Science Concepts and Processes: GED Test Prep

Evidence, Models, and Explanation

Scientists look for evidence. The job of a scientist is to observe and explain the observations using factual evidence, and develop models that can predict unobserved behavior.

Scientific evidence should:

• be carefully documented and organized
• be quantified as much as possible
• be reproducible by other scientists

Scientific explanations should:

• be consistent with observations and evidence
• be able to predict unobserved behavior
• be internally consistent (two statements in the same explanation should not contradict each other)

Scientific models should:

• be consistent with observations
• be consistent with explanations
• be able to predict unobserved behavior
• cover a wide range of observations or behaviors

Equilibrium and Change

A favorite pastime of scientists is figuring out why things change and why they stay the same. On one hand, many systems seek to establish equilibrium. In organisms, this equilibrium is called homeostasis. It is the tendency of organisms to maintain a stable inner environment, even when the outside environment changes. When people sweat, they are trying to cool off and maintain their equilibrium temperature.

Contrary to a common misconception, equilibrium is not a state of rest at which nothing happens. At chemical equilibrium, reactants continue to form products, and products continue to form reactants. However, the rate of formation of reactants is the same as the rate of formation of products, so that no net change is observed.

Equilibria are fragile states, and a little change, a tiny force, is often enough to disturb them. Think of a seesaw in balance. A little puff of wind, and the balance is gone. The same is true of chemical equilibrium—increase the pressure or temperature, and the equilibrium will shift. Your body is pretty good at keeping a steady temperature, but when you get sick, you are thrown out of balance; up goes your temperature, and out the window goes your homeostasis.

A change is often a response to a gradient or a difference in a property in two parts of a system. Here are some examples of common gradients and the changes they drive.

• Difference in temperature—causes heat to flow from hotter object (region) to colder object (region).
• Difference in pressure—causes liquid (water) or gas (air) to flow from region of high pressure to region of low pressure.
• Difference in electric potential—causes electrons to flow from high potential to low potential.
• Difference in concentration—causes matter to flow until concentrations in two regions are equalized.

Measurement

An established principle in science is that observations should be quantified as much as possible. This means that rather than reporting that it's a nice day out, a scientist needs to define this statement with numbers. By nice, two different people can mean two different things. Some like hot weather. Some like lots of snow. But giving the specifics on the temperature, humidity, pressure, wind speed and direction, clouds, and rainfall allows everyone to picture exactly what kind of a nice day we are having.

For the same reason, a scientist studying the response of dogs to loud noise wouldn't state that the dog hates it when it's loud. A scientist would quantify the amount of noise in decibels (units of sound intensity) and carefully note the behavior and actions of the dog in response to the sound, without making judgment about the dog's deep feelings. Now that you are convinced that quantifying observations is a healthy practice in science, you will probably agree that instruments and units are also useful.

In the following table are the most common properties scientists measure and common units these properties are measured in. You don't need to memorize these, but you can read them to become acquainted with the ones you don't already know.

You should also be familiar with the following devices and instruments used by scientists:

• balance: for measuring mass
• graduated cylinder: for measuring volume (the bottom of the curved surface of water should always be read)
• thermometer: for measuring temperature
• voltmeter: for measuring potential
• microscope: for observing very small objects, such as cells
• telescope: for observing very distant objects, such as other planets

Evolution

Most students tend to associate evolution with the biological evolution of species. However, evolution is a series of changes, either gradual, or abrupt in any type of system. Even theories and technological designs can evolve.

Ancient cultures classified matter into fire, water, earth, and air. This may sound naive and funny now, but it was a start. The important thing was to ask what is matter, and to start grouping different forms of matter in some way. As more observations were collected, our understanding of matter evolved. We started out with air, fire, earth, and water, and got to the periodic table, the structure of the atom, and the interaction of energy and matter.

Consider how the design of cars and airplanes has changed over time. Think of a little carriage with crooked wheels pulled by a horse and a plane with propellers. The car and the plane have evolved as well.

So did our planet. According to theory, 200 million years ago all the present continents formed one super-continent. Twenty million years later, the super-continent began to break apart. The Earth is still evolving, changing through time, as its plates are still moving and the core of the Earth is still cooling.

Form and Function

There is a reason why a feather is light as a feather. In both nature and technology, form is often related to function. A bird's feathers are light, enabling it to fly more easily. Arteries spread into tiny capillaries, increasing the surface area for gas exchange. Surface area and surface to volume ratio are key issues in biology and chemistry. A cell has a relatively large surface to volume ratio. If it were larger, this ratio would increase. Through the surface, the cell regulates the transport of matter in and out of the cell. If the cell had a bigger volume, it would require more nutrients and produce more waste, and the area for exchange would be insufficient. Notice the difference between the leaves of plants that grow in hot dry climates and the leaves of plants in cooler, wetter climates. What function do the differences in form serve? Did you realize that a flock of birds tends to fly forming the shape much like the tip of an arrow? Several years ago, curved skis were brought onto the market and have almost replaced traditional straight-edge skis. There are countless examples of how form develops to serve a useful function. Your job is to open your eyes to these relationships and be prepared to make the connections on the GED Science Exam.

This chapter has shown you that there are common threads in all areas of science and that scientists in different disciplines use similar techniques to observe the patterns and changes in nature. Try to keep these key principles in mind, since they are bound to reappear—not only on the GED, but in your daily life as well.