For Mr. Pasteur, how
noticed that flies and mold did appear on rotting meat, however he questioned whether life
could arise from non-living and inanimate materials. In another example, Louis Pasteur was
charged with determining the source of fermentation by wine producers. When grape juice is
fermented by yeast, the result is ethanol. However, if grape juice is fermented by bacterium,
noxious chemicals result. During Pasteur’s time, the mechanism and source of fermentation
was unknown. For students, anytime they ask a question based on something they see…
that is observation.
2) Hypothesis – at the college level, when students are asked to define the term Hypothesis they
repeat what they learned in K-12; that a Hypothesis is an educated guess. This is not
necessarily true, nor is it a proper definition of a Hypothesis. A true Hypothesis is a predicted
outcome, or explanation, to a problem, based on current knowledge about that problem.
Furthermore, a proper Hypothesis is testable and falsifiable. Furthermore, there are two types
of Hypotheses. The Null Hypothesis is a negative outcome: for example, we could say that
‘incubating grape juice with bacteria does not cause ethanol fermentation’. An Alternative
Hypothesis would state ‘incubating grape juice with bacteria does cause ethanol fermentation’.
3) Experimentation – an experiment is a detailed approach to testing possible outcomes to our
hypothesis. When testing the theory of Spontaneous Generation, Pasteur created glass
flasks with S-shaped necks that were open to the air. He then boiled the meat broth contents
of each flask long enough to kill any living organisms (all based on previous experiments). He
found that as long as the flasks remained intact, air was able to enter the flask through the
S-shaped neck but the broth remained clear. Only when the S-shaped neck was broken did
the broth turn cloudy from microbial growth. In doing so he showed that living organisms could
not arise from inanimate objects. With the process of Fermentation, Pasteur used his flasks
but filled them with boiled grape juice. He then placed bacteria in some flasks, and yeast in
others. He was then able to show that only fermentation to ethanol occurred in the flasks
containing the yeast. The flasks containing bacterium produced noxious products. Every
scientist since has carefully designed ways to test their Hypothesis.
4) Analysis – in this phase of the Scientific Method, data obtained from experimentation is
examined. At the most fundamental level, students can graph their data when appropriate. It
is the graphic representation of numbers that often reveals patterns. Further in a student’s
academic career, analysis of data will include statistical measures (mean, median, mode).
Once statistics is completed at the collegiate level, many more techniques are used (analysis
of variance, regression analysis).
5) Conclusion – now that the data has been collected and analyzed, it is time to decide what it
means. In an appropriate Conclusion, a scientific never says their Hypothesis was right or
wrong. Rather, a scientist will state that the data either supports the Hypothesis, or rejects the
Hypothesis. Beginning in the third/fourth grade students are encouraged to discuss what their
data means, how they would change the experiment and how this information relates to their
everyday life. At the collegiate level, students are expected to complete the same discussion.
Life Science Summer Institute - Classification
What is Taxonomy?
Taxonomy is the classification living things. Humans seem to have an inherent need to classify
the world around, to make order out of chaos. As classification systems have evolved over time,
each has been consistent in starting with large groups, then breaking those groups down into
smaller groups; hence classification can be seen like an ever branching tree.
The ancient Greek philosopher Aristotle classified living things into two main groups, animals
and plants. Carolus Linnaeus (1707-1778) was a Swedish taxonomist who expanded upon
Aristotle’s classification system. Linnaeus developed a binomial system of nomenclature (twopart names for each species [e.g., Homo sapiens]). He developed a system of classification for
all known plants. The Linnaean classification system has be expanded upon based on DNA
comparison of organisms.
Current Classification System
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Genus and species are used together as the scientific name for a species, such as canis familiaris.
Can you come up with your own mnemonic device to remember these?
Domains
Domains are a relatively new grouping (1990) within taxonomy. Domains are the highest taxa,
and therefore the most inclusive. There are three domains Archaea, Bacteria, and Eukarya.
Prokaryotes
The members of the Archaea and Bacteria domains are composed of prokaryotic cells. In
general, prokaryotic cells are small, lack membrane bound organelles, lack complexity, and their
genetic material is not bound by a membrane.
Eukaryotes
The members of the domain Eukarya are composed of eukaryotic cells. Eukaryotic cells are
larger than prokaryotic cells, have membrane bound organelles, and posses a nucleus.
Remember that you are made of eukaryotic cells.
Kingdoms
Within the current classification system, there are four kingdoms with the domain Eukarya.
These are Plantae, Animalia, Fungi, and Protisita.
Life Science Summer Institute - Classification
Protists
Do you have a place in your house where items that really do not have a place belong end up?
We tend to call this a junk draw. The kingdom Protista can be considered the junk drawer of
scientific taxonomy. Basically, if an organism, does not meet the characteristics of the other
three kingdoms, it is classified as a protest. Protists are usually single celled. They can be
autotrophs or heterotrophs. Some examples include: protozoa, algae, and slime molds.
Plants
The members of the plant kingdom are distinguished by the following characteristics:
• They have cell walls and specialized organelles called chloroplasts
• They are multicellular
• They are autotrophic (makes own food)
Some examples include: Trees, mosses, ferns
Fungi
The members of the kingdom fungi are distinguished by the following characteristics:
• They have a cell walls like plant cells do; fungi were once classified as plants
• They are heterotrophic (cannot make own food); this is what distinguishes fungi from
plants
Some examples include: Yeast, mushrooms
Animals
The members of the animal kingdom are distinguished by the following characteristics:
• Most animals are motile at one point in their lives
• Heterotrophic (cannot make own food)
Some examples include: Worms, insects, vertebrates, humans
Classification
Organisms within similar characteristics in each kingdom are grouped together into phyla within
that kingdom. Organisms within a phylum are grouped into a class; organisms within a class are
grouped into an order, and so on, until each organism is placed into a species. Typically, no two
organisms can occupy the same species, however sometimes you will find organisms list as subspecies.
Tree of Life
This web site allows you to enter an organism common name and learn its scientific name, as
well as how it is classified. You can also find organisms that are related to the organism. This is
a great resource for teaching classification, evolution, and diversity.
http://www.tolweb.org/tree/
What is a bug?
Most of the creepy crawly things we call bugs are actually classified as follows:
„ Domain = Eukarya
Kingdom= Animalia
„ Bugs belong to a phylum called Arthropoda
Life Science Summer Institute - Classification
Characteristics of Arthropods
1. Bilateral symmetry
2. Segmented body
3. Hard exoskeleton
4. Jointed legs
5. Many pairs of limbs
Classes of Arthropods
There are many classes of arthropods. A few of the most notable are: insects, arachnids,
myriapods, and crustaceans.
