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Objective: To investigate the effect of using different carbon source on the growth of yeast cells.

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NAME: FARAH NADZIRAH ROSLI CLASS: ALM 7 M 13 Title: Using Different Carbon and Source for Growth Objective: To investigate the effect of using different carbon source on the growth of yeast cells. Background summary: Growth depends upon both the type of the nutrients available and their concentration. Cells are largely made up of the four elements: carbon, hydrogen, oxygen and nitrogen with smaller, but significant, quantities of phosphorus and sulphur. Accounting as they do for 90% of the cell's dry mass, all six elements are essential for growth. Hence, like all living organisms, microorganisms require an energy source, a carbon source and a range of nutrients for metabolic and cell growth. Microorganisms are small, easily dispersed and quick to multiply given a suitable environment. They grow on a wide diversity of substrates making them ideal subjects for commercial application. The microorganisms need organic carbon source, such as carbohydrates, as most of them are heterotrophic. Carbohydrates act as a respiratory substrate of cells. Microorganisms also need a nitrogen source for synthesis of DNA, RNA, ATP, coenzymes and chlorophylls. Apart from that, each species has its own optimum conditions within which it grows best. Respiration involves a series of metabolic pathway, which is a series of enzyme-controlled chemical reaction, where the product of one reaction becomes the substrate for the following reaction. It consist of two different type: aerobic respiration and anaerobic respiration. ...read more.


The gas dissolves in water to produce carbonic acid: CO2 + H2O H2CO3 Carbonic acid in water dissociates producing H+ and CO32- ions: H2CO3 2H+ + CO32- H+ ion produced make the solution become acidic. Thus, sodium hydroxide of known concentration is used to neutralise the acid contained in a 25 ml of each sample: H+ + OH- H2O The higher the volume of sodium hydroxide needed to neutralise the solution, the higher the concentration of acid present in the solution. The higher the production of acid by yeast, the faster the rate of respiration. It is essential to note that yeast cells in distilled water produced little CO2 because they do not have a source of sugar. Apart from that, distilled water is also acidic in nature causing it to be able to undergo neutralization by sodium hydroxide. The relative rates of respiration are linked with the growth of the yeast. When the yeasts are able to utilise a certain carbon source very well, it is said to be in a suitable growing condition. The yeast cells will grow faster by multiplying its number over time. The increase number of yeasts results in more respiration to occur in the culture medium. This experiment can be further extended to find the relative growth rate of yeast in different sugars by removing a sample from the culture at regular intervals. ...read more.


It is essential to take a concordance value between the first and second titration for calculating the accurate average titre value. The first and the second titre must not differ from 0.20cm3. To ensure that this is achieve, the titration must be done carefully with the conical flask containing the sample is swirled continuously during the titration. This is to ensure that the sodium hydroxide solution and the acid in the sample react evenly. In this experiment, the other variables are kept constant. For example, the amount of nitrogen, phosphorus and sulphur sources, which are ammonium phosphate and ammonium sulphate, are the same for every sample. The samples are kept in an incubator with the same temperature, at 25�C, for an overnight. Each flask is plugged with cotton wool during the incubation so that no carbon dioxide can escape from the conical flask to the atmosphere. Besides that, the volume and the percentage of the sugar solutions used are the same for sucrose and glucose, as well as the concentration of sodium hydroxide used to titrate the sample. These are to ensure that the effect observed is only caused by the different carbon source. The solutions only have a minimal risk to us but a safety precaution must also be taken. Take care to rinse any yeast spillage from skin in case of possible irritation. Conclusions: The respiration rate of yeasts is faster when glucose is used as the carbon source compared to that of sucrose because yeasts can utilise glucose better than sucrose for respiration. ...read more.

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