Investigating the rate of respiration

In a nutshell

There are several factors that can impact the rate of respiration. By using a respirometer, you will be able to investigate the effect of temperature on the rate of aerobic respiration in small organisms.

Equations

The first equation is the word and symbol equation for respiration. The second equation is the formula used to calculate the volume of oxygen taken in by the insect. The rate of respiration is calculated from the volume of oxygen.

WORD EQUATION	SYMBOL equation
$glucose + oxygen \rightarrow carbon\space dioxide + water$	$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O$
$volume\space of\space oxygen = \pi \times (radius \space of \space the \space manometer)^2 \times (distance\space moved \space by \space the \space coloured \space liquid)$	$V = \pi r^2 h$
$rate\space of \space respiration = {volume \space of \space oxygen \over time}$	$R = {V\over t}$

Variable definitions

QUANTITY NAME	symbol	UNIT NAME	UNIT
$volume \space of \space oxygen$	$V$	$cubic \space centimetre$	$cm^3$
$radius \space of \space the \space manometer$	$r$	$centimetre$	$cm$
$distance \space moved \space by \space the \space coloured \space liquid$	$h$	$centimetre$	$cm$
$rate \space of \space respiration$	$R$	$volume \space per \space minute$	$cm^3/min$
$time$	$t$	$minute$	$min$

Equipment list

The following equipment list can be used to conduct an experiment to evaluate the effect of temperature on the rate of respiration.

EQUIPMENT	USE
Test tubes	To hold the soda lime granules, cotton wool, woodlice and glass beads.
Water bath	To control the temperature of the apparatus.
Soda lime granules	To absorb the $CO_2$ produced by the respiring woodlice.
Cotton wool	To ensure the woodlice do not come into contact with the soda lime.
Live woodlice	To act as the test for this investigation.
Glass beads	To act as the control for this investigation.
Respirometer: manometer, calibrated scale, syringe	To measure the rate of respiration.
Stopwatch	To ensure the same set period of time for each experiment.
Thermometer	To measure the temperature of the water bath.

Experiment 1: Investigating the rate of respiration in living organisms

Experimental variables

The independent variable is the one you change. The dependent variable is the one which depends on what has been changed, therefore it is the one that is measured. The control variable is one which has been kept constant.

Independent variable	$The\ temperature\ of\ the\ water\ bath.$
Dependent variable	$The\ distance\ moved\ by\ the\ coloured\ liquid\ in\ the\ manometer.$
Control variable	$The\ set\ time\ period\ before\ measuring\ the\ distance\ travelled\ by\newline the\ liquid\ in\ the\ manometer.$

Safety precautions

When carrying out experiments, it is very important to consider safety precautions. This is so you and others do not get hurt.

HAZARD	RISK	SAFETY MEASURE
Soda lime	Soda lime is corrosive and can damage the eyes and skin.	Make sure to wear safety goggles and gloves when handling soda lime.

Method

This is your instructions on how to complete the experiment.

Biology; Biology practicals; KS4 Year 10; Investigating the rate of respiration — A. Control tube, 1. Glass beads, 2. Soda lime granules, 3. Closed tap, 4. Manometer filled with coloured liquid, 5. Syringe, 6. Water bath, B. Test tube, 7. Woodlice, 8. Soda lime granules.

1.	Add the granules of soda lime into two separate test tubes. Place a ball of cotton wool above the soda lime.
2.	To the first tube, place woodlice on top of the cotton wool. To the second test tube, place glass beads with the same mass as the woodlice. Tip: Ensure that the woodlice do not come into contact with the soda lime.
3.	Set up the respirometer as illustrated in the diagram above.
4.	Using the syringe, set the fluid in the manometer to a specific level. Then leave the apparatus in the water bath for a set period of time. Note: Set the water bath to $15\ \degree C$ .
5.	You will begin to notice a decrease in the volume of air in the test tube with the woodlice. This to due the woodlice using up the oxygen inside the tube for respiration. This decrease in volume causes a reduction in the pressure inside the tube, resulting in the coloured liquid in the manometer to move towards the tube containing the woodlice.
6.	After waiting for the set period of time, measure the distance moved by the coloured liquid in the manometer. Record this value in a table.
7.	Repeat steps 1-5. This time, set the water bath to higher temperatures (e.g., $20\ \degree C$ and $25\ \degree C$ ), in order to investigate how changing the temperature can affect the respiration rate.

Analysis

This is how you can use your data to be able to form conclusions.

1.	You will now have a table with a list of temperatures and the distance moved by the coloured liquid in the manometer.
2.	For each temperature, calculate the volume of oxygen taken in by the woodlice per minute. $V = \pi r^2 h$
3.	For each volume of oxygen, calculate the rate of respiration. $R = {V\over t}$
4.	You should then plot the rate of respiration and temperature onto a graph. The rate of respiration should be on the $y$ -axis as it is based on the dependent variable. The temperature should be on the $x$ -axis as it is the independent variable. Draw a line through the points on the graph.

Conclusion

Your graph should show that as the temperature increases, the rate of respiration also increases until an optimum temperature is reached, after which it decreases. This is because molecules tend to have more energy and move around more at higher temperatures, therefore more chemicals reactions are likely to happen. However, temperatures above the optimum temperature can damage the structure of the enzymes and cause them to become denatured. As a result, chemical reactions will no longer occur and respiration will stop.

Biology; Biology practicals; KS4 Year 10; Investigating the rate of respiration

Evaluation

Once you have completed your experiment, it will be important to consider the quality of your data and how accurate your results are. Identify potential sources of random or systematic error and suggest possible improvements and further investigations. Furthermore, when using live organisms in biological experiments, it is important to take care to avoid harming them. Think about the safety and ethical concerns that may arise when using organisms such as woodlice.