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The Mystery of Food - Microbes: Useful and Harmful

Grade 5CBSE

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

🔑Concepts

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Microbes are tiny organisms that are invisible to the naked eye and can only be seen using a microscope.

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There are four main types of microbes: Bacteria, Fungi, Protozoa, and Viruses.

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Useful Microbes: Bacteria like Lactobacillus are used to turn milk into curd. Yeast (a fungus) is used in baking bread because it releases Carbon dioxide (CO2CO_2) gas, making the dough rise.

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Decomposition: Some microbes act as decomposers, breaking down dead plants and animals into simpler nutrients, which helps in cleaning the environment.

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Harmful Microbes: These are also called 'Pathogens' or 'Germs'. They cause diseases like the common cold, tuberculosis, and malaria, and can cause food poisoning.

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Food Preservation: Methods used to prevent microbial growth in food include dehydration (removing H2OH_2O), salting, sweetening, and pasteurization.

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Temperature Control: Most microbes cannot grow at very low temperatures (near 0∘C0^\circ C) or very high temperatures (near 100∘C100^\circ C).

📐Formulae

CO2 (Carbon Dioxide gas released during fermentation)CO_2 \text{ (Carbon Dioxide gas released during fermentation)}

H2O (Moisture needed for microbial growth)H_2O \text{ (Moisture needed for microbial growth)}

Freezing Point of Water=0∘C\text{Freezing Point of Water} = 0^\circ C

Boiling Point of Water=100∘C\text{Boiling Point of Water} = 100^\circ C

💡Examples

Problem 1:

A baker adds yeast to dough and leaves it for 2 hours. If the initial volume of the dough was 500 ml500 \text{ ml} and it doubled due to CO2CO_2 production, what is the new volume?

Solution:

500 ml×2=1000 ml500 \text{ ml} \times 2 = 1000 \text{ ml}

Explanation:

Yeast undergoes fermentation and releases CO2CO_2 bubbles that get trapped in the dough, causing it to increase in volume.

Problem 2:

A scientist is testing the effect of temperature on bacteria. If the room temperature is 37∘C37^\circ C and the freezer temperature is −18∘C-18^\circ C, what is the temperature difference?

Solution:

37−(−18)55\begin{array}{r} 37 \\ - (-18) \\ \hline 55 \end{array}

Explanation:

The difference is calculated by subtracting the lower temperature from the higher temperature: 37−(−18)=37+18=55∘C37 - (-18) = 37 + 18 = 55^\circ C.

Problem 3:

Why is salt used to preserve pickles?

Solution:

Salt removes H2OH_2O (moisture) from the food.

Explanation:

Microbes require moisture to grow. By adding salt, we remove water through osmosis, making it difficult for microbes to survive.