Summary of topic 2.5
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1. The document discusses ecosystem structure and function, including the three main biotic components - producers, consumers, and decomposers. 2. It describes energy flow through ecosystems via photosynthesis and respiration. Producers use photosynthesis to convert light energy from the Sun into chemical energy stored in glucose. Consumers and decomposers release this energy through cellular respiration. 3. As energy passes between trophic levels, about 90% is lost through respiration and waste at each level. This limits the amount of energy available to higher levels in the food chain.
Summary of topic 2.5
- 2. Ecosystem Structure • There are 3 main biotic components in any ecosystem: – Producers • Plants, algae and cyanobacteria • They are able to create food using sunlight energy • Also referred to as photoautorophs – Consumers • • • • Obtain energy through eating other organisms They do not possess chlorophyll and can’t photosynthesise Also referred to as heterotophs They may be herbivores or carnivores – Decomposers • • • • Bacteria and fungi 123 Obtain food though the breakdown of dead organic matter Create humic material and are important in recycling nutrients Some bacteria are chemoautotrophic decomposers (they use a similar process to photosynthesis which uses energy from oxidation reactions rather than sunlight)
- 3. Energy Flow • Energy flow through an ecosystem occurs by 2 processes: • Photosynthesis 6CO2 + 6H2O C6H12O6 + 6O2 • Respiration C6H12O6 + 6O2 6CO2 + 6H2O
- 4. Energy Flow Photosynthesis Inputs Outputs Transformations Process Respiration Light Energy, H2O, CO2 Glucose, O2 Glucose, O2 Energy, H2O, CO2 Light Energy Chemical Energy Chemical Energy Kinetic Energy + Heat Chlorophyll traps light energy, this energy used to split water molecules, H from water combined with CO2 to produce glucose Oxidation reactions inside cells break down glucose to release energy
- 5. Energy Flow • About half of the Sun’s total radiation is visible light • Only visible light is useful for photosynthesis • Producers use very little of the visible light available to produce biomass (about 0.06% of the Sun’s total radiation is captured by producers) – The remainder is reflected, transmitted or is not the correct wavelength of light for photosynthesis. Photosynthesis itself is not an efficient process (typically 0.1 - 2.0% efficient)
- 6. Energy Flow • Producers make energy available to consumers in the form of stored chemical energy (glucose) • This energy is lost as it passes through each trophic level due to respiration and defaecation (typically 90% is lost between each level) • Eventually all of the initial available energy is lost by being converted into heat which radiates away from the Earth. The Sun re-radiates energy to the Earth (which is therefore an Open System)
- 7. Howard Odum • Ecologist who made the first full analysis of a whole ecosystem – Silver Spring, a stream in Florida • He measured all inputs and outputs in terms of organic matter and energy • He calculated productivity in kcal m-2 yr -1 • He represented his data as a productivity diagram and an ecosystem model • In his models he developed a symbol language similar to that used in electronics
- 11. The Water Cycle (The Hydrological Cycle)
- 12. Productivity • Primary Productivity (PP) – The gain in energy or biomass by producers per unit area per unit time • Secondary Productivity (SP) – The gain in energy or biomass by heterotrophs per unit area per unit time PP involves the conversion of solar energy – it is dependent on the amount of sunlight, temperature, CO2 etc. SP involves feeding or absorbtion – it is dependent on how much food is available and how efficiently it can be turned into biomass
- 13. Gross Productivity • Gross Primary Productivity (PP) – The total gain in energy or biomass by producers per unit area per unit time, not taking any losses due to respiration into account • Secondary Productivity (SP) – The gain in energy or biomass by heterotrophs per unit area per unit time, not taking any losses due to respiration and defaecation into account Losses are caused at each trophic level by respiration You could compare this idea to money flow - your GROSS income is the total amount of money you earn - your NET income is the amount of money you have after losses due to taxation etc.
- 14. Net Productivity • Net Primary Productivity (PP) – The total gain in energy or biomass by producers per unit area per unit time, taking losses due to respiration into account (R) • Net Secondary Productivity (SP) – The gain in energy or biomass by heterotrophs per unit area per unit time, taking losses due to respiration (R) and defaecation (F) into account The net productivity values are more useful as they give you information about how much energy or biomass is available from one trophic level to the next
- 15. Net Primary Productivity (103 kJ m-2 yr-1) Maximum Net PP in Some Biomes 120 100 80 60 40 20 0
- 17. Calculations NPP = GPP – R GPP (from photosynthesis) NPP R NSP = GSP – F – R R NSP F
- 18. Questions 1. Without referring to your notes, draw an outline of the carbon, nitrogen and water cycles 2. Why is not all of the energy assimilated by one trophic level available to the next one? 3. Without referring to your notes, write formulas for the calculation of NPP and NSP (defining each term)
- 19. Questions Biome Mean NPP (kg m-3 yr-1) Desert 0.003 Tundra 0.14 Temperate grassland 0.60 Savannah 0.90 Temperate forest 1.20 Tropical rainforest 2.20 1. Compare and contrast the NPP of each biome 2. Why is there a difference between the NPP of temperate grassland and savannah?