Classifying Bugs
Arthropods
Insect
Arachnid
Crustacean
Myriapod
three body parts
two body parts
two main body parts
long segmented body
three pairs of legs
four pair of legs
five to seven pairs of
legs
one or two pair of
legs per segment
one pair of antenna
no antenna
two pairs of antennae
short or long
antennae
may or may not
have wings
no wings
no wings
no wings
use gills to breathe
Life Science Summer Institute - Classification
Life Science Institute - Diversity
Galapagos Islands
Located about 600 miles west of Ecuador
Consists of 13 volcanic islands and numerous islets and rocks
Discovered by accident in 1535
First scientific study dine in 1835 by Charles Darwin while aboard the HMS Beagle
Galapagos Finches
One of the animals Darwin study war the finch. Each island had a population of finches that
were a little different from each other. These differences were due to the habitat and the
available food.
Diversity of Beak Forms
Each type of beak could function in a slightly different manner, allowing those individuals to
exploit different food sources
Natural Selection
Organism who exhibit characteristics that make them best suited to their environment will
survive and produce the most offspring. “Survival of the fittest” refers to the one who can
produce the most offspring and thus pass on his/her traits to their offspring. Adaptations will be
passed on to future generations that allow individuals to better survive.
Niches
A niche is the role of an organism in an ecosystem. An organism’s niche includes all of the
resources utilized, relationships, and activities in which the organism engages. Each species is
uniquely adapted to its niche.
Bird’s Feet
The feet of birds are also adapted to their role in the environment.
Habitat Requirements
What do organisms need to survive? What happens when these items aren’t available?
Biotic Potential
A J curve represents the maximum rate a population can increase under ideal conditions. People
in this type of population have as much food as they need as much water as they need as much
space as they need; this is known as the biotic potential.
Biotic potential is influenced by food, birth rate, death rate, access to medicine etc.. This J curve
is not very realistic.
Limiting Factors
Because our environments are not always ideal, a J curve is really not the way populations grow.
At some point things become limited and a population reaches what is known as its carrying
capacity.
Life Science Institute - Diversity
Some of the limiting factors that increase the death rate of a population include interspecies
competition, intraspecies competition, disease, predators, and natural disasters. All of these play
an important role in controlling population size. One of the more interesting things that control
population size is the age of reproduction.
If a girl has a baby at the age of 12, then her child has a baby at the age of 12, and that girl has a
baby at the age of 12, the first girl will be a great, great grandmother by the time she is 60. On
the other hand, if a girl waits until she is 30 to have her first child and then that child waits until
she is 30 to have a child; the first girl will only be a grandmother at 60.
S Curve
When we graph a population showing size controlled by limiting factors we get an S shaped
curve as opposed to the J curve we discussed earlier. Looking closely at the S curve you can see
that initially the population grows very rapidly, but as limiting factors increase the death rate, the
population begins to level off.
Carrying Capacity
Population growth is also affected by carrying capacity. Carrying capacity is the number of
organisms an ecosystem can support indefinitely without using up its resources faster than they
can be replaced. The carrying capacity is the leveling off that we show in the S curve in the
previous slide.
Human Interference
Humans often interfere with the carrying capacity of animal populations. One way is by
increasing the available food source by planting gardens or providing bird feeders. Think about
the number of squirrels in your neighborhood. Humans can also have an impact by decreasing
available space through habitat destruction. When humans remove predators, the natural balance
is disrupted.
Life Science Summer Institute – Evidence of Evolution
Reflections of a Distant Planet
A. Scientists use physical analysis to surmise events that have happened in the past.
B. For example, the Barrington crater has been studied in order to identify that an asteroid
is its most likely cause.
C. Evolution is similar in that it requires understanding of a great convergence of
evidence.
1. It requires understanding of how physical, chemical, and biological processes
interact in order to analyze past events.
Early Beliefs, Confusing Discoveries
A. Naturalists study living things in their environment, and as early as 2,000 years ago
were categorizing living things.
B. The original view of life was that all things were part of a “great chain of being,” which
meant that all organisms were never changed after being “created” and existed as
perfect beings.
C. Around the 1800s this concept started to change as new evidence started to accumulate
in three main areas: biogeography, comparative morphology, and fossil records.
D. Biogeography is the study of patterns of distribution of living things in their
environment.
1. As explorers started to expand the “known” world, new species were discovered in
remote locations.
2. Some species resembled other known species but were different enough that it
might not seem that way. For example, large flightless birds were found on several
continents.
3. Some species looked the same, but had very different reproductive structures.
E. Comparative morphology is the study of anatomical similarities between different
species.
1. Naturalists were finding body parts with no function, leg bones in snakes or tail
bones in humans. This greatly contradicted the idea that all organisms were created
perfectly.
F. Fossil evidence was being uncovered as erosion or quarrying was exposing new rock
layers.
1. Deeper rock layers held simpler forms of life.
2. Also unearthed were large animals with no living representatives.
G. Taken as a whole, this new evidence was both confusing and provided the basis for
evolutionary theory.
A Flurry of New Theories
A. Squeezing New Evidence into Old Beliefs
1. Cuvier was studying change in the fossil record and noticed periods where many
species died around the same time and that many of the fossils he found were not
represented today.
a. He proposed that many species were now extinct.
b. He also noted evidence of changes in earth’s surface, noting fossils of sea life
on mountainsides far from modern oceans.
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Life Science Summer Institute – Evidence of Evolution
c. Cuvier described catastrophism: that previously unknown geologic forces
changed the environment and led to extinctions.
1. We now know this is not entirely true; geological processes have not
changed over time.
B. Voyage of the Beagle
1. Darwin became the naturalist on the Beagle which sailed around the world.
a. Darwin read Lyell’s Principles of Geology, which is a theory of uniformity:
gradual repetitive changes shaped the earth.
b. These changes required a great deal of time, more so than the 6,000 years,
which was the age that many believed earth to be.
c. Lyell proposed that long, slow changes over millions of years could have
shaped the earth.
C. Natural Selection
1. Darwin cataloged many species during his travels and tried to correlate their traits
to environments in which they lived.
2. Darwin read an essay by Malthus, an economist, which proposed that human
population reproduce beyond past their resources and in doing so create competition
for scarce resources.
3. Darwin applied this concept to all biological organisms.
a. All organisms over-reproduce, which creates competition and a struggle to
survive.
b. Organisms within species vary in certain physical traits; some traits lead to
better survival, also called fitness.
c. If a trait enhances an organism’s evolutionary fitness, it is called an adaptation
or adaptive trait.
d. Later, this was called natural selection, a driving force for evolution: if an
individual has a trait that is better suited to the environment, it leads to better
survival. Better survival means more opportunities to reproduce, which means
more opportunities to spread that adaptive trait to successive generations.
D. Great Minds Think Alike
1. Wallace sent an essay that outlined a theory similar to natural selection to Darwin.
2. In 1959, Darwin published On the Origin of the Species. Many scientists accepted
evolution as change over time, but it took genetic research to provide later evidence
for the acceptance of natural selection.
