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10.7 Required Practicals: The Human Nervous System

GCSE Biology · AQA · Chapter 10: The Human Nervous System

A free GCSE Biology lesson for AQA (8461) from OBA School: required practical 7: planning and carrying out an investigation into the effect of a factor on human reaction time. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

  • Plan a valid investigation into a factor affecting reaction time
  • Identify independent, dependent and control variables, and deal with ethical issues
  • Convert ruler-drop distances to reaction times and calculate means
  • Evaluate the method and suggest improvements

Key words

  • Reaction time: The time between a stimulus and a person responding to it.
  • Hypothesis: A testable idea, e.g. “caffeine reduces reaction time”.
  • Valid: The results answer the question asked, because other variables were controlled.
  • Resolution: The smallest change a measuring instrument can show, e.g. 1 mm on a ruler.
  • Ethics: Making sure the investigation is safe and fair for the people taking part, with their consent.

Aim, hypothesis and variables

Aim: to find out how one factor affects reaction time. Reaction time involves the conscious brain (unlike a reflex): the eyes detect the falling ruler, the brain decides, and impulses go to the hand muscles.

Factors you could test: practice, dominant vs non-dominant hand, caffeine (e.g. cola or coffee), distraction (music, talking), tiredness, time of day, type of stimulus (sight vs sound).

  • Independent; Example: dominant vs non-dominant hand Hand used to catch the ruler
  • Dependent; Example: dominant vs non-dominant hand Reaction time (from the distance the ruler falls)
  • Control; Example: dominant vs non-dominant hand Same person dropping and catching; same ruler; same starting position; same gap between finger and thumb; no warning before the drop; same time of day; no caffeine beforehand

Method: the ruler-drop test

  • 1. The person being tested sits with their forearm resting on a table, hand over the edge.
  • 2. A partner holds a 30 cm ruler vertically, with the 0 cm mark level with the top of the thumb. The thumb and finger are about 2 cm apart, not touching the ruler.
  • 3. Without warning, the partner drops the ruler. The person catches it as fast as possible.
  • 4. Read the distance at the top of the thumb, to the nearest 0.5 cm.
  • 5. Repeat at least 5 times, then repeat with the other condition (e.g. the other hand).
  • 6. Convert each distance to a time using a conversion table or the equation below, and calculate the mean.

Ethics and safety: participants must agree to take part and can stop at any time. If testing caffeine, use a small, safe amount, and do not use anyone who has heart problems, is pregnant or is sensitive to caffeine. Keep results anonymous. Mop up spilled drinks.

Processing results

A falling object speeds up, so time is not proportional to distance. Use a conversion table, or:

Formula: reaction time t = √(2d ÷ g) where d is the distance fallen in metres and g = 9.8 m/s²

  • Time (s); 5 0.101; 10 0.143; 15 0.175; 20 0.202; 25 0.226; 30 0.247

Worked example: dominant vs non-dominant hand

Catch distances (cm). Dominant: 14, 12, 15, 13, 11. Non-dominant: 18, 21, 17, 20, 19.
Means: dominant = 65 ÷ 5 = 13.0 cm; non-dominant = 95 ÷ 5 = 19.0 cm.
Times: t = √(2 × 0.130 ÷ 9.8) = 0.163 s; t = √(2 × 0.190 ÷ 9.8) = 0.197 s.

Answer: Dominant hand mean reaction time 0.163 s; non-dominant 0.197 s

Evaluating the method

  • The person learns to catch better with practice; Improvement Give a few practice drops first, or alternate conditions
  • The person may predict when the ruler will drop; Improvement Vary the time before each drop; no countdown
  • Results vary a lot between people; Improvement Test many people; compare means; use the same person for both conditions
  • Ruler can be read only to about 0.5 cm; Improvement Use a computer reaction-time test (records in ms)
  • Other factors (tiredness, caffeine earlier in the day); Improvement Test at the same time of day; ask participants to avoid caffeine before

Common mistakes

  • Calling reaction time a reflex. Catching a ruler involves the conscious brain, so it is slower than a reflex.
  • Treating distance as proportional to time. Use the conversion table or t = √(2d ÷ g).
  • Forgetting to convert cm to m before using the equation.
  • Drawing a line graph for a categoric independent variable (e.g. which hand). Use a bar chart.

Revision questions

Try these, then check your answers below each one.

Question 1. In a ruler-drop test of the effect of caffeine on reaction time, what is the dependent variable? (Choose from: Amount of caffeine, Reaction time (distance the ruler falls), Length of the ruler, Person dropping the ruler.)

Answer: Reaction time (distance the ruler falls)

Working: You measure the distance the ruler falls, which gives the reaction time.

Question 2. True or false? Giving a countdown before dropping the ruler makes the results more valid.

Answer: False

Working: A countdown lets the person anticipate the drop, so it no longer measures true reaction time.

Question 3. Why should participants have some practice drops before results are recorded? (Choose from: To make the test shorter, To tire them out, To reduce the effect of learning on the results, To warm up the ruler.)

Answer: To reduce the effect of learning on the results

Working: Practice drops reduce the learning effect, so later changes are due to the independent variable.

Related lessons

Continue in the full course

This lesson is section 10.7 (ARPBH1007) of our free GCSE Biology course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Biology course.

 

 

 

 

 

 

 

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