CYCLES

Question 1

Nitrogen Cycle

Answer 1

Plants absorb Nitrate (NO3-) using active transport which REQUIRES ATP:
Some of the Nitrate is lost to the atmosphere as Nitrogen through denitrifying bacteria which are anaerobes and therefore thrive waterlogged soil,
Some of the Nitrate has been gained from Nitrogen in the atmosphere using Nitrogen-fixing bacteria which breaks the triple bond in Nitrogen to convert it to AMMONIA using the enzyme Nitrogenase as a catalyst, (to do this nitrogen-fixing bacteria use ATP and organic compounds gained from soil) lightning can also convert Nitrogen to AMMONIA, ammonia helps in amino acid production, otherwise ammonia is gained through decay of organic material
Plants combine Nitrate with carbohydrates to make PROTEINS
Plants are eaten and Nitrogen is passed along food chain
When the Nitrogen-rich matter dies, it is broken down by saprobionts using diffusion,( as saprobionts respire aerobically, they release CO2 which can also be used by the plant), and converted to Ammonium ions(NH4+)
Nitrifying bacteria convert the Ammonium ions (NH4+) into Nitrite (NO2-) and then Nitrite (NO2-) into Nitrate (NO3-) in a process called nitrification which is exothermic, thus releasing that is used by nitrifying bacteria to make ATP
Remember that Nitrifying bacteria, Nitrogen-Fixing bacteria and Saprobionts are aerobic, therefore they will require oxygen

Question 2

How Detritivores help Saprobionts

Answer 2

Break plant tissue into smaller pieces giving a larger surface area for Saprobionts to work
Aerate the soil which helps the Saprobionts to respire aerobically
Excrete useful minerals such as urea, which Saprobionts can metabolise

Question 3

Advantage of growing leguminous plants

Answer 3

They contain nitrogen-fixing bacteria in their root nodules, which convert nitrogen to ammonium
This ammonium is released on decomposition and converted to nitrates by nitrifying bacteria
Therefore there is a less need for fertilisers

Question 4

Role of Nitrogen Fixing bacteria in the Nitrogen Cycle

Answer 4

Convert nitrogen into ammonia
Add usable nitrogen to an ecosystem
Nitrogen-Fixation requires a lot of ATP which is obtained from respiration of products of photosynthesis.
Nitrogen-Fixing bacteria respire aerobically, therefore providing lots of ATP, however the nitrogen-fixing bacteria uses NITROGENASE as a catalyst which only respires anaerobically. The aerobic respiration helps remove O2 for nitrogenise to work

Question 5

why do enzymes which work in anaerobic conditions require that the environment is kept cool

Answer 5

this is because anaerobic respiration would increase the temperature of the environment which could lead to the enzyme becoming denatured

Question 6

Eutrophication

Answer 6

Fertilisers drain into rivers and lakes increasing levels of nitrate and other nutrients (LEECHING)
Algae absorbs this nitrate and uses it for protein synthesis eventually causing an algal bloom, this blocks sunlight for other plants which eventually die
Nutrients run out and algae die too
Bacteria decompose the dead matter and as they respire aerobically they consume Oxygen
Lack of Oxygen begins to kill aquatic life (deoxygenation)
Bacteria decompose the dead matter into ammonium compounds which is converted to nitrate by nitrifying bacteria
This could lead to an increased nitrate in drinking water which could cause human illness
Nitrate concentrations in rivers and lakes can be reduced by increase rainfall as it dilutes nitrate which in turn stops eutrophication.
Eutrophication will be faster in warmer weathers as more heat means that bacteria will have higher kinetic energy