energy cycles Flashcards
Producers
Plants
- produce their own carbohydrates from carbon dioxide (autotrophs)
- start of a food web
Energy transfer between trophic levels
- Biomass and its stored energy is transferred through trophic levels very inefficiently
- most energy is lost due to respiration and excretion
Consumers
Heterotrophs that cannot synthesise their own energy
- obtain chemical energy through eating
Why is dry mass a representative measure of biomass
- Water content in tissues varies
- heating until constant mass allows standardisation of measurements
- for comparison
Biomass
Measured in terms of:
- mass of carbon
- dry mass of tissue per given area
How is 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
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
Calculating net primary production
NPP = GPP - R
R = respiratory losses to the environment
Gross primary production
- Chemical energy stored in plant biomass, in a given area / volume
- total energy resulting from photosynthesis
Net primary production
- Chemical energy stored in plant biomass after respiratory losses
- available for plant growth and reproduction - create biomass available to other trophic levels
Calculating net production of consumers (N)
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
Why is productivity measured per area
Per hectare (for example) is used because environments vary in size
- standardises 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 transfer inefficient from sun -> producer
- Wrong wavelength of light - not absorbed by chlorophyll
- light strikes non- photosynthetic region (bark)
- light reflected by clouds / dust
- lost as heat
Why is energy transfer inefficient after producers
- Respiratory loss - energy used for metabolism (active transport)
- lost as heat
- not all plant / animal eaten (bones)
- some food undigested (faeces)
Farming practices to increase energy transfer for crops
- Simplifying food webs to reduce energy / biomass
- herbicides kill weeds -> less competition
- fungicides reduce fungal infections
- results in 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
Importance of nitrogen to organisms
Used to create
amino acids / proteins
DNA
RNA
ATP
Nitrogen cycle stages
Nitrogen fixation
nitrification
denitrification
ammonification
Nitrogen fixation
- Nitrogen fixing bacteria break triple bond between two nitrogen atoms in nitrogen gas
- fix this nitrogen into ammonium ions
