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Plan an Investigation: Can Stimulants Affect Reaction Times?

In this worksheet, students will look at how to write a hypothesis and consider different variables when planning a scientific investigation on how stimulants can affect reaction times.

'Plan an Investigation: Can Stimulants Affect Reaction Times?' worksheet

Key stage:  KS 3

Year:  Year 8 Science worksheets

Curriculum topic:   Biology: Structure and Function of Living Organisms

Curriculum subtopic:   Health

Difficulty level:  

Worksheet Overview

Did you know that it takes approximately 0.1 seconds to blink our eyes?


Image of an eye


It happens so quickly that we don't even think about it! It's because we don't think about it we call it a reflex. Reflexes are involuntary, so we have no control over them. So when dust hits our eye, we automatically blink, we don't control this.


Reaction times are similar to reflexes except we can control them. Our reaction time refers to how quickly we respond to something, for example how quickly we might catch a ball. 


Reaction times can be improved over time with practice. For example, a sprinter responds quickly to the starting pistol when racing. Athletes train to increase their reaction time to help them to win a race.


Stimulants can also improve our reaction times. Stimulants are any drug that speeds up messages to the brain and nerves, which means when we take them, we react faster. This is why athletes normally have to do a drugs test before they're allowed to compete, to make sure that nobody has taken a drug that would give them an unfair advantage over other athletes.There are special rules athletes have to follow -  if certain chemicals are found in their blood during a test, they could be banned from competing in their sport.


Image of medicines


Examples of stimulants are caffeine (found in coffee, tea and fizzy drinks) which is legal. Then there's cocaine, ecstasy and amphetamines, which are all illegal. 


Image of alcohol, coffee and cigarette


Some drugs can slow down our reaction times. These are called depressants. These chemicals slow down the messages to the brain and nerves. Some examples include alcohol, cannabis, solvents (such as aerosols and glue) and heroin. 


So how do scientists know that stimulants make you react faster?  They conducted experiments! Doing experiments allows us to answer questions.


Let's consider the statement: 


Stimulants affect human reaction time.


When investigating something, we need to form a hypothesis, which is the scientific term for an idea about how something works or how it changes. You have to do experiments to see if your hypothesis (idea) is correct.


Our hypothesis might be that 'caffeine will speed up reaction times because caffeine is a stimulant and speeds up messages in our nervous system.'  We then test this idea using experiments.


Cola has caffeine in it, so we can use it to see if it has an effect on reaction time. The stimulant is the factor we are investigating - this is known as the independent variable.


Image of a cola can


There are many ways to measure reaction times and one of these is using a ruler. This experiment involves measuring the time it takes to catch a ruler (the reaction time) before and after drinking a caffeine drink, like cola. This is known as the dependent variable.


Image of reaction time experiment


Control variables are things we control so that they don't interfere with our experiments. For example, if one student drinks half a glass of cola and another student has a whole glass, this could affect the results, as the amount of caffeine taken will be different. 


Other control variables might be the length of the ruler, where the the ruler is dropped from, the person doing the catching or where the person catching the ruler places their hand.


In this activity, we will plan an investigation to find out if stimulants speed up reaction times.


Let's get started!


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