Ecological Energetics and Nutrient Cycles Flashcards
What is the first law of thermodynamics and what implications does this have for ecological energetics?
- Energy can’t be created or destroyed, but can be changed from one form into another
- Energy flows through an ecosystem, and so for an ecosystem to exist it must have an external source of energy
- This is most often provided through sunlight - plants trap light energy using chlorophyll and convert it into chemical energy by producing organic molecules from inorganic.
define photoautotroph
producers that make their own food from inorganic molecules, water and carbon dioxide using sunlight as an energy source
define chemoautotroph
producers that use chemical energy to make their own food
give some examples of chemoautotrophs
- Some species of bacteria living in deep caves with no available light make organic substances using the mineral in the rock as a source of chemical energy
- Nitrifying bacteria are chemoautotrophs
define heterotroph
can’t make their own food, therefore rly on other living organisms to provide them with organic molecules
what do food chains indicate?
- Feeding relationships in an ecosystem
- Energy flow through an ecosystem (direction of arrows) from one trophic level to another
- Each feeding level is known as a trophic level. Producers are always the first trophic level, primary consumers the second, etc.
how many levels are there in a food chain?
Most food chains have 3 or 4 trophic levels but in aquatic ecosystems there may be as many as 6
what are detritus food chains?
food chains that start with dead organic matter - eg decomposers (eg fungi) or detritivores (eg woodlice)
why do food chains only have a small amount of levels?
- Energy is lost at each level so there is less available to transfer to the next
- on a long food chain the small amount of energy gained at the end of the chain wouldn’t be energetically favourable
what are food webs?
a complex linked combination of many food chains. This is because most organisms feed on more than one type of organism
what should be considered when drawing a pyramid of numbers, biomass or energy?
- Producers (trophic level 1) are always at the base of the pyramid
- Drawn symmetrical about the centre
- Bar width must be in proportion to the numbers/biomass of organisms in each trophic level
- Bars must all the same depth
Define pyramid of numbers
a bar diagram indicating the relative numbers of organisms in a food chain, or total numbers of all organisms at each of the trophic levels in a food web
how is the data for a pyramid of numbers collected?
To obtain the data all organisms are counted in theory, but in practice a small area is randomly sampled and multiplied up to give an estimate of the total population size (eg quadrats, nets, humane trapping).
describe the general shape of a pyramid of numbers
Predators are normally larger and smaller in number than their prey, so the pyramid sometimes works, but in the instance of eg oak trees and insects, it can be inverted
name the problems with pyramids of numbers
When very large numbers are involved at any trophic level, it is nearly impossible to scale the bars accurately
Gives quantitative information but doesn’t give indication of the relative mass of organisms at each trophic level - results in inverted pyramids
Only shows numbers of organisms at any one given time
define pyramids of biomass
shows the mass of all living organisms, at a particular trophic level, per unit area or volume, at a particular time
how is the data for a pyramid of biomass collected?
- Random quadrats have all organisms harvested and weighted (wet/fresh mass) and average mass is calculated for each trophic level and multiplied by the number of organisms
- Some scientists prefer dry mass - drying organisms to constant mass - more accurate but more time consuming and means organisms are killed in the process
what are the problems with a pyramid of biomass?
- only show the number of organisms present at any one time (standing crop) - can cause inverted pyramid as it doesn’t take into account changes in biomass over a period of time (eg zooplankton and phytoplankton)
- Difficult to obtain the wet or dry mass of eg an oak tree - should the mass be the entire mass of the tree, or just the edible leaves?
what is the benefit of using a pyramid of biomass rather than numbers?
Overcomes problem of the size of organisms, therefore less likely to be inverted
define pyramid of energy (productivity)
measures productivity (how much new material is produced) for each level in an ecosystem, during a fixed period of time
what are the units for pyramids of energy?
kJm^-2y^-1
what is the benefits of using a pyramid of energy?
- Energy content of tissues varies, and so these pyramids give more accurate info than biomass
- Are never inverted - particularly useful in comparing ecosystems
- often takes into account annual changes
what are the problems with a pyramid of energy?
values are hard to obtain
how much incipient energy do primary producers utilise from sunlight?
