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Flashcards in Energy Transfer and Nutrient Cycles Deck (18):


Photosynthesis produces glucose which is then broken down in respiration that goes on to make biological molecules such as cellulose
Chemical energy stored in a plant
Mass of carbon or dry mass of its tissue per unit area per time
Dry mass - mass of organism with water removed
Sample taken of organism
dried - low temperature and measured over a long period - you know you have reading when it is constant mass
Mass of carbon is normally 50% of dry mass
Biomass changes so it is important that a time period is used
kg m-2 yr-1


Measuring dry mass using a calorimeter

Burn a sample of biomass and the energy released is used to heat a known volume of water
Change in temp used to calculate the chemical energy of the dry biomass



GPP = Gross primary production - total chemical energy converted from light energy by plants, in a given area, in a given time
Energy lost as heat as respiratory loss
Remaining chemical energy is the net primary production (NPP)
NPP= energy available for growth and reproduction


Net production for Consumers

About 90% of energy is lost and does not reach the next trophic level
Some is indigestible and are egested as faeces
Some lost to the environment through respiration or excretion of urine
Net production: Chemical energy in ingested food - (Chemical energy lost in faeces - Energy lost through respiration)


Inputs to increase NPP in crops

Reuse of waste products - natural fertilisers
Greenhouses - CO2, temp, lighting
Selective breeding
GM crops
Increasing ground coverage


Chemical pesticides

+ Act quickly
+ Easily applied
- Can target other species
- Repeatably used = expensive
- Developed resistance
- Bio accumulation or bio magnification


Biological control (Natural predator)

+ Specific to predator
+ Does not need to be re-introduced
+ Unlikely that resistance will develop
- Takes time to take effect
- Possibility of control predator becoming pest


Integrated Control

Providing suitable habitats for natural predators
Removing pests mechanically
Using biological agents
Using pesticides as a last resort
Preventative measures such as crop rotation and intercropping


Nitrogen fixation

Nitrogen gas in the atmosphere turned into nitrogen-containing compounds.
Nitrogen fixing bacteria, Rhizobium, in root nodules turn nitrogen into ammonia, which can be used by plants
Root nodules found on leguminous plants (peas, bean)
Have a mutualistic relationship with plants - are provided with carbohydrates for their service



Nitrogen compounds from dead organisms are turning into ammonia by saprobionts (decomposing bacteria) which goes on to form ammonium ions
Animal waste also contains nitrogen compounds



Ammonium ions in the soil are changed into nitrogen compounds that can be used by plants (nitrates)
Nitrifying bacteria, Nitrosomonas change ammonium ions into nitrites
Nitrobacter change nitrites into nitrates



Nitrates in the soil are converted into nitrogen gas by denitrifying bacteria - use nitrous in the soil to carry out respiration and produce nitrogen gas
Happens under anaerobic conditions in waterlogged soil


Other ways that Nitrogen gets into soil

Atmospheric fixation (lightning)
Artificial fertilisers - in the Haber process


Need for phosphorus

To make biological molecules such as phospholipids, DNA and ATP
Phosphorus found in rocks and dissolved in ocean and phosphate ions (PO4 3-)
Phosphate ions dissolved in water in the soul can be assimilated by plants and other producers


Phosphorus cycle

Phosphate ions in rocks are released into soil by weathering
Phosphate ions are taken into the plants through the roots
Phosphate ions are taken into plants through the roots.
Mycorrhizae greatly increase the rate at which phosphorous can be assimilated
Phosphate ions transferred through the food chain as animals eat the plants and are in turn eaten by other animals
Phosphate ions lost from the animals in waste products
When plants and animals die, saprobionts break down and release phosphate ions into the soil for assimilation by plants
Also release phosphate ions from urine and faeces
Weathering of rocks also releases phosphate ions into sea, lakes and rivers - taken by aquatic producers such as algae and passed on to birds
The waste produced by birds is known as guano and contains a high proportion of phosphate ions
Guano returns phosphate ions to soil and is a natural fertiliser


Loss of nutrients in farming

By harvesting plants the taken in nutrients (nitrogen or phosphorus) are taken with them and not returned to the soil


Environmental issues of fertilisers?

More applied than needed - leaching into waterways - water soluble compounds in the soil are washed away - can lead to eutrophication



- Mineral ions leached from fertilised fields lead to rapid growth of algae in ponds and rivers
- Large number of algae block light from the plants below
- Plants die as they can't photosynthesise
- Bacteria feed on dead plant matter
- Bacteria reduce the oxygen concentration through aerobic respiration
- Fish and aquatic organisms die due to not enough dissolved oxygen