AQA A-level Biology Energy Transfers A* Notes

Energy
Trsfers

, Nutrient Cycles
• organisms made of 'recycled' chems
• Cycled between biotic + abiotic environment
• by producers + microbes
• Built into complex org mols (carbs, proteins, lipids etc.)
• Org mols passed thru food chains
• eventually returned to abiotic environment as simple inorganic mols - by decomposers
* no nutrient cycling + life w/o producers and decomposers




Producers
Simple inorganic mols Complex organic mols
Decomposers




* BIOTIC = LIVING
* ABIOTIC = NON-LIVING

• inorganic mols = nutrients
• Carbon , hydrogen + oxygen needed in largest amount
• Growth of producers limited by availability of minerals (eng: nitrate + phosphate)

, Phosphorous Cycle
* ion = PHOSPHATE
* element = PHOSPHOROUS
• phosphorous critical for all living things
• in DNA - for cell div/ pro synthesis , RNA , ATP - energy for growth
• Phospholipids in cell membr T
• Functioning of some enzymes

• in ph cycle main reservoir of phosphorus = minerals in rocks
• Phos cycle - no gaseous phases

* phosphorous mainly exists as phosphate ions in sedimentary rock deposits

Process
1. Sedimentary rock deposits formed by sea depositing layers of sediment
2. Brought to surf over time through geo activity
3. Weathering + erosion dissolve phosphate ions allowing them to be absorbed by Plants
4. Plants are eaten by animals
5. Animals excrete excess phosphate in waste products (e,g: guano (bird faeces ))
6. When animals + plants die, broken down by saprobiotic bac + fungi
7. Releases phosphate ions into water/soil
8. Dissolved ions trans into lakes + oceans
9. Ultimately form rocks via sedimentation




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, Saprobiotic baeria + fungi

• do not digest food
• Use extra cellular digestion - related ph ions + am comps
• secrete digestive enzymes
• Large to small sol mols
• Further broken down by aerobic resp into inorganic mols


Nitrogen Cycle
• crucial for DNA, RNA + ATP
• Main reservoir = nitrogen gas in atmosphere
• 90% of air = nitrogen
• Nit gas diff in + out of gas but can't be used in this form (need nitrate ions)

• nitrogen gas = N N
• Lots of energy to break bonds

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4 processes in nitrogen cycle: - Don't forget to
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1. Nitrogen fixation N
2. Nitrification N
3. Denitrification D
4. Ammonification A

Nitrogen Fixation
• nitrogen fixing bac - reduce nitrogen (using hyd mol from water ) into ammonia / ammonium
ions
• Live freely in soil/water
• Or in nodules on roots (e.g: legume / clover plants)

• Mutualist relationship (type of simbiotic relationship)
• Plant obtains AAs from bac + bac gets sugars from plant



* plant will be high in proteins as has lots of AAs
• Bac has nitrogenase (lowers AA of nitrogen) + ATP