BYA5 SECTION 14.9

Decomposition and recycling maintain the balance
of nutrients in an ecosystem

Nutrient Cycles

Elements are taken up by producers (plants) / stored as organic matter
Passed on across trophic level / consumer digest and absorb food / stored as organic matter
Decomposers decay detritus and excretory products / return inorganic ions to environment / taken up by producers
Warm temp / higher enzyme activity / faster decomposition

Table 9-14-1: Use of nutrients in plants and animals

	PLANTS	ANIMALS
CARBON	Organic substances / lipids / proteins / ATP / chlorophyll	Organic substances / lipids / proteins / ATP / chlorophyll
NITROGEN	- Amino acid / nucleotide synthesise - In RNA, DNA, proteins, ATP	- Amino acid / nucleotide synthesise - In RNA, DNA, proteins, ATP
IRON	- In cytochromes / ETC - Needed for enzymes such as catalase to work - Synthesis of chlorophyll	- In cytochromes / ETC - Needed for enzymes such as catalase to work - Part of Hb
IODINE		Contained in thyroxine (hormone)
MOLYBDENUM	Nitrate reductase / reduces nitrates during synthesis of amino acids

Carbon Cycle

Producers, consumers, decomposers
1. Add CO₂ to the air by respiration
2. Carbon is stored in tissues as organic matter (carbohydrates, lipids, proteins)
3. Carbon is passed along food web by feeding
Plants remove CO₂ from air by photosynthesis
Animals excrete carbon as waste products
Decomposers decay detritus and excretory products / add carbon to soil
1. Detrivores digest detritus to small pieces / large surface area
2. Saprophytes digest smaller detritus by
  1. Extracellular digestion by secreting enzymes
  2. Absorb resulting nutrients across plasma membrane
  3. Releases inorganic matter (CO₂, H₂O, mineral ions) into soil
Fossil fuels
1. Combustion releases CO₂ into air
2. Fossilisation of carbon atoms in organic compounds in dead remains (plants, animals) and excretory products (animals)
Respiring organisms must not die to release stored carbon / differs from other cycles

Respiration, Photosynthesis and CO₂

Photosynthesis takes up more CO₂ than is released by respiration
CO₂ concentration
- Higher at night than at daylight; light-dependent reaction cannot take place
- Peaks at winter time due to high oil consumption; low rate of photosynthesis due to cooler temp, shorter day length, loss of leaves
Variation in a graph due to wind mixing CO₂ with the surrounding air
- Graph should show conc over whole area rather over a specific area
Rate of photosynthesis and respiration are balanced in a rain forest
- Forests grow for a long time and have stored lots of carbon in their tissues, other plants have stored carbon as cellulose and lignin

Nitrogen Cycle

*processes involved in restoring nitrate conc in soil after cultivation is abandoned

1) Assimilation (→Building up organic molecules)

Plants take up NITRATE NO₃/AMMONIA NH₃ from the soil by active transport
1. Used to synthesis amino acids / synthesise proteins / new cells and tissues
Primary consumers feed on plants
1. Proteins are digested into amino acids and absorbed
2. Amino acids synthesise new proteins
Nitrogen is passed along the trophic level through the food web

2) Ammonification*

3) Nitrification*

4) Denitrification

5) Nitrogen Fixation*

N₂(g) is converted to nitrates by lightning N₂(g) + O₂ → NO₃^-NITROGEN GAS IS CONVERTED TO NH₃/NH₄⁺
By Haber process: N₂(g) + H₂→ ammonia NH₃
1. //used to make fertilisers / added to soil / leakage of ions into river
By Nitrogen-fixing bacteria by anaerobic nitrogenase
Live free in soil/nodules on the roots of legumes (peas, beans)
NH₄⁺ is assimilated by legumes into amino acids
1. //Mutualistic relationship → bacteria get their carbon-containing compounds from the plant while the plant gets nitrates

References and Further Reading
AQA (2006) GCE Biology/Biology (Human) 2006 specification, [PDF]

BYA5 SECTION:

14.9