Edexcel iGCSE Biology - ecology and the environment notes

  • Created by: samo1
  • Created on: 31-10-18 02:15


  • an ecosystem = the interaction between a community of living organisms and their environment 
  • the environment consists of all the conditions that surround and living organism 
    both the living, non-living things and physical surroundings 
  • a population = all the organisms of same closely-closely-related species in an area
  • a habitat = the place where an organism lives
  • a community = all species found in an ecosystem at a particular time

[ biodiversity ] 

definition: the amount of variation in species in an ecosystem

measured by: 

  1. no. of different species present, the “richness” 
  2. relative abundance (population no.) of each species, the “evenness” 

important because:

  • more stable, if an ecosystem is dominated by one or few species, it’s likely to be affected by ecological disaster, for example, genetic diseases
  • protection from rapid environmental changes, when there is more interdependence in the food web, if one were to become extinct, it wouldn’t be a big problem
  • protection from physical changes
  • climate change/ global warming

simpson’s index:

D = 1 - ∑ ( n / N )

[ sampling ]


  • quadrats
  • line or belt transects
  • posters
  • pitfall traps
  • nets

[ factors affecting the abundance & distribution of organisms ] - abiotic

light intensity

some plants have evolved for optimum growth in bright sunlight. An example of this is a cactus house plant. Cacti originally come for deserts where they grow in bright sunlight. If you were to put a cactus in a dark corner of a room, the plant wouldn’t grow well. 


both animals and plants have evolved to grow healthily at their optimum temperatures. If you put either a cactus or orchid houseplants outside in cold temperature, they would die. 

moisture level

many plants cannot survive in waterlogged soils, their roots are unable to respire, they rot and the plant dies. other plants, such as pitcher plants, grow best in bogs where the moister levels are high. 

soil pH/ water pH

the pH of soils can have a huge effect on the plants that are able to grow in them. some plants, grow best in acidic soils and will quickly die if planted in alkaline oils. others, prefer alkaline soils. some, can grow in both, these plants are unusual in that their flower colour changes in different soils. 

the pH of water can also affect the aquatic organisms that are found there. different species have evolved to survive at different pH levels found within water.

soil mineral content

many plants require high levels of soil minerals to grow well. an example of this is magnesium, which is required to produce chlorophyll, plants with unnatural yellow leaves may have a magnesium deficiency. 

wind intensity & direction

many organisms prefer more sheltered locations. plant seed are more likely to settle and germinate there, and animals which depend upon these are more likely to live close by. 

CO2 level - plants

carbon dioxide is a reactant in photosynthesis which means plants need it to survive. areas which higher levels of carbon dioxide are likely


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