About Fossils
A. Fossils are mineralized bones, teeth, shells, seeds, spores, or other hard body parts.
B. Fossils form when an organism dies, and its carcass is trapped in volcanic ash or
sediment; as water seeps in, metals and inorganic compounds replace the minerals in
the body part.
C. Fossils are rare because of how they form; the conditions had to be perfect.
D. The Fossil Record
1. The fossil record may be incomplete, but it provides some valuable clues about
species lineage.
2. It was long believed that whales were relatives of land animals because of
similarities in their jaws, but there was no conclusive fossil evidence.
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Life Science Summer Institute – Evidence of Evolution
3. DNA comparisons demonstrated a relationship with artiodactyls – hippopotamuses,
camels, pigs, deer, sheep, and cows.
4. In 2000, two complete fossils were found that demonstrated a transition between
land and water with a whale-like skull and sheep-like ankle bones.
E. Radiometric Dating
1. Radioisotopes decay at a constant rate into predictable products, daughter elements.
2. Because the decay of the isotopes is constant, the rate (half-life) can be determined,
and the time since its formation can be calculated back in time.
3. Carbon 14 dating can be used to date fossils up to 60,000 years old.
4. Older fossils are dated by examining the volcanic rock around the fossil or layers
below the fossil.
Putting Time Into Perspective
A. Layers of sedimentary rock provide a critical reference point for earth’s history.
B. Transitions between layers mark boundaries in a geological time scale.
C. Drifting Continents, Changing Seas
1. A model was proposed in which there was a single world continent, named
Pangaea, which at one time extended from pole to pole surrounded by a single huge
ocean.
2. The theory of continental drift explains the separation of the continents and the
formation of great mountain ranges as the continents collided.
3. Sea-floor spreading and plate tectonics theory show that the earth’s crust is moving.
4. Continental drift and plate tectonics accounted for the discovery of similar fossils
on different sides of the Atlantic Ocean.
5. It is also proposed that, based on evidence, Gondwana was an older supercontinent
that incorporated all of the continents in the southern hemisphere.
6. It is believed that at least five times in earth’s history a supercontinent existed.
7. As plate tectonics moved the land masses around and the environments changed,
organisms that were once the same species were forced to adapt to these new
conditions, driving evolutionary processes.
Similarities in Body Function
A. Comparative morphology provides evidence of evolutionary lineage.
B. Some comparative morphology focuses on homologous structures, or homology, which
means similar body features in different organisms.
C. Morphological Divergence
1. A similar body part that appears but is modified in different organisms is considered
morphological divergence and is strong evidence of evolutionary change.
2. Consider the vertebrate forelimb; the basic structure of the forelimb is seen in
reptiles.
3. The genes that drive its development are the same, but small modifications caused
by mutations cause variation in what the limb looks like and, therefore, its function.
D. Morphological Convergence
1. Not all similar body parts are homologous; sometimes the same structure arises in
different ways. This is morphological convergence.
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Life Science Summer Institute – Evidence of Evolution
2. Consider wings: many organisms have wings, and while all are used for some
variation of flight, how the wings developed was different.
E. Comparative Embryology
1. The development of an embryo into an adult organism is orchestrated by master
genes.
2. Mutations in master genes tend to be lethal, so master genes are highly conserved in
evolution, meaning that there is little change in their sequences.
3. Homeotic genes function in laying out the body plan of an organism because of the
conservation of the genes; embryos of a certain lineage tend to look similar and
develop in similar ways.
Biochemical Similarities
A. Biochemical similarities, especially in DNA and proteins, are important evidence of
lineage.
B. Most mutations are neutral, but some lead to selection.
C. As two populations diverge, they accumulate different sets of mutations; these pools of
mutations are evidence of common ancestry.
D. Comparing genomics is common and leads to identification of estimated divergence.
E. Amino acid sequences can also be used to study divergence, especially when a protein
is used for the same function in different organisms.
Measuring Time
A. The K-T boundary consists of unusual clay that was deposited 65 million years ago and
is high in iridium.
B. Iridium is rare on earth but common on asteroids.
C. It is hypothesized that an asteroid struck earth 65 million years ago and influenced earth
in a big way.
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Life Science Summer Institute - Introduction to Ecology
Introduction
The purpose of this course is to give you a basic understanding of biological topics, such
as the environment, selected body systems, and genetics that may be of interest to you.
The intent is for you to gain knowledge so that you can understand biology related news
topics and make educated choice related to science in your life. Let’s begin our
exploration of biology.
What is Biology?
This is a course that many of you may have waited to take for a variety of reasons, but as
we start the course, we should ask, what is biology? Biology comes from the Greek
prefix bio, which means life and the Greek suffix -ology, which means study of or
science; therefore biology is the study of life. Biology is a very broad area and there are
many fields of study within this science. Some of these are Zoology, the study of
animals; Ecology, the study of the environment; and Botany, the study of plants. This list
is extensive.
What is Ecology?
The first topic we will cover in Biology 1010 is ecology. Again we have another word
ending in -ology, which means the study of or science. The Greek prefix eco- means
environment; therefore ecology is the study of the interaction of organisms with their
environment.
Biosphere
Before we go any further there are some terms we should define. The first is biosphere.
If we break this word down we can understand its meaning. We’ve seen the prefix biobefore when we discussed biology, remember that is means life. The word sphere means
circle; therefore the biosphere is the thin layer around the earth’s surface where life is
supported. The biosphere is considered a closed system with regards to materials. This
is because there are a finite amount of materials on the planet; no new materials are being
made. This means that materials must be recycled. Think about aluminum cans. There
is certain amount of aluminum on the planet; no new aluminum can be made. So in order
to make new aluminum cans, old aluminum cans must be recycled.
The biosphere is open with regards to energy. This means that an endless amount of
energy comes into the earth from the sun. In addition, energy is also lost from the earth
and living organisms in the form of heat. This exchange of energy is constant.
Ecosystems
Ecosystems are defined as all the living organisms in a given area and their interactions
with their environment.
There are many different kinds of ecosystems including the Chesapeake Bay, Old growth
forests, and the Florida everglades.
Life Science Summer Institute - Introduction to Ecology
Components of an Ecosystem
Within an ecosystem there are both living (biotic components) and nonliving or (abiotic)
components. Examples of Biotic components include plants, animals, small organisms,
Examples of non-living or abiotic components include air, temperature, and the chair you
are sitting on.
In order for an ecosystem to survive it needs both biotic and abiotic components.
What is a Species?
The organisms within an ecosystem are broken down by a classification system. The
gentleman who developed this classification system was Carl Linnaeus.
Linnaeus broke things down into the following hierarchy
Kingdom, Phylum, Class, Order, Family, Genus and Species.
For purposes of this course, we will only look at the species level.
