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7324090
Pack 17 - Energy, Ecosystems and Nutrient cycles
Description
Revision for pack 17
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a level
biology
eutrophication
nutrient cycles
biology
pack 17 - nutrient cycles and ecosystems
as - level
Mind Map by
Jacob Shepherd
, updated more than 1 year ago
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Jacob Shepherd
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Resource summary
Pack 17 - Energy, Ecosystems and Nutrient cycles
Food chains and energy transfer:
Most plants convert energy from sunlight into chemical energy in organic comounds
Nitrates and phosphates are required to make these organic compounds
Food chains:
Producers:
Photosynthetic organisms manufacture organic substances
Consumers:
Consume other organisms to obtain their energy
Primary consumers eat producers
Secondary consumers eat primary consumers
Saprobionts
Extracellular digestion
Break down things to absorbable parts
Assimilated
Trophic levels
Energy flows from primary producers to consumers. Each group is said to be at a certain trophic level
e.g. grass-->rabbit-->fox
There are usually only 4 or 5 trophic levels due to the inefficiency of energy transfer
Food webs:
In any habitat, many food chains are inter-linked to form food webs
Some organisms will be in more than one trophic level
The greater the number of interactions, the more stable the food web is
Biomass
Total mass of living material in a specific material in a specific area at a given time
All organisms contain a variable volume of water
Dry mass is measured by drying the sample in an oven at 100 degrees until a constant mass is reached.
Issues:
Organisms must be dead
Only small samples can be taken
Sample may not be representative
Measured in dry mass per given area in a given time
Calorimetry can be used to estimate the chemical energy store in dry mass
1. Sample of dry material weighed
2. Burnt in pure oxygen in a sealed chamber
3. Bomb is surrounded by water bath
4. Heat of combustion causes temp. of the water to rise
Energy transfer and Productivity
90% of energy from the sun is lost, even more is lost of the energy hitting a leaf:
Some energy used for evaporation
Some energy is reflected by cuticle
Not all light hits the cuticle
Not all wavelengths used in photosynthesis
Low CO2 Conc. may limit photosynthesis
Gross primary production (GPP) and net primary production (NPP)
GPP = The chemical energy store in a plant biomass, in a given area volume at a given time
NPP = Chemical energy store in plant biomass after respiratory losses to the environment
NPP = GPP - R
Less than 10% NPP in plants available to consumers
Not all plant eaten
Some used in respiration for ATP production
Some lost in egestion and excretion
Plant material is difficult to digest
Less than 20% available from secondary to tertiary
Not all consumed
Some parts are lost in faeces
Lost in excretion
Net production of consumers
N = I - (F+R)
I = Chemical energy
F = chemical energy lost to environment
R = Respiratory loss
Productivity and farming practices
Increasing the efficiency of energy transfer leads to higher yields
Intensive farming techniques:
Restrict movement - less energy used in muscle contraction
Environment kept warm - reduce heat loss from the body
Optimum amount of food for max growth
Predators excluded so no loss to other organisms
Chemical and biological control of agricultural pests
Pesticides
Effective ones should:
Be specific to only one organism
Biodegrade
Not accumulate
Development of genetic resistance
Mutation confers resistance
Pests without mutant allele are killed by pesticide
Organisms with allele for resistance survive
Breed to pass on allele
Biological Control
Eradicating pests may mean that other pests can multiply
Very specific, once introduced the organisms reproduce themselves
Pests can't become resistant
Integrated control systems
Aim to keep pests are acceptable levels
Choose varieties of animals/plants that are resistance to pest
Providing habitats close to crops for natural predators
Monitor crops for signs of pests
Remove pests mechanically
Use biological agents
Use pesticides
Nutrient cycles
Saprobiotic organisms:
Activate a gene that makes digestive enzymes
Enzymes are secreted and hydrolyse surrounding material into soluble compounds
Compounds are absorbed by cells and assimilated
Nitrogen cycle
Ammonification
Production of ammonia from organic nitrogen containing compounds
Carried out by saprobiotic organisms
Nitrification
Oxidation of ammonium ions to nitrate ions
Then oxidation of nitrite ions to nitrate ions
Nitrogen Fixation
Reduce gaseous nitrogen to ammonia
Denitrification
Denitrifying bacteria convert soil nitrates into gaseous nitrogen in anaerobic conditions
Phosphorus cycle
Role of Mycorrhizae
This is the association between certain types of fungi and most plants
Fungi act as extension of plants to increase surface area
Plants provide organic compounds
Mycorrhizae provide water and minerals and resist drought
Fertilisers
Natural fertilisers
Dead and decaying remains of animals and plants
Animal waste
More expensive
Artificial fertilisers
Mined from rocks and deposits
Convert into different forms and blended to give balance of minerals
Agricultural ecosystems
Intensive food production means minerals are taken away
Nitrogen is needed for growth (amino acids)
Environmental issues:
Leeching occurs:
This is the process by which nutrients are removed from the soil
Rainwater dissolves soluble nutrients, this is carried into watercourses
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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