10.2 - energy transfer through ecosystems Flashcards
how is energy transferred through ecosystems
between trophic levels
what is gross primary productivity
- the rate at which light from sun catalyses production of new plant material
- plants use at least 25% of material they produce for own metabolic needs and respiration
- rest of the material is stored as NPP
what is net primary productivity
- material produced by photosynthesis stored as new plant body tissue
- NPP of different ecosystems depends on abiotic and biotic factors which affect plant growth
- it is less than GPP as some of the energy is lost in plant respiration
how is productivity summarised
equation
GPP = NPP + R
where R is rate of respiration
how is energy transferred between trophic levels
- sunlight is the source of energy for all living systems (light intensity is a limiting factor for ecosystems)
- only small amount of the energy available to an organism is transferred to next trophic level
- some is never taken in, some is lost before being transferred
why is energy lost at each trophic level
- transfer of energy to the surroundings in respiration
- inedible parts lsot to organisms and broken down by decomposers
why is some energy never taken in at each trophic level
- some parts of food are not eaten
- some parts of food are indigestible
- plants can’t use all light energy as some is in the wrong wavelength
energy losses along a food chain
- some energy is lost as it’s undigested and so unused material in the faeces
- most material is used to drive respiration - exothermic process so energy lost to surrounding
- some plant material lost in metabolic waste products such as urea
what is the process of making new biomass known as
secondary production
what is the efficiency of energy transfer
- the proportion of energy in one trophic levels that is available to the next
efficiency formula e.g.
of the 240,000 kJm^2/y in the biomass of producers. 24,000 kJm^2/y are available to primary consumers. Calculate the efficiency
(24,000 / 240,000) x 100
= 10%
useful nutrients
- plants are responsible for producing most organic molecules
- require inorganic nutrients such as CO2 and nitrates to do so
- plants take nitrates from soil water to produce amino & hence proteins, and to produce nucleotides used to build DNA and RNA
cycling of nutrients
- respiration and other metabolic processes release inorganic compounds to the environment
- producers take these up to make organic compounds
why can plants not use nitrogen in air
- because nitrogen is an inert (unreactive) gas
- only nitrogen in form of nitrates is useful for plants from soil water
- it is taken up to make protein - protein is passed along the food chain
nitrogen cycle
- NH3 (ammonia) becomes NO2- (nitrite ion) due to nitrifying bacteria
- NO2- becomes NO3- (nitrate ion) due to more nitrifying bacteria
- NO3- can be converted to N2 in air by denitrifying bacteria and then back to NH3 by nitrogen fixing bacteria
- OR NO3- takes up nitrate and becomes plant protein
- the plant protein can become dead organic matter due to death
- OR plant protein becomes animal protein due to consumption of food
- animal protein then turns to dead organic matter due to waste matter and death
- decomposers then convert dead organic matter to NH3 again
