Energy Flow & Nutrient Cycles Flashcards
How is energy lost at each trophic level?
In things that can’t be eaten (eg bones and faeces), and respiration
Food chains
PRODUCERS - plants photosynthesise, converting sunlight energy into energy forms that can be used by other organisms
PRIMARY CONSUMERS - the organisms that eat the producers
SECONDARY CONSUMERS - eat primary consumers (and so on through the trophic levels)
Some energy is lost at every stage
Reasons for loss of energy at each tropic level
- Around 60% of the available energy is never taken in by the organism
- plants can’t use all the light energy that reaches their leaves (may be wrong wavelength)
- some parts of organism can’t be digested
- some part of organism aren’t eaten eg bones
Gross Productivity
The rest of the available energy that is absorbed by the body
Respiratory Loss
30% of total energy available is lost due to respiration
Net Producivity
The amount of energy available to become biomass, and is what is available to the next trophic level
Net Productivity equation
gross productivity - respiratory losses
Percentage efficiency of energy transfer
net productivity of trophic level / net productivity of previous level
answer*100
Changes in percentage efficiency throughout the food chain
as you go further up the food chain, energy transfer becomes more efficient
efficiency varies between types of organisms
Pyramids of numbers
shows the number of organisms at each trophic level
Pyramids of biomass
shows the amount of biomass (in kgm^-2) at each trophic level at a single moment in time
Biomass
dry mass of an organism
Pyramids of energy
show the amount of energy available in each trophic level in kilo-joules per square meter per year (the net productivity of each trophic level)
Natural ecosystem
Hasn’t been changed by human activity
Intensive farming
changing an ecosystem by controlling the biotic and abiotic conditions to make it more favourable to crops and/or livestock so that the crops/livestock can have greater net productivity
Three ways intensive farming increases productivity
- increase efficiency of energy conversion
- remove growth limiting factors
- increase energy input
Examples of intensive rearing of livestock
- kept in warm indoor pens where movement is restricted
- high energy food that is low in indigestible material
- slaughtered young, when more energy is being transferred to biomass
Benefits of intensive farming
more food can be produced at lower costs in a shorter space of time
Herbicides
kills weeds that provide competition, so crops receive more energy
Fungicides
kill damaging fungal infections, so the crops don’t have to use energy fighting infections
Insecticides
kill insect pests that eat and damage crops, so less biomass is lost from crops
Problems with chemical pesticides
*may kill other insects that aren’t pests *eating lots of primary consumers that all contain some pesticide may adversely affect a secondary consumer *expensive
Biological agents used to reduce pest numbers
*natural predators *parasites (lay eggs or live within pests, either killing it or reducing its ability to function
Problems with biological agents
*natural predators may become a pest species themselves *biological agents can affect other non-pest species *may be less cost effective than chemical pesticides
