energy and ecosystems Flashcards
why is dry biomass more accurate than wet biomass
- organisms contain different amounts of water in their tissues
- dry biomass allows for compasrison between biomass of different organisms
What is biomass
Biomass is the total mass of living material / mass of carbon /dry mass in a specific area at a given time
What is biomass
Biomass is the total mass of living material / mass of carbon /dry mass in a specific area at a given time
Why can you not use fresh mass to measure biomass
Varying water levels make it unreliable as water content of a sample varies
What are the units for dry mass
Grams per square metre of grams per cubic metre
Why are only small samples taken for dry mass
Organisms must be killed
How do you obtain dry mass
dry by heating Heat at 100* or over , to confirm your sample is dry repeat until mass stops decreasing - heat until constant mass. low temperature is used to avoid burning
How do you then calculate the biomass from dry mass
1) burn dry biomass in pure oxygen in a calorimeter,with a known volume of water this breaks the bonds and released the energy as heat which increases the temp of water
2) measure temperature increase
3) calculate energy transferred
= SHC water x water volume x temp change / mass of dry biomass
What does biomass contain
Chemical energy store , which is produced during photosynthesis
What is gross primary production( GPP)
GPP is the chemical energy stored in plant biomass in a given area or volume in a given time
How much of this energy is used for respiration
20-50%
What is net primary production (NPP)
The chemical energy stored in plant biomass after respiratory losses to the environment
An area of vegetation 5m by 5m produces 40000kj energy in a year . Calculate GPP
Area =25 m2
40000/25 =1600 kjm-2year-1
Why does NPP vary
Environmental temperature
Type of plants growing and their density
Day length and light intensity
Availability of soil nutrients
What happens when rate of photosysnethesis increases
More carbon (biomass enters the food chain
What is NPP also known as
The energy left over that is available to ththe plant to create new biomass - available to the next tropic level in a foodweb
How do you work out the net production of consumers
N=I-(F+R) where N= net production , I= chemical energy store in ingested food , F= chemical energy lost to environment in faeces and urine and R= respiratory losses
What are the units for rates of productivity and why
Kjha-1year-1.
Kj for energy
Ha-1 is an area , we have to standardise the results to enable the environments to be compared l- it takes into account that different environments will vary in size
Per year - takes into account the impact seasons will have on rain , light and heat ( affecting soil quality , nutrients etc )- it provided an annual average to allow fair comparisons between environments
How do you work out % efficiency
Energy available after transfer / energy available before the transfer
X100
what are the issues with bomb calorimetry
- organisms must be killed
- normally only made on a small sample which may not be representative
- can take a long time to fully dehydrate a sample as the sample has to be heated at a relatively low temperature to ensure it doesnt burn
- prescice equiptment is needed which might not be available
( prescise digital balance for the mass of the plant samoke and a precise thermometer too)
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why is their air surrounding the bomb calorimeter
- draught excluder - decreases amount of heat lost to enviroment . air reduces loss of heat
insulation reduces gain of heat
what is the purpose of the copper container
transfers heat from burning sample to water
why do we use a crucible
it is a heat proof container
what is the point of a stirrer
distributes heat energy so ensures even temperature - no hot spots
what are ignition wires used for ( only in certain models )
electrical current is passed through causing the sample to burn
what is the point of the vessel with oxygen
ensures all of the sample is burnt
what are autotrophs
producers
how do autotrophs grow
they use energy from sunlight to produce glucose
why does a mouse have a higher respiratory rate than an elephant
- higher surface area to volume ratio and therefore more heat is lost to surroundings and it needs to maintain this