What is a species? – Do donkey’s and horses belong to the same species?
A species is a group of related organisms that when bred produce the same type of
organism that is then able to breed again.
Even though a donkey and a horse look alike, when they are bred they produce a mule. A
mule is sterile. It can not reproduce and therefore a horse and a donkey belong to
different species.
Species role in the ecosystem
An ecosystem is made up of many different types of species. Each species occupies a
particular niche or role in the ecosystem.
Again we turn to familiar organisms – the squirrel and chipmunk – Again, like the horse
and donkey they look alike and feed on similar food, but they are different species.
Squirrels nest in trees, chipmunks nest in the ground. Squirrels are generally unmarked
in their coats (fur); chipmunks typically have markings on their backs so they blend into
their environment.
Populations and Communities
A population is a group of species that occupy a specific area. For example, you may
read an article about the population of white tailed deer living in Watkins Park. Since
populations do not live in isolation from one another, communities are groups of
populations in a specific area. Using Watkins Park as our example there are many
different populations of trees, squirrels, flowers, mice, birds, etc... that live there.
Cell Structure and Function
Processes of Life
A cell is indeed the structural/functional unit of life. As such, cells exhibit the same characteristics as living organisms,
only at a microscopic level. These characteristics are: Growth (an increase in size of cells and/or number of cells),
Reproduction (via Meiosis or Mitosis), Responsiveness (movement and/or physical and chemical changes on response to
a stimulus) and Metabolism (chemical reactions for catabolism (breakdown down of molecules for energy) and anabolism
(using energy to create larger molecules). At the collegiate level these characteristics are further divided into: Growth,
Adaptation, Responsiveness, Reproduction, Metabolism, Respiration, Movement, and Homeostasis.
Cell Types
As we currently know life on Earth, there are two general types of cells. Prokaryotes do not have a membrane
surrounding their DNA, and therefore have no nucleus. In fact, Prokaryotes have no internal membranes, possessing
only a cell membrane. These cells are small (less than 1 micrometer in diameter), simple in their internal structure and
include the Bacteria and Archaea. Prokaryotes are highly organized within the cytoplasm, with regional areas for DNA,
carbohydrates and other molecules. Prokaryotes can also have external structures, including flagella. While simple, these
organisms are by no means unimportant.
Any cell that contains internal membranes will therefore possess organelles, including a nucleus. This is the definition of
all other cells, Eukaryotes. Eukaryotes are larger 10-100 micrometers in diameter), have more complex internal
structures and specialized organelles, and include Algae, Protozoans, Fungi, Animals and Plants.
Prokaryotic Cells
Prokaryotic cells may possess any, or all, of the following
structures.
• Glycocalyx: a protein/polysaccharide based coating
that exists in two forms. As a densely packed
capsule, it enables a bacterium to avoid human
immune system cells and prevent dessication. As a
loosely packed slime layer, it prevents dessication and
allows bacteria to stick to each other in cellular
arrangements. Prokaryotic flagella provide
movement, and fimbriae and pili allow cells to attach
to objects in their environments, and provide for a
DNA exchange mechanism between cells.
• Bacterial Cell Wall: there are three basic types of
bacterial cells walls. Gram+ are mostly carbohydrate, Gram- have a small carbohydrate layer followed by a lipid
layer, and Acid-Fast walls are mostly a waxy substance. Each wall has specific characteristics. In the word of
antibiotics, these cell wall type can determine the efficacy of a given drug. While some bacteria are pathogens, there
are many that are commonly found on the human body and are an integral part of our physiology. In fact, commonly
known as probiotics, our normal flora is crucial to vitamin K production, immune system function and overall
gastrointestinal health.
• Archaea Cell Wall: is primarily protein. These bacteria live in extreme environments and are not considered
pathogens in humans.
• Cell membranes: much like that of eukaryotic cells, but slightly simpler. Since prokaryotes do not have organelles,
the cell membrane must perform many functions including transport, boundary maintenance, intercellular recognition,
biochemistry and DNA replication.
Eukaryotic Cells Components: Plasma
membrane = boundary, Cytoplasm = intracellular fluid &
organelles, Nucleus = control
• Plasma Membrane ~ Fluid Mosaic Model
Made of a Phospholipid bilayer (mostly unsaturated Fatty
Acids, cholesterol, integral proteins (transport) and
peripheral proteins (enzymes, structural)). This structure
exhibits Selective permeability - only non-polar molecules
can cross the membrane easily. Polar molecules must be
moved across the membrane using protein channels and
carriers. Furthermore, eukaryotic cells have glycoprotein
molecules on the external surface serving as receptors for
regonition.
•
•
Specializations. Eukaryotic cells have many external structures.
Microvilli are projections of the plasma membrane that increase
surface area; Tight Junctions (made of integral proteins) are
impermeable connections between cells; Desmosomes are
proteinaceous cell junctions that are flexible with tensile strength;
and Gap Junctions are protein based tubes running between cells
that allow them to share cytoplasm.
Cytoplasmic Organelles. Mitochondria (ATP energy production),
Smooth Endoplasmic Reticulum (non-protein synthesis), Rough
Endoplasmic Reticulum (protein synthesis), Nucleus (control and
regulation), Golgi (modify, package and transport proteins),
Microtubules (structural support, spindle), Microfilaments
(movement), Cilia (move mucus and fluid), Flagella (propulsion).
Cell Transport
The primary organelle responsible for moving molecules is the plasma membrane, and some membrane bound sacks
called vesicles. How a molecule is transported across the membrane depends on its chemical characteristics. Polar
(charged) molecules are generally not permeable across the cell membrane. Therefore, these molecules must be
transport across protein based channels and carriers that span the length of the phospholipid bilayer. Conversely, nonpolar (non-charged) molecules are permeable across the membrane, so they simply move across without proteins.
• Passive Transport Mechanisms. Passive is defined as movement of molecules without the use of chemical
energy (ATP), with a concentration gradient (molecules moving from high concentration to low concentration).
There are three forms:
o Diffusion - permeable molecules moving from high to low concentration (nonpolar)
o Facilitated Diffusion – a molecule diffusion by moving across a channel or protein (polar)
o Osmosis – movement of water with its gradient across a semi-permeable membrane. Osmosis can be
visualized by placing wilted celery in water and watching it rehydrate. Osmosis also comes with a set of
terms.
ƒ Solution = solvent (water) + solute (chemical stuff) and should always equal 100%
ƒ Osmolarity = a measure of solute. High osmolarity means lots of chemical stuff. Areas with high
osmolarity will pull water toward it.
