Ch 9: Organisms and the environment

• Energy flow in an ecosystem


  1. Light energy from sun absorbed by chlorophyll in producers and converted to chemical energy (glucose) during photosynthesis

  2. Energy passed from one trophic level to another by feeding

  3. Energy lost between trophic levels as heat during respiration, in uneaten body parts, through undigested matter egested as faeces, and through waste products excreted as excretory products

  4. About 90% of energy lost when transferring from one trophic level to another

  5. Food chains generally short to ensure greater amount of energy available to final consumer

  6. Five or more trophic levels rare as insufficient energy to support final consumer

  
• Producers


  First organism on food chain/web that makes its own food by photosynthesis, containing chlorophyll which absorbs light energy and converts it to chemical energy
• Consumers


  Organisms that obtain energy by feeding on other organisms

  Primary consumers (herbivores): Eat plants, trophic level 2

  Secondary consumers (carnivores): Eat primary consumers, trophic level 3

  Tertiary consumers (carnivores): Eat other carnivores, trophic level 4

  Apex predator: Top of food chain/web, trophic level depends
• Decomposers


  Organisms that feed on decaying organic matter, obtaining energy by breaking down dead organisms, faeces and excretory products
• Pyramid of numbers


  • Represents the numbers of each organism in a pyramid

  Number of organisms decreases from lower to higher trophic levels

  Explained by energy losses between trophic levels

  
• Pyramid of biomass


  • Represents the total biomass of each organism in a pyramid

  Total biomass decreases from lower to higher trophic levels

  Explained by energy losses between trophic levels

  
• Pyramid of numbers vs pyramid of biomass

  Pyramid of numbers can be inverted, pyramid of biomass is always upright

  Biomass is directly proportional to energy, numbers not always proportionate to energy

  
• Carbon cycling in an ecosystem


  Carbon dioxide in atmosphere converted to glucose in plants by photosynthesis

  Carbohydrates in plants transferred to other organisms during feeding

  Glucose converted to carbon dioxide during respiration

  Carbon in dead organisms converted to carbon dioxide during decomposition

  Carbon in dead organisms converted to fossil fuels when stored underground for long periods

  
• Carbon sink


  An area that stores carbon compounds for a long period of time, storing more carbon than it releases

  Examples: Forests and oceans

  
• Deforestation


  Releases carbon stored in trees back into atmosphere as carbon dioxide
• Use of fossil fuels


  Releases carbon stored in fossil fuels back into atmosphere as carbon dioxide
• Increased atmospheric CO2


  Enhances greenhouse effect, leading to global warming