Nutrient cycles Flashcards
Describe how the carbohydrates in the dead leaves in the beech wood would be recycled by the activity of detritivores and microorganisms and the carbon dioxide made available for plants. (7)
Detritivores break leaves into small pieces / increase surface area;
Deposit faeces;
Increases rate of microbial action;
Bacterial fungi decompose / break down leaves or organic matter;
Secretion of enzymes for digestion;
Absorption of sugars;
Respiration by detritivores/ microorganisms;
Release of carbon dioxide;
Carbon dioxide used in photosynthesis;
The concentrations of carbon dioxide in the air at different heights above ground in a forest changes over a period of 24 hours. Use your knowledge of photosynthesis to describe these changes and explain why they occur. (5)
- High concentration of carbon dioxide linked with night/darkness;
- No photosynthesis in dark/night / light required for photosynthesis/light-dependent reaction;
- (In dark) plants (and other organisms) respire;
- In light net uptake of carbon dioxide by plants/plants use more carbon dioxide than they produce/ rate of photosynthesis greater than rate of respiration;
- Decrease in carbon dioxide concentration with height;
- At ground level fewer leaves/less photosynthesising tissue/more animals/less light
The carbon dioxide concentration was monitored at ground level in the centre of a small roundabout. The measurements were made on a summer day. Describe and explain how you would expect the concentration of carbon dioxide to fluctuate over the period of 24 hours. (5)
1 Higher carbon dioxide concentration at night/during darkness;
2 Photosynthesis only takes place during light;
3 Photosynthesis removes carbon dioxide and respiration adds carbon dioxide;
4 Respiration taking place throughout 24 hours;
5 Quantitative consideration such as that in plants overall
photosynthetic rate greater than respiration rate;
6 Human effect such as additional carbon dioxide from heavy
daytime traffic/street lighting could prolong photosynthesis;
Explain the role of bacteria in making carbon in dead plant remains available to plants. (4)
decomposers/ saprotrophs;
release enzymes and digest detritus/extracellular digetsion
absorb products of digestion/ suitable e.g. that relates to
these are respired and CO2 released;
CO2 diffuses in through the stomata
used by plants in photosynthesis/ enters leaves;
What is a carbon neutral ecosystem?
A carbon neutral ecosystem is one where carbon fixation and carbon release are balanced over the long term. Carbon neutral ecosystems include mature forests, where new growth is balanced by death
and decay.
How do Nitrogen fixing bacteria help to use atmospheric nitrogen?
The nitrogen in N2 is “fixed” into
useful compounds by nitrogen fixing bacteria. They reduce nitrogen gas to ammonia:
(N2 + 6H → 2NH3), which dissolves to form ammonium ions(NH )4 +
. This reaction is catalysed by the
enzyme nitrogenase and it requires a great deal of energy: 15 ATP molecules need to be hydrolysed to fix each molecule of N2.
Where do we find nitrogen fixing bacteria?
Some nitrogen-fixing bacteria are free-living in soil, but most live in colonies inside the cells of root nodules of leguminous plants such as clover or peas. This is a classic example of mutualism, where both species benefit. The pea plants gain a source of useful nitrogen from the bacteria, while the bacteria gain carbohydrates from the plant, which they respire to make the large amounts of ATP they need to fix
nitrogen.
What is nitrification and how do bacteria do it?
Nitrifying bacteria can oxidise ammonia to nitrate in two stages: first forming nitrite ions
(NH4+ ——–> NO2-
then forming nitrate ions NO2- —-> NO3
This oxidation reaction is exothermic,
releasing energy, which these bacteria use to make ATP, instead of using respiration.
What is ammonification?
Microbial saprobionts break down proteins in detritus to form ammonia in two stages: first they digest proteins to amino acids using extracellular protease enzymes, and then they remove the amino groups from amino acids using deaminase enzymes to from ammonia ) (NH4+.) The deaminated amino acids, now containing just the elements CHO, are respired by the saprobionts to CO2 and H2O
What is denitrification?
The anaerobic denitrifying bacteria convert nitrate to N2 and NOx gases, which are
then lost to the air. This represents a constant loss of “useful” nitrogen from soil, and explains why nitrogen fixation by the nitrifying bacteria and fertilisers are so important.
