The video explains the nitrogen cycle, starting with atmospheric nitrogen, which makes up 78% of the air. It covers nitrogen fixation by Rhizobium bacteria in leguminous plant roots, converting nitrogen to ammonia. Nutrifying bacteria then convert ammonia to nitrites and nitrates, which plants absorb to make proteins. Animals obtain these proteins by consuming plants. The cycle continues as dead plants and animal waste decompose, releasing ammonia, which is again converted to nitrates. Denitrifying bacteria convert nitrates back to atmospheric nitrogen, maintaining its constant level in the air.

What percentage of the air is constituted by nitrogen?

• 21%

• 78%

• 50%

• 10%

Why can't atmospheric nitrogen be used directly by plants and animals?

• It is too cold

• It is too heavy

• It is not in a usable form

• It is toxic

Which bacteria live in the root nodules of leguminous plants and help in nitrogen fixation?

• Azotobacter

• Rhizobium

• Clostridium

• Nitrosomonas

What is the first compound that atmospheric nitrogen is converted into during nitrogen fixation?

• Nitrites

• Ammonia

• Nitrogen dioxide

• Nitrates

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What do nitrifying bacteria convert ammonia into?

• Nitrogen gas

• Carbon dioxide

• Nitrites and then nitrates

• Proteins

Apart from bacteria, what natural phenomenon can also fix nitrogen?

• Volcanic eruptions

• Earthquakes

• Tsunamis

• Lightning strikes

How do plants use the nitrates absorbed from the soil?

• To make proteins

• To make carbohydrates

• To make fats

• To make vitamins

Tags

NGSS.MS-LS2-1

NGSS.MS-LS2-3

How do animals obtain the nitrogen they need?

• By absorbing it through their skin

• By eating plants

• By drinking water

• By breathing

Tags

NGSS.MS-LS2-1

What happens to nitrogenous wastes from dead plants and animals?

• They turn into nitrates directly

• They evaporate

• They decay and release ammonia

• They become fossil fuels

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What role do denitrifying bacteria play in the nitrogen cycle?

• They convert nitrates back to atmospheric nitrogen

• They fix nitrogen in the soil

• They help plants absorb nitrates

• They convert ammonia to nitrites

Tags

NGSS.MS-LS2-1