Topic 5B: Energy Transfer and Nutrient Cycles Flashcards
What are biotic factors?
Give an example
- Living
e.g. predators, food availability, pathogens
What are abiotic factors?
Give an example
- Non-living
e.g. temperature, light availability, water availability, pH, salinity
Define ecosystem
- All organisms and the biotic & abiotic factors in an area
Define population
- All organisms of one species in a habitat
Define community
- All organisms of all species in a habitat
Define habitat
- The place an organism lives
Define niche
- The role of a species in an ecosystem
Define trophic level
- Each stage of a food chain
What productivity values do plants have?
- GPP -> total amount of energy made by a producer (units = given area per unit time - kJ/m^2/yr)
- NPP -> biomass accumulated
- R -> respiratory losses
How is NPP calculated?
NPP = GPP - R
What productivity values to animals have?
- I -> total energy ingested
- R -> respiratory losses
- F -> faeces and urine
- N -> net productivity
How is net productivity (N) calculated?
N = I - (R + F)
How do you calculate energy transfer efficiency?
- N/I x100
How is energy lost from the sun to a producer?
- Light reflected
- Not all light shines on photosynthetic areas
How is energy lost between producers and primary consumers?
- Respiration
- Heat
- Not all of the producer eaten - e.g. deep roots
- Some not digested - e.g. cellulose
How is energy lost between consumers?
- Respiration, heat
- Not all eaten - e.g. bones
How do you make dry biomass?
- Put in an oven on a low temperature - prevent combustion
- Regularly measure the mass
- When the mass remains constant - all the water has been removed - now dry
What unit do you measure dry biomass in?
kg/m^2
Describe calorimetry
- Estimates the amount of energy stored in dry biomass
- Burn a sample of dry biomass completely to heat a known volume of water
- Change in temperature is used to calculate the chemical energy of the dry biomass
What is mass of carbon?
- Organisms are made of organic compounds that contain carbon
- Mass of carbon is a good biomass indicator
- Very difficult to measure
- Mass of carbon is around 50% of dry biomass
- Measured in kg/m^2/yr - accounts for seasonal changes
What are the two types of decomposers?
- Saprobiotic microorganisms -> extracellular digestion - secrete enzymes to hydrolyse molecules - then absorb the smaller molecules produced (fungi, bacteria etc)
- Detritivores -> feed on dead / decaying matter, digest in the body (earthworms, maggots etc)
In farming what are 2 methods of reducing lost energy?
- reducing energy lost to other organisms
- reducing energy lost through respiration
What are ways of simplifying food webs?
Chemical pesticides
- Insecticides -> kill pests, less biomass lost, grow more, inc NPP
- Herbicides -> kill weeds, removes direct competition, removes pest food sources
Biological agents
- Parasites -> Kill insect / reduces its function, live or lay eggs on pest, viruses / bacteria - kill pests
How are these methods of simplifying food webs best used?
- As integrated systems
- Use both chemical and biological
- Reduces pest numbers further than one method alone
- Even more inc in NPP
What are ways of reducing respiratory losses?
Controlling conditions
- Restrict movement -> Small pens, indoors, warm
- Less energy wasted on maintaining body temperature
- More biomass produced, inc NP and energy transfer efficiency
What are the benefits of reducing respiratory losses?
- More food produced in less time
- Lower cost
What are issues with methods of reducing respiratory losses?
- Ethics
- Pain, distress caused
- Restricts the natural behaviour of animals
Why are fertilisers needed?
- Crops take in minerals from soil as they grow
- When they are harvested these are taken with them
- They do not die and decompose there - nutrients not recycled back in by decomposers
- Nutrients also lost as animals eat plants and are then moved away
What do fertilisers do?
- Replace lost minerals and increase energy efficiency
What are artificial fertilisers?
- Inorganic
- Pure chemicals
- Powders / pellets
What are natural fertilisers?
- Organic matter
- Manure, composted vegetables, crop residue, sewage sludge
What are issues with fertilisers?
- Too much applied - overflow leaches into waterways
- Happens when fertiliser applied before heavy rainfall
- Change the nutrient balance of the soil - can cause crop death
How do natural fertilisers have less issues?
- Minerals are contained in organic molecules
- They need to be decomposed first
- Cause a more controlled release - less likely to leach away
What nutrients are less likely to leach?
- Phosphates
- Less soluble
What causes eutrophication?
- Excess nutrients
Describe the process of eutrophication
- Mineral ions from fields cause rapid algal growth
- Algae blocks sunlight from reaching plants below
- Plants die as they cannot photosynthesise
- Bacteria feed on dead plants - aerobically respire reducing O2 concentration
- Fish & aquatic organisms die - not enough dissolved O2
How do fungi help plants?
- Form symbiotic relationships with plant roots - mycorrhizae
- Long, thin strands (hyphae) - inc SA to absorb ions and water
- Fungi gain compounds such as glucose from the plant
Describe the nitrogen cycle
nitrification nitrification denitrification
[Ammonium ions] —-» [nitrites] —-» nitrate —-» N2 in air
^ feeding l absorption l
l (animals)«—– (plants)«———-
l death & excretion l l death nitrogen
——————————–(decomposers) fixation
ammonification
What things contain nitrogen compounds?
- Proteins
- DNA
What is nitrification?
- Ammonium ions to nitrogen compounds for plants - oxygen added
- Done by nitrifying bacteria
What is denitrification?
- Nitrates in the soil are converted to nitrogen gas
- Done by bacteria
- In anaerobic conditions only –> aerate soil, not waterlogged
What is nitrogen fixation?
- Nitrogen from the atmosphere turned to nitrogen containing compounds
- Done by bacteria in the root nodules of leguminous plants
- N2 -> ammonia -> ammonium ions
- Form a mutualistic relationship
What is ammonification?
- Saprobionts turn nitrogen compounds from dead organisms into ammonia
- Also done to animal waste
Describe the phosphorus cycle
(fish)—-»(birds) (plants)———–»(animals)
l l / \ / \
(algae) [guano]—-»[soil]«–(decomposers)«–[urine&]
l ^ [faeces]
[seas&] l
[lakes] «——————- [rock]
What things contain phosphates?
- DNA
- ATP
- Phospholipids
How are phosphates released from rocks?
- Weathering releases phosphates from rock to soil and bodies of water
How do plants obtain phosphates?
- Absorb them through the roots from the soil
How do phosphates travel from the sea to the soil again?
- Phosphates taken in by aquatic producers
- Passed along the food chain to fish and then sea birds
- Waste from sea birds - guano - high proportion of phosphates which are returned to the soil
- Often used as a natural fertiliser
