13 - Energy and Ecosystems Flashcards
producers
photosynthesising organisms
consumers
organisms that obtain energy through the consumption of other organisms
saprobionts
decomposing organisms
biomass
total mass of living material in a particular area at a given time (measured in grams/squared metre OR grams/cubed metre)
stages in a food chain/web are called
trophic levels
calorimetry can be used to
estimate the chemical energy store in dry mass
bomb calorimetry process
- sample of dry material weighed
- sample burnt in pure oxygen in sealed chamber (bomb)
- bomb is surrounded by water bath
- heat of combustion causes temperature rise in water
calculated energy released from mass of burnt biomass
most of the sun’s energy is not converted into organic matter because:
over 90% of sun’s energy is reflected into space by clouds and dust, or absorbed by the atmosphere
some wavelengths of light cannot be absorbed or used for photosynthesis
light may not fall on a chlorophyll molecule
rate of photosynthesis may be limited by several factors
net primary production calculation (for producers)
NPP = GPP - R
GPP gross primary production
R respiratory losses
biomass/energy decreases at each trophic level because:
some of the organism is not consumed, some of the organism is consumed but not digested so is excreted as faeces, dissipation of heat from respiration, energy is used to maintain body temp
most food chains only have 4/5 trophic levels because
biomass decreases as trophic level increases, this means insufficient energy is available to support a large enough breeding population at higher trophic levels
reasons plants need nitrogen and the nitrogen cycle
it is present in DNA, RNA, amino acids, ATP, chlorophyll and most vitamins
nitrogen gas is insoluble so cannot be absorbed by plant roots
nitrogen cycle is required to enable plants to absorb nitrogen
ammonification
decomposition of urea, amino acids, proteins nucleic acids and vitamins by saprobionts produces ammonia
these become ammonium ions in the soil
nitrification by nitrifying bacteria
ammonia is oxidised by nitrifying bacteria to nitrite (nitrate III) and then nitrate V
plant roots can absorb the nitrates
nitrogen fixing by nitrogen fixing bacteria in root nodules
bacteria have a symbiotic relationship with root nodules, convert N2 in the soil to ammonia
free living nitrogen fixing bacteria
convert nitrogen in soil to ammonia, get enegy from oxidising organic molecules
denitrification (effect and where it commonly occurs)
denitrifying bacteria use nitrates as an energy source, convert them to N2
reduces the amount of nitrates in soil
occurs commonly in waterlogged soil (little O2)
phosphorus cycle
- phosphate ions exist in sedimentary rocks
- sedimentary rocks under the ocean get brought up to the surface by geographical uplifting
- weathering and erosion results in dissolved phosphate ions
- dissolved ions absorbed from the soil by plant roots and are incorporated into biomass
- animals feed on the plants so absorb phosphate
- exces ions are excreted and accumulate as waste materials
- death of plants and animals allow sapriobionts o decompose biomass
- phosphate ions released into soil and water
- phosphate ions are transported in rivers/streams to lakes and oceans where they form sedimentary rocks
mycorrhizae
symbiotic associations between certain fungi and plant roots
act as an extension of plants root system and greatly increase SA of roots
increases absorption of water and minerals
fungi benefit by recieving organic substances
natural (organic) fertilisers
dead and decaying remains of dead plants and animals, as well as animal wastes (eg. manure)
artificial (inorganic) fertilisers
compounds that have been mined from rocks before being converted into different forms and combined
leaching
rainwater dissolves soluble nutrients in soil (eg. nitrates)
these are carried deep into soil, eventually beyond reach of plant roots
leached nutrients enter watercourses such as stream which may drain into freshwater lakes
process of eutrophication
- leached nitrate ions enter lakes
- causes nitrate concentration to increase, and the plants an dparticularly algae to grow rapidly
- this is because nitrate concentration is no longer a limiting factor
- algae grow on surface and prevent sunlight penetrating to plants beneath
- these plants cannot photosynthesis and so die
dead plants are decomposed by saprobionts which use the oxygen in the water to respire - oxygen concentration in the water falls and so aerobic organisms in the water die from lack of oxygen
