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Maharashtra State BoardSSC (Marathi Semi-English) 9th Standard [इयत्ता ९ वी]
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Syllabus

Useful Microorganisms - Yeast

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Topics

  • Introduction
  • Role of Yeast in Fermentation and Its Applications
  • Experiment
  • Bio-remediation

Introduction:

Yeast is a unicellular fungus that reproduces asexually through a process called budding. It is a heterotrophic microorganism, meaning it relies on external carbon compounds for nutrition. Yeast belongs to the eukaryotic group of cells and includes over 1500 species. During fermentation, yeast converts carbohydrates, such as sugars, into alcohol and carbon dioxide. This process allows yeast to grow and multiply rapidly in a sugar-rich environment. Yeast plays a significant role in various industries, including baking, brewing, and winemaking, due to its ability to carry out fermentation efficiently.

Role of Yeast in Fermentation and Its Applications:

  1. Bread is made by using a yeast solution prepared through fermentation, where yeast converts carbohydrates into carbon dioxide and alcohol. The dough rises because the carbon dioxide produced by yeast during fermentation forms bubbles, creating air pockets in the dough. When the dough is baked, the trapped carbon dioxide expands, making the bread spongy and soft.
  2. In sugar factories, molasses, a carbohydrate-rich byproduct of sugarcane juice, is fermented with Saccharomyces yeast to produce ethanol as the primary product. Ethanol (C₂H₅OH) is used in various industries as a base for spirits and other alcohols and also serves as a smokeless, high-quality fuel. Besides molasses, grains like maize, barley, and other carbohydrate-rich materials are used for industrial ethanol production.
  3. Sugars like glucose and fructose in grape juice are fermented with yeast to produce alcohol, which is further used in the production of wines. The fermentation process not only produces alcohol but also esters and secondary alcohols, enhancing the flavour and quality of the final products.

Experiment

1. Aim:

To observe fermentation by yeast and identify yeast cells and budding under a compound microscope.

2. Requirements

Active dry yeast, sugar, lukewarm water, transparent balloon, bottle, limewater, glass slide, coverslip, and compound microscope.

3. Procedure

  • Mix one spoonful of dry yeast and two spoonfuls of sugar with lukewarm water in a bottle.
  • Attach a transparent balloon to the mouth of the bottle. Observe the balloon after 10 minutes; it inflates as gas accumulates inside.
  • Add limewater to the gas in the balloon, collect it in a beaker, and observe. The limewater turns milky, indicating the presence of carbon dioxide.
  • Take a drop of the solution from the bottle on a glass slide, place a coverslip, and observe under a microscope.
  • Identify colourless, oval yeast cells, some showing budding with small round bodies (daughter cells).

Yeast Cells

4. Conclusion

The balloon inflates as the yeast ferments the sugar, releasing carbon dioxide. The presence of carbon dioxide is confirmed by limewater turning milky. Under the microscope, yeast cells and budding (asexual reproduction) are visible. This experiment demonstrates yeast's role in fermentation and its reproduction process.

Bio-remediation:

  1. Yarrowia lipolytica is a type of yeast used in bioremediation to absorb toxins released during the production of palm oil and heavy metals from industrial processes.
  2. Saccharomyces cerevisiae, commonly known as baker’s yeast, is used to absorb the pollutant arsenic, helping to clean contaminated environments.
  3. Alcanivorax bacteria are employed to clean up oil spills in oceans by breaking down and consuming the hydrocarbons present in the spilled oil.
  4. Candida utilis is utilized in waste treatment to digest organic waste and reduce pollution in wastewater systems.
  5. Pichia pastoris is known for its ability to degrade phenolic compounds, it is used in the treatment of industrial effluents.
  6. Rhodotorula yeast absorbs heavy metals like cadmium, lead, and mercury, making it useful for detoxifying polluted water.

These microorganisms play a critical role in reducing pollution and restoring environmental balance through the process of bioremediation.

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