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The Invisible Living World: Beyond Our Naked Eye - Microorganisms and food

Grade 8CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Microorganisms are classified into four major groups: Bacteria, Fungi, Protozoa, and some Algae. Viruses are also considered microscopic but reproduce only inside the cells of a host organism.

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Friendly Microorganisms: Lactobacillus promotes the formation of curd. Yeast is used in the baking industry for making bread and cakes because it produces CO2CO_{2} during respiration, causing the dough to rise.

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Fermentation: The process of conversion of sugar into alcohol by the action of yeast. This was discovered by Louis Pasteur in 18571857.

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Medicinal use: Antibiotics are medicines produced from microorganisms (like bacteria and fungi) to kill or stop the growth of disease-causing microbes. Examples include Penicillin and Streptomycin.

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Food Preservation: Methods like chemical preservation (using Sodium benzoate), salting, sugar (reduces moisture), and heat/cold treatments (Pasteurization).

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Pasteurization: Heating milk to about 70∘C70^{\circ}C for 1515 to 3030 seconds and then suddenly chilling it to prevent the growth of microbes.

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Nitrogen Fixation: Certain bacteria like Rhizobium (found in root nodules of leguminous plants) and blue-green algae fix atmospheric nitrogen (N2N_{2}) into nitrogenous compounds to increase soil fertility.

📐Formulae

Sugar→YeastAlcohol+CO2\text{Sugar} \xrightarrow{\text{Yeast}} \text{Alcohol} + CO_{2}

Pasteurization Condition: T≈70∘C, time (t)=15−30 seconds\text{Pasteurization Condition: } T \approx 70^{\circ}C, \text{ time } (t) = 15 - 30 \text{ seconds}

Atmospheric Nitrogen (N2)→Nitrogen FixationNitrogenous Compounds (e.g., Nitrates)\text{Atmospheric Nitrogen } (N_{2}) \xrightarrow{\text{Nitrogen Fixation}} \text{Nitrogenous Compounds (e.g., Nitrates)}

💡Examples

Problem 1:

During the process of making bread, why does the dough increase in volume?

Solution:

The addition of yeast leads to fermentation. Yeast breathes anaerobically and releases CO2CO_{2} gas. The bubbles of the gas fill the dough and increase its volume.

Explanation:

The chemical reaction involves: Sugar→Ethyl Alcohol+CO2↑\text{Sugar} \rightarrow \text{Ethyl Alcohol} + CO_{2} \uparrow. The trapped carbon dioxide gas bubbles expand, making the bread light and fluffy.

Problem 2:

How does adding common salt help in preserving meat and pickles?

Solution:

Salt draws out moisture from the food through a process called osmosis.

Explanation:

Microorganisms require moisture to grow. By reducing the water content (H2OH_{2}O) and creating a high-salt environment, the growth of bacteria is inhibited, preventing spoilage.

Problem 3:

A baker uses 500 g500\text{ g} of flour and adds yeast. If the dough volume increases by 200%200\%, what is the final volume ratio compared to the initial volume?

Solution:

Initial volume = VV. Increase = 200% of V=2V200\% \text{ of } V = 2V. Final volume = V+2V=3VV + 2V = 3V.

Explanation:

The ratio of final volume to initial volume is 3VV=3:1\frac{3V}{V} = 3:1. This expansion is due to the rapid production of CO2CO_{2} by yeast cells.