Energy and ecosystems Flashcards
Describe how biomass is formed in plants
During photosynthesis plants make organic compounds from atmospheric or aquatic CO2
Most sugars synthesised are used by the plant as respiratory substrates
Rest is used to make other groups of biological molecules
How can biomass be measured
Mass of carbon or dry mass of tissue per given area
How can dry mass to tissue be measured
Sample dried in oven
Sample weighed and reheated at regular intervals
Until mass remains constant
Why is dry mass more representative than fresh mass
Water volume in wet samples will vary but not affect dry mass
Describe how the chemical energy stored in dry biomass can be estimated
Using colorimetry
Known mass of dry biomass is burnt so the heat energy released is used to heat water. The increase in temperature is used to calculate energy of biomass
Explain how features of a calorimeter enable valid measurement of heat energy released
Stirrer - evenly distributes heat energy
Air/insulation - reduced heat loss and gain to and from the surroundings
Water - has a high SHC
What is GPP
Chemical energy store in plant biomass, in a given area or volume, in a given time
Total energy transferred into chemical energy from light energy during photosynthesis
What is NPP
Chemical energy store in plant biomass after respiratory losses to environment taken into account
Formula for NPP
NPP = GPP - R
Importance of NPP
NPP is available for plant growth and reproduction
NPP is also available to other trophic levels in the ecosystem
What is primary or secondary productivity?
The rate of primary or secondary production, respectively
State the units used for primary or secondary productivity
kJ ha-1 year-1 (unit for energy, per unit area, per year)
Explain why these units for primary or secondary productivity are used
Per unit area → takes into account that different environments vary in size
Standardising results to enable comparison between environments
Per year → takes into account effect of seasonal variation (temperature etc.) on biomass
More representative and enables comparison between environments
Explain why most light falling on producers is not used in photosynthesis
Light is reflected
Light misses chlorophyll
CO2 concentration is a limiting factor
State the formula for net production of consumers
N = I - (F + R)
I is the chemical energy stored in ingested food
F is the chemical energy lost to the environment in faeces and urine
State the formula for efficiency of energy transfer
Energy or biomass available after transfer / before transfer x 100
Explain why energy transfer between trophic levels is inefficient
Heat energy is lost via respiration
Energy lost via parts of organism that aren’t eaten (eg. bones)
Energy lost via food not digested → lost as faeces
Energy lost via excretion eg. urea in urine
Explain how crop farming practices increase energy transfer efficiency
Simplifying food webs to reduce energy
Herbicides kill weeds → less competition so more energy to create biomass
Pesticides kill insects (pests) → reduce loss of biomass from crops
Fertilisers e.g. nitrates to prevent poor growth due to lack of nutrients
Explain how livestock farming practices increase energy transfer efficiency
Reducing respiratory losses within a human food chain
Restrict movement and keep warm → less energy lost as heat from respiration
Selective breeding to produce breeds with higher growth rates
Explain the role of saprobionts in recycling chemical elements
Decompose (break down) organic compounds
By secreting enzymes for extracellular digestion
Absorb soluble needed nutrients and release minerals ions
Explain the role of mycorrhizae
Mycorrhizae = symbiotic association between fungi and plant roots
Fungi =act as an extension of plant roots to increase surface area
To increase rate of uptake of water and inorganic ions
In return, fungi receive organic compounds
Give examples of biological molecules that contain nitrogen
Amino acids / proteins or enzymes / urea / DNA or RNA / chlorophyll / ATP or ADP / NAD or NADP
Key stages of the nitrogen cycle
Describe the role of bacteria in nitrogen fixation
Nitrogen gas converted into ammonia which forms ammonium ions by nitrogen fixing bacteria
Describe the role of bacteria in ammonification
Nitrogen compounds are broken down and converted to ammonia which forms ammonium ions in soil
By saprobionts
Describe the role of bacteria in nitrification
Ammonium ions in soil converted into nitrites then nitrates
So root hair cells can be uptake by AT
By nitrifying bacteria in aerobic conditions
Describe the role of bacteria in denitrification
Nitrates in soil converted to nitrogen gas
By denitrifying bacteria in anaerobic conditions
Suggest why ploughing (aerating) soil increases its fertility
More nitrification
Less denitrification
Give examples of biological molecules that contain phosphorus
Phospholipids / DNA or RNA / ATP or ADP / NADP / TP or GP / RuBP
Describe the phosphorus cycle
Phosphate ions in rocks released (into soils / oceans) by erosion / weathering
Phosphate ions taken up by producers and incorporated into their biomass
Rate of absorption increased by mycorrhizae
Phosphate ions transferred through food chain
Some phosphate ions lost from animals in waste products (excretion)
Saprobionts decompose organic compounds eg. DNA in dead matter / organic waste,
releasing phosphate ions
Explain why fertilisers are used
To replace nitrates / phosphates lost when plants are harvested
improves efficiency of energy transfer
Describe the difference between artificial and natural fertilisers
Natural fertilisers are organic such as sewage and ions released during decomposition by saprobionts
Artificial contain inorganic compounds of nitrogen, phosphorous and potassium
Explain the key environmental issue arising from use of fertilisers
Phospahtes dissolve in water leading to leaching of nutrients into lakes
This leads to eutrophication :
- Rapid growth of algae so light is blocked
- Less photosynthesis
Explain the key advantage of using natural fertiliser over artificial fertiliser
Less water soluble so less leaching → eutrophication less likely
Organic molecules require breaking down by saprobionts → slow release of nitrate / phosphate etc.
