The scientific method

1.State and

i dentify problem Observation

Hypothesis Gather and Conclusions

analyze data

2 .Collect information

Experiments

When we plan an experiment, we need to use control and variable groups. These groups must have the same conditions, such as: age, sex, temperature, food, seasons of year etc. Also we can use only one control group and few variable groups. After the experiment, the conclusion is made. If this hypothesis was tested many times it could contribute to a scientific theory.

Metric System and Measuring

Life scientists must often measure the height, width, mass, volume and temperature of an organism or its surroundings. Measurements give people exact descriptions of some features of living things. Throughout the world, many scientists use the metric system for their measurements.

The metric system is based on units and prefixes (Table 1.1).

The metric unit of length is the meter. It is often used to measure the heights of organisms. For convenience, we can use km, cm, mm, microns.

The gram is the metric unit used to measure mass. As you see, the mass of an organism is usually measured in kg, gm, mg.

Volumes in life science are measured in liters and milliliters. A milliliter is also known as a cubic centimeter.

Thermometers are used to measure temperature. Life scientists measure temperatures in degrees Celsius.

The speed of an organism is measured in km or cm per hour, minute or second. The cheetah runs as fast as 71 km per hour.

Table 0.1.

Metric System

Measuring	Fundamental unit	Quantity	Numerical value	Symbol	English equivalent
Length	Meter	Kilometer Centimeter Millimeter Micrometer Nanometer Angstrom	1,000 m 0,01 m 0,001 m 0,000001 m 0,000000001 m 0,0000000001 m	m km cm mm mm nm A	39,4 inches 0,62137 miles 0,3937 inches
Mass	Gram	Kilogram Milligram Microgram	1,000 g 0,001 g 0,000001 g	g kg mg mg	0,035 ounces 2,2 pounds
Time	Second	Millisecond Microsecond	0,001 sec 0,000001 sec	sec msec msec
Volume (solids)	Cubic meter	Cubic centimeter Cubic millimeter	0,000001 m3 0,000000001 m3	m3 cm3 mm3	1,308 cubic yards 0,061 cubic inches
Volume (liquids)	Liter	Milliliter Microliter	0,001 liter 0,000001 liter	l ml ml	1,06 quarts