5.3 Energy and ecosystems Flashcards
How is biomass formed in plants?
• During photosynthesis, plants make organic compounds from CO2
• Most sugars synthesised are used by the plant as respiratory substrates
• Some used to make other biological molecules, forming biomass
How can biomass be measured?
Mass of carbon or dry mass of tissue per given area
How can dry mass of tissue be measured?
• Dry sample in oven at 100°C
• Weigh and reheat at regular intervals
• Until mass remains constant (all water evaporated)
Why is dry mass more representative than fresh mass?
Water volume in wet samples will vary but will not affect dry mass
How can the chemical energy stored in dry biomass be estimated using calorimetry?
• Known mass of dry biomass fully combusted
• Heat energy released heats a known volume of water
• Increase in temperature of water is used to calculate chemical energy of biomass
What is gross primary production?
• Chemical energy store in plant biomass per given area
• 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 taken into account
• NPP = GPP – R
What is primary or secondary productivity?
• Rate of primary or secondary production
• kJ ha-1 year-1
Why are these units used?
• Per unit area takes into account that environments differ in size, standardising results, enabling comparison
• Per year takes into account seasonal variation so more representative, enabling comparison
Why is most light not used in photosynthesis?
• Light is reflected / wrong wavelength
• Light misses chlorophyll
• CO2 concentration or temperature is a limiting factor
What is net production in consumers?
• Chemical energy store in consumer biomass after faeces/urine and respiratory losses taken into account
• N = I – (F + R)
Why is energy transfer between trophic levels inefficient?
• Heat energy lost via evaporation
• Not all parts of organism eaten (bones)
• Not all food digested (faeces)
• Energy lost via excretion (urine)
How do farming practices increase energy transfer efficiency?
• Simplifying food webs (eg. Herbicides, pesticides, fungicides) so more energy to create biomass
• Fertilisers to provide nutrients
• Reducing respiratory losses (eg. Restrict movement, keep warm, slaughter while young, treat with antibiotics, selective breeding) so more energy used to create biomass
