3.5.4 Nutrient cycles Flashcards
1
Q
Order of stages in the nitrogen cycle
A
- nitrogen fixation
- ammonification
- nitrification
- denitrification
2
Q
Describe the nitrogen fixation stage of the nitrogen cycle
A
- starts with nitrogen gas
- ends with ammonia
- nitrogen fixing bacteria
3
Q
Describe the ammonification stage of the nitrogen cycle
A
- starts with nitrogen containing compound (eg protein, DNA)
- ends with ammonia
- saprobiontic bacteria
4
Q
Describe the nitrification stage of the nitrogen cycle
A
- starts with ammonia
- ends with nitrites and then nitrates
- nitrifying bacteria (aerobic)
5
Q
Describe the denitrification stage of the nitrogen cycle
A
- starts with nitrates
- ends with nitrogen gas
- denitrifying bacteria (anaerobic)
6
Q
How do farmers avoid the denitrification stage?
A
- want well drained and aerated soil
- use ploughing
7
Q
How do saprobionts work?
A
- secrete enzymes
- hydrolyse large insoluble molecules into smaller soluble molecules (starch-> glucose, proteins -> amino acids)
- decompose nitrogen containing compounds (urea, proteins, DNA, RNA)
- and produce ammonium compounds
- absorb soluble products
8
Q
What are microrrhizae?
A
- associations between fungi and plant roots
- which increase the surface area available for absorption of more water and minerals
- important aid in uptake of minerals (eg phosphates and nitrates)
9
Q
How do plants and micorrhizae have a mutuality relationship?
A
- plants - increased water and mineral uptake
- micorrhizae - organic compounds eg glucose
10
Q
What are the advantage of nitrogen fertilisers?
A
- increased crop growth
- increased rate of photosynthesis
- increased rate of productivity
11
Q
What are the disadvantages of nitrogen fertilisers?
A
- reduced species diversity. Nitrogen rich soils favour rapidly growing species with outcompetes other species
- leaching of nutrients into watercourses
- eutrophication a build up of nutrient salts in watercourses
12
Q
What is leaching?
A
- where water soluble nutrients dissolve in rainwater
- and are washed out of soil
- they can run into watercourses
- eg streams and rivers that feed into freshwater lakes
13
Q
Describe and explain the process of eutrophication
A
- nutrients leached into watercourses
- causing algal bloom
- algae block light so light is a limiting factor
- plants and algae die because they can’t photosynthasise
- saprobiotic bacteria break down dead plant material
- and use up oxygen during aerobic respiration
- aerobic organisms die due to lack of oxygen for respiration
- less competition for anaerobic organisms
- their populations increase and they release toxic wastes (eg hydrogen sulphide) as they decompose material- water becomes putrid
14
Q
How does a fertiliser increase productivity?
A
- more nitrates lead to increased growth
- because plants can use the nitrogen to make organic molecules like protein and DNA
- leads to an increased rate of photosynthesis and increased productivity
15
Q
Why are fertilisers added to agricultural ecosystems?
A
- crops repeatedly grown on same area of land
- mineral ions taken up but plant and transported off the land when plants are sold
- so levels of ions in the soil decrease
- limits rate of photosynthesis for next crops as less nitrates available
- so fertilisers added to maintain productivity and increase rate of photosynthesis
16
Q
Why is crop rotation beneficial?
A
- grow crops with nitrogen fixing bacteria (e.g. legumes)
- different crops use different minerals/salts/nutrients/ions
- different crops have different pests and diseases
