Energy Transfers in and Between Organisms: Energy and Ecosystems - Measuring Biomass Flashcards
Define the term biomass
- The mass of living material in an organism
How can biomass be measured?
- Mass of carbon an organism contains
- I.e Dry mass of its tissue per unit area
What is dry mass?
- Mass of the organism with the water removed
How is dry mass measured?
- A sample of the organism is dried, often with an oven using a low temperature until sample reaches a constant mass
- This value can be scaled up to give the total dry mass (biomass) of the total population in the area being investigated
What are the typical units for biomass?
- kg m^-2 yr^-1
Why is time quoted in the units?
- Biomass changes over time
How can you estimate the amount of energy stored in biomass?
- Burn the biomass in a calorimeter
- A sample of dry biomass is burnt and energy is released to heat a known volume of water
- The change in temperature of the water is used to calculate the chemical energy of the biomass
How much energy is used to raise the temperature of 1kg of water by 1°C? (J/kg°C)
- 4200 Joules
- Or 4.2 Joules for 1g of water
List some of the components of a bomb calorimeter
- Thermometer
- Insulated container
- Sealed bomb with oxygen
- Water
- Motorised stirrer
What is the importance of the insulated container?
- To reduce heat loss to the environment by radiation
Why is oxygen present in the sealed container?
- To allow complete combustion to occur
Why is there a motorised stirrer?
- To evenly distribute heat
What is gross primary production (GPP)?
- The total amount of chemical energy converted from light energy by plants, in a given area/volume and time
What is respiratory loss?
- Heat that is lost to the environment when organisms respire
Approximately how much of the gross primary production is lost to the environment due to respiration?
- 50%
What is net chemical production (NPP)?
- The energy left in a plant after respiratory loss is subtracted from the gross primary production
Give the equation that describes the relationship between GPP, R and NPP (NPP as subject)
- NPP = GPP - R
What is primary production called when it is expressed as a rate?
- Primary productivity
How is the net primary production used?
- NPP is energy available to the plant for growth and reproduction
- Also energy is available to organisms at the next stage in the food chain
What is net production in consumers (N)?
- Net production (N) is the total chemical energy consumers store after energy losses have been subtracted from the chemical energy of the ingested food
List the different ways energy is lost in plants and animals
- Not all energy is absorbed / material is indigestible
- Respiratory loss
- Excretion
How is some energy not absorbed in plants?
- Some light misses the leaf and the chlorophyll
- Some wavelengths of light are not absorbed
How does respiratory loss differ in plants and animals?
- Animals have a higher respiratory loss
- Animals move more, so more heat is generated from more metabolic reactions
How is some energy not absorbed in animals?
- Animals may not eat the whole biomass (e.g roots)
- Some of biomass is indigestible (cellulose/fibre in humans) and is excreted
What is the formula for calculating net production?
• N = I - (F+R)
- N = net production
- I = chemical energy in ingested food
- F = chemical energy lost in faeces and urine
- R = energy lost through respiration
What is the net production of consumers also known as?
- Secondary production
What is net production known as when expressed as a rate?
- Secondary productivity
What is the formula of the efficiency of energy transfer?
- % efficiency of energy transfer = (net production of trophic level / net production of previous trophic level) x 100
How does the efficiency of energy transfer differ across the food chain?
- As you move up a food chain (from producers to consumers) energy transfer usually becomes more efficient
- Higher proportion of plant biomass is indigestible or not eaten by consumers
