Biology, 13: Human influences on ecosystems

• The carbon cycle:

  
• Carbon dioxide is converted into complex carbon compounds in plants during photosynthesis
• Respiration returns carbon back into atmosphere as carbon dioxide
• Carbon in complex compounds passes along the food chain through feeding

  Some carbon is released due to respiration
• Organisms die, decaying body is digested by decomposers

  The decomposers respire, releasing carbon dioxide directly into the atmosphere
• Dead organisms that decay are converted to other complex carbon compounds

  Heat and pressure produces oil from it

  It can be burned for energy, releasing CO2 during combustion
• Deforestation is the permanent destruction of large areas of forest and woodland
• Deforestation can result in loss of habitat for species and possibly leading to extinction
• Deforestation results in greater risk of flooding, top layer of rich soil can also be lost
• Deforestation leads to more CO2 released into the air as it is burned or left to rot

  Less CO2 is absorbed as well
• Deforestation affects the water cycle, as less water is held due to lack of trees for transpiration
• Deforestation leads to increase in soil erosion:

  There are no roots holding the soil together

  Essential nutrients is lost by leaching

  Loss of nutrients makes it difficult to regrow tree
• Water pollution is the adding of substances to the environment that can cause harm
• Discarded rubbish can be swallowed by animals

  Entangle organisms

  Breaks down, releasing toxins and affecting surrounding organisms

  Breaks down and swallowed by animals, affecting their health
• What is eutrophication?


  Nitrate ions leaches into the lake due to runoff

  There is an increase rate of growth of photosynthesising organisms, particularly algae at the surface

  Algae bloom occurs, blocking light to plants in deep water

  Deep water plants die as they can't photosynthesise

  Bacteria feeds on decayed plants, increasing in number as well

  Bacteria respires more rapidly to make material for growth and reproduction

  Respiration takes dissolved O2 from water

  Other aquatic organisms cannot respire as well due to less O2

  Most aquatic plants and animals will die
• Eutrophication: