How ecosystems work Flashcards
Biomass
- mass of organisms
Productivity
- rate at which materials are produced
- energy transferred to a trophic level
Why does biomass of grass in ungrazed area decrease?
- reduced photosynthesis due to long leaves blocking light
- greater competition for water, nutrients, minerals
- leaves dying
Why are there low levels of primary productivity in grazed area?
- larger number of animals trample grass
- overgrazing
- grass unable to recover
- little photosynthesis takes place
- to much excretion
How fall in predators affects food chain / grassland productivity
- decrease in predators results in an increase in predators’ prey, e.g. herbivores, fewer are killed
- this leads to overgrazing by increased number of herbivores
- reduction in producers, less primary productivity
- less food for herbivores, herbivores die
- increase in other carnivores
How changes in % of dead organic matter changes the number of species
- less organic matter, fewer nutrients
- unstable substrate
- few species can tolerate conditions
- pioneer species colonise
- increased organic matter suits more species
- increased competition
- climax community established, fewer species where good soil is
Climax community
- plant community that no longer changes in specie composition
- due to succession
- dominant species most abundant
Net primary production (NPP)
- rate of production of new biomass
- that is available to the next tropic level
- NPP = GPP - respiration
Why only a small % of the light energy falling onto a leaf is converted into chemical energy
- light reflected away from leaf
- some light passes straight through leaf
- plant cannot use all wavelengths of light
- photosynthesis is not efficient
Why only 10% of energy locked up in secondary consumers is transferred to tertiary consumers
- secondary consumers respire / loss as heat
- they lose energy when they move around
- not all of them are eaten
- they have indigestible parts
- decomposition of secondary consumers
Why decomposers have greatest energy transferring in
- they obtain energy from all trophic levels
Why is slash and burn farming considered unsustainable
- after a long time total biomass has not returned to original
- fewer roots could lead to less water retention
- fewer roots will lead to more soil erosion
- leaf litter is loer so there will be less nutrients
How biodiversity could change by the practice of slash and burn
- change in habitats
- more light allowed in
- exposure to wind (loss of shelter from wind)
- exposure to light changes plant populations
- may lead to soil erosion
- plants cannot get established
- animals might migrate
- changes in plants causes changes in types of animals
Plagioclimax
- a sub climax
- factor e.g. grazing that maintains the subclimax
How a grazed grassland could develop into a woodland community
- remove grazer
- allow different species to colonise
- competitive effects, change in soil
- will go through several stages
- succession occurs
- climax community established
- change in specie composition
Factor that could affect population size of predator
- climate
- territory size
- diseases
- predation
- water/food supply
Gross primary productivity
- Chemical energy fixed/ carbohydrates stored in producers by photosynthesis
- the rate at which producers capture ad store a given amount of chemical energy as biomass in a given length of time
Role of decomposers in food chain
- decompose dead remains
- using external digestion
- to release nutrients (nitrates)
Why is productivity lower in colder areas than tropical areas
- temperature lower
- slower enzyme activity
- shorter growing season, less sunlight
- less photosynthesis
- less water
Ways energy is lost
- respiration
- faeces/indigestible material
- nitrogenous waste
Why are food chains of limited length
- small proportion reaches next level
- insufficient energy to support another level
Why is it important that compost is not allowed to become water logged or compacted
- compact gives rise to anaerobic conditions
- aerobic respiration not possible
- denitrifying organisms break nitrogen containing into nitrogen
Reasons for causes of desertification
- overgrazing
- lack of rainfall
- climate change, e.g global warming
Explain the process of desertification
- loss of vegetation due to overgrazing
- trampling compacts soil and removes plants
- soil is exposed to wind and sun
- soil blown away, evaporation of water from soil
- loss of roots loosens soil
Way to prevent desertification
- put in a barrier, e.g. hedges, to reduce wind speed and provide shelter
- use plants that are drought resistant, these plants can survive
- plant fuel crop, sustainable
- rain water harvesting, irrigate land
- control grazing, e.g. density of animals to prevent loss of vegetation cover
- supply water to live stock
Biotic factor
- involve other living organisms
Abiotic factor
- involve physical/chemical non-living things
Explain why GPP increases greater than NPP
- more energy is used in metabolism in bigger plants
- for protein synthesis and flower initiation
- herbivores cannot digest all parts
- more photosynthesis tissue
Relationship between GPP, NPP and respiration
- GPP - NPP = R
- biomass production reduced by respiration
Why only a proportion of the organic material, formed using CO2, will become plant tissues
- respiration of some of the organic material
- energy is required for synthesis of molecules, movement and active transport
Abiotic factors that can affect gross primary production
- light intensity, duration, wavelength
- temperature
- CO2 concentration
- pH
Why does oxygen uptake increase for dead plant material
- dead plant material is decomposed
- by the action of microorganism
- which respire aerobically
- more dead material provides more nutrients which leads to an increase in microorganism
Why might there be a high number of predators
- GPP increases
- indicating high plant population
- plants releases O2 by photosynthesis
- more plants mean more herbivores
- more food for predators
How plant species vary as a result of succession
- difference communities at different distances
- few species near beach, more further away as organic matter increases with distance, increasing number of niches
- pioneer species colonise empty inorganic surfaces, penetrating rock breaking it up, allowing organic material to accumulate
- increased organic matter results in increased water retention, mineral content
- less hostile conditions, larger plants can be supported
- better adapted plants out compete others, dominant specie is usually largest and most abundant
- eventually climax community is reached. specie range is constant and dominated by a few species
Explain the difference between abiotic and biotic factors
- biotic factors involve organisms and abiotic factors are physical/chemical non-living factors