0.5-1%
name reasons why energy might be unavailable for primary producers
- Some wavelengths can’t be absorbed by chlorophyll
- Some energy is transmitted through the leaf and misses the chloroplasts
- Some light is reflected from the leaf surface/atmosphere
- Some is lost in photosynthetic reactions (these are quite inefficient) in the form of heat
- Some energy is lost in the evaporation of water (eg from leaf surface)
give the equation for calculating photosynthetic efficiency
Photosynthetic efficiency = (Amount of energy incorporated into carbohydrate)/(amount of energy falling on the plant)
define gross primary production
the energy in organic compounds produced by plants in photosynthesis
* This energy is not all available to the next trophic level
what are the units for GPP?
kJm^-2y-1
why do nutrients cycle through an ecosystem, rather than flow like energy?
here is a finite amount of matter available on earth for organisms to use and build their bodies
name differences between energy flow and nutrient cycling in an ecosystem
- nutrient cycles also involves transfer from producer to consumer, between consumers and through the decomposer food chain
- the nutrient enters the producer from within the ecosystem (eg. plants absorb CO2 in photosynthesis that has already been in the carbon cycle)
describe photosynthesis
inorganic carbon dioxide is taken in by plants from the atmosphere or from solution in water and is fixed during photosynthesis into organic sugars
describe ingestion, digestion and assimilation
carbon passes along the food chain due to consumers feeding on organisms, by digestion and assimilation of complex organic compounds when carbon is incorporated into the cells and tissues of organisms
define respiration
carbon is returned to the air when organic compounds are respired, producing ATP and CO2 as a byproduct.
define decay and decomposition
when saprobiotic microorganisms break down the organic molecules in dead organisms and release CO2 (again via respiration)
define fossilisation
when dead organisms are preserved in environments hostile to decay eg. coal, oil, gas and peat. This carbon is then released millions of years later by combustion.
name some processes that add CO2 to the atmospheric pool
respiration
combustion
decomposition
name some processes that remove CO2 from the atmospheric pool
photosynthesis
fossilisation
how can organic compounds in plants be converted to carbon dioxide in the atmosphere?
- fossilisation and combustion
- respiration
- animal feeding and respiration
- animal feeding, animal death and respiration in decomposers
- plant death and respiration in decomposers
name some nitrogen containing compounds
proteins, nucleic acids, ATP
how does availability of nitrogen affect plant growth?
Proteins are responsible for growth of plants, so availability of nitrogen to plants determines how much new plant biomass can be produced
how much gaseous nitrogen in present in the atmosphere and why isnt it used by plants?
79% of atmosphere
is very stable so relatively unreactive and can’t be used directly by plants
how do autotrophs obtain nitrogen?
from nitrate ions (NO3-) taken up during active transport, or as ammonium ions (NH4+) taken from the soil or water
how do heterotrophs obtain nitrogen?
from the digestion and assimilation of organic materials (plants or other animals). Excess nitrogen is then excreted (urine) or digested (faeces), or ends up as non-living organic matter following death
what role do saprobiotic organisms play in the nitrogen cycle?
recycle the nitrogen containing compounds produced by heterotrophs via decay and decomposition to its useable inorganic form, via mineralisation. This involves the stages of ammonification and nitrification.
what role do detritivores (eg earthworms) play in the nitrogen cycle?
Detritivores (eg earthworms) are involved in the decay process provide additional benefits, in that their burrows aerate and drain the soil, thus encouraging the activity of aerobic bacteria while reducing the activity of anaerobic bacteria
give the four main processes in the nitrogen cycle
nitrogen fixation
ammonification
nitrification
denitrification
give three ways nitrogen fixation can occur
nitrogen fixing bacteria
haber process
lightning
describe how nitrogen fixing bacteria go about nitrogen fixation
- occurs in aerobic conditions
- reaction is catalysed with nitrogenase - can occur at 20ºC rather than high temperatures required in Haber process
- N2 + 6H^+ + 6e^- -> 2NH3
give an example of nitrogen fixing bacteria
Azobacter
Rhizobium is the bacteria that lives symbiotically in the root nodules of leguminous plants (gets carbohydrate for energy, provides ammonia to produce amino acids - mutualistic relationship)
what is nitrogen fixation
reduction of nitrogen gas from the air (or air pockets in soil) to ammonia
why is nitrogen fixation through bacteria beneficial?
it enriches the soil - farmers will grow legumes and allow them to decay into soil as part of crop rotation
how is the haber process used?
used to make fertilisers that are added to the soil
how much of nitrogen is fixed on average by lightning?
5%
how is lightning fixed by nitrogen?
Provides the energy to break the bonds in diatomic nitrogen, allowing the formation of oxides of nitrogen which then dissolve in rainwater - washed into the soil where they can be absorbed by plants as nitrates
describe the process of ammonification
- Saprophytic bacteria or fungi feed on dead organisms or their organic waste, releasing ammonia (NH3), which forms ammonium ions (NH4+) in water
- Process aided by earthworms, as these detritivores feed on the dead organisms, breaking them into smaller pieces (larger SA), and will distribute the dead material throughout the soil
describe the conditions needed for nitrification to occur
- Requires oxygen so will only occur most rapidly in well-aerated soils or well-oxygenated water.
