Cycles Within Ecosystems - Nitrogen Cycle - GCSE Biology (9-1)

Chemical Recycling and Element Cycling
📌 A constant recycling of chemicals occurs on Earth, involving the movement of elements between the living and nonliving world (air, water, soil, rocks).
🦠 Bacteria play a key role by breaking down complex organic molecules and returning elements to the environment for reuse.
🧪 The video focuses on the cycling of two specific elements: carbon and nitrogen.

The Nitrogen Cycle
💧 Nitrogen is essential for biological compounds like DNA, proteins, amino acids, and vitamins, even though 78% of the atmosphere is unreactive nitrogen gas ($\text{N}_2$).
🛠️ Nitrogen fixation converts $\text{N}_2$ gas into usable nitrates, primarily done by bacteria in the root nodules of legumes or through lightning strikes.
🌱 Plants can only absorb nitrogen in the form of nitrates, using them to build proteins before passing them along the food chain.
🔄 Decomposition returns nitrogen from dead organisms or waste to the soil as ammonia ($\text{NH}_3$).

Key Bacterial Roles in the Nitrogen Cycle
🦠 Nitrogen-fixing bacteria convert atmospheric $\text{N}_2$ gas into nitrates.
🍄 Decomposing bacteria convert organic nitrogen from dead organisms into ammonia in the soil.
🧪 Nitrifying bacteria convert ammonia first to nitrites, and then to nitrates, making nitrogen available for plants again.
💨 Denitrifying bacteria convert excess nitrates back into atmospheric nitrogen gas ($\text{N}_2$), completing the cycle.

Key Points & Insights
➡️ The nitrogen cycle involves four main types of bacteria performing distinct functions: fixing, decomposing, nitrifying, and denitrifying.
➡️ Although the air is $\sim$78% nitrogen gas, it is unreactive and cannot be used directly by organisms until fixed into nitrates.
➡️ Plants utilize nitrogen only after it has been converted from $\text{N}_2$ gas into nitrates by fixing bacteria or lightning.

📸 Video summarized with SummaryTube.com on Feb 04, 2026, 02:05 UTC