Flashcards · Biology · Respiration
Core Practical: Investigating the Rate of Respiration
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What does a respirometer measure?
The rate of respiration, by the oxygen consumed by living organisms.
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What is the job of the soda lime?
It absorbs the carbon dioxide made by the organisms.
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Why does the drop of coloured liquid move towards the tube?
Oxygen is used and the carbon dioxide is absorbed, so the volume and pressure of the gas fall.
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What is the purpose of the cotton wool?
It keeps the organisms away from the soda lime.
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What is the purpose of the water bath?
It keeps the tube at a steady chosen temperature.
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Name two types of organism that can be used in a respirometer.
Germinating seeds and small invertebrates, such as woodlice or maggots.
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Why are dry seeds not used?
They respire very slowly, so the drop would hardly move.
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What is the independent variable in the temperature practical?
The temperature of the water bath.
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What is the dependent variable?
The distance moved by the drop in a set time.
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Name three variables that must be controlled.
Mass of organisms, volume of the apparatus, time, mass of soda lime, width of capillary tube.
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What is in the control tube?
Glass beads, or boiled and cooled seeds, instead of living organisms.
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Why leave the tubes in the water bath before starting?
So the gas inside reaches the temperature of the water, which stops it changing volume and moving the drop.
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How do you calculate the rate?
The distance moved divided by the time taken.
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What is the formula for the volume moved along the capillary tube?
Volume = \(\pi r^2 h\), where r is the radius of the tube and h is the distance moved.
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Why does the rate fall at a very high temperature?
The enzymes that control respiration are denatured.
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What should you do with an anomalous result?
Repeat it, and leave it out of the mean.
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Why is soda lime dangerous?
It is corrosive, so wear eye protection and gloves.
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How should small animals be treated in the practical?
Handled gently, kept in the tube for a short time and returned unharmed.
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Name the labelled parts of the respirometer and say what each one does. 
Soda lime absorbs carbon dioxide. Cotton wool keeps the seeds away from the soda lime. The seeds respire and use oxygen. The bung seals the tube. The coloured drop in the capillary tube moves as the volume of gas falls, and the ruler measures the distance. The water bath and thermometer keep the temperature steady.
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Describe and explain the pattern in these results. The distance moved, and so the rate of respiration, increases as the temperature rises from 10 to 40 degrees, because the enzymes work faster. At 50 degrees it falls because the enzymes are denatured.