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 nitrates, which plants use to make proteins. Animals obtain these proteins by consuming plants. Decomposition of dead plants and animal waste releases 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 atmosphere is made up of nitrogen?

• 78%

• 21%

• 99%

• 50%

Why can't plants and animals use atmospheric nitrogen directly?

• It is too heavy to be absorbed.

• It is not in a usable form.

• It is too rare in the atmosphere.

• It is toxic to them.

What is the role of Rhizobium bacteria in the nitrogen cycle?

• They fix nitrogen into ammonia.

• They convert nitrates to ammonia.

• They release nitrogen gas into the atmosphere.

• They decompose dead plants.

How can nitrogen fixation occur besides through bacteria?

• Through lightning strikes.

• Through photosynthesis.

• Through animal digestion.

• Through plant transpiration.

What do plants use nitrates for?

• To produce oxygen.

• To absorb sunlight.

• To store energy.

• To make proteins.

How do animals obtain the nitrogen they need?

• By eating plants.

• By absorbing it through their skin.

• By drinking water.

• By breathing it in.

What happens to nitrogenous wastes from dead plants and animals?

• They evaporate into the atmosphere.

• They decay and release ammonia.

• They turn into carbon dioxide.

• They are absorbed directly by plants.

What is the role of denitrifying bacteria in the nitrogen cycle?

• They convert ammonia to nitrates.

• They fix nitrogen into ammonia.

• They convert nitrates back to atmospheric nitrogen.

• They decompose organic matter.

Why does the percentage of nitrogen in the atmosphere remain constant?

• Because it is constantly recycled through the nitrogen cycle.

• Because it is a stable element.

• Because it is continuously produced by plants.

• Because it is not used by any organisms.

What is the overall process described in the video known as?

• Water Cycle

• Oxygen Cycle

• Carbon Cycle

• Nitrogen Cycle