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Living Things - Microorganisms and Disease

Grade 5IB

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

🔑Concepts

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Microorganisms are tiny living organisms that are invisible to the naked eye and require a microscope to be seen. Major groups include Bacteria, Viruses, Fungi, and Protists.

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Pathogens are 'germs' or harmful microorganisms that cause infectious diseases. Common examples include the Influenza virus and the bacterium SalmonellaSalmonella.

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Microorganisms require specific conditions to grow and multiply: warmth (optimal temperatures often between 20∘C20^{\circ}C and 40∘C40^{\circ}C), moisture (H2OH_2O), and a food source like glucose (C6H12O6C_6H_{12}O_6).

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Many microorganisms are beneficial. For example, yeast is a fungus used in baking that undergoes fermentation: C6H12O6→2C2H5OH+2CO2C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2. The CO2CO_2 gas causes bread to rise.

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Decomposers are microorganisms that break down dead organic matter, recycling nutrients back into the ecosystem.

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Prevention of disease involves hygiene practices, vaccinations, and food safety techniques like pasteurization, where milk is heated to 72∘C72^{\circ}C to kill harmful bacteria.

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Microorganisms are measured in micrometers (μm\mu m), where 1μm=10−6m1 \mu m = 10^{-6} m.

📐Formulae

C6H12O6→yeast2C2H5OH+2CO2C_6H_{12}O_6 \xrightarrow{\text{yeast}} 2C_2H_5OH + 2CO_2

Magnification=Size of ImageActual Size of Object\text{Magnification} = \frac{\text{Size of Image}}{\text{Actual Size of Object}}

T(K)=T(∘C)+273.15T(K) = T(^{\circ}C) + 273.15

1 mm=1,000μm1 \text{ mm} = 1,000 \mu m

💡Examples

Problem 1:

A student views a bacterium that is 2μm2 \mu m long under a microscope with a magnification of 500×500 \times. What is the size of the image seen through the lens in millimeters (mmmm)?

Solution:

1mm1 mm

Explanation:

Using the formula Image Size=Actual Size×Magnification\text{Image Size} = \text{Actual Size} \times \text{Magnification}, we get 2μm×500=1,000μm2 \mu m \times 500 = 1,000 \mu m. Since 1,000μm=1mm1,000 \mu m = 1 mm, the image size is 1mm1 mm.

Problem 2:

Explain why bread dough increases in volume when yeast and sugar (C6H12O6C_6H_{12}O_6) are added.

Solution:

Production of CO2CO_2.

Explanation:

The yeast consumes the sugar through fermentation. This chemical reaction produces Carbon Dioxide (CO2CO_2) gas. The gas bubbles get trapped in the dough, causing it to expand or 'rise'.

Problem 3:

If a colony of bacteria doubles every 2020 minutes, how many bacteria will be present after 11 hour if starting with 1010 bacteria?

Solution:

80 bacteria80 \text{ bacteria}

Explanation:

In 11 hour, there are three 2020-minute intervals. The population growth follows N=N0×2nN = N_0 \times 2^n, where nn is the number of doublings. 10×23=10×8=8010 \times 2^3 = 10 \times 8 = 80.