B13- Energy and Ecosystems Flashcards
How is energy transferred in ecosystems?
The process of photosynthesis transforms light energy into chemical energy held in biological molecules.
The chemical energy in these biological molecules can then be used by other organisms within the community known as consumers (i.e. the organisms in higher trophic levels)
Trophic level
A level in a food chain or ecological pyramid occupied by a group of organisms with similar feeding mode.
Food chain
A linear sequence of organisms through which nutrients and energy pass as one organism eats another.
Saprobiont
Organisms that live off decaying organic matter, breaking it down into simpler substances.
Gross primary production
Gross primary production (GPP) is the amount of chemical energy stored in carbohydrates within plants (during photosynthesis)
Gross primary productivity (GPP) is the rate at which plants are able to store chemical energy via photosynthesis
Net primary production
Net primary production (NPP) refers to the amount of energy available to herbivores in the plant’s biomass after plant respiratory losses
Net primary production AND productivity
Net primary productivity (NPP) is expressed using units of energy/mass per unit area per unit time
NPP of producers is also available to decomposers - bacteria & fungi
- Break down dead plant & animal materials → gain the chemical energy stored in the dead matter
Do this by:
- Secreting digestive enzymes onto the surface of the dead organism → enzymes break down the dead matter into small soluble food molecules → molecules are then absorbed by the decomposers
This process of decomposition also helps to release organic nutrients back into the environment (eg. the soil) which are essential for the growth of plants and other producers.
Primary & Secondary Productivity
Primary production - the store of chemical energy in the biomass of producers
Secondary production - the store of chemical energy in the biomass of consumers; not all of this biomass is transferred to higher trophic levels, because:
- Not all of the biomass of the food is eaten (e.g., roots, bones) - the chemical energy in these structures are lost of the environment
- Consumers can’t digest everything they consume
- Lots of chemical energy is lost through respiration (mainly thermal energy) and during excretion
Net production of Consumers
The energy that is left for the consumer to store as new biomass is the net production of consumers
N = I - (F + R)
Where:
I = the chemical energy store in ingested food
F = the chemical energy lost to the environment in faeces and urine
R = the respiratory losses to the environment
Calculating Primary and Secondary productivity/efficiency
The efficiency of energy transfer can refer to the percentage of energy that is transferred from the sun to producers
- % Efficiency = (gross primary productivity ÷ light energy falling on the producer) × 100
OR the percentage of energy that is transferred from one trophic level to a higher trophic level
- % Efficiency = (chemical energy in consumer ÷ chemical energy in ingested food) × 100
The Effect of Farming
Farming practices can increase the efficiency of energy transfer in order to increase the total amount of energy available for human consumption. This can be achieved by:
- Reducing the energy lost by crops to other organisms (e.g. pest species that feed on crops) by chemical pesticides (Insecticides & herbicides)and biological agents (e.g., ladybugs, which eat aphids…) farmers often use both methods to tackle pest.
- Reducing the energy lost by livestock (e.g. cattle) through respiration by keep livestock in pens → movement is restricted → less energy lost through respiration and keeping livestock indoors and in heated pens → reduces respiration rate needed to maintain a body temperature. These practice ensure more chemical energy is stored as biomass and not lost to respiration → increases the net production.
Nitrogen Fixation
- Atmospheric nitrogen gas (N2) is converted into nitrogen-containing compounds
- These compounds can be used by plants
- These bacteria are found in root nodules and have a symbiotic relationship with plants
Ammonification
- Nitrogen compounds in waste products (e.g., urine & faeces) and dead organisms are converted into ammonia by saprobionts - a decomposer (bacteria/fungi)
- The ammonia form ammonium ions in the soil
Nitrification
Ammonium ions in the soil are converted into nitrates by nitrifying bacteria → nitrates used by plants & denitrifying bacteria …
Denitrification
- Denitrifying bacteria use nitrates in the soil during respiration
- Nitrogen gas is produced, which returns to the atmosphere
The Phosphorus Cycle
- Phosphorus in rocks is released into soil and water in the form of ions (PO43-) by weathering (erosion)
- Phosphate ion is taken up by plants through their roots OR absorbed from water by algae
- Ions are then transferred by to consumers during feeding
- Ions in waste products and dead organisms are released back into the soil or water via decomposition by saprobionts
- The phosphate ions can now be taken up and used once again by producers OR may be trapped in sediments that, over very long geological time periods may turn into phosphorus-containing rock once again
Agricultural Ecosystems & Fertilisers
Agricultural ecosystems are not like natural ones, as crops/livestock are removed from fields, instead of dying & decomposing naturally
- Mineral ions are not returned to the soil by microbes
- Nitrogen & Phosphorus cycle is disrupted
- (Over a long time) the soil concentrations of ions will decreases → decrease in crop yields / meat / milk yields
Adding fertilisers to fields is a way of replacing minerals lost
→ ensures high livestock / crop yield
Natural Fertilisers
Natural (Organic) fertilisers
- Made up of organic material from dead & decomposing remains + waste products
- Examples: Manure, composted veg, crop residues & sewage
- Improves soil structure
- Released over long periods of time
- Not very concentrated, so large amounts needed
Artificial (Inorganic) fertilisers
- Made up of inorganic matter (powders or pellets) that contain pure chemical compounds -e.g., ammonium nitrate
- Very concentrated, so smaller amounts are needed
- Easy to apply
- Increased crop yield
Environmental Issues Caused By Fertilisers
Crop plants are unable to use all the fertiliser provided, the soluble nitrate and phosphate ions in the excess fertiliser are not taken up by the crop plants and remain in the soil water
- Leaching can occur: minerals dissolve in & are transported by rainwater into ponds, lakes, streams & rivers
- This is more likely to occur from artificial fertilisers
- Can lead to eutrophication - rapid growth of algae (algal bloom)
Algal bloom → blocks sunlight from aquatic plants → die (along with some algae) →decomposing bacteria feed on dead organic matter + increase in number → oxygen is used by these bacteria → causes the death of fish & insects