ƒ Hypertonic = high solute & low water
ƒ Hypotonic = low solute & high water
ƒ Isotonic = same solute and water
Hypertonic = more solute Æ water loss from cell Æ cell crenates
Hypotonic = less solute Æ water enters cell Æ cell lyses
Isotonic = equal solute Æ no net diffusion of water
•
Active Transport Mechanisms. Active transport mechanisms use
chemical energy, move large items and/or move chemicals from low
to high concentration (against the gradient). There are several
methods, the most common are listed below.
o Exocytosis = cells use a membrane bound sack to secrete
molecules to the outside
o Phagocytosis = cells taking in solids using a membrane
bound sack (translates to cell eating)
o Pinocytosis = cells taking in fluid using a membrane bound
sack (translates to cell drinking)
o Receptor Mediated Endocytosis = a cell takes in a molecule
that first binds to a membrane receptor.
•
Factors affecting transport rates: The size of the molecule (larger molecules will require endocytosis of some
sort), Temperature (to a point, the warmer it is the faster things move), Presence / absence of pumps or carriers
(remember, polar molecules cannot move across the membrane on their own), Particle charges (related to the
polar molecule impermeability), Concentration gradients (for passive mechanisms to be used, there must be a
difference in the concentrations of the given molecule)
Cellular Metabolism
Introduction
For cells to carry out their many functions, they must use energy. This energy can exist in
many forms; and the transfer of energy between storage forms and usable forms drives the need for
metabolic reactions. While the chemical reactions are sometimes difficult and generally not
introduced until Middle or High School, the concept of energy transfer can be presented to younger
students.
Furthermore, even at the collegiate level students often think “Animal cells do respiration,
Plants do photosynthesis.” While this statement is not incorrect, it is not entirely correct. It’s
important to point out that Plants make food molecules using Photosynthesis, then they use those
food molecules to get energy using Respiration.
Reactions Underlying Metabolism - We begin by defining applicable terms.
• Catabolism = breaking down of larger molecules into smaller molecules by breaking chemical
bonds. Realize a chemical bond represents the interaction between atoms and electrons. If a
cell can break these bonds using enzymes, energy will be released. The job of the cell is to tie
that energy to an action.
• Anabolism = building up larger molecules by linking together smaller molecules. Cells will
perform anabolic reactions whenever they need to store nutrient molecules for a later use.
• Oxidation = a chemical reaction that results in a molecule losing oxygen and electrons
• Reduction = a chemical reaction that results in a molecule gaining oxygen and electrons.
Oxidation and Reduction are tied to each other and are how cells transfer energy back and
forth. The First Law of Thermodynamics tells us that “energy is neither created nor destroyed,
it changes form.” This is exactly what cells are up to, they change the form of energy from
stored up chemical bonds, to a molecule that is in use (ATP).
• ATP = a high energy molecule used by cells to perform most of their activities. ATP is so high
energy it cannot be stored. Hence, cells must constantly recycle spent ATP molecules (called
ADP) or create new ones. ATP chemically is an Adenosine with three Phosphate groups
attached. The third group can come off the molecule easily. It is this “popping off” of the
phosphate group that allows the cell to do work (the definition of energy). Since cells cannot
store ATP, energy is ultimately stored within chemical bonds of larger molecules. For
example, plants store energy in the form of starch (long chains of glucose sugar units); animals
store energy in the form glycogen (long chains of glucose units, but put together in a different
way). The term Kinetic Energy (energy that is in use or motion) is used to describe ATP.
• Enzymes = molecules (usually proteins) that make chemical reactions happen faster.
• Electron carriers / Coenzymes NAD, FAD, NADP = since cells are breaking molecules apart,
chemically there will be leftovers in the form of Hydrogen atoms and electrons. These particles
are picked up and used later to make ATP. Coenzymes are molecules that can bind the
hydrogen and electrons. NAD and FAD are in respiration; NADP is found in photosynthesis.
Every time a cell breaks a molecule, or significantly rearranges it… a coenzyme is reduced.
For example, NAD + hydrogen ions + electrons Æ NADH. This is entirely reversible.
The chemical reactions
The big picture ~ a cell is breaking apart Carbon atoms inside a molecule. Each time it breaks
a bond, it obtains energy it will use to make ATP. Sometimes, ATP is made immediately. Most of the
time, ATP is made later. How it ATP made? When a cell breaks a bond it can create hydrogen and
electron atoms that are picked up by the coenzymes. Coenzymes in the mitochondria are oxidized;
which results in the release of the hydrogens and electrons. The hydrogens and electrons are
serving as an energy form, much like gasoline is used to fuel a car engine. The mitochondria will use
these to make ATP.
Aerobic Cellular Respiration = when a cell breaks apart glucose in an effort to get the energy
stored in the chemical bonds. It is a lengthy process with many steps and many enzymes. The
overall chemical equation is: C6H12O6 (glucose) + O2 (oxygen) + ADP Æ CO2 (carbon dioxide)+ H2O
(water) + ATP. This process yields a lot of ATP (net 36 ATP for each glucose started).
Anaerobic Cellular Respiration = used by yeast, bacteria and muscle cells. The byproducts
are many and depend on the organism and the specific chemistry it conducts. Most common are
Lactic Acid fermentation (used by the bacteria that make yogurt, and muscle cells) and Ethanol
fermentation (used by yeast in making bread and alcoholic beverages). The overall chemical
equation for the latter is: C6H12O6 (glucose) + ADP Æ CO2 (carbon dioxide)+ H2O (water) + ATP +
Ethanol. Aerobic respiration does not result in a large amount of ATP (2 net ATP for each glucose
started).
Aerobic Respiration includes three processes.
1. Glycolysis - one 6carbon glucose molecule is broken into two equal parts (3carbons each).
After a series of chemical reaction steps that requires using 2ATP, a total of 4ATP molecules are
made (2net). The products are three carbon pieces that are broken down further in the next step.
2. Citric Acid Cycle – in this cyclic phase inside a
mitochondria, one 3carbon molecule is
eventually broken down into three 1carbon
molecules. There are many steps along the way.
Essentially, the cell is building and breaking
molecules to get at the energy stored in their
bonds. At the collegiate level, students are
required to learn the names of each molecule
along the way and to understand the size of each
molecule in terms of numbers of carbons.
3. Electron Transport Chain – once the
hydrogens and electrons are released, the
mitochondria will play a ‘hot potato game’. This
electron is high energy, it is held by special
proteins and passed along. At each protein,
some of that extra energy is absorbed. The
energy is used to move hydrogen ions to create
a stockpile. Once completed, the hydrogens are
allowed to moved across an enzyme. As they
move across the enzyme to provide the energy
needed to tag that extra phosphate group onto
ADP to make ATP.
Photosynthetic Chemicals and Structures
The big picture: whereas respiration is catabolic, photosynthesis is anabolic. Autotrophic organisms
(plants included) using pigments (chlorophyll) to capture light energy (a photon). That photon
generates a high energy electron which is passed through a series of electron carriers. As in
respiration, the excess energy of this excited electron is harvested, and used to make ATP. What
students often don’t know is that Photosynthesis has two parts: Light Dependent Reactions, and the
Light Independent Reactions.
