Energy Transfers And Productivity Flashcards
What do ecosystems contain
All the living components (i.e. biotic factors such as organisms and their interactions)
All the non-living components (i.e. abiotic factors such as temperature and rainfall)
What are primary producers
Transfer light energy from the sun to synthesise organic molecules eg glucose in photosynthesis
They then use respiration to transfer energy from glucose into ATP
This acts as an immediate source of energy for living organisms
The rest of the glucose is used to make other biological molecules that the plant requires
How does the producer play a key role in the food chain
The chemical energy in these biological molecules can then be used by other organisms within the community known as consumers (i.e. the organisms in higher trophic levels)
How many tropic levels are there
Primary consumers (herbivores or omnivores) feed on producers
Secondary consumers (carnivores or omnivores) feed on primary consumers
Tertiary consumers (carnivores or omnivores) feed on secondary consumers
Can be more but oftener limited by insufficient energy
What are decomposers
Organisms tha break down dead and decaying material of organisms from all trophic levels
What are the 2 types of decomposers
Saprobionts - bacteria and fungi - carry out extra-cellular digestion, secrete enzymes onto dead/decaying matter which then break it down into a food source
Detritivores- earthworms,woodlice, millipedes and centipedes - feed on dead/decaying material whilst directly breaking down material - they also increase the SA for bacteria and fungi to act upon
What are food webs
These show all the different interactions that exist within a community
However not as accurate as don’t show actual energy
What is biomass
The total mass of living material in a specific area at a given time
- use the dry mass
-or the amount of carbon an organism contains
It is measured in grams per square metre or grams per cubic metre in an aquatic system
How does biomass change overtime
For example, the biomass of deciduous trees decreases over autumn and winter as they lose their leaves
This means that biomass is sometimes given with units of time as well
This shows the average biomass of an organism within a given area over that time period
For example, if the average biomass of a group of oaks trees over the course of a year is found to be 13,000 kg, the biomass may be given as 13,000 kg y⁻¹ (this means 13,000 kg per year)
If the average biomass of 1 m² of a grass field over the course of a year is found to be 0.15 kg m⁻², the biomass may be given as 0.15 kg m⁻² yr⁻¹ (this means 0.15 kg per square metre per year)
How is calorimetry used to estimate chemical energy stored in biomass
This involves burning the sample of dry biomass in a piece of equipment known as a calorimeter
The burning sample heats a known volume of water
The change in temperature of the water provides an estimate of the chemical energy the sample contains
What are the limitations of calorimetry
It can take a long time to fully dehydrate (dry out) a plant sample to find its dry mass
This is partly because the sample has to be heated at a relatively low temperature to ensure it doesn’t burn
Depending on the size of the sample, the drying process could take several days
Precise equipment is needed, which may not be available
A very precise digital balance should be used to measure the mass of the plant sample as it is drying (to detect even extremely small changes in mass)
It is preferable to use a very precise digital thermometer when measuring the temperature change of the water in the calorimeter (again, to detect even very small temperature changes)
The more simple and basic the calorimeter, the less accurate the estimate will be for the chemical energy contained within the plant sample
This is due to heat energy from the burning sample being lost and not being transferred efficiently to the water
A bomb calorimeter ensures that almost all the heat energy from the burning sample is transferred to the water, giving a highly accurate estimate
What is the method for carrying out calorimetry
Weigh the crucible (heat-proof container) without the sample first
Place the sample in the crucible
Place the crucible in the oven
Set the oven to a low temperature (if the temperature is too high the sample may burn, which would cause it to lose biomass)
Remove and weigh the crucible (containing the sample) at regular intervals during the drying process
Once the mass of the crucible (and sample) stops decreasing and becomes constant, the sample is fully dehydrated (all the water has been removed)
From this final constant mass, subtract the original mass of the crucible (without the sample in it) to find the dry mass of the sample
Why is only some of the suns light available to be used
Over 90% is reflected back
Not all wavelengths of light can be absorbed and used for photosynthesis
Light may pass straight through the leaf and not fall on a chlorophyll molecule
May be other limiting factors
What is gross primary productivity
The total quantity of the chemical energy stored in plant biomass in a given area or volume
Easily comparable as is in an area/ volume
What are the units of GPP
Gross primary productivity is expressed using units of energy/mass per unit area per unit time
Time must be included as it is a rate
For example
Mj m–2 y-1 (megajoules per square metre per year)
kg km-2y-1 (kilograms per square kilometre per year)
