Metric System and Unit Conversions

The Metric System

Science uses the metric system because it is based on units of 10, making it simpler and more consistent. Units like meters (length), grams (mass), and liters (volume) can be scaled up or down using prefixes like kilo-, centi-, or milli-. For example, 1 kilometer (km) = 1000 meters (m).

Dimensional Analysis: Converting Between Units

To convert between units, scientists use dimensional analysis, which involves multiplying by conversion factors. A conversion factor is a ratio that equals 1 and allows you to cancel units.

Example:

Convert 2,500 milligrams (mg) to grams (g).

We know:

1 gram = 1,000 milligrams

So the conversion factor is:

1 g / 1,000 mg

Now multiply:

2,500 mg × (1 g / 1,000 mg) = 2.5 g

The mg units cancel, and you're left with grams.

Always make sure the unit you want to cancel is diagonal from itself in the fraction so that it cancels out.

Percent Change

Percent change is used to describe how much a value increases or decreases compared to its original value. It's especially useful in biology when looking at population growth, enzyme activity, or other measurements that change over time.

A positive percent change indicates that the value increased, while a negative percent change indicates that it decreased.

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