Light Dependent Reactions
1. The pigment Chlorophyll resides within a reaction
center. When particles of light (photons) hit the
chlorophyll molecule, an electron is excited to a
higher energy level and is ejected from this structure.
This electron will not pass through a series of carriers
which will absorb the excess energy.
2. These events are very similar to cellular respiration in that the high energy electron is passed
through a series of imbedded molecules. The energy is used to pump hydrogen ions creating
a stockpile. In the end, hydrogen
ions flow through the enzyme
and are used to make ATP. In
cyclic, the electron returns to its
original
photosystem.
In
noncyclic, the electron ends up
elsewhere.
Light-Independent Reactions
The energy used made in the Light Dependent Reactions is used to make glucose in this phase.
Essentially, yet another enzyme controlled cycle pulls in a three 1carbon molecules and releases one
3carbon molecule. Then, two of those 3carbon molecules are bound together to create a glucose
(6carbon).
Life Science Summer Institute - Genetics
Introduction
The first branch of genetics we will study is Mendelian genetics. Mendelian genetic is named
for Gregor Mendel a monk who lived in the 1800’s. He worked during a time when no one knew
anything about chromosomes and DNA, but he was able to determine the very basics of how
traits are inherited. He did his work in the monastery garden on pea plants. Interestingly he
presented his work to the scientific community and they were unable at the time to understand
how important his work was. Mendel’s work was lost for almost 50 years.
Dominant versus recessive
In order to understand Mendelian genetics, we need to define some terms. Traits can either be
recessive or dominant. Dominant traits mask or cover up other traits. If a dominant trait is
present, this is what we will see. In the common abbreviation used in inheritance, dominant
traits are represented with capital letters. Recessive traits are masked or covered up by dominant
traits. Recessive traits are presented by lower case letters.
Mendel’s Principles
What did Mendel actually figure out from studying his pea plants? First he found out that
heredity is not blending; he found that traits come in either a recessive or dominant form.
Mendel also figured out that there are units of heredity. Today we know these units of heredity
as genes. He determined that every individual has a pair of these units for each trait. This means
that you have two copies of each gene for each trait. Remember the homologous chromosomes?
One came from your mother and one came from your father. Each has a gene for the same trait,
like eye color. What we know from Mendel’s work is that you have two copies, but they don’t
need to be identical. For example, your mother could have given you a gene for blue eyes, while
your father gave you a gene for brown eyes. Different forms of the gene are celled alleles.
During meiosis, the homologous chromosomes separate; therefore so do the alleles. Half of the
gametes produced by you would have the allele for blue eyes and the other half would have the
allele for brown eyes. This is why we say the egg and sperm are haploid. When the egg and
sperm come together a new diploid organism is formed.
Alleles
An allele is a form of a gene. Recessive alleles will be represented by a lower case letter, while
dominant alleles will be represented by a capital letter.
Homozygous versus heterozygous
You have two alleles for each trait. You received one from your mother and one from your
father. If the two alleles you have are the same, you are homozygous. If the alleles are of the
dominant form, then you are homozygous dominant. If both your alleles are the recessive form,
then you are homozygous recessive. If you have one dominant allele and one recessive allele,
then you are heterozygous. The only time you can see a recessive trait is when the individual is
homozygous recessive, because there are no other traits to mask the recessive trait.
Life Science Summer Institute - Genetics
Genotype versus phenotype
Two more terms that you need to know are genotype and phenotype. The genotype is the alleles
present in an individual. Unless you are homozygous recessive for a trait, you probably do not
know your genotype. The term heterozygous and homozygous refer to genotype.
The phenotype is what an individual looks like. For example, your phenotype would be whether
you have blue or brown eyes. If you have a dominant phenotype, you can either be homozygous
dominant or heterozygous.
Punnet squares
Now that we have mastered terminology, let’s look at how we can determine the genotypes and
phenotypes of offspring. To determine the genotype and phenotype, we are going to use a device
called a Punnet square.
Ear lobe attachment
Let’s see how to use a Punnett square by using an easily observable trait. The trait we will
observe is ear attachment. Unattached ear lobes are dominant to attached ear lobes; therefore
individuals with unattached ear lobes can have the genotype EE or Ee. Attached ear lobes have
the genotype ee.
Punnett square
What would happen if two people that are heterozygous for ear lobe attachment had children.
Both of the parents have the genotype Ee. This means that half of the mother’s eggs would have
the E allele and the other half would have the e allele. Half of the father’s sperm would have the
E allele and the other half would have the e allele.
Punnett square
To make a punnett square we will place the possible alleles from the mother across the top of the
square and the possible alleles from the father along the left side of the square. Now it is like
cross multiplying.
Punnett square
In the first square the mother contributes an E and the father contributes an E. The child has the
genotype EE.
Punnett square
In the second square in the first row, the mother contributes an e, while the father contributes an
E, so the child has an Ee genotype.
Punnett square
In the first square of the second row, the mother contributes an E, while the father contributes an
e, therefore the child has the genotype Ee.
Punnett square
In the final square, each parent contributes an e, so the child has the genotype ee.
Life Science Summer Institute - Genetics
Genetics Questions
From this punnet square, there are several questions that can be asked. I could ask what
percentage of the children have unattached ear lobes. The answer to this question would be 75%.
This is because three of the four boxes have least one dominant allele.
Genetics Questions
I could also ask what percentage of the children are heterozygous. The answer to this question is
50%, since two of the four boxes have the genotype Ee.
Genetics Questions
Another question that I could pose is the ratio of the dominant allele to the recessive allele. The
answer would be 3:1, since three of the boxes have a dominant allele and only one has recessive
alleles only.
Genetics Questions
I could also ask what the ratio of homozygous dominant to heterozygous to homozygous
recessive. The answer to this question is 1:2:1. When doing genetics questions, be sure you are
doing what is being asked.
Genotypic and phenotypic ratios
The discussion on the previous slide was about genotypic and phenotypic ratios. Phenotypic
ratios ask you to show the number of children that would have the dominant phenotype
compared to the number of children hat would have the recessive phenotype. Genotypic ratios
ask you show the number of children who are homozygous dominant compared to the number of
children who are heterozygous compared to the number of children who are homozygous
recessive.
Theoretical ratios
Looking at the ratios mentioned in the previous slides, does this mean that if a couple has four
children, they will see these ratios in their family? The answer is no. Each time the parents have
a child it is the luck of the draw as to which alleles will end up in the offspring. It is like tossing
a coin. You may have a streak where you have several heads in a row; however if you toss the
coin enough times you will end up with 50% heads and 50% tails. Punett squares show the
theoretical ratios that would occur if large numbers of individuals were born from a specific
pairing.
