Download - Biology & The Scientific Method
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BIOLOGY & THE SCIENTIFIC METHOD
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Science-an organized
way of gathering and analyzing evidence about the natural world.
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What is Biology?
Biology—a science that employs scientific methodology to study living things. It is the science, and study, of life.
Bio- means life, and –ology means the study of
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The Scientific Method
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Scientific Method-
Precise method used by scientists that separates science from other ways of studying & learning.
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Observing and Asking Questions
Scientific investigations usually begin with an observation, the act of noticing and describing events or processes in a careful, orderly way. For example, researchers observed that marsh grass grows taller in some places than others. This observation led to a question: Why do marsh grasses grow to different heights in different places?
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Inferring and Forming a Hypothesis
After posing questions, scientists use further observations to make inferences, or logical interpretations based on what is already known.
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Observation____________________Inference__________________
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Observation or Inference ?Students are working with a newly discovered organism. Is their statement an observation or an inference?
___ 1. The organism frowned to show it did not like strangers.___ 2. The organism is green with pink spots.___ 3. The organism lives near other organisms.___ 4. The organism moved away from us because it was scared.___ 5. The organism made gurgling noises.___ 6. The organism had four spines on its back.___ 7. The organism has one blue eye and two green eyes.___ 8. The organism moves really slow so he must be old.
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Steps to the Scientific Method
1. State the problem.
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2. Research / Gather
Information
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3. Form a Hypothesis
Hypothesis- an educated guess; often based on inferencesMake it short & definitive.an “if then” statement
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Inferring and Forming a Hypothesis
Researchers inferred that something limits grass growth in some places. Based on their knowledge of salt marshes, they hypothesized that marsh grass growth is limited by available nitrogen.
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4. Test the Hypothesis
Develop a controlled experiment -an experiment that contains only one experimental variable.
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Controlling Variables
It is important to control variables because if several variables are changed in the experiment, researchers can’t easily tell which variable is responsible for any results they observe.
The variable that is deliberately changed is called the independent variable (also called the manipulated variable).
The variable that is observed and that changes in response to the independent variable is called the dependent variable (also called the responding variable).
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Controlled Variables-All other variables in the experiment that are kept the same
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Control and Experimental Groups
Typically, an experiment is divided into control and experimental groups.
A control group is exposed to the same conditions as the experimental group except for one independent variable.
.
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Designing Controlled Experiments
The researchers selected similar plots of marsh grass. All plots had similar plant density, soil type, input of freshwater, and height above average tide level. The plots were divided into control and experimental groups.
The researchers added nitrogen fertilizer (the independent variable) to the experimental plots. They then observed the growth of marsh grass (the dependent variable) in both experimental and control plots.
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Collecting and Analyzing Data
Scientists record experimental observations, gathering information called data. There are two main types of data: quantitative data and qualitative data.
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Quantitative Data-deals with numbersdata which can be measuredEx>length, height, area, volume, weight, speed, time, temperature, humidity, cost sound levels
Quantitative Quantity
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Collecting and Analyzing Data
In the marsh grass experiment, it could include the number of plants per plot, plant sizes, and growth rates.
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Qualitative Data-deals with a descriptiondata that can be OBSERVED but not measured
Ex>colors, textures, smells, tastes, appearance
Qualitative Quality
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Collecting and Analyzing Data
In the marsh grass experiment, it might include notes about foreign objects in the plots, or whether the grass was growing upright or sideways.
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There are 30 students in the class.
Quantitative
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The freshman class has positive school spirit.
Qualitative
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This coffee has a serving temperature of 150oF.
Quantitative
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Bobby’s coffee is in an orange mug.
Qualitative
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5. Analyze Data & Draw Conclusions
Analyze experimental results and record observations
Organize data into graphs & tables
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Is your hypothesis supported?
If a hypothesis is proven incorrect, change the hypothesis, not the data
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Drawing conclusions
Experiments must be reproducible and produce consistent results. A hypothesis can change based on results of an experiment.
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In the experiment, analysis showed that marsh grasses grew taller than controls by adding nitrogen.
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Drawing Conclusions
The original hypothesis is reevaluated and revised; new predictions are made, and new experiments are designed.
Hypotheses may have to be revised and experiments redone several times before a final hypothesis is supported and conclusions can be drawn.
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Example 1State the Problem: Is Raid the best insecticide on the market?
