Energy and ecosystems Flashcards
What are producers?
Plants
produce their own carbohydrates from carbon dioxide
the start of the food web
Energy transfer between trophic levels
between each trophic level, most of the energy is lost due to respiration and excretion. The remaining energy is used to form the biomass.
What are consumers?
heterotrophs that cannot synthesise their own energy
obtain chemical energy through eating
Biomass
measured in terms of mass of carbon and dry mass of tissue per given area
How is the dry mass of tissue estimated?
Sample of organism dried in oven below 100C (avoiding
combustion + loss of biomass)
sample reweighed at regular intervals
all water removed when mass constant
Why is dry mass a representative measure of biomass?
Water content in tissues varies
heating until constant mass allows standardisation of measurements
for comparison
Calorimetry
Laboratory method used to estimate chemical energy stored in dry biomass
Calorimetry method
Sample of dry biomass is burnt
energy released used to heat known volume of water
change in temperature of water used to calculate chemical energy
Gross primary production
the chemical energy stored in plant biomass, in a given area or volume
It is the total energy resulting from photosynthesis.
Net primary production
The chemical energy stored in plant biomass taking into account the energy that will be lost due to respiration
How to calculate net primary production?
NPP = GPP - R
R = respiratory losses to the environment
How to calculate NPP in consumers?
N = I - (F + R)
I = chemical energy store in ingested food
F = chemical energy store in faeces / urine
R = respiratory losses
units of productivity rates
kJ Ha-1 year-1
kJ is the unit for energy
Ha is the unit area
Why is productivity measured per area?
Because environments vary in size
it standardizes the results so environments can be compared
why is productivity measured per year?
More representative of productivity
takes into account effects of seasonal variation (temperature) on biomass
environments can be compared with a standardised amount of time
Why is energy inefficient after the producer?
Respiratory loss - energy used for metabolism (active transport)
lost as heat
not all plant / animal eaten (bones)
some food undigested (faeces)
Why is energy transfer inefficient from sun to producer?
Wrong wavelength of light - not absorbed by chlorophyll
light strikes nonphotosynthetic region (bark)
light reflected by clouds / dust
lost as heat
Farming Practices to increases energy transfer for crops
Simplifying food webs to reduce energy / biomass:
herbicides kill weeks = less competition
fungicides reduce fungal infections = more energy used to create biomass
fertilisers such as nitrates to promote growth
Farming practices to increase energy transfer for animals
Reducing respiratory losses (more energy to make biomass)
restrict movement
keep warm
slaughter animal when young (most energy used for growth)
selective breeding to produce breeds with higher growth rates
saprobionts
Feed on remains of dead organisms and their waste products (faeces / urea) and break down organic molecules
secrete enzymes for extracellular digestion
Mycorrhizae
Symbiotic relationship between fungi and roots of plants
fungi act as extensions of roots
increase surface area of system
- increasing rate of absorption
mutualistic relationship as plants supply fungi with carbohydrates
Nitrogen cycle stages
Nitrogen fixation
nitrification
denitrification
ammonification
Importance of nitrogen in organisms
Used to create:
amino acids / proteins
DNA
RNA
ATP
nitrogen fixation
Nitrogen fixing bacteria break triple bond between two nitrogen atoms in nitrogen gas
fix this nitrogen into ammonium ions
Nitrogen fixing bacteria
Fix nitrogen gas into ammonium ions
free living in soil
or form mutualistic relationship on root nodules of leguminous plants
give plants N in exchange for carbohydrates
Nitrification
Ammonium ions in soil are oxidised to nitrite ions
nitrite ions are oxidised to nitrate ions by nitrifying bacteria
denitrification
Returns nitrogen in compounds back into nitrogen gas in atmosphere by anaerobic denitrifying bacteria
Phosphorus cycle
Phosphate ions in oceans and soil.
absorption = phosphate ions in plants
consumption = phosphate ions in animals
excretion = returned to ocean or soil
decomposition = phosphate ions from waste/remains
erosion = returned to oceans and soil
deposition = phosphate ions in rocks
importance of phosphorus
Used to create:
DNA
RNA
ATP
phospholipid bilayers
RuBP / GP/ TP
ammonification
Proteins / urea / DNA can be decomposed in dead matter and
waste by saprobionts
return ammonium ions to soil - saprobiotic nutrition
Fertilisers
Replace nutrients (nitrates and phosphates) lost from an ecosystem’s nutrient cycle when crops are harvested or livestock removed
can be natural (manure) or artificial (inorganic chemicals)
Natural fertilisers advantages
Cheaper than artificial fertilisers
often free if farmer has own animals - recycle manure
organic molecules have to be broken down first by saprobionts so leaching is less likely
Artificial fertilisers advantages
Contain pure chemicals in exact proportions
more water-soluble, so more ions dissolve in water surrounding soil.
higher absorption
Natural fertilisers disadvantages
Exact minerals and proportions cannot be controlled
Artificial fertilisers disadvantages
High solubility means larger quantities can leach away with rain
= risking eutrophication
reduce species diversity as favour plants with higher growth rates e.g., nettles
Leaching
When water-soluble compounds are washed away into rivers / ponds
for nitrogen fertilisers, this can lead to eutrophication
eutrophication
When nitrates leached from fields stimulate growth of algae
algal bloom
can lead to death of aquatic organisms
How does eutrophication lead to the death of aquatic organisms?
Algal bloom creates blanket surface of water blocking light so plants cannot photosynthesize and die
aerobic bacteria feed and respire on dead plant matter
eventually, aquatic organisms die due to lack of dissolved oxygen in water
mutualistic relationships
A type of symbiotic relationship where all species involved benefit from their interactions
role of saprobionts in the nitrogen cycle
They use enzymes to decompose proteins/DNA/RNA/urea
releasing ammonium ions
