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The Invisible Living World: Beyond Our Naked Eye - What Are Microorganisms?

Grade 8CBSE

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

🔑Concepts

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Microorganisms are living organisms that are too small to be seen with the naked eye, typically measured in micrometers (1μm=10−6m1 \mu m = 10^{-6} m).

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They are classified into four major groups: Bacteria, Fungi, Protozoa, and some Algae. Viruses are also microscopic but are considered borderline living as they reproduce only inside a host cell.

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Fermentation is the process of conversion of sugar into alcohol by yeast, releasing carbon dioxide (CO2CO_2).

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Medicinal use: Antibiotics are medicines produced from bacteria and fungi to kill or stop the growth of disease-causing microorganisms (e.g., Penicillin).

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Biological Nitrogen Fixation: Certain bacteria like RhizobiumRhizobium and blue-green algae can fix atmospheric nitrogen (N2N_2) into usable nitrogenous compounds for plants.

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Pasteurization: A process of heating milk to about 70∘C70^\circ C for 1515 to 3030 seconds and then suddenly chilling it to kill microbes.

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Pathogens: Microorganisms that cause diseases in humans, plants, and animals. Carriers like houseflies or the female AnophelesAnopheles mosquito transfer these pathogens.

📐Formulae

Sugar→YeastAlcohol+CO2\text{Sugar} \xrightarrow{\text{Yeast}} \text{Alcohol} + CO_2

Total Magnification=Magnification of Eyepiece×Magnification of Objective\text{Total Magnification} = \text{Magnification of Eyepiece} \times \text{Magnification of Objective}

Nitrogen Fixation: N2→Nitrates/Nitrites\text{Nitrogen Fixation: } N_2 \rightarrow \text{Nitrates/Nitrites}

💡Examples

Problem 1:

A student uses a compound microscope to observe a slide of AmoebaAmoeba. If the eyepiece magnification is 10x10x and the objective lens magnification is 45x45x, calculate the total magnification.

Solution:

10×45=450x10 \times 45 = 450x

Explanation:

The total magnification of a microscope is the product of the power of the eyepiece and the objective lens. Using vertical multiplication: 45×10450\begin{array}{r} 45 \\ \times 10 \\ \hline 450 \end{array}

Problem 2:

In the process of pasteurization, milk is heated from a room temperature of 25∘C25^\circ C to a target temperature of 70∘C70^\circ C. What is the temperature increase required?

Solution:

70∘C−25∘C=45∘C70^\circ C - 25^\circ C = 45^\circ C

Explanation:

To find the temperature difference, we subtract the initial temperature from the final temperature: 70−2545\begin{array}{r} 70 \\ - 25 \\ \hline 45 \end{array}

Problem 3:

Identify the gas released when yeast is added to a sugar solution during fermentation.

Solution:

Carbon Dioxide (CO2CO_2)

Explanation:

Yeast breaks down sugar (glucose) in the absence of oxygen to produce ethanol and carbon dioxide gas. The chemical representation is: C6H12O6→2C2H5OH+2CO2↑\text{C}_6\text{H}_{12}\text{O}_6 \rightarrow 2\text{C}_2\text{H}_5\text{OH} + 2CO_2 \uparrow