Test: Microorganisms Friend & Foe- 3 - Class 8 MCQ

Fermentation takes place when yeast is added to grape juice and left for a week.

Viruses are quite different from other microorganisms. They reproduce only inside the host organism: bacterium, plant or animal cell.

The release of carbon dioxide gas causes dough to rise when yeast is added to it. (Fermentation)

- Microorganisms are incredibly versatile and can thrive in diverse environments.
- They are present in:
- Air, water, and soil: Microorganisms like bacteria, fungi, and viruses inhabit these mediums.
- Hot springs and deserts: Extremophiles are adapted to survive in extreme conditions.
- Inside the bodies of plants and animals: Many microorganisms exist symbiotically or as pathogens.
- Therefore, the correct answer is D: All of the above, as microorganisms inhabit all mentioned environments.

Microorganisms, including bacteria, fungi, protozoa, and algae, are classified as microbes primarily because they are small organisms that cannot be seen without the aid of a microscope. This characteristic of requiring magnification for observation is the defining feature that groups them together.

Here are some key points regarding the classifications and characteristics of microorganisms:

• Option A is incorrect because while many microorganisms can reproduce independently, it is not a universal trait across all environments.
• Option B is wrong since microbes are typically microscopic and not visible to the naked eye.
• Option D is also incorrect as not all microorganisms are harmful; many are beneficial or neutral in their interactions with humans.

- Certain soil bacteria play a crucial role in the nitrogen cycle.
- These bacteria convert nitrogen compounds, such as nitrates, into nitrogen gas (N₂).
- This process is known as denitrification.
- Nitrogen gas is an inert form and makes up about 78% of the Earth's atmosphere.