Question Video: Describing an Experiment to Measure Reflex Reaction Times | Nagwa Question Video: Describing an Experiment to Measure Reflex Reaction Times | Nagwa

# Question Video: Describing an Experiment to Measure Reflex Reaction Times Biology • Second Year of Secondary School

You are planning an investigation to measure reflex-reaction times. The method is outlined below: 1. Your partner holds out their hand with a gap between their thumb and fingers. 2. Hold the ruler with the 0 cm mark leveled with their thumb. 3. Drop the ruler. 4. Record the distance shown on the ruler where your partner catches it. 5. Use a conversion chart to convert distance to reaction time, in seconds. 6. Repeat at different times of day. Which of the following describes a way to make this study more accurate and reliable? [A] Changing the person dropping the ruler each time [B] Changing the person catching the ruler each time [C] Using a different ruler every time so the reaction time with different rulers can be measured [D] Repeating the study three times and determining the median reaction time [E] Repeating the study three times and calculating the mean reaction time for each time of day.

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### Video Transcript

You are planning an investigation to measure reflex reaction times. The method is outlined below. (1) Your partner holds out their hand with a gap between their thumb and fingers. (2) Hold the ruler with the naught centimeter mark leveled with their thumb. (3) Drop the ruler. (4) Record the distance shown on the ruler where your partner catches it. (5) Use a conversion chart to convert distance to reaction time in seconds. (6) Repeat at different times of the day. Which of the following describes a way to make this study more accurate and reliable? (A) Changing the person dropping the ruler each time. (B) Changing the person catching the ruler each time. (C) Using a different ruler every time so the reaction time with different rulers can be measured. (D) Repeating the study three times and determining the median reaction time. Or (E) repeating the study three times and calculating the mean reaction time for each time of day.

This question is asking about measuring reflex reaction times. To be able to understand what is being measured here and so decide on the most accurate and reliable way of carrying out the study, let’s start by reviewing some key facts about reflexes. We’ll remove the answer choices for now so there is enough room for the explanations.

A reflex is a response to a stimulus that occurs without the need for conscious thought. A stimulus is a change in the environment, such as the light getting brighter. And a response is a change in the body that occurs as a reaction to a stimulus, such as narrowing of the pupil in the eye. The main reason for us having reflexes is to protect our body from injury. Seeming as they are automatic, our bodies can react to potentially harmful stimuli without thinking about them, saving us precious moments.

But how do reflexes work? The reflex arc is a pathway that the nervous impulse follows to carry the information to the effector, the muscle or gland, which is going to carry out the response. The stimulus, the change in environment, is detected by a receptor, which triggers the nervous impulse. This impulse passes down the sensory neuron to the central nervous system. Here, it passes the impulse onto the relay neuron, which then passes the impulse onto the motor neuron. The motor neuron finally triggers the effector to carry out the response.

If we look at the experiment described in the question, the stimulus is the dropping of the ruler, the receptors are cells in the retina of the eye, and the response is catching the ruler. So the faster the person’s reflex reaction, the shorter the distance the ruler falls through the hand of the catcher. To make the study more accurate, we need to make the experimental method as similar as possible each time results are collected. Only one thing should be changed at a time. This is the independent variable, and here it is time of day. This means that option (A), changing the person who drops the ruler; option (B), changing the person catching the ruler; and option (C), using a different ruler every time, are not the correct answers.

This leaves us with options (D) and (E), so let’s now look at these more closely. They both talk about repeating the study and do not mention that anything in the method has changed except for time of day. So this means they will both be more accurate than (A), (B), and (C). But what about reliability? Reliability refers to the consistency of results. Therefore, the more times you repeat the experiment, the more reliable it is, because anomalous results, ones that do not fit in with the overall pattern, can be spotted and removed and an average can be taken.

There are three types of average: mean, median, and mode. Two of these have been mentioned in the question, so which one is the best to use for reliability? The median is the center of a set of data. If you wrote all the results out in order, it would be the middle number. The mean is calculated by adding all the results up and dividing by the number of results. Unlike the mean, the median does not rely on all the results, so the mean gives us a better overall reliable idea of the result for that person. Therefore, the correct answer is (E). The best way to make this study more accurate and reliable is repeating the study three times and calculating the mean reaction time for each time of day.

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