Nutrient Cycles

What are detritivores?

• Organisms that feed off of dead organisms and waste like worms or maggots

• The start off decomposition as they break down organisms orally and consume the dead matter

• They increase the surface area for saprobionts

What are saprobionts?

• Organisms that feed off dead matter and waste

• These are organisms like bacteria and fungi that do extracellular digestion

• In extracellular digestion:

  • Saprobionts secrete enzymes onto dead organisms

  • This hydrolyses biological molecules within the dead matter such as DNA, RNA, ATP, phospholipids, etc.

  • They then absorb the soluble products by diffusion

What is mycorrhizae?

• A symbiotic relationship between plant roots and a fungus- the fungus forms an extension of the plant roots

• The fungus gets glucose from the plant through photosynthesis

• Plant roots gain an increased surface area for the absorption of phosphates and nitrates

What is a symbiotic relationship?

A relationship between two organisms where at least one benefits

What is guano?

Excrement from seabirds that contain high concentrations of nitrogen, phosphorous and potassium- crucial in the nitrogen and phosphorous cycle

What types of weathering are there?

• Biological- weathering by the action of living organisms

• Physical- weathering by the disintegration of rocks by water for example

• Chemical- weathering due to chemical reactions changing the composition of rocks

What is commensalis?

A symbiotic relationship where one species benefits and the other is neither harmed or benefits

What happens within the nitrogen cycle?

• Nitrogen is fixed from the atmosphere and it cannot be used directly by any organism

  • Nitrogen fixing bacteria (rhizobium) fix this nitrogen into ammonia/ammonium ions

• Nitrifying bacteria through a two step oxidation reaction convert ammonium ions into nitrite ions, then nitrate ions by nitrification

We can then have one of two routes:

• Denitrification- Denitrifying bacteria in anaerobic conditions (being compact or waterlogged soil) can denitrify nitrate ions back into nitrogen in the atmosphere

OR

• Nitrates are actively transported in the root hair cells of plants/algae (producers) and plants use this to make N containing compounds

• Consumers then eat these plants and they use the nitrogen from the producers to make their own biological molecules

• By death of plants and the death/excrement of animals, saprobionts can hydrolyse biological molecules containing nitrogen like DNA and amino acids, then absorb the soluble products by diffusion and then convert the nitrates into ammonia (ammonification)

• When these saprobionts die, they release ammonia/ammonium ions back into the soil 

Why do denitrifying bacteria not need aerobic conditions?

Nitrogen is the final electron acceptor in their electron transport chain instead of oxygen

Why may carnivorous plants thrive in compact and waterlogged soil?

• There are very low concentrations of oxygen in waterlogged soil

• The nitrate concentration decreases and more denitrifying bacteria convert the nitrates into nitrogen in the atmosphere (the rate of denitrification increases)

• Carnivorous plants do not have to rely on nitrogen in the soil from bacteria to obtain their nitrogen- they do so by consuming other organisms

• Because non-carnivorous plants are not likely to survive in waterlogged and compact soil, there is less competition for the carnivorous plants

What happens in the phosphorous cycle in water sources?

• Phosphorous containing compounds in rocks are released into water sources by weathering

• These phosphates are absorbed (by active transport) into algae and other aquatic producers

• Consumers feed off of these plants and use the phosphorous to make biological molecules

Two paths:

Death and Excretion

• When these producers and consumers die or excrete waste, saprobionts will hydrolyse biological molecules containing phosphorous in the dead matter then absorb the soluble products

• When saprobionts die they will release phosphorous containing compounds back into water sources

Seabirds

• Seabirds will then eat the fish and use the phosphorous to make P containing compounds in their own bodies

• Seabirds excrete waste that is very high in phosphorous (called guano) back into either water sources or into soil

What happens in the phosphorous cycle on land?

• Phosphorous containing compounds in rocks are released into the soil by weathering or from the guano of seabirds

• These phosphates are absorbed by active transport into the root hair cells of plants to make P containing compounds

• These producers are then eaten by consumers that will use the phosphates to make P containing biological molecules

• By the death of plants and the death/excretion of animals, saprobionts will hydrolyse the biological molecules containing phosphorous and absorb the soluble products to make P containing compounds

• When saprobionts dies, they will release phosphates back into the soil

What happens in leaching?

Excess fertiliser runs off of farmland and enters water sources as fertilisers are soluble

Why is leaching a problem for farmers, people and for the environment?

• If a farmer uses too much fertiliser and it runs off of the farmland, it’s a very expensive waste of money

• It can contaminate the water sources of humans- leads to blue baby syndrome for example

• Causes eutrophication

Why is manure a more safe fertiliser to use?

• It is natural and releases/leaches less and more slowly as it has to be decomposed by saprobionts first

• Artificial fertilisers are more problematic as they release ions directly into the soil in huge amounts

How is leaching affected by solubility

The more soluble the ions in the fertiliser are, the faster and more extensive leaching is

What are leguminous plants?

• They are plants will balls on their roots called root nodules that contain nitrogen fixing bacteria- a mutualistic relationship

• Nitrogen fixing bacteria get glucose from the photosynthesising plant

• The leguminous plant is able to get nitrate ions directly from the bacteria which could be advantageous even in waterlogged soil

Why may leguminous plants be useful for farmers?

• The nitrogen fixing bacteria in their root nodules increase the nitrate concentration of the soil

• Therefore farmers may plough leguminous plants roots into their soil to increase the nitrate concentration

What happens in eutrophication?

• Fertiliser is leached off of farmland and the runs into water sources

• Algae absorb these nitrates/phosphates by active transport and grow exponentially

• This forms an algal bloom which can block light from the body of water

• Plants below the algal bloom are unable to photosynthesise and produce glucose so they die

• Saprobionts hydrolyses the biological molecules in the dead matter

• As they respire, they use up the oxygen in the body of water

• This means that fish and other aerobically respiring organisms cannot respire aerobically as there is not enough oxygen and so they die