Taking measurements and working with variables

Many experiments involve taking measurements of physical quantities, such as temperature, volume, and mass. Measurements should be both accurate and precise. 

Key Fact: Measurements are more reliable if they are repeated several times and an average is taken.

1. Measuring equipment 

   
   

Biology experiments often require equipment to measure mass, volume, temperature, time, or length. To ensure a reliable reading when using measuring equipment, it is often wise to repeat a measurement several times and then work out an average. 

Some examples for measuring equipment can be a stopwatch (to measure time), a balance to measure mass, a measuring cylinder to measure volume, thermometers to measure temperature, rulers to measure distance, etc.

2. Accuracy and precision

   
   

The words accurate and precise have slightly different meanings in science. A measurement is accurate if it is very close to the true value being measured. A measurement is precise if repeating the measurement several times produces the same (or a very close) value. 

Precise but inaccurate - Imagine you measure the temperature of a beaker of warm water four times with a digital thermometer. All four readings show the same number to two decimal places, but the thermometer is faulty. The readings are precise but inaccurate. 

Accurate but not precise - Now imagine you use a different thermometer that isn’t faulty, but the readings are all slightly different. Perhaps the tip of the thermometer was in a different patch of water each time. The readings are accurate, but they aren’t precise. 

Accurate and precise - Finally, you stir the water before taking the temperature, and all four readings are the same and correct. They are accurate and precise. Whenever you take measurements, try to be accurate and precise :)

Things that might change during an experiment are called variables. There are three important types of variables: independent, dependent, and control variables. 

Key Facts: An experiment deliberately changes the independent variable. The Dependent variable is measured to obtain the experiment’s results. 

3. Experimental variables 

   
   

Let’s take a look at a specific example to explain all this! An experiment measures how quickly an enzyme digests starch in test tubes kept at three different temperatures: hot (60°C), body temperature (37°C), and cold (4°C).

One variable - the independent variable - is deliberately varied in experiments. In this experiment, the temperature is the independent variable.

Control variables are the ones that are kept constant so they don’t affect the dependent variable. In this experiment, the volume and concentration of reactants in each test tube are control variables. Each test tube contains a mixture of starch and the enzyme amylase, which digests starch. Also, a water bath maintains a constant temperature in each test tube. 

The dependent variable is the variable you measure to get your results. In this experiment, time is the dependent variable because starch is digested at different rates at each temperature. 

4. Scientific controls 

   
   

Some experiments involve what’s called a scientific control. This helps rule out the effects of unwanted variables, making the results more reliable. In the example following, the control is set up the same as the main test, except that the organisms being tested are not included. This reveals whether changes in the dependent variable are caused by the organisms or by other factors. 

This experiment tests for the presence of carbon dioxide produced by respiring organisms. In a tube, we have a hydrogen carbonate indicator that changes from yellow to red when carbon dioxide is present, living organisms of some kind, and a gauze. Carbon dioxide, as mentioned previously, changes the indicator from yellow to red. 

The control is exactly the same but has no living organisms. Now we have the tube with the hydrogen carbonate indicator, but no organisms on the gauze. If the solution in this tube does not change color, any color change in the first tube must be caused by the organisms. 

Final Thoughts

Taking accurate and precise measurements, understanding different types of variables, and using proper controls are all essential parts of working scientifically. Together, these practices ensure that experiments are reliable, repeatable, and meaningful, helping scientists uncover real insights about the living world.

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By Iva Trpeski