How to Write An Experimental Science Project Question


Building an Experimental Science Project Question


New Science Terms

controlled variables
dependent variable
experimental question
independent variable

An experimental question is a cause-effect question.

Note: Things that can be changed or change on their own are called variables.

In an experimental question, the variable that causes another variable to change  is called the independent variable. The  variable that is affected (caused to change) is called the dependent variable

For example:
In the question, “How does water affect plant growth?”

1. what has been affected? PLANT GROWTH
what is the cause of the plant growth? WATER

In the example experimental question, “How does water affect plant growth?,” the independent variable and dependent variable are too general.

Yes! There is one independent variable which is water, but —
1. What is the source or kind of water? Tap water, distilled water, ocean water, lake water, etc….
2. How much water?
3. What is the temperature of the water?

Yes! There is one dependent variable which is plant growth, but—
1. What kind of plant? A specific type of tree, shrub, houseplant, seedling–etc..
2. What kind of plant growth? Increase in leaves, increase in height of the plant, etc…

A good testable experimental question that identifies one specific independent variable and one specific dependent variable might be:

How does the amount of tap water affect the height of pinto bean seedlings?

The question points out one specific cause–AMOUNT OF TAP WATER–and what it will be affecting–height of pinto bean seedlings?

More About Experimental Science Project Questions


The direction of the plant's leaves depends on the direction of the Sun. Sunlight is the cause—independent variable—and a change in the direction of the leaves is the response—dependent variable.

Tropism is any type of cause-effect plant movement. Phototropism is plant movement toward a light. The light is the cause-independent variable--and the plant movement is the effect--dependent variable.

New Science Terms




The question, “How do plants grow toward a light?,” is not an experimental question that could easily be determined. How this happens occurs inside the plant resulting in the stems bending toward the light and it is not something you could easily discover by experimenting. While the question does identify an effect–plants growing toward a light, the question does not identify a cause nor does it identify the type of plant or light source.

You could discover how different things (called variables) affect the plant’s growth toward light. In other words, the growth of the plant toward the light DEPENDS ON what variables?

Examples of variables that might CAUSE a plant’s growth toward light include,  sources of  light-sun, lamp, etc.., color of the light, distance of the plant from the light, direct or indirect light– barriers, etc….

Things that MIGHT CAUSE  a plant to grow toward light = INDEPENDENT VARIABLES

Plant growth toward light is the effect= DEPENDENT VARIABLE

Following are examples of experimental science project questions:

1. What affect does the amount of sunlight have on the rate pinto bean seedlings grow toward the light?

2. How does the color of artificial light effect the rate pinto bean seedlings grow toward the light?


46870: Plant Science Experiments-photosynthesis, tropism, variables, independent variable, dependent variable Plant Project Ideas: Mind-Boggling Experiments You Can Turn Into Science Fair Projects