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Our Home: Earth, a Unique Life Sustaining Planet - Plants, animals, and microorganisms

Grade 8CBSE

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

🔑Concepts

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Earth's uniqueness is defined by the presence of the Biosphere, a narrow zone where lithosphere, hydrosphere, and atmosphere interact to support life. The atmosphere contains approximately 78%78\% Nitrogen, 21%21\% Oxygen, and 0.03%0.03\% Carbon Dioxide.

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Plants act as primary producers through photosynthesis, converting solar energy into chemical energy. The process requires chlorophyll, sunlight, CO2CO_2, and H2OH_2O.

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Microorganisms are classified into five major groups: Bacteria, Fungi, Protozoa, Algae, and Viruses. They play a vital role in decomposition and nutrient cycling, such as the Nitrogen Cycle where N2N_2 gas is converted into nitrates.

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The Nitrogen Cycle involves processes like nitrogen fixation by bacteria such as RhizobiumRhizobium found in the root nodules of leguminous plants, converting atmospheric N2N_2 into usable forms like NO3−NO_3^-.

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Interdependence: Animals (consumers) depend on plants (producers) for oxygen and food, while plants depend on animals for CO2CO_2 and on microorganisms for soil nutrients released through decomposition.

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Microorganisms are used in the production of antibiotics (e.g., Penicillin), curd (using LactobacillusLactobacillus), and alcohol (through fermentation by Yeast).

📐Formulae

6CO2+6H2O→ChlorophyllSunlightC6H12O6+6O26CO_2 + 6H_2O \xrightarrow[Chlorophyll]{Sunlight} C_6H_{12}O_6 + 6O_2

C6H12O6+6O2→6CO2+6H2O+EnergyC_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy}

Magnification=Objective Lens Magnification×Eyepiece Magnification\text{Magnification} = \text{Objective Lens Magnification} \times \text{Eyepiece Magnification}

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

💡Examples

Problem 1:

Calculate the total magnification of a compound microscope used to observe microorganisms if the eyepiece has a power of 10x10x and the objective lens has a power of 45x45x.

Solution:

Total Magnification=10×45=450x\text{Total Magnification} = 10 \times 45 = 450x

Explanation:

The total magnification of a microscope is the product of the magnifying power of the individual lenses used.

Problem 2:

During photosynthesis, if a plant consumes 66 molecules of CO2CO_2 and 66 molecules of H2OH_2O, how many molecules of Oxygen (O2O_2) are released?

Solution:

6CO2+6H2O→C6H12O6+6O26CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2 Therefore, 66 molecules of O2O_2 are released.

Explanation:

According to the balanced chemical equation for photosynthesis, the ratio of Carbon Dioxide consumed to Oxygen produced is 1:11:1.

Problem 3:

A scientist is studying a soil sample and finds that the nitrogen content increased by 1515 units due to RhizobiumRhizobium activity but decreased by 77 units due to denitrifying bacteria. Calculate the net change using vertical arithmetic.

Solution:

15−78\begin{array}{r} 15 \\ -7 \\ \hline 8 \end{array}

Explanation:

The net change in nitrogen is the difference between the nitrogen fixed by beneficial bacteria and the nitrogen released back into the atmosphere by denitrifying bacteria.