chapter 23 - ecosystems Flashcards
(32 cards)
What are ecosystems?
- its the distrubution of organisms that are controlled biotic and abiotic factors
What is meant by tropic level?
- each stage of the food chain
What is gross primary productivity and what is it made up of?
- its the total amount of energy made by producers
- its made up of respiratory loss and net primary production(biomass)
What is the difference between respiratory loss and net primary production?
- respiratory loss, the energy used by organisms for respiration (e.g active transport, movement, heat)
- net primary production, is the amount of chemical energy a producer stores as biomass
why is the energy tranfer from the sun to the producer very low(roughly 2%)?
- wrong wavelength
- light strikes non photosynthetic region
- light reflected
- lost as heat
why is energy tranfer from the producer to the primary consumer low(roughly 10%)?
- there is respiratory loss, plant uses energy for metabolism(e.g active transport)
- lost as heat
- not all the plant is eaten(roots)
- some food is not digested
Why is the energy tranfer from the primary consumer to the secondary consumer low(roughly 10-15%)?
- there is respiratory loss, primary consumer uses energy for metabolism (e.g muscle contraction)
- lost as heat
- not all the animal is eaten
- some of the food not digested (e.g faeces)
describe and explain the two ways in which we can increase energy tranfer in crop plants?
- shorten the food web, reduce competition so the plant has more energy to create biomass(herbicide to kill weeds, fungicide to reduce infection, insecticide to chemically control pests)
- fertilisers(e.g nitrates), prevent growth being limited by lack of nutrients
What four ways can we increase the energy transfer in animals and livestock?
- reduce respiratory loss, restrict movement and so less respiration and more energy is used to make biomass
- slaughter animal while growing
- controlled diet, higher yield of food will be digested
- keep predators away
What way can we increase energy transfer in both animals and plants?
- artificially select organisms with a high yield
What are the two ways to measure biomass?
- dry biomass
- mass of carbon
How is dry biomass used to measure biomass?
- a sample is taken of biomass and is warmed until the mass is constant (all the water has evapourated)
- the temperature must be low to avoid combustion as there would be a loss of biomass/co2
Why isnt a wet sample used when using the dry biomass method in measuring biomass?
- the amount of water in biomass samples varies a lot
- and so dry biomass gives a more representative sample
How is energy stored in biomass calculated and explain how it works?
- calorimetry
- burn a sample of biomass completely
- heat a known volume of water
- measure the temperature change of water
- calculate energy released
how is the mass of carbon used to measure biomass?
- organisms are made from organic compounds
- mass of carbon is a good indicator for biomass
- difficult to measure
- carbon is about 50% of the dry biomass
What is succession?
- a series of changes in a species composition in a given place over time
explain the process of succession
- an area is colonised by pioneer species, this changes the enviornmental conditions to make it less hostile(increase in nutrients)
- this allows other species to outcompete the preceeding species
- continues until climax community is reached (woodland)
What is a climax community?
- final stage of succesion, few species dominate, and stable equilibrium of species
As succession takes place what increaeses?
- biodiversity
- niches
- plant height
- soil depth
- h20 + nutrients available
As succession takes place what decreases?
- light intensity at ground
describe primary succession
- starts from newly formed land (e.g volcanic rock)
- harsh abiotic factors (e.g no soil, little H20/nutrients)
describe secondary succession
- starts from land where vegetation has been cleared (e.g human deforestation/forest fire)
- less harsh abiotic factors(soil already exists, more h20/nutrients available)
- much faster
- pioneer species can be larger
describe deflected succession
- a community that remains stable because human activity prevents natural succession from taking place (mowing)
- this stops succession and stops tall plants growing and these plants can outcompete low growing grass
- grassland becomes climax community
What are the 3 ways in which nitrogen fixation occurs?
- industrially
- with the use of bacteria
- lightning
