5.3 Energy & Ecosystems Flashcards
What are most of the sugars synthesised by plants used as in plants?
Respiratory substrates (e.g. glucose)
What are remaining sugars not used in respiration/as respiratory substrates used for?
Making other groups of biological molecules (e.g. starch)
What is biomass made of?
The different groups of biological molecules formed from sugars synthesised by plants during photosynthesis
What is biomass? (there are two definitions)
- Mass of living/biological material excluding water of an organism or tissue
- Chemical energy stored within the organism or tissue
Biomass can be measured in terms of:
- dry mass of an organism or tissue IN A GIVEN AREA
- mass of CARBON an organism or tissue contains
What can the chemical energy store in dry biomass be estimated by?
Calorimetry!
What is dry mass?
Mass of organism or tissue after all water has been removed
Why is biomass sometimes given with units of time?
Biomass can change over time (e.g. biomass of deciduous trees decreases during autumn & winter as leaves are lost)
Typical units of biomass
kgm^-2 or kgm^-3
How does calorimetry work (general overview)?
- Burn a sample of dry biomass in a calorimeter
- The burning sample heats a known volume of water
- The change in temperature of water provides an estimate of the chemical energy of the sample
What is the name of the more precise/accurate calorimeter, and how is it more precise/accurate than a classroom calorimeter?
Bomb calorimeter
1. Stirrer - ensures heat is evenly distributed throughout the water
2. Oxygen - ensures complete combustion of the sample
Formula to calculate chemical energy stored in dry mass via calorimetry
temp increase x mass of water x 4.2 (J per °C) / mass of food
Organisms can be divided into 3 groups, according to how they obtain energy - what are they?
- Producers/Autotrophs
- Consumers/Heterotrophs
- Saprobionts
What are producers/autotrophs?
Organisms that use light energy & inorganic molecules (CO2 & H2O) to make organic molecules (glucose)
What are consumers/heterotrophs?
Organisms that get energy by consuming other organisms
What are saprobionts?
Organisms that feed on other organisms but not exactly a predator (eg. parasites)
What do saprobionts do?
Break down complex organic molecules into simple inorganic molecules.
This releases the inorganic substances back into the ecosystem - material is always recycled!
Why is so little of the energy available from the Sun captured by plants/producers in photosynthesis?
- some is the wrong wavelength (eg. plants can’t use green light to photosynthesise)
- other factors limit rate of photosynthesis (eg. CO2 concentration)
- light may hit a non-photosynthetic part of the plant
Why is only around 10% of chemical food energy passed on between organisms in a food chain?
- some parts are left uneaten (eg. bones)
- decay of dead material (eg. bacteria may decay some material)
- excretion (eg. energy lost in faeces)
- exothermic reactions (eg. heat lost in respiration)
Define gross primary productivity (GPP)
The chemical energy store in plant biomass, in a given area or volume
Define net primary productivity (NPP)
The chemical energy store in plant biomass after respiratory losses to the environment have been taken into account
What is the formula linking GPP and NPP?
NPP = GPP - R
R: respiratory losses to the environment
What is NPP available for?
Plant growth and reproduction, and other trophic levels in the ecosystem (eg. herbivores & decomposers)
What are the units of GPP?
kJ m^-2 yr^-1
J m^-3 hr^-1
Why do warm-blooded (endothermic) animals have greater respiratory losses than cold-blooded (exothermic) animals?
They need to constantly respire to maintain a constant body temperature (they have a higher respiration rate)
What parts of all plants cannot be digested by most animals?
Cellulose cell walls
Formula for net production of consumers (N)
N = I - (F + R)
I: chemical energy store in ingested food
F: chemical energy lost to environment in faeces & urine
R: respiratory losses to environment
Methods of increasing production of crop plants
- Use biological control/pesticides: pests decrease biomass of crops
- Fertilisers/crop rotation: increases mineral ions in soil
- Greenhouses/artificial light: maximises rate of photosynthesis
Methods of increasing production of animals raised for meat
- Keep animals in confined spaces (although ethically questionable) - reduces energy loss via respiration
- Keep warm (although $$ to install heaters) - reduces energy loss via respiration
- Easily digested food (preferably high protein) - reduces energy loss via undigested food
