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The Invisible Living World: Beyond Our Naked Eye - How Are We Connected to Microbes?

Grade 8CBSE

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

🔑Concepts

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Microorganisms are tiny organisms that cannot be seen with the naked eye and are measured in micrometers (μm\mu\text{m}). 1 μm=10−6 m1\ \mu\text{m} = 10^{-6}\ \text{m}.

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Classification: Microbes are classified into four major groups: Bacteria, Fungi, Protozoa, and Algae. Viruses are also considered microscopic but reproduce only inside the host organism.

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Fermentation: The process of conversion of sugar into alcohol by yeast. The chemical representation is C6H12O6→Yeast2C2H5OH+2CO2+EnergyC_6H_{12}O_6 \xrightarrow{\text{Yeast}} 2C_2H_5OH + 2CO_2 + \text{Energy}.

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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 usable nitrates.

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Pathogens: Disease-causing microorganisms. They can be transmitted through air, water, food, or physical contact (e.g., Tuberculosis is caused by bacteria, Malaria by the protozoan Plasmodium).

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Food Preservation: Methods like pasteurization involve heating milk to about 70∘C70^\circ\text{C} for 1515 to 3030 seconds and then suddenly chilling it to prevent the growth of microbes.

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Vaccines: These consist of dead or weakened microbes introduced into the body to produce antibodies, which provide immunity against specific diseases.

📐Formulae

Magnification(M)=Size of ImageSize of Object\text{Magnification} (M) = \frac{\text{Size of Image}}{\text{Size of Object}}

1 mm=1000 μm1\text{ mm} = 1000\ \mu\text{m}

1 μm=1000 nm1\ \mu\text{m} = 1000\ \text{nm}

C6H12O6→yeast/anaerobic2C2H5OH+2CO2C_6H_{12}O_6 \xrightarrow{\text{yeast/anaerobic}} 2C_2H_5OH + 2CO_2

💡Examples

Problem 1:

If a bacterium has an actual length of 2 μm2\ \mu\text{m} and it appears to be 4 mm4\text{ mm} long under a microscope, calculate the magnification of the lens.

Solution:

M=4 mm2 μm=4000 μm2 μm=2000M = \frac{4\text{ mm}}{2\ \mu\text{m}} = \frac{4000\ \mu\text{m}}{2\ \mu\text{m}} = 2000

Explanation:

First, convert both values to the same unit. Since 1 mm=1000 μm1\text{ mm} = 1000\ \mu\text{m}, then 4 mm=4000 μm4\text{ mm} = 4000\ \mu\text{m}. Dividing the image size by the actual size gives a magnification of 2000x2000x.

Problem 2:

A scientist is comparing the sizes of two microbes. Microbe A is 80,000,000 nm80,000,000\ \text{nm} and Microbe B is 34,567,892 nm34,567,892\ \text{nm}. Calculate the difference in their sizes in nanometers.

Solution:

80000000−3456789245432108\begin{array}{r} 80000000 \\ -34567892 \\ \hline 45432108 \end{array}

Explanation:

To find the difference, we subtract the size of Microbe B from Microbe A. The result is 45,432,108 nm45,432,108\ \text{nm}.

Problem 3:

How many molecules of Carbon Dioxide (CO2CO_2) are produced if 55 molecules of glucose (C6H12O6C_6H_{12}O_6) undergo complete fermentation by yeast?

Solution:

5×2=10 molecules of CO25 \times 2 = 10\ \text{molecules of } CO_2

Explanation:

According to the fermentation equation, 11 molecule of glucose produces 22 molecules of CO2CO_2. Therefore, 55 molecules of glucose will produce 5×2=105 \times 2 = 10 molecules of CO2CO_2.

How Are We Connected to Microbes? Class 8 Notes & Examples