- Low temps will slow down nitrate formation, most nitrates are therefore formed in soils in the spring and summer when most plant growth occurs
describe the stages that are carried out by nitrifying bacteria in the process of nitrification
- Oxidation of ammonium ions/ammonia into nitrites (NO2-) by nitrifying bacteria of the genera Nitrosomonas
- Oxidation of nitrites into nitrates (NO3-) by nitrifying bacteria of the genera Nitrobacter
what type of autotrophs are nitrifying bacteria?
chemoautotrophs - they derive their energy from the synthesis of organic molecules from these oxidation reactions
what happens to nitrates after they are producing in nitrification?
- Nitrates produced are absorbed by active transport (energy required - optimally in aerobic conditions) to make proteins
- Nitrate is very soluble and so can be washed out of soils as a result of heavy rain by a process known as leaching.
what are the conditions that allow denitrification to take place?
Takes place in soils with a high nitrate content, but also anaerobic conditions usually caused by waterlogging. It can significantly reduce soil fertility.
describe the process of denitrification
- Reduced nitrate (NO3-) to atmospheric nitrogen and oxygen
- Oxygen can be used by bacteria in aerobic respiration, while nitrogen gas escapes to the atmosphere
- Leads to loss of nitrates in the soil and so reduces soil fertility
define producer
an organism that manufactures organic substances from inorganic substances using energy
how much of GPP is used for respiration on average?
50%
define net primary production
the energy that a plant has available for growth, or for the other trophic levels, ie the remainder after the GPP is used for respiration
What is the least efficient stage in the food chain after the producers, and what is the normal percentage efficiency? Why does this trend exist?
producers to primary consumers
5-10%
- much plant material (producers) can’t be accessed, eg. roots, tree trunks
- much plant material is difficult to digest eg. few organisms have enzymes necessary to digest cellulose and lignin
- excretory losses - metabolic waste eg urea is excreted and the energy contained within it isn’t transferred to the next trophic level
- much of the organic content that is eaten primary consumers is used in respiration to generate ATP. the energy lost through respiration is lost as heat as a byproduct.
- some plants or plant parts enter the decomposer food chain and so aren’t available to rimary consumers
why are respiratory losses particularly high in mammals and birds?
they are endotherms.
the maintenance of high and constant body temperature requires high metabolic activity and consequently high levels of respiration and unavoidable heat loss.
describe the efficiency of energy transfer between consumers
- generally more efficient (10-20%)
- still low due to excretory losses, uneaten structures, entry into the decomposer chain, or being used in respiration
Name some methods used to increase primary productivity of plants
- removing the limiting factors affecting growth (eg glasshouses providing extra light, heat and carbon dioxide. however most plants in NI are grown outside)
- use of fertiliser
- reducing effect of pests
- appropriate spacing of crops ( balance between spacing enough to limit competition, but also to maximise coverage)
give some techniques used in intensive farming of livestock
- confinement of animals (less energy used for movement, less lang utilised and manure more evenly spread)
- keeping warm, often produced by animals themselves due to confinement (reduces energy required to produce heat and maintain body temp)
- high energy foods such as silage, and high protein foods such as soya meal
Name the issues with intensive farming practices
- ethical concerns (eg confined animals suffer from high stress levels, bone and joint damage etc)
- disease more likely to spread among confined animals
- overuse of antibiotics to control disease leads to antibiotic resistance
- reduced genetic diversity in selective breeding also leads to greater risk of disease
- increased pollution from increased use of fossil fuels/farmland waste
- pesticide use can cause bioaccumulation up food chains
- fertilisers can leach into waterways and cause eutrophication
- pesticide use and monoculture leads to reduction in biodiversity and habitat loss
what is secondary productivity?
the energy used in the production of new tissue in animals
- crop farmers are concerned with increasing primary productivity (crop growth), livestock farmers are concerned with both primary productivity (if producing their own animal feeds) and secondary productivity
give a simplified formula for the energy budget of a cow
secondary productivity = consumed - (respiration + urine + faeces)
describe how farmers want to manipulate the energy budget of their livestock to maximise growth
- maximise secondary production by using high energy foods
- reduce respiration, urine and faeces, most easily done with respiration by confinement
how do the oceans work as a buffer for carbon dioxide?
they contain a reserve of hydrogencarbonate (HCO3-) ions which can take up or return carbon dioxide to or from the atmosphere