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Research: Find information on the topic in books, the Internet, calling a customer service rep. for the product
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Hypothesis: If Raid is the best insecticide on the market, then it will kill insects 30% faster than three other insecticides.
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Test the hypothesis in a controlled experiment
Spray 4 separate containers with equal amounts of 4 different insecticides (one of which is Raid). Cover each one with the same type and size glass. Add equal amounts of the same type of insects (10) to each glass. Place them side-by-side and time the results.
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Data
Container #
#living 1 min
#living 2 min
#living 3 min
#living 4 min
1 (Raid) 10 0 0 02 10 10 8 43 10 10 6 34 10 10 4 2
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ConclusionRaid is the best insecticide on the market. It killed insects 30% faster than three other insecticides.
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Scientific Theories
In science, the word theory applies to a well-tested explanation that unifies a broad range of observations and hypotheses and that enables scientists to make accurate predictions about new situations.
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Theory- explanation of events or things based on knowledge gained from many observations and investigationsThe “WHY”
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Scientific Theories
Evidence may support several related hypotheses in a way that inspires researchers to propose a scientific theory that ties those hypotheses together.
A useful theory that has been thoroughly tested and supported by many lines of evidence may become the dominant view among the majority of scientists.
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Scientific Theories
No theory is considered absolute truth. Science is always changing; as new evidence is uncovered, a theory may be revised or replaced by a more useful explanation.
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Law-a statement about what happens in nature and seems to be true all of the timeThe “What”
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GRAPHING
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Graph-a visual display of information
used by scientists to display data collected during a controlled experiment
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Parts of a Graph
1. Title2. Independent variable3. Dependent variable4. Scales for each variable5. Legend
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Title-
a concise statement usually placed above the graph that identifies what the graph is about
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Independent Variable-
the variable that is controlled by the experimenteroften includes time (dates, minutes, hours), depth (feet, meters), temperature…what you changeplaced on the X-axis
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Dependent Variable-
variable that is directly affected by the independent variablethe result of what happens because of the introduction of the independent variableplaced on the Y-axis
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Which battery brand is most reliable?
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Scales for each Variable
range must include all data pointsmust take up an appropriate amount of spaceoften starts at zero and climbs based on consistent intervals Example: multiples of 2, 5, 10, 100
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Legend-a short descriptive narrative explaining the graph’s datashould be short & concise and usually placed under the graph
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Temperature (oC)
Breathing Rate (per minute)
10 1515 2518 3020 3823 6025 5727 25
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Breathing Rate of Freshwater Sunfish
10 15 18 20 23 250
10
20
30
40
50
60
70
Temperature oC
Brea
thin
g Ra
te (p
er
min
ute) Is this scaled properly?
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Time After Eating (hours)
Glucose (ml) / L of blood Person A
Glucose (ml) / L blood Person B
0.5 170 1801 155 1951.5 140 2302 135 2452.5 140 2353 135 2254 130 200
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0.5 1 1.5 2 2.5 3 40
50
100
150
200
250
300
350
400
Series 3Person B
Glucose Levels of Two People
Time After Eating (hours)
Gluc
ose
(ml)
/ L o
f Blo
od
Where is 3.5?
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A graph takes info displayed in a table and makes it easier to observe trends
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Characteristics of Life
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All life on earth shares several unifying characteristics.
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1. Living things are made of cells
cells—small, self-contained units that are the building blocks of life
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Unicellular and Multicellular organisms Unicellular- a single cell carries out
all of life’s functions Ex> bacteria
Multicellular- trillions of cells can be working together to carry out life functions, having specialized functions within the organism
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2. Living things grow & developorganisms absorb raw materials and process them into new tissues and structures
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Single celled organisms grow larger, while multicellular organisms grow by their cells dividing over and over.
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3. Living things obtain & use energy
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Characteristics of Living Things
For example, leaves obtain energy from the sun and gases from the air. These materials then take part in various chemical reactions within the leaves.
Animals ingest organisms like plants or other animals who have already consumed plants themselves.
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Metabolism-A set of chemical reactions that occur in living organisms in order to maintain life.
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4. Living things respond to their environment
stimulus—anything detected in an organism’s environment that causes it to reactEx. light, odor, sound, heat
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Some responses are behavioral, such as a rabbit running from a predator or a plant moving its leaves to face incoming sunlight.
