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Advanced Biology: Unit One Introduction
Objectives:
• Describe the steps of the scientific method.
• Create an experiment using correct experimental design.
• Distinguish between true observations and inferences.
• Differentiate between a control group and an experimental group and
between dependent and independent variables.
• Critique and analyze experimental design and data
• Explain the procedure followed and the importance of a controlled
experiment or a double-blind study.
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Identify the properties/characteristics of life
Distinguish between various types of reproduction
Describe the organization of life within a complex organism.
Explain how natural selection affects survival of a species.
Identify factors invalidating a study’s conclusions.
Vocabulary:
hypothesis * observation * qualitative data * biology *
quantitative data * control group * experimental group *
dependent variable * independent variable * double blind *
metabolism * homeostasis * tissues * organs * organ
systems * autotroph * inference * heterotroph *
adaptation
natural selection * evolution * operational definition *
placebo/placebo effect * cells * convergent evolution * divergent
evolution
Bio – “life”
- logy “the study of”
Characteristics of life:
1)
All life is composed of one or more cells (the unit of life). More
complex organisms show organization of cells into tissues (“very
thin” in French – so named by Bichat during the French
Revolution). Tissues may be organized into organs ( a group of
many tissues working toward a common function Ex: the heart
contains nervous tissue, muscle tissue, vascular tissue, etc. in
order to function as a pump in the circulatory (organ) system).
Organs can be arranged into organ systems (Ex: circulatory
system, digestive system, nervous system, etc.)
Cells
to Tissues
to Organs
to
Organ systems
2)
3)
4)
Life requires energy for growth, repair, etc. Plants use the sun’s
energy to photosynthesize. They are autotrophs (“self feeding”)
or “producers”. Animals are heterotrophs (other feeders) or
“consumers”. To extract energy from our food, we must
metabolize it. Metabolism is the chemical reaction within cells
that maintains life, using food to provide the necessary energy.
Living things maintain a relatively stable internal environment in
spite of their external environment. The ability to keep conditions
constant is called “homeostasis”. For example, cells maintain a
relatively stable balance of Na+, K+, and Cl- ions. And, we
maintain a relatively stable body temperature.
Organisms reproduce, grow, and develop.
* Reproduction may be asexual, such as a bacterium dividing
through binary fission or a yeast “budding”. Conjugation PRIOR
to asexual reproduction can allow genetic variability. Asexual
cellular reproduction involves mitosis.
* Reproduction can be sexual, such as the production of egg and
sperm through meiosis.
5)
Organisms respond to their environment. This can be a simple
stimulus/response like a plant bending toward the sun or a more
complex response developing over time and generations. This is
considered an adaptation.
Organisms that don’t adapt to their environment are less likely to
survive. Organisms born with less desirable traits are also less likely
to survive and reproduce. This is natural selection, also known as
“survival of the fittest” (Darwin). Those organisms with the
characteristics that best let them survive in their environment will thrive
and reproduce. For example, those with coloration that blends with
their environment (camouflage) are less likely to be seen by their
predators/prey. Those without beneficial characteristics may not
survive to reproduce so their genes will be lost. Remember,
evolution does not occur in individuals, only in populations of species
due to their genetic variability over time. This is evolution (the change
in a species’ traits over time).
When organisms of different species living in similar environments
begin looking more like each other (for example: polar bears, baby
seals, and arctic hares all have white fur), it’s called convergent
evolution.
When organisms of the same species begin looking different from
each other because they live in very different environments (Ex: tan
desert hares with large ears for heat release versus white arctic hares
with small ears for heat conservation), it’s called divergent evolution.
Both forms of evolution are driven by natural selection. If a brown
rabbit is born into a litter of artic hares, it’ll be seen by a predator and
eaten, thereby removing its genes from the gene pool. If a brown rabbit
is born into a litter in the desert, it blends into its environment and is
more likely to survive, reproduce, and conserve its genes.
There are several ways to study living organisms:
• Natural studies – pure observation of organisms in their environment
• Controlled experiments
• Double-blind studies
A controlled experiment is performed using the scientific method.
The Scientific Method involves the following steps:
1) Problem statement - An explanation of what will be studied and
why.
2) Hypothesis - What you think the experiment will prove (an
educated guess or prediction) and what background
information/studies makes you believe this is the case.
3) Experimental design - This includes a very specific explanation
of the steps to be followed. This must be clear enough that people
not familiar with your experiment will be able to duplicate the
experiment exactly. The control group (everything is kept standard)
and experimental group(s) (1 variable) should be clearly identified.
