SCIENCE. The intellectual process using all available mental and physical resources to better understand, explain, quantitate, and predict normal as well as unusual natural phenomena
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Scientific hypotheses must be proposed in a waythat enables them to be tested
Some hypotheses are tested by performing controlled experiments, as you will learn in the next section
Other hypotheses are tested by gathering more data:
In the case of the mystery illness, data would be collected by studying the location of the event; by examining air, water, and food people were exposed to; and by questioning people about their actions before falling ill
Some hypotheses would be ruled out
Others might be supported and eventually confirmed
Even though conditions in the external environment may vary widely, most organisms must keep internal conditions, such as temperature and water content, fairly constant to survive
The process by which they do this is called homeostasis (hoh-mee-oh-STAY-sis)
Homeostasis often involves internal feedback mechanisms that work in much the same way as a thermostat
Just as a thermostat in your home turns on the heat when room temperature drops below a certain point, you have an internal “thermostat” that makes your body shiver if your internal temperature drops too low
The muscle action involved in shivering produces heat, thus warming your body
In contrast, if you get too hot, your biological thermostat turns on “air conditioning” by causing you to sweat.
Sweating helps to remove excess heat from your skin
When birds get cold, they hunch down and adjust their feathers to provide maximum insulation
Often internal stimuli help maintain homeostasis
For example, when your body needs more water to maintain homeostasis, internal stimuli make you feel thirsty
Because researchers need to replicate each other's experiments and most experiments involve measurements, scientists need a common system of measurement:
Most scientists use the metric system when collecting data and performing experiments
The metric system is a decimal system of measurement whose units are based on certain physical standards and are scaled on multiples of 10
A revised version of the original metric system is called the International System of Units, or SI
The abbreviation SI comes from the French Le Système International d'Unités.
Because the metric system is based on multiples of 10, it is easy to use
Notice in the table at right how the basic unit of length, the meter, can be multiplied or divided to measure objects and distances much larger or smaller than a meter. The same process can be used when measuring volume and mass
Now that you know the basic units of the metric/SI system, it is important that you understand how to go from one unit to another. The skill of converting one unit to another is called dimensional analysis
Dimensional analysis involves determining in what units a problem is given, in what units the answer should be, and the factor to be used to make the conversion from one unit to another.
Let’s see how dimensional analysis works. Suppose you are told to convert 2500 grams to kilograms. This means that grams are your given unit and you must express your answer in kilograms. The conversion factor you choose must contain a relationship between grams and kilograms that has a value of 1.You have two possible choices:
1000 grams / 1 kilogram = 1
1 kilogram / 1000 grams = 1
To convert one metric unit to another, you must multiply the given value times the conversion factor. Remember that multiplying a number by 1 does not change the value of the number. So multiplying by a conversion factor does not change the value, just the units.
Now, which conversion factor should you use to change 2500 grams into kilograms? Since you are going to multiply by the conversion factor, you want the unit to be converted to cancel out during the multiplication. This is just what will happen if the denominator of theconversion factor has the same units as the value you wish to convert.Since you are converting grams into kilograms, the denominator of the conversion factor must be in grams and the numerator in kilograms. The first step in dimensional analysis, then, is to write out the value given, the correct conversion factor, and a multiplication symbol between them:
Microscopes are devices that produce magnified images of structures that are too small to see with the unaided eye
Light microscopes produce magnified images by focusing visible light rays
Electron microscopes produce magnified images by focusing beams of electrons
Since the first microscope was invented, microscope manufacturers have had to deal with two problems: What is the instrument's magnification—that is, how much larger can it make an object appear compared to the object's real size? And how sharp an image can the instrument produce?