Recessive trait disease
Recessive traits are traits that are inherited through a recessive allele. In order for an individual
to display a recessive trait, they must inherit a recessive allele from each of their parents. Some
diseases are inherited through recessive traits and can be very devastating. Among them are
Tay-Sachs disease, Cystic fibrosis, and Phenylketonuria (PKU). Individuals that inherit one
recessive allele for one of these diseases, but also inherit one dominant allele that mask the
recessive allele are known as carriers for the disease. If there is a history of one of these genetic
diseases in the family, an individual will often be testing to see if they are a carrier.
Life Science Summer Institute - Genetics
Dominant traits
Dominant traits are those that are inherited by a dominant allele. People tend to think that
dominant traits are not harmful, but a few genetic disorders are caused by the presence of a
dominant trait. These include Marfan syndrome, hypercholesterolemia, Huntington’s disease,
and achrondroplasia. In order for an individual to inherit a dominant trait, one of their parents
must have has the trait. Both dominant and recessive traits in families can be traced using a
pedigree analysis.
Non-Mendelian inheritance
Not all traits are inherited in a simple Mendelian fashion. These traits are passed from one
generation to the next through non-mendelian inheritance. Some examples of non-Mendelian
inheritance include polygenic traits, incomplete dominance, multiple alleles, co-dominance, sex
linked traits, sex influenced traits, and environmental influenced traits. We will explore each of
these is further detail.
Polygenic traits
All of the traits that Mendel observed were inherited from a single gene. Today we know that
many traits are influenced by many genes. When a phenotype is the result of the influence of
many genes it is called a polygenic trait. Polygenic traits show a bell curve distribution of
phenotypes. Take skin color for example. If you look around at the people in your workplace,
you will notice that they all have different skin colors. Even within your own family, you will
notice these differences. There is an average skin color and most people are a few shades lighter
or darker than this average. Very few people have no skin colorations at all and very few people
have the maximum amount of skin color. The distribution of skin color is therefore bell shaped,
with most of the individuals falling around the average skin color.
Incomplete dominance
One of Mendel’s rules was that heredity is not blending. However, there are some traits that do
show blending. These traits show incomplete dominance. As an example if you crossed a red
carnation with a white carnation, based on Mendel’s rules you would expect the offspring to be
red or white. This is not the case because the offspring would actually be pink. Because we see
blending this is an example of incomplete dominance. Another example of incomplete
dominance is the chocolate Labrador retriever, which results from a yellow Labrador crossed
with a black Labrador.
Multiple alleles
Do you remember the blood types we discussed during the immune system portion of the
course? There were four different blood types, A, B, AB, and O. How is this possible if blood
type is on a single gene? According to Mendel’s rules there would only be three different
genotypes and two different phenotypes. This does not account for the four blood types seen in
human populations. The four blood types exist because there are three alleles in the population
for blood type, IA, IB, and i. Both IA and IB are dominant to i.
Life Science Summer Institute - Genetics
Co-dominance
In addition to have three alleles, blood type is also unusual in that neither IA nor IB is dominant to
the other. In the blood type AB, the individual has the alleles IA and IB. Both of these alleles
make an antigen. IA make the A antigen and IB makes the B antigen. These individuals end up
with both genes making something that is seen in the phenotype of the individual. This is an
example of co-dominance. Co-dominance is different from incomplete dominance in that there
is no blending of the traits. Both the A antigen and the B antigen are being made.
Blood type alleles
Let’s take a moment to look at the possible genotypes and phenotypes for blood type. If a person
has type A blood, they must have the IA allele. They might have another IA allele or they may
have the recessive i allele. A person with type B blood must have the IB allele. Their second
allele can either be another IB or a recessive i. A person with type O blood has the recessive trait
and must have two i alleles.
Blood typing and paternity
Before current paternity testing methods using DNA, blood typing was the sole method of
determining paternity. This was not as accurate as today’s DNA testing. If two men had the
same blood type, there was no way to exclude either one of them. This method did not allow for
the proving of paternity, it only excluding individuals from paternity if a punnet square between
the mother and the individual in question could not produce a box with the child’s blood type.
Sickle cell disease
Another example of co-dominance can be seen in sickle cell disease. There are two possible
alleles for hemoglobin, HbA and HbS. HbA is the normal allele. A person that is completely
normal has the genotype HbA HbA. An individual with sickle cell disease has two copies of the
HbS allele. Individuals that have sickle cell trait, also known as a carrier, have one HbA allele
and one HbS allele. To test for sickle cell trait, blood cells are placed under low oxygen. If some
of the cells sickle, the person has sickle cell trait. A person with sickle cell trait produced both
normal hemoglobin and sickled cell hemoglobin. It has been found that the presence of some
sickled cell hemoglobin protects individuals from a disease called malaria.
Sex chromosomes
The X chromosome contains information that does not related to sexual characteristics; therefore
there are some traits that will be inherited on the X chromosome. Recall that females have two
copies of the X chromosome, while males only have one copy of the X chromosome. Males also
have a Y chromosome. Females are homozygous for their sex chromosomes, while males are
heterozygous for their sex chromosomes. Where do men get there X chromosomes? They
inherit their X chromosome from their mother; they will inherit the Y chromosome from their
fathers.
Sex chromosomes
Since males only have one copy of the X chromosome, if they get a chromosome with a certain
trait they are going to show that trait. Women have two copies of the X chromosome, so they
can mask a recessive trait just like in regular Mendelian genetics. These women are considered
carriers for these traits, since they do not display the trait but have the ability to pass it on.
Life Science Summer Institute - Genetics
Sex-linked traits
Examples of sex-linked traits are hemophilia and color blindness. Men are more likely to display
sex-linked traits compared to females. For women to be color blind, the need to inherit two color
blind X chromosomes, one from their mother and one from their father. Males will show color
blindness with only one color blind X chromosome. Since males get there X chromosome from
their mothers, the mother of a color blind male will have to be at least a carrier for the color blind
trait. Males cannot be carriers for a sex linked trait.
Sex influenced traits
Some traits that are not carried on the sex chromosomes are influenced by the hormones
produced by a certain sex. These are called sex influenced traits. These traits are found on the
autosomal chromosomes and are inherited in a normal Mendelian way, but they are only
expressed when certain hormones are present. Sex influenced traits include male pattern
baldness and fraternal twins.
Environmental Influences
Other traits are influenced by the external environment. A good example of this is the Siamese
cat. Siamese cats produce more melanin in the parts of their body that are cooler; therefore
Siamese cats are darker on their nose, ears, tail, and feet. Areas that stay warmer do not produce
as much melanin and remain a lighter color.
Life Science Summer Institute – Flow of Matter and Energy
Food Chains
We will now begin to look at food chains. A food chain is a linear representation of the
organisms within an ecosystem. It is defined by who eats whom.
Components of a food chain include the following:
The producer or Autotroph – these are the organisms that can make their own food – in order to
do this, they are usually green (contain chlorophyll) – green plants are autotrophs.
Organisms that eat autotrophs are known as primary consumers or herbivores – they gain their
energy by eating plants. Vegetarians are primary consumers or herbivores. Other examples
include deer, sheep, and giraffes.
Organisms that feed on the primary consumers are known as secondary consumers. Another term
for a secondary consumer is a carnivore or meat eater. Lions are secondary consumers; the
majority of predators are secondary consumers
Organisms that feed on the secondary consumers are known as tertiary consumers – certain large
birds like the bald eagle or hawk; humans often fall into this category as well
Organisms that feed on the tertiary consumers are known as quaternary consumers. Take a
minute to see if you can think of any organisms that would fit into this category.
However, in a food chain the consumer level rarely goes beyond a quaternary level. We will
discuss why this is in a few moments.
Detritus Food Chain
All of the organisms of a food chain eventually perish. When they do, they become food for the
other type of food chain, the detritus food chain. When an organism like a bird or squirrel dies, it
is fed on by scavengers (hyenas, vultures, crows), what is not eaten by these consumers is broken
down by decomposers such as bacteria and fungi.
The detritus food chain serves a very important role within the ecosystem because it helps to
recycle the nutrients needed by the autotrophs or plants to grow.
You should now stop the lecture and work on the cooperative activity in the condensed version.
If you have trouble with this, review this lecture again from the beginning.
Life Science Summer Institute – Flow of Matter and Energy
Food Webs
Food chains are not very realistic. Our ecosystems are really made up of more complex systems
known as food webs. The real benefit of a food web is that it creates more stability in the
ecosystem.
In a food chain, if one part of the chain dies or is eaten, there is nothing for the other members to
feed on so eventually the whole chain dies.
In a food web, there are interlocking food chains. Therefore, if one or two members of the
complex group die, there is still food for the rest of the organisms.
You should now use your lecture text and the information you have gained to work on the food
web cooperative activity in the guide. This is a little tricky so just be persistent.
Photosynthesis
We now turn our attention to Basic Energy Concepts.
The two basic energy concepts are photosynthesis and respiration.
Photosynthesis is the process used by producers to capture light energy and transform it into
glucose or sugar.
How do they do this?
First, they are able to absorb carbon dioxide from the atmosphere. The carbon dioxide combines
with water (already in the plant) and as long as light and chlorophyll (remember that’s the
pigment that makes plants appear green) are present, glucose can be produced.
Make sure you become familiar with this formula.
Cellular Respiration
The next process is cellular respiration. Cellular respiration in essence is the reverse of
photosynthesis. However the two processes are different. Cellular respiration can be done by
ALL organisms. Photosynthesis can ONLY be done by producers.
The whole goal of cellular respiration is to take glucose and burn it to create ATP. Cellular
respiration can occur either with oxygen (aerobic respiration – think about running a marathon)
or without oxygen (anaerobic respiration – think running a fast sprint). The biggest difference
between these two types of respiration is that aerobic respiration produces lots of ATP while
anaerobic only produces a few.
Why is ATP so important?
ATP is the universal energy source.
Life Science Summer Institute – Flow of Matter and Energy
Think about a dollar bill – In the United states, you can take a dollar bill anywhere and exchange
it for merchandise. ATP is the same thing in organisms. It can be used to create energy to
perform all kinds of functions including digest your food, allow your muscles to work, or your
brain to function.
Trophic pyramids
We will now move into energy transfer through an ecosystem.
Organisms within a food web occupy a specific level known as a trophic level. The producers or
plants occupy the first level; the primary consumers occupy the second level and so on.
The most important thing to remember is that not all the energy that is made at each level is
capable of being transferred to the next.
REMEMBER the 10% rule – Only 10% of the energy that enters one trophic level is passed on
to the next level.
Example – If plants are able to fix 100,000 kcal of energy, the primary consumer that eats those
plants is only able to obtain 10,000 kcal of energy from those plants. Secondary consumers that
feed on these consumers are then only able to obtain 1000 kcal of energy, Tertiary consumers
only 100 kcal of energy and quaternary consumers only 10 kcal of energy.
This is why most food chains and food webs do not go beyond the quaternary consumer level.
Trophic pyramids
Something else you should notice about the trophic pyramid is that the number of organisms
decreases as you increase trophic levels.
Because of the 10% rule the amount of biomass decreases as you increase trophic levels.
There are several reasons for this decrease in biomass:
First not all the material at each level is consumed – think about corn. You only eat the kernels –
you don’t eat the cob, the plant stalk, and the roots.
Secondly, not all the material that is eaten is digested – think about fiber.
Finally, a large amount of the material that is eaten is used to provide the energy needed to do
everyday things that keep us alive.
Life Science Summer Institute – Flow of Matter and Energy
Short versus Long food chains
Why is it better to eat plants vs. animals?
Let’s look at the Figure in our condensed version. If plants have 100,000 kcal and people eat
them directly, they are obtaining 10,000 kcal of energy.
However, if we feed the plants to cows, and then eat the cows, we are only getting 1000 kcal of
energy
Don’t forget the 10% rule.
Bioaccumulation
Bioaccumulation is a bad thing that has been happening in our ecosystems for a really long time.
Bioaccumulation is the build up of toxic materials in our environment. Examples include lead,
(think about the questionnaire you answer when you take your young child to the doctor or to the
articles recently about children being poisoned by the lead in the drinking fountains in the
District) cadmium and mercury – It has recently been recommended to significantly reduce your
intake of certain fish particularly if you are pregnant because they may contain high levels of
mercury.
Another famous example is DDT – DDT was a pesticide banned in 1972. This pesticide was
used heavily during WWII to kill insects including lice. The problem is that when DDT went
into the ground, instead of breaking down completely, it broke down into DDE which was
VERY stable. DDE was absorbed by phytoplankton (producers), zooplankton (primary
consumers), small fish (secondary consumers), larger fish (tertiary consumers) and finally large
birds such as the bald eagle and osprey (quaternary consumers)
Unlike a trophic pyramid where biomass decreases as you go up the pyramid, in a
bioaccumulation pyramid the level of toxicity increases as you go up. Therefore the birds that
fed on these fish accumulated large amounts of DDE in their system. DDE blocks calcium
absorption.
Calcium is necessary for strong egg shell formation. When the birds sat on their eggs the eggs
cracked and eventually the bald eagle was close to extinction. Because the DDT was banned, we
have brought this bird back as our national treasure.
Another substance that can bioaccumulate in an ecosystem is PCB. Like DDT, PCB’s were used
as a form of pesticide. The production of PCB’s were halted in the 1970’s because they of their
tendency to bioaccumulate.
Now that we have completed this section of the course outline, please go back and make sure
that you have filled in all of the blank spaces and answered the questions in the cooperative and
test yourself activities.