5.3 - Energy & Ecosystems

• What does an ecosystem include?

  all the living organisms in a particular area, and all the non-living (abiotic) conditions.
• What 2 ways do Plants use sugars from photosynthesis?

  1. respiratory substrates

  2. to synthesise other biological molecules
• Define Biomass

  the organic matter mass of organism with chemical potential energy stores
• How can biomass be measured?

  • In terms of the mass of carbon that an organism contains or the dry mass of its tissue per unit area per unit time
• what are the Units for biomass?

  gm-2 when an area is being sampled, gm-3 when a volume (e.g. a pond) is being sampled
• How is water removed from samples when measuring dry mass?

  - dried in an oven at low temperatures

  - weighed at refular intervals until the mass reading is constant
• how can you estimatine chemical energy store in dry biomass?

  Using calorimetry: Energy released = specific heat capacity of water x volume of water (cm3) x temperature increase of water
• Why is bomb calorimetry preferable to simple calorimetry?

  the closed-vessel design prevents heat from escaping, allowing for a highly accurate reading
• Define Gross primary production (GPP)

  Total chemical energy, converted from light energy, in plant biomass within a given volume or area
• Define Respiratory loss (R)

  The approximately 50% of GPP that is lost to the environment as heat when plants respire. (the remaining chemical energy is NPP)
• Define Net primary productivity (NPP)

  Total chemical energy available for plant growth, reproduction, and energy transfer to other trophic levels after respiratory losses, stored in the plant's biomass.
• Mathematical relationship between GPP, NPP and R

  NPP = GPP - R, where R represents respiratory losses
• How is Primary production espressed?

  expressed as a Rate, ie. the total amount of chemical energy or biomass in a specific area over a given time period

  - typical units: kilojoules per hectare per year ( kJ ha-1 year-1)

  - when rate value is measured its called primary productivity
• What are the Reasons for most of the Sun's energy not being converted to organic matter

  - Most solar energy is absorbed by atmosphere or reflected by clouds.

  - Photosynthetic pigments cannot absorb some wavelengths of light.

  - Not all light falls directly on a chlorophyll molecule. Energy lost as heat during respiration/photosynthesis
• what estimated percentage of chemical energy stored in consumer's food is transfered to next tropic level?

  between 1-10%, this is the consumer's net production
• how can you calculate net production of consumers?

  N = I - (F + R), where I is chemical energy from ingested food, F is energy lost as faeces and urine, and R is respiratory losses
• Define Secondary productivity (net production of consumers)

  Rate of secondary production or biomass in a specific area over a given time period (e.g. kJ ha-1 year-1)
• What are the reasons for biomass decrease along a food chain?

  - Energy lost in nitrogenous waste (urine) & faeces.

  - Some of the organism is not consumed.

  - Energy lost to surroundings as heat
• General equation for % efficiency

  Energy converted to a useful form (J) x 100 / Total energy supplied (J)
• Limitation of food chain length

  Energy is lost at each trophic level, so there is insufficient energy to support a higher trophic level
• Pyramid of biomass

  Diagram that shows the biomass at each trophic level
• Advantage of pyramid of biomass over pyramid of numbers

  Shape of pyramid of numbers may be skewed since a small number of producers can support many consumers
• how can the relationships between members of a community in an ecosystem be described?

  food chains or food webs
• What is each stage in a food chain called?

  a trophic level
• How are producers autotrophic?

  able to extract both energy and matter from abiotic environment (energy from sun, and 98% of their dry mass from CO2 in the air or water), with the remaining 2% from water minerals and soil.
• Define detritus

  The dead organic matter, such as fallen leaves, twigs, and other plant and animal wastes
• define saprobionts

  A microorganism that feeds on dead plants or animals and waste products using extracellular digestion
• Farming practices to increase energy transfer efficiency

  Exclusion of predators, artificial heating, restriction of movement, controlled feeding at the optimum
• Average number of trophic levels

  4 to 5
• disadvantages of food chains

  1. dont provide number of species

  2. dont provide other consumer food sources

  
  

  (food webs combat point 2)
• What 2 methods of energy loss do farming practices aim to combat, in order to increase energy availbility for human consumption?

  1. the energy lost to other organisms, eg.pests, can be reduced

  2. the energy lost through respiration can be reduced
• What is the impact of food web simplification?

  Reduces energy loss to other organisms
• Farmers aim to simplify the food web - what 3 methods may they use?

  1. Reduce pest numbers using chemical pesticides (eg. insecticides & herbicides)

  2. Biological agent use to reduce biomass loss (eg. natural preditors)

  3. Integrated systems of chemical and biological methods increas NPP maximally.
• Farmers aim to reduce Respiratory losses - what 2 methods may they use?

  They increase net biomass production of livestock by controlling conditions they live in.

  
  

  1. kept in pens so movement is restricted

  
  

  2. kept warm indoors, so less energy is wasted generating body heat, not given out to surroundings by radiation, convection or conduction.
• define Arable farmers

  Those that grow crops such as wheat, barely and oats
• define pastoral farmers

  those that rear livestock
• What do Arable farmers want to maximise compared to Pastoral farmers?

  Arable - NPP

  Pastoral - NP
• define intensive farming

  farming in developed nations to feed general population, ten times more productive than subsistence, designed to maximise productivity by making use of appropriate technology.
• define substistence farming

  farming crops grown to feed individuals/families, pretty inefficient.
• what are the 7 broad categories of farming techniques that increas productivity?

  1. Selective Breeding

  2. Fertilisers

  3. Pest Control

  4. Factory Farming

  5. Large Fields

  6. Monoculture

  7. Mechanisation