Scientific Investigations

Today it’s common knowledge that DNA stores & passes on genetic information from parents to child. However, this has not always been the case! In the 1940’s most scientists thought that DNA was too simple to do this (just 4 bases), & that protein did this job instead. Scientific Investigations

How did scientists come to figure out that DNA was the carrier of genetic information? How do scientists generally test their ideas? The Scientific Method Scientific Investigations

The scientific method is a systematic (or orderly) way of exploring the world around us. Most scientific investigations have several distinct steps. Scientific Investigations

A hypothesis proposes a possible cause-effect relationship between two things. Many times a hypothesis is phrased as an “if-then” statement “Ifwe give the rats twice as much food as normal, then their hair will grow twice as long.” The Hypothesis

A hypothesis identifies the independent variable (the variable that will be manipulated), the dependent variable (the effect or response), & the controlled variables (which are all held constant…for example we will make sure that all the mice are of the same species.) The Hypothesis

Many scientific experiments also include a control group. A control group is a group that is identical to the experimental subjects in every way except that they are never exposed to the independent variable. The Hypothesis

Reporting Data Scientific studies investigate cause-effect relationships. The potential cause is called the “independent variable”. The potential effect is known as the “dependent variable” (because it “depends” upon the cause) A Van de Graff generator

Identify Independent and Dependent variable. You can easily do this by identifying the cause (Ind.) and the effect (Dep.) of the investigation…

Reporting Data When graphing scientific data, the independent variable is usually represented as “x”, while the dependent variable is represented as “y”. You will remember from algebra class that the x-axis runs horizontally, while the y-axis runs vertically.

Reporting Data Scientists often use charts, graphs, diagrams, and tables to illustrate their findings. This is because graphs give us an easy way to visually illustrate a potential relationship.

Tell the relationship shown by the graph: 3 1 No Relationship Inverse Relationship 4 2 Direct Relationship Nonlinear Relationship

Reporting Data A bar graph is good for measuring data on similar things.

Reporting Data A circle graph (or “pie chart”) is commonly used to show parts of a whole.

Reporting Data A chart is useful for organizing and presenting numerical data

Reporting Data 3 more mathematical tools: Mean: The Average Median: The middle number in a group of numbers Mode: The number that appears most often in a set of numbers

Reporting Data Math is often called the “universal language” because the rules are the same everywhere in the world.

Anytime scientists analyze data, they also make inferences (tentative ideas drawn from the information they have). If a lot of evidence seems to support an inference, scientists might get brave enough to call it a conclusion. Scientific Investigations

HOWEVER, even a lot of strong evidence does not PROVE a conclusion to be true. Just one single piece of contrary evidence can disprove a conclusion. Scientific Investigations

For example, “global warming” has recently come under fire, with many scientists saying that it isn’t being caused by CO2 levels. Scientific Investigations

Ex: Some people believed that living organisms could come to life from non-living matter, such as broth giving rise to microbes, etc. Many scientists (and Christians) disagreed, and the battle became so heated that Paris Academy of Sciences offered a reward to anyone who could conclusively resolve it. Louis Pasteur did so & claimed the prize in 1864. Scientific Investigations

Refutation of Spontaneous Generation

Scientists must be able to REPEAT an experiment before they can accept the findings. Repeating the experiment establishes that it was credible, and that the results are valid. Ex: Cold Fusion Scientific Investigations

Once a pattern has been established by predictable results, scientists might develop a theory to explain related results. In scientific conversation, a theory is not just a reasonable guess, but a well supported explanation. Scientific Investigations

Like all forms of scientific knowledge, any theory is considered to be conditional. New scientific data could cause a theory to be revised or even rejected altogether. Scientific Investigations

Finally, a model is a simplified version of reality. A model shows the relevant parts without showing every last detail. Ex. Solar System models do not include all 63 moons of Jupiter Scientific Investigations A boy holding the sun in a solar system model

Watson & Crick made a DNA model in the 1950’s to show its structure, building upon Rosalind Franklin’s work. Shape = Double Helix A Lego model of DNA

Finally, in 1962 they were awarded the Nobel prize for “their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material”. Major Scientific Breakthroughs:

Section 2 & 3 Lab Procedures and Reporting Data

Lab Procedures & Equipment • Use “Common Sense”: • Keep electricity away from water • Never point the mouth of a container that is being heated toward a person, never put your face over it either. • Use tongs when handling hot objects. • Don’t taste, touch, or smell unknown chemicals • Report all accidents (no matter how small) IMMEDIATELY to your instructor (ME)

Lab Safety Symbols SymbolMeaningExplanation:

SymbolMeaningExplanation:

Common Lab Equipment: PictureNameUse

Forceps Mortar & Pestle Ring Stand Spatula Watch Glass

The Compound Light Microscope: • Most high school and college labs use the compound light microscope to magnify objects so that they can study them. • Typically, these microscopes magnify objects 10-400X, depending on which objective is used.

The Compound Light Microscope: • The microscope’s ocular (a.k.a. “the eyepiece”) typically has a magnification power of 10X. • The nosepiece usually holds 3 or 4 objectives which range in power from 4X-40X. • Total magnification power can be found by multiplying the ocular power by the nosepiece power.

Find the total magnification power: • Let’s assume that the ocular is a 10X ocular. What would the total magnification be if the nosepiece is: • 4X • 10X • 12X • 20X • 25X • 40X

The Compound Light Microscope: • The field of view is the part of the specimen that you can actually see. • The higher the magnification, the smaller the field of view becomes • The more you zoom in, the less of the specimen you can see (because you are focusing on a small part) Mites on a plant stem

The Compound Light Microscope: • A few quick things to remember about microscopes: they are expensive instruments that require care when handling them. • When carrying a microscope, grasp the microscope arm with one hand, and place the other hand under the base. • Be careful not to scratch the lenses or eyepiece. (don’t clean them with anything but lens paper)

Parts of a Compound Microscope:

Reporting Data • Scientists use the Metric System (or Systeme International) for all measurments. • Commonly Abbreviated SI. • Works by units of 10. • This ensures that scientists can clearly communicate their results to other scientists, no matter what language they speak.

Reporting Data • The Metric System has certain base units used for measuring different things • Meter (for length) • Gram (for mass) • Liter (for volume) • Second (for time) • O Celsius (for temp.)

Reporting Data • The base units are then given a prefix to tell us their size. Examples: • Kilometer (base x 103) • Meter (base unit) • Centimeter (base x 10-2) • Millimeter (base x 10-3) • Micrometer (base x 10-6) • Nanometer (base x 10-9)

How to use the Metric System:

Scientific Investigations