organisation of an ecosystem

• what do the arrows in food chains represent?

  direction of energy transfer
• why is the number of prey generally larger than number of predators?

  a predator needs to eat lots of prey's the amount of energy passed from prey to predator isn't enough to meet the predators energy need
• primary consumers issues / benefits:

  • cellulose in cell walls is difficult to digest
  • don't have to catch prey first
• secondary consumers (predators) issues / benefits :

  • food (prey) is high in protein and fat, so relatively easy to digest
  • animals move about so they have to catch them
• one limitation of using food chains?

  • food chains suggest that each type of consumer eats only one other type of organism
  • whereas most consumers eat a variety of different foods
• prey numbers affected by:

  • weather conditions, disease, competition affecting food supply
  • disease
  • population balance between different types of prey for a particular predator
• predator numbers affected by:

  • disease
  • competition balance between different types of prey
• explain why predator and prey numbers rise and fall in cycles in a stable community

  • as prey numbers go up, there is more food for predators, so predator numbers increase after an interval
  • as predators numbers increase, prey numbers start to fall as more are eaten
  • after an interval, fall in prey animals means fewer predators survive and breed, so predators numbers fall too
  • as predators numbers fall, fewer prey animals are eaten and prey numbers begin to increase again (cycle repeats)
• define abundance

  how many individuals of a species there are
• define distribution

  where the individuals of a species are located
• what are the biotic factors affecting the distribution of organisms?

  • food availability
  • new competitors
  • new predators arrive
  • new pathogens/disease
• what are the abiotic factors affecting the distribution of organisms?

  • temperature
  • wind (intensity + direction)
  • availability of oxygen (aquatic animals)
  • carbon dioxide levels (for plants)
  • soil pH and mineral content
  • moisture levels
• how to measure abundance?

  place quadrats randomly
• why random sampling placement?

  to avoid bias ( which wouldn't be representative)
• what is a quadrat?

  a square frame often subdivided into smaller squares

  used to sample plants because is isn't possible to count every example
• when do you use a line transect?

  to measure a change across a habitat
• what is a line transect?

  when quadrats are placed at regular sample points and the abundance of the organisms within each is recorded
• define organic compounds

  compounds produced by living things and contain carbon (and hydrogen)

  eg glucose, starch, fats
• define carbon sink

  absorbs more carbon dioxide than it releases eg oceans and soil
• define carbon source

  releases more carbon dioxide than it absorbs eg volcanoes
• define detritus

  dead organisms
• where does the carbon in fossil fuels originally come from?

  organic compounds in detritus
• define transpiration

  evaporation of water from inside leaves to release water vapour into the atmosphere through stomata
• why is water so important to living organisms?

  • a solvent used to transport glucose etc around organisms
  • a habitat for many organisms - in and off water so important for ecosystems
• describe the water cycle

  • precipitation - water droplets fall form clouds as rain, hail, snow etc
  • percolation (and infiltration)- water trickles through gaps in soils and rocks
  • water from soil absorbed by plant roots. this is transpired and respired into atmosphere
  • surface run off - into bodies of water. this evaporates into water vapour
  • water vapour in atmosphere condenses into liquid, forming clouds
• examples of producers?

  plants, algae and plankton
• define consumer

  cannot make its own food so it has to eat another organism
• describe how carbon in dead leaves is recycled for use by plants

  Decomposers break down organic material in detritus, to become organic compounds in decomposers.

  Decomposers such as bacteria and fungi carry out respiration, releasing the stored carbon back into the air, (as CO2), which plants can then access and restore through carbon fixation in photosynthesis.
• what happens to the organic compounds in plants during respiration?

  converted to CO2 in atmosphere
• give two reasons why deforestation increases the amount of carbond dioxide in atmosphere

  • lots of trees logged are then burnt as fuel. this releases stored carbon from trees
  • trees act as a carbon sink, so by removing the sink, means less carbon capture
• what is the process that moves carbon from detritus to fuels?

  fossilisation
• what is the process that moves carbon from decomposers to the atmosphere?

  respiration
• what do plants use CO2 absorbed from photosynthesis for?

  to produce organic compounds
• what does limestone release during volcanic eruptions?

  co2
• what happens as a result when global transpiration reduces?

  more intense rain - > flooding
• why is percolation being reduced?

  urbanisation
• the water cycle is affected by changes in the...

  carbon cycle