IntroductionCatalase is a widespread enzyme, found in nearly all aerobic cells (animals, plants and microbes). It protects the cell from the toxic effects of hydrogen peroxide, generated as a waste by-product of cell metabolism. It does this by catalysing the decomposition of hydrogen peroxide (a powerful and potentially harmful oxidizing agent) into molecular oxygen and water. The reaction can be summarised by the equation:2H 0 2H 0 + 0Different plant materials contain very different amounts of catalase activity and this is what I will be looking at.
Catalase is located in a cell organelle called the peroxisome. Peroxisomes in plant cells are involved in photorespiration (the use of oxygen and production of carbon dioxide) and symbiotic nitrogen fixation (the breaking apart of the nitrogen molecule to reactive nitrogen atoms). Hydrogen peroxide is produced during these chemical processes and must be removed to prevent damage to cellular structures. If hydrogen peroxide is added to tissue containing the enzyme catalyse bubbles are produced, this is evidence of oxygen production and confirms that there was catalyse present.
Catalase has one of the highest turnover rates for all enzymes: one molecule of catalase can convert 6 million molecules of hydrogen peroxide to water and oxygen each minute.
AimsTo investigate the amount of catalyse in varying plant tissuesHypothesisThe more a plant is respiring, the higher the catalyse activity and the more oxygen will be produced.
VariablesThere are many variables, which could affect my results these are:•Temperature- the higher the temperature, the higher the rate of reaction up to a certain point. Whilst the optimum temperature of catalyse is probably higher than room temperature, about 20 degree Celsius, I shall and keep my experiment reacting at room temperature which is about 22 degrees Celsius.
•Surface area-the bigger the surface area the quicker the reaction will occur as the hydrogen peroxide reacts with the catalyse. I shall over come this by cutting all the tissues into 3 mm cubes.
•Time-I will leave the experiment for 5 minutes in order to give enough time for the reaction to occur.
•The concentration of Hydrogen Peroxide-In order to make the experiment a fair test I shall use 10 volume of the hydrogen peroxide.
•Amount of tissue-the amount of tissue will help determine the amount of catalyse that will be present, which in turn will affect the amount of oxygen given off. In order to keep the fair test I will use the same weights (3grams) each time.
SafetyWhen working with the hydrogen peroxide I have to be extremely careful as it can cause burns to skin or clothing as it is a corrosive. I will have to make sure that if I spill any or get any on me I wash it off using plenty of water and if severe seek medical attention. When working with it I shall use eye protection and gloves.
PilotIn order to make sure my equipment and experiment works I am going to trial it.
The tissues I shall use will be:•Apple•Potato•Carrot•TurnipApparatusI will be using:•A 1 cm syringe•Glass delivery tube•Stopwatch•Boiling tube•Clamp•Litre beaker•Inverted barrel of a 20 cm syringe•Chopping board•Knife•Weighing scalesMy method is generally adding hydrogen to different plant tissues which may or may not contain varying amounts of catalyse, I will measure the amount of catalyse present by the amount of oxygen produced. Below you can see a diagram of how it was set up.
Pilot Method1)Prepare all tissues by chopping them up into 1cm³ squares and weighing them out to weigh 3grams. I decided on 3 grams as it wasn't too little to get a reaction and wasn't too much for the hydrogen peroxide to react with....