Glycolysis is the first stage of respiration, it occurs when one molecule of glucose is split into two smaller molecules of pyruvate. It takes place in the cytoplasm of the cell and also its anaerobic so it does not need oxygen to take place. It occurs in two stages known as Phosphorylation and Oxidation.
In the first stage glucose is phosphorylated by adding two phosphates from two molecules of ATP to give a hexose phosphate. This is split through hydrolysis (the splitting of a molecule using water) and then two molecules of triose phosphate and two molecules of ADP are created. Then the triose phosphates are oxidised which means they lose hydrogen and form two molecules of pyruvate. Coenzyme NAD+ collects the hydrogen ions and forms NADH+ H+. Overall four molecules of ATP are produced but two were used up at the beginning so there’s a net gain of 2 ATP.
Also the different sugar concentrations which are available have different properties such as Monosaccharide’s combine by a condensation reaction, glucose and fructose are monosaccharide’s as they both have a single sugar molecule :-
Both glucose and fructose are hexose sugars C6H1206. However Sucrose is a disaccharide because it’s made from two monosaccharide sugar molecules stuck together. Sucrose is made from glucose + fructose which are the main sugar which is transported around plants in the phloem. Disaccharides are when glycosidic bonds join sugars together. Hydrolysis is the reverse, this is the reverse when a water molecule reacts with the glycosidic bond and breaks it apart. Also Starch maybe used this is a polysaccharide which is made up of lots of sugar molecules stuck together. Starch is made up of two other polysaccharides of alpha-glucose; it’s made up of amylose which is a long unbranched chain of alpha-glucose, it’s very compact and its coiled structure makes it good for storage. Amylopectin is a long branched chain of alpha-glucose; it has many side branches which makes it good for storage.
However, respiration of yeast can also take place anaerobically. This process does not require oxygen. This process breaks down carbohydrates and it gains a small amount of energy in the form of ATP. Pyruvic acid is broken down in respiration when formed by breaking down of glucose molecules; this can't be done in the same way as in aerobic respiration. When anaerobic respiration is taking place carbon dioxide and ethanol is formed. The reaction for this process is:
C6H12O6 → 2C2H5OH + 2CO2 + ATP
Enzymes are biological catalysts they catalyse every metabolic reaction in the bodies of living organisms, they are all globular proteins. A catalyst is a substance that speeds up a chemical reaction without being used up in the reaction itself.
In a chemical reaction a certain amount of energy needs to be supplied in order for the reaction to take place this called the activation energy, enzymes lower the activation energy required for the reaction to take place.
Prediction
I predict that as I increase the concentration of glucose the rate of reaction will increase therefore the fermentation of yeast will increase. This is because the glucose acts as the substrate concentration which is binding to the enzyme zymase which is in the yeast. There will be a increase in the speed of the reaction as the glucose (substrate) is added this is because substrate concentration affects the rate of reaction up to a certain point. The higher the substrate concentration the faster the reaction but only to a certain point as there will be too many substrate molecules and there will be no difference.
Also I predict that glucose and fructose will have the fastest rate of reaction upon the fermentation of the yeast this is because glucose and fructose are both monosaccharide’s and the others have more than one sugar molecule therefore they will take longer because they have to undergo hydrolysis and then start there reaction also the higher the temperature the faster the rate of reaction, this is due to the kinetic energy as the enzymes are more likely to collide with the substrate and fill the active site.
Equipment List
- 6 boiling tubes – used to carry out the experiment.
- Thermometer - accurate to 0.1ºC. I will use the same thermometer each time so my results are fair.
- 6 Syringe – this will be used to measure accurate amounts of the sugar concentrations used in the experiment.
- Pen – this will be used to record the results
- 1M solution of glucose – used to carry out the experiment and how long it takes for yeast to respire.
- Stopwatch – needs to be very accurate as this will calculate how long it takes for the reaction to take place.
- Large bowl – this will be half full of water
- Burette – used to calculate the amount of Carbon Dioxide given off.
- Rubber bung – used to stop the Carbon Dioxide escaping from the boiling tube into the atmosphere.
- Rubber tubing – used to link the boiling tube to the burette.
- Water bath – used to keep the temperature constantly at 40 degrees.
- 5 beakers – used to hold the different sugar concentrations in.
- Yeast – used in the experiment to react with glucose for the reaction to take place.
- Boiling tube rack – used to hold all the boiling tubes.
- Spatula – used to move the yeast around.
- Clamp – to hold the burette upside down.
- Large beaker – to hold yeast suspension in.
Safety
During the experiment standard lab safety procedures must be carried out i.e. no bags left on the floor, no running and lab coats must be worn. Make sure that all electrical equipment is away from any water e.g. the water bath. Don’t carry water across the room because if you spill it, it could be hazardous and could cause an accident.
Method
- Collect all the above equipment.
- Turn the water bath on and set it to 40 degrees. Make sure you are working in a clean and tidy place with no distractions.
- Set all the boiling tubes into the rack and get one of the boiling tubes and using a syringe accurately measure 5ml of glucose.
- Using the clamp set it up above the bowl of water and attach the burette tightly so it does not become unattached. Invert the burette into the bowl about half way down so it gets filled with water to the top.
- Fill the burette up with water past the marking so there is enough water in there also fills the large bowl with water and turn the burette very carefully and quickly upside down.
- Poor the measured glucose out of the beaker into a boiling tube and measure out exactly the right amount of yeast and add it to the boiling tube.
- Make sure the temperature of the water bath is at 40 degrees so it’s a fair experiment then add the rubber bung to the top of the boiling tube.
- Using the rubber tubing allow it to run from the top of the rubber bung down into the large bowl of water and through a tight gap of the burette.
- Start the stopwatch as soon as you add the rubber bung and both mixtures are getting mixed.
- Record how long it takes until no more Carbon Dioxide is released and the level of water stops and doesn’t get reduced any more.
- For each different sugar Concentration follow out Steps 1 – 10.
Variables
- Concentration of Solution - this must be kept the same as altering this will increase or decrease the rate of reaction and therefore won’t give an accurate reading.
- The temperature must be kept the same at all times as altering this means there will be more or less kinetic energy which means the rate of reaction can be affected.
- Also there must be the same amount of yeast used in each individual boiling tube as more yeast will slow the reaction down and will respire more slowly.
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Change of pH may result in a change in the bonds of the enzyme. The active site will be disrupted and the enzyme will be denatured.
- Also when you shake the boiling tube u might shake it more for one and less for the other therefore it will interfere how fast the rate of reaction will occur.
By Mohammed Nabeel
