1.10 The Nitrogen Cycle

1. 1.10 The Nitrogen Cycle (Sec 4.3 pg 92 – 95) CRASH COURSE VIDEO: http://www.youtube.com/watch?v=leHy-Y_8nRs&feature=c4-overview-vl&list=PL8dPuuaLjXtNdTKZkV_GiIYXpV9w4WxbX

2. Even though nitrogen (N) is the most abundant gas in the atmosphere, organisms cannot use it in atmospheric form (N2). • N2is very stable and will not break down.

3. N is an essential component of biological molecules (DNA, proteins, etc).

4. For this reason, the N cycle is extremely important. • There are 3 key stages in the cycle (please refer to Fig.2 p.93 and your Data Pages for diagrams of the N cycle):

5. Nitrogen fixation: • Nitrogen gas (N2) is combined with hydrogen (H2) to form ammonia (NH3). • the process of N fixation is carried out by bacteria, many of these bacteria live in the soil, others live on the nodules of plants called legumes (Fig 3 p.93). • Extra NH3dissolves in the soil to become NH4+, ammonium

6. Nitrification: • Turns ammonium NH4+ into NO3- (nitrate ions); nitrate is required by many plants for optimal growth. • process done by bacteria in the soil; the process is called nitrification. • Nitrate ions are absorbed by plants to make amino acids, DNA, proteins, etc.

7. Decomposition and Denitrification: • When organisms die, nitrates and ammonium leave the body. It is converted back into N2 gas by decomposing bacteria (this is called denitrification).

8. Animals obtain their N by consuming plants, or by consuming organisms that have consumed plants; plants are essential for providing N to the food chain!