Biology & The Scientific Method

BIOLOGY & THE SCIENTIFIC METHOD

Science-an organized

way of gathering and analyzing evidence about the natural world.

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

The Scientific Method

Scientific Method-

Precise method used by scientists that separates science from other ways of studying & learning.

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?

Inferring and Forming a Hypothesis

After posing questions, scientists use further observations to make inferences, or logical interpretations based on what is already known.

Observation____________________Inference__________________

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.

Steps to the Scientific Method

1. State the problem.

2. Research / Gather

Information

3. Form a Hypothesis

Hypothesis- an educated guess; often based on inferencesMake it short & definitive.an “if then” statement

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.

4. Test the Hypothesis

Develop a controlled experiment -an experiment that contains only one experimental variable.

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).

Controlled Variables-All other variables in the experiment that are kept the same

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.

.

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.

Collecting and Analyzing Data

Scientists record experimental observations, gathering information called data. There are two main types of data: quantitative data and qualitative data.

Quantitative Data-deals with numbersdata which can be measuredEx>length, height, area, volume, weight, speed, time, temperature, humidity, cost sound levels

Quantitative Quantity


In the marsh grass experiment, it could include the number of plants per plot, plant sizes, and growth rates.

Qualitative Data-deals with a descriptiondata that can be OBSERVED but not measured

Ex>colors, textures, smells, tastes, appearance

Qualitative Quality


In the marsh grass experiment, it might include notes about foreign objects in the plots, or whether the grass was growing upright or sideways.

There are 30 students in the class.

Quantitative

The freshman class has positive school spirit.

Qualitative

This coffee has a serving temperature of 150oF.

Quantitative

Bobby’s coffee is in an orange mug.

Qualitative

5. Analyze Data & Draw Conclusions

Analyze experimental results and record observations

Organize data into graphs & tables

Is your hypothesis supported?

If a hypothesis is proven incorrect, change the hypothesis, not the data

Drawing conclusions

Experiments must be reproducible and produce consistent results. A hypothesis can change based on results of an experiment.

In the experiment, analysis showed that marsh grasses grew taller than controls by adding nitrogen.

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.

Example 1State the Problem: Is Raid the best insecticide on the market?

Research: Find information on the topic in books, the Internet, calling a customer service rep. for the product

Hypothesis: If Raid is the best insecticide on the market, then it will kill insects 30% faster than three other insecticides.

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.

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

ConclusionRaid is the best insecticide on the market. It killed insects 30% faster than three other insecticides.

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.

Theory- explanation of events or things based on knowledge gained from many observations and investigationsThe “WHY”

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.

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.

Law-a statement about what happens in nature and seems to be true all of the timeThe “What”

GRAPHING

Graph-a visual display of information

used by scientists to display data collected during a controlled experiment

Parts of a Graph

1. Title2. Independent variable3. Dependent variable4. Scales for each variable5. Legend

Title-

a concise statement usually placed above the graph that identifies what the graph is about

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

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

Which battery brand is most reliable?

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

Legend-a short descriptive narrative explaining the graph’s datashould be short & concise and usually placed under the graph

Temperature (oC)

Breathing Rate (per minute)

10 1515 2518 3020 3823 6025 5727 25

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?

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

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?

A graph takes info displayed in a table and makes it easier to observe trends

Characteristics of Life

All life on earth shares several unifying characteristics.

1. Living things are made of cells

cells—small, self-contained units that are the building blocks of life

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

2. Living things grow & developorganisms absorb raw materials and process them into new tissues and structures

Single celled organisms grow larger, while multicellular organisms grow by their cells dividing over and over.

3. Living things obtain & use energy

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.

Metabolism-A set of chemical reactions that occur in living organisms in order to maintain life.

4. Living things respond to their environment

stimulus—anything detected in an organism’s environment that causes it to reactEx. light, odor, sound, heat

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.

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.

Homeostasis-The body’s ability to regulate its internal physiology to maintain stability in response to fluctuations in the outside environment

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.

5. Living things have the ability

to reproduce

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

Two main types of reproduction1.sexual2.asexual


Most plants and animals engage in sexual reproduction, in which cells from two parents unite to form the first cell of a new organism.

There are examples of unicellular organisms and multicellular organisms that can reproduce sexually or asexually.

Organism-An individual living thing

Ex. tree, frog, human

6. Living things evolve


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.


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.

MICROSCOPES

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)

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.

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)

Parts of a Compound Light Microscope

Coarse focus adjustment knob

Focuses the image under low power Usually the bigger knobMakes larger adjustments

Fine focus adjustment knob

Sharpens the image under all powers Usually the smaller knob

Fine Adjustment

Knob

Arm

Supports the body tube and is used to carry the microscope

Arm

Body Tube

Connects the eyepiece to the nosepiece Usually moves during focusing

Body Tube

Eyepiece

The lens you look through Usually at 10X magnification

Eyepiece

Nosepiece

a.k.a. revolving nosepieceholds all the objectives and it revolves

Nosepiece

Base

Supports the microscope and used for carrying the microscope

Base

Stage

Used to support the slide

Stage

Stage Clips

Used to hold the slide in place

Stage Clips

Diaphragm

Used to regulate the amount of light

Diaphragm

Light Source

Provides light

Light Source

Low Power Objective

Has the lowest magnification and is the shortest objective

Low power objective

Medium Power Objective

increases the magnification

Medium Power Objective

High Power Objective

Provides the most magnification and is the longest objective.

High Power Objective

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.

Example

Calculate the magnification of a microscope with an eyepiece magnification of 10 and objective magnification is 30.

Answer: 10 X 30 = 300

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.

Microscope Care

Always carry with 2 handsOnly use lens paper for cleaningDo not force knobsKeep objects clear of desk and cords

EyepieceBody Tube

Revolving NosepieceArm

Objective Lens

StageStage Clips

Coarse FocusFine Focus

Base

DiaphragmLight

Place the Slide on the MicroscopeUse Stage Clips Click Nosepiece to the lowest (shortest) settingLook into the EyepieceUse the Coarse Focus

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?

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Biology & The Scientific Method