Pack 17 - Energy, Ecosystems and Nutrient cycles

Food chains and energy transfer:
1. Most plants convert energy from sunlight into chemical energy in organic comounds
  1. Nitrates and phosphates are required to make these organic compounds
2. Food chains:
  1. Producers:
    1. Photosynthetic organisms manufacture organic substances
  2. Consumers:
    1. Consume other organisms to obtain their energy
    2. Primary consumers eat producers
    3. Secondary consumers eat primary consumers
  3. Saprobionts
    1. Extracellular digestion
      1. Break down things to absorbable parts
        Assimilated
3. Trophic levels
  1. Energy flows from primary producers to consumers. Each group is said to be at a certain trophic level
  2. e.g. grass-->rabbit-->fox
  3. There are usually only 4 or 5 trophic levels due to the inefficiency of energy transfer
4. Food webs:
  1. In any habitat, many food chains are inter-linked to form food webs
  2. Some organisms will be in more than one trophic level
    1. The greater the number of interactions, the more stable the food web is
Biomass
1. Total mass of living material in a specific material in a specific area at a given time
  1. All organisms contain a variable volume of water
2. Dry mass is measured by drying the sample in an oven at 100 degrees until a constant mass is reached.
  1. Issues:
    1. Organisms must be dead
      1. Only small samples can be taken
        Sample may not be representative
3. Measured in dry mass per given area in a given time
4. Calorimetry can be used to estimate the chemical energy store in dry mass
  1. 1. Sample of dry material weighed
    1. 2. Burnt in pure oxygen in a sealed chamber
      1. 3. Bomb is surrounded by water bath
        4. Heat of combustion causes temp. of the water to rise
Energy transfer and Productivity
1. 90% of energy from the sun is lost, even more is lost of the energy hitting a leaf:
  1. Some energy used for evaporation
  2. Some energy is reflected by cuticle
  3. Not all light hits the cuticle
  4. Not all wavelengths used in photosynthesis
  5. Low CO2 Conc. may limit photosynthesis
2. Gross primary production (GPP) and net primary production (NPP)
  1. GPP = The chemical energy store in a plant biomass, in a given area volume at a given time
  2. NPP = Chemical energy store in plant biomass after respiratory losses to the environment
  3. NPP = GPP - R
3. Less than 10% NPP in plants available to consumers
  1. Not all plant eaten
  2. Some used in respiration for ATP production
  3. Some lost in egestion and excretion
  4. Plant material is difficult to digest
4. Less than 20% available from secondary to tertiary
  1. Not all consumed
  2. Some parts are lost in faeces
  3. Lost in excretion
5. Net production of consumers
  1. N = I - (F+R)
    1. I = Chemical energy
    2. F = chemical energy lost to environment
    3. R = Respiratory loss
Productivity and farming practices
1. Increasing the efficiency of energy transfer leads to higher yields
2. Intensive farming techniques:
  1. Restrict movement - less energy used in muscle contraction
  2. Environment kept warm - reduce heat loss from the body
  3. Optimum amount of food for max growth
  4. Predators excluded so no loss to other organisms
Chemical and biological control of agricultural pests
1. Pesticides
  1. Effective ones should:
    1. Be specific to only one organism
    2. Biodegrade
    3. Not accumulate
  2. Development of genetic resistance
    1. Mutation confers resistance
      1. Pests without mutant allele are killed by pesticide
        Organisms with allele for resistance survive
        Breed to pass on allele
2. Biological Control
  1. Eradicating pests may mean that other pests can multiply
  2. Very specific, once introduced the organisms reproduce themselves
  3. Pests can't become resistant
3. Integrated control systems
  1. Aim to keep pests are acceptable levels
  2. Choose varieties of animals/plants that are resistance to pest
    1. Providing habitats close to crops for natural predators
      1. Monitor crops for signs of pests
        Remove pests mechanically
        Use biological agents
        Use pesticides
Nutrient cycles
1. Saprobiotic organisms:
  1. Activate a gene that makes digestive enzymes
    1. Enzymes are secreted and hydrolyse surrounding material into soluble compounds
      1. Compounds are absorbed by cells and assimilated
2. Nitrogen cycle
  1. Ammonification
    1. Production of ammonia from organic nitrogen containing compounds
    2. Carried out by saprobiotic organisms
  2. Nitrification
    1. Oxidation of ammonium ions to nitrate ions
      1. Then oxidation of nitrite ions to nitrate ions
  3. Nitrogen Fixation
    1. Reduce gaseous nitrogen to ammonia
  4. Denitrification
    1. Denitrifying bacteria convert soil nitrates into gaseous nitrogen in anaerobic conditions
3. Phosphorus cycle
4. Role of Mycorrhizae
  1. This is the association between certain types of fungi and most plants
  2. Fungi act as extension of plants to increase surface area
  3. Plants provide organic compounds
    1. Mycorrhizae provide water and minerals and resist drought
5. Fertilisers
  1. Natural fertilisers
    1. Dead and decaying remains of animals and plants
    2. Animal waste
    3. More expensive
  2. Artificial fertilisers
    1. Mined from rocks and deposits
    2. Convert into different forms and blended to give balance of minerals
  3. Agricultural ecosystems
    1. Intensive food production means minerals are taken away
  4. Nitrogen is needed for growth (amino acids)
  5. Environmental issues:
    1. Leeching occurs:
      1. This is the process by which nutrients are removed from the soil
        Rainwater dissolves soluble nutrients, this is carried into watercourses
      2. This can lead to eutrophication
        1) Nitrate ion concentration increases due to leaching
        2) Algae bloom - upper layers become densely populated
        3) Algae absorb light - light cannot penetrate lower levels
        4) Light becomes the limiting factor for plants below - they die
        5) Lack of dead plants no longer the limiting factor for saprobionts, so they grow
        6) Saprobionts require oxygen for respiration, increased oxygen demand
        7) Oxygen concentration in water reduces, nitrates released from decaying organisms
        8) Oxygen now limiting factor for fish - they die
        9) Less competition for anaerobic respiration, so anaerobic organisms increase
        10) Anaerobic organisms continue to decompose material and release nitrate and toxic waste

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Pack 17 - Energy, Ecosystems and Nutrient cycles

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