Other examples can include a plant producing a poisonous chemical to ward off insects from eating its leaves.
Plants and animals can detect changes such as light, temperature, and even gravity.
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Organisms and their cells function best at certain temperatures, pH levels, solute concentrations, etc. They must maintain these levels from becoming too high or low.
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Homeostasis-The body’s ability to regulate its internal physiology to maintain stability in response to fluctuations in the outside environment
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In low light environments, your pupils dilate and allow more light to pass into the eye. This is a response to a stimulus- low light level. This also is an example of maintaining homeostasis, using energy to maintain constant light levels in the eye.
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5. Living things have the ability
to reproduce
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Reproduction-Biological process by which new individual organisms are produced.A fundamental feature of all known life—each individual exists as a result of reproduction
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Two main types of reproduction1.sexual2.asexual
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Characteristics of Living Things
Most plants and animals engage in sexual reproduction, in which cells from two parents unite to form the first cell of a new organism.
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There are examples of unicellular organisms and multicellular organisms that can reproduce sexually or asexually.
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Organism-An individual living thing
Ex. tree, frog, human
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6. Living things evolve
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Characteristics of Living Things
Over generations, groups of organisms evolve, or change over time.
Evolutionary change links all forms of life to a common origin more than 3.5 billion years ago.
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Characteristics of Living Things
Evidence of this shared history is found in all aspects of living and fossil organisms, from physical features to structures of proteins to sequences of information in DNA.
For example, signs of one of the first land plants, Cooksonia, are preserved in rock over 400 million years old.
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MICROSCOPES
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Anton Van Leeuwenhoek
found that by placing glass lenses (lenses refract light) at certain distances from each other, he could enlarge objects in his field of visionInvented the 1st microscope (light microscope)
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Leeuwenhoek developed what is called a simple microscope since it had only one lens. We mostly use compound microscopes since they have more than one lens.
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Important Microscopy Terms
Magnification Resolving Powerthe comparison of the real size of a specimen with that of the one viewed under themicroscope
a.k.a. resolutionrefers to the clarity of the specimen viewed under the scope
Image of pollen grain with good resolution (left) and poor resolution
(right)
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Parts of a Compound Light Microscope
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Coarse focus adjustment knob
Focuses the image under low power Usually the bigger knobMakes larger adjustments
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Fine focus adjustment knob
Sharpens the image under all powers Usually the smaller knob
Fine Adjustment
Knob
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Arm
Supports the body tube and is used to carry the microscope
Arm
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Body Tube
Connects the eyepiece to the nosepiece Usually moves during focusing
Body Tube
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Eyepiece
The lens you look through Usually at 10X magnification
Eyepiece
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Nosepiece
a.k.a. revolving nosepieceholds all the objectives and it revolves
Nosepiece
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Base
Supports the microscope and used for carrying the microscope
Base
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Stage
Used to support the slide
Stage
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Stage Clips
Used to hold the slide in place
Stage Clips
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Diaphragm
Used to regulate the amount of light
Diaphragm
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Light Source
Provides light
Light Source
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Low Power Objective
Has the lowest magnification and is the shortest objective
Low power objective
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Medium Power Objective
increases the magnification
Medium Power Objective
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High Power Objective
Provides the most magnification and is the longest objective.
High Power Objective
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Calculating magnification
1. Determine the magnification of the eyepiece (ocular lens) and each objective.
2. Multiply the magnification of the eyepiece with the magnification of the objective you are using.
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Example
Calculate the magnification of a microscope with an eyepiece magnification of 10 and objective magnification is 30.
Answer: 10 X 30 = 300
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Objectives of Microscope Lab
To learn the parts of the microscope.To find specimens using low and high power.To make a wet mount.To view your own human cheek cells under the microscope.
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Microscope Care
Always carry with 2 handsOnly use lens paper for cleaningDo not force knobsKeep objects clear of desk and cords
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EyepieceBody Tube
Revolving NosepieceArm
Objective Lens
StageStage Clips
Coarse FocusFine Focus
Base
DiaphragmLight
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Place the Slide on the MicroscopeUse Stage Clips Click Nosepiece to the lowest (shortest) settingLook into the EyepieceUse the Coarse Focus
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Follow steps to first focus using low powerClick the nosepiece to the longest objectiveDo NOT use the Coarse Focusing KnobInstead use the Fine Focus Knob to bring the slide into viewWhat can you find on your slide?