The independent variable (the variable being manipulated by the
experimenter) in the experimental group(s) and the dependent
variable (responding variable) being assessed must be clearly
identified. Operational definitions (Ex: “Growth” means height) must
be clear. The number of individuals studied, the amount of time they
were studied or the number of trials completed by the individuals,
and a clear identification of the individuals (Ex: Oak trees at three
years of age. White, male Americans between the ages of 20 and
25. Etc.) is essential.
Control group – this is a group of individuals monitored during the
experiment that receive “normal” treatment.
Experimental group – this is a group similar in composition (Ex: same
age, species, and size of plants) to the control group, also given
“normal” treatment EXCEPT for one variable (Ex: same amount of
light, water, same soil, etc, BUT given 1 mg of vitamin D weekly.)
Independent variable - What the scientist changed from the “normal”
condition. Ex: Growing plants under blue light waves only.
Everything else is kept the same as in the control group.
Dependent variable – this is what the researcher EXPECTS to be
affected by manipulating the independent variable. (Ex: I will
measure plant growth under blue light because I think that light
wave will increase growth.)
Operational definition – a specific explanation of terms or
measurements (Ex: “Growth”, in this experiment means total
biomass. For the purposes of this experiment, vitamin E refers to
alpha-tocopherol only.) How measurements will be taken is also
very important when reporting your experimental design.
4)
Observation/Data Collection and Reporting – anything you can
see, hear, taste, smell, or physically feel or measure is a true
observation. It is important to avoid inferences. (Ex: “I heard
yelling in the hall.” is an observation. Unless you actually saw it,
adding, “There was a fight going on” is an inference, an
assumption. This could be called “jumping to conclusions” and
must be avoided.) Observations can be “qualitative” (nonnumerical), such as “it turned blue” or “quantitative” (numerical),
such as the item stood 3 inches tall, there were 5 episodes of . . .,
etc. Qualitative data can sometimes be made numerical to help
with comparisons between groups. Ex: “On a scale of 1 to 10,
my pain was a 5.”
Tables, graphs, grids, and sample calculations should be used to
report numerical data clearly and efficiently.
5) Analysis and Conclusion – This summarizes your data and states
whether you feel this supports or refutes your hypothesis. Any
unusual results should be addressed here (don’t ignore them).
These should be explained along with any concerns about the
experimental design, accuracy of data collection, equipment
problems or limitations, etc.
Double-blind studies –a controlled experiment usually done when the
experimental subjects are human and the experimental variable is a
medication or vitamin. This is to eliminate the placebo effect. In this
case, neither the test subject nor the person administering the
medication/vitamin know whether they have the true product or the
placebo. This prevents undue influence on the subjects by the
provider of the pills and factors in a possible psychological effect.
Placebo effect – this is when people report feeling better due to
treatment with an inert (non-medicinal) substance, i.e. the placebo.
It is important to use a critical eye when examining the conclusions
given in other people’s experiments. Many inaccuracies or prejudices
can be incorporated into a conclusion. This is especially true when
the study is funded by a company that stands to benefit if the “right”
conclusions are published.
Ex: A study done on the East Coast found that there was not a
problem with “acidity” in the lakes. Yet, the pH levels were so low
(acid) that fish could not live in the lakes. However, the conclusion
was based on the operational definition defining a pH problem as
existing only when the pH dropped lower (something like 4.5) than
could sustain life. So, using their criteria for a “pH problem”, they
could conclude there was no problem. Ex: A recent study concluded
vitamin E did not help prevent blood components from sticking.
Because the study defined Vitamin E as alpha-tocopherol, the
conclusion was right. However, many of us consider Vitamin E to be a
complex of 4 tocopherols and 4 tocotrienols with gamma-tocopherol
being the agent that reduces stickiness.
Other factors that might invalidate a study’s conclusions:
Scientists often use inferences when forming their final conclusions.
Since inferences are assumptions (based on their observations)
they can be wrong.
Human error is always a possibility when performing experiments. A
procedure can be performed incorrectly or the results could be
misread.
Equipment can be faulty or not sensitive enough for certain
measurements.
Cause/effect relationships must be scrutinized. Often, 2 things
correlate, but one does not cause the other. Ex: In Europe, the
stork population and human population grew at about the same rate
over a period of 10 years. Although children used to be told that
storks brought new babies to a home, the growth of the stork
population certainly did not cause the growth of the human
population. Both were probably related to a good environment for
reproduction. So, be wary of cause/effect conclusions.
Studies must also contain adequate sample sizes. Conclusions cannot
be accurately drawn when too few subjects are tested.
Studies must continue for long enough periods of time. The effects of
many substances might not be seen for months or even years.
The age, pre-trial health, and sometimes sex of the subjects must be
considered to draw valid conclusions.