Nutrients cycles

Question 1

what is the simple sequence that is present in all nutrient cycles

Answer 1

1) The nutrient is taken up by producers (plants) as simple, inorganic molecules.
2) The producer incorporates the nutrient info complex organic molecules.
3) When the producer is eaten, the nutrient passes into consumers (animals)
4) It then passes along the food chain when these animals are eaten by other consumers.
5) When the producers and consumers die, their complex molecules are broken down by saprobiontic microorganisms (decomposers) that release the nutrient in its original simple form.

Question 2

Why are saprobionts so important in nutrient cycles

Answer 2

• The are the driving forces that ensure that nutrients are released for reuse.
• Without them, nutrients would remain locked up as part of complex molecules that cannot be taken up and used again by plants.

Question 3

In what form do plants take up most of the nitrogen they require

Answer 3

Nitrate ions (NO3-)

Question 4

How are nitrate ions absorbed by plants

Answer 4

Active transport from the soil into the roots

Question 5

How do consumers obtain nitrogen-containing compounds

Answer 5

By eating and digesting plants or other animals that contain nitrogen compounds

Question 6

What are the four main stages in the nitrogen cycle

Answer 6

• Ammonification
• Nitrification
• Nitrogen fixation
• Denitrification

Question 7

Why is the release of nitrate ions by decomposition most important in natural ecosystems

Answer 7

There are very few nitrate ions available from other sources.

Question 8

Describe ammonification (nitrogen cycle)

Answer 8

• Ammonification is the production of ammonia from organic nitrogen containing compounds.
• In nature these compounds include urea, proteins, nucleic acids and vitamins.
• Saprobiontic microorganisms (fungi and bacteria mainly