Cartoon Homework• Microbes involved in the Nitrogen Cycle

are:– Nitrogen fixing bacteria– Saprobionts– Denitrifying bacteria– Nitrifying bacteria

• Make up a cartoon character for each

e.g. Dangerous Dave the Denitrifying Bacteria (Baddie)

• Draw out a line diagram of the N Cycle from p.95 – inserting your characters in the correct place.

The Nitrogen Cycle

AQA book p.95-97

Specification Reference: 3.4.6

Syllabus

• The role of microorganisms in the carbon and nitrogen cycles in sufficient detail to illustrate the processes of saprobiotic nutrition, ammonification, nitrification, nitrogen fixation and denitrification.

• (The names of individual species are not required.)

Objectives• How is Nitrogen recycled in

ecosystems?• What is the role of saprobiotic

microorganisms in recycling?• What do you understand by the

terms ‘ammonification’, ‘nitrification’, ‘nitrogen fixation’ and ‘denitrification’?

• Where does Nitrogen enter the living component of an ecosystem?

• Where does Nitrogen enter the non-living component of an ecosystem?

Introduction p.95

1. Name 2 organic compounds which contain nitrogen

2. Name 3 inorganic compounds which contain nitrogen

3. Why is Nitrogen gas not used by many organisms?

4. In what form do plants obtain nitrogen?5. In what form do animals obtain nitrogen?6. Give 2 reasons why a soil may be low in

nitrate.

Introduction Answers p.95• Name 2 organic compounds which contain nitrogen

Protein nucleic acids• Name 3 inorganic compounds which contain nitrogen

Ammonium ions, Nitrate, Nitrite• Why is Nitrogen gas not used by many organisms?

Unreactive so difficult to combine into other compounds• In what form do plants obtain nitrogen?

Nitrate through the roots by ACTIVE TRANSPORT• In what form do animals obtain nitrogen?

Eating and digesting other things so nucleic acids and protein

• Give 2 reasons why a soil may be low in nitrate.Leaching of soluble nitrate, soil is waterlogged, little other

source of nitrate apart from decomposition/fertilisers

What do you understand by the terms ‘ammonification’,

‘nitrification’, ‘nitrogen fixation’ and ‘denitrification’?

Denitrification

• Nitrates nitrogen gas• Anaerobic – in waterlogged soil• Denitrifying bacteria live in soil• Reduces productivity

Nitrification • Ammonium ions nitrite• Nitrite nitrate• Both oxidation reactions releasing energy

for the bacteria which carry out the reactions

• This energy is used to synthesise sugar/food for the bacteria (a bit like photosynthesis- organisms are called photoautotrophs, but in this case the energy comes from reactions so the organisms are called chemoautotrophs)

• Aerobic reactions needing oxygen (air spaces in soil)

• To increase productivity soil should be well ploughed and not waterlogged

Ammonification

• Organic nitrogen compounds (urea, proteins, nucleic acids) ammonia

• Ammonia forms ammonium ions in soil

• Saprobiotic microbes decompose faeces, urine and dead organisms

• Saprobiotic microbes live in soil• Nitrogen is returned to the non-living

component of the ecosystem

Nitrogen fixation

• Nitrogen gas nitrogen containing compounds• Needs lots of energy (ATP)• Carried out by microbes free living in soil which

make ammonia which is then used to make amino acids for themselves. When they die the nitrogen compounds become available to plants through ammonification and nitrification

• Also carried out by mutualistic n-fixing bacteria . These live in root nodules of legumes (peas beans, clover) mutual means both benefit – bacteria get carbohydrates made in the plant by photosynthesis, the plant gets amino acids from the bacteria

• Aerobic bacteria but Anaerobic process• Increases productivity

Root nodules - nitrogen fixation

Nitrogen fixing Rhizobia bacteroids

Nitrogen fixation

• Lightning produces nitrogen oxides which dissolve in rain and fall to the soil

• Haber process – combines H and N to make AMMONIA

• High temperature, pressure plus catalyst needed

• Makes fertilizer – added to fields to increase productivity

Formula for nitrogen fixation – a reduction reaction

+Pi

Nitrogen cycle picture1. Aerobic processes in purple, anaerobic in black2. Shade in red any organic compounds3. Shade in blue any inorganic compounds4. Shade in yellow all bacteria5. Shade in green all process names6. Productivity in orange7. Make a key for these colours8. How does nitrogen enter the living/non living

part of the ecosystem?

Plenary

• Triominoes• In pairs