Chapter 13 - Energy in Ecosystems

• Describe how biomass is formed in plants.

  During photosynthesis

  Plants make organic compounds from atmospheric or aquatic Co2.

  Most sugars synthesised are side by plants as respiratory substrates.

  Rest used to make other groups of biological molecules - form biomass
• How can biomass be measured?

  Mass of carbon or dry mass of tissue per given area.
• Describe how dry mass of tissue can be measured.

  Sample dries in oven at 100 degrees (avoid combustion)

  Sample weighed and reheated at regular intervals until max remains constant.
• Explain why dry mass is more representatives that fresh mass.

  Water volume in wet samples will vary

  Dry mass not impacted by amount of water.
• Describe how chemical energy stored in dry biomass can be estimated.

  Calorimetry

  1. Known mass of dry biomass is fully combusted

  2. Heat energy released heats know volume of water

  3. Temperature of water used to calculate chemical energy of biomass.
• Explain how features of a calorimeter allow valid measurement of heat energy released.

  Stirrer - evenly distributed heat

  Air / insulation - reduces heat loss and gain to and form surroundings

  Water - has high specific heat capacity.
• What is gross primary production?

  Chemical energy store in plant biomass in a give area or volume in a given time

  Total energy transferred into chemical energy from light energy during photosynthesis.
• What is net primary production?

  Chemical energy store in plant biomass after respiratory losses to environment taken into account.
• State the formula for NPP.

  NPP = GPP - R
• Explain the importance of NPP in ecosystems.

  NPP is available for plant growth and reproduction

  NPP is also available to the trophic levels in ecosystems such and herbivores and decomposers.
• State the units for primary or secondary productivity.

  KJ ha ^-1 year ^-1
• Explain why the unto for primary or secondary productivity are used.

  Per unit area - takes varying environment size into account

  - standardising results and allowing for comparison

  Per year - takes in to account effect of seasonal variation on biomass

  - More representative and enables ocmapyrison between environments.
• Explain why most light falling on producers is not use din photosynthesis.

  High reflected or wrong wavelength

  Light misses chlorophyll / chloroplasts/ photosynthetic tissue

  Co2 conc. or temperature is limiting factor.
• State the formula for net production of consumers.

  N = I - (F + R)

  I = the chemical energy store in ingested food

  F = the chemical energy lost to the environment in faeces and urine
• State the formula fro efficiency of energy transfer.

  Energy or biomass available for transfer/ energy or biomass available before transfer.

  (x 100 if percentage)
• Explain why energy transfer between trophic levels is inefficient.

  heat energy lost via evaporation

  Energy lost via parts of organisms that aren't eaten

  Energy lost via food not digested - lost as faeces

  Energy lost via excretion e.g in urea
• Explain how crop farming practices increase efficiency of energy transfer.

  Simplifying food webs to reduce energy / biomass losses to non human food chains.

  Herbicides kill weeds - less competition so more energy to create biomass

  Pesticides kill insects - Reduce loss of biomass from crops

  Fungicides reduce fungal infections - more energy to create biomass

  Fertilisers - to prevent poor growth due to lack of nutrients.
• Explain how livestock farming practises increase efficiency of energy transfer.

  Reducing respiratory losses within human food chain.

  Restrict movement and keep warm - less energy lost as heat from respiration.

  Slaughter animals young - most energy used for growth

  Treated with antibiotics - prevent loss of energy due to pathogens

  Selective breeding to produce breeds with higher growth rates.
• Explain the role of saprobionts in recycling chemical elements.

  Decompose organic compounds e.g proteins urea and DNA

  By secreting enzymes for extracellular digestion.

  Absorb soluble needed nutrients and release mineral ions
• What is mycorrhizae?

  Symbiotic association between fungi and plant roots
• Explain the role of mycorrhizae.

  Fungi acts as an extension of plant roots to increase surface area of root system

  Increased rate of uptake of ions and water

  Fungi then receive organic compounds e.g carbohydrates.
• Give examples of biological molecules that contain nitrogen.

  Amino acids

  Proteins/enzymes

  Urea

  DNA/RNA

  Chlorophyll

  ATP or ADP
• Describe the diagram of the nitrogen cycle.

  
• Describe the role of bacteria in nitrogen fixation.

  Nitrogen gas converted t ammonia forming ammonium ions in soil

  By nitrogen fixation bacteria
• Describe the role of bacteria in ammonification.

  Nitrogen containing compounds e.g proteins or waste from organism are broken down / decomposed.

  Converted to ammonia forming ammonium ions in soil

  By saprobionts
• Describe the role of bacteria in nitrification.

  Ammonium ions in soil convert nitrites to nitrates via two step oxidation reaction

  - for uptake by plant root hair cell by active transport

  By nitrifying bacteria in aerobic conditions
• Describe the role of bacteria in denitrification.

  Nitrates convert soil into nitrogen gas

  By denitrifying bacteria in anaerobic conditions
• Suggest why ploughing or aerating soil increases its fertility.

  More ammonium converted to nitrite and nitrate / more ammonification

  Less nitrate converted to nitrogen gas / less denitrification/ fewer nitrifying bacteria.
• Give examples of biological molecules that contain phosphorous.

  Phospholipids

  DNA or RNA

  ATP or ADP

  NADP

  Triose phosphate or GP
• Describe the phosphorous cycle.

  1. Phoshpate ions in rocks release by erosion and weathering

  2. Phosphate ions taken up by producers / plants /algae and incorporated into their biomass

  3. Phosphate ions transferred through food chain

  4. Some phosphate ions lost from animal in waste products

  5. Saprobionts decompose organic compounds e.g DNA in dead matter
• Explain why fertilisers are used.

  To replace nitrates/ phosphates lost when plants are harvested and livestock removed

  Those removed from soil and incorporated into biomass cant be released back into the soil through decomposition by saprobionts

  Improve efficiency of energy transfer - increasing productivity and yield.
• What is a natural fertiliser?

  Contain inorganic compounds of nitrogen phosphorous and potassium
• What is an artificial fertiliser?

  Organic e.g manure compost sewage - ions released during decomposition by saprobionts.
• Explain key environmental issues with use of fertilisers.


  Phosphates / nitrates dissolve in water leading to leaching of nutrients into lakes/oceans and rivers.
• Describe eutrophication as a result of fertilisers.

  Rapid growth of algae in pond / river blocking light

  Submerged plants die due to lack of photosynthesis

  Saprobionts decompose dead pant matte rising oxygen in respiration.

  Less oxygen for fish to aerobically respire leading to their death.
• Explain the key advantages of using natural fertiliser use over artificial fertiliser.

  :less water soluble so less leaching - less eutrophication

  Organic molecules require breakdown by saprobionts - slow release of nitrates