Nutrient Cycles

Question 1

Significance of phosphorus to living organisms

Answer 1

Plants convert inorganic phosphorus into biological molecules (e.g. DNA, ATP, NADP)
Phosphorus is passed to consumers via feeding

Question 2

Role of bacteria in nitrogen fixation

Answer 2

Mutualistic nitrogen-fixing bacteria in nodules of legumes & free-living bacteria in soil
Use enzyme nitrogenase to reduce gaseous nitrogen into ammonia

Question 3

Role of bacteria in ammonification

Answer 3

1. Saprobionts feed on and decompose organic waste containing nitrogen
2. NH3 released
3. NH3 dissolves in water in soil to form NH4+

Question 4

Role of bacteria in denitrification

Answer 4

Anaerobic denitrifying bacteria convert soil nitrates back into gaseous nitrogen

Question 5

2 main environmental issues caused by the use of fertilisers

Answer 5

1. Leaching: nitrates dissolve in rainwater and ‘runoff’ into water sources
2. Eutrophication: water source becomes putrid as result of algal bloom

Question 6

What happens during eutrophication

Answer 6

1. Aquatic plants grow exponentially since nitrate level is no longer a limiting factor
2. Algal bloom o water surface prevents light from reaching the bottom and plants die
3. Oxygen levels decrease as population of aerobic saprobionts increases to decay dead matter, so fish die.
4. Anaerobic organisms reproduce exponentially and produce toxic waste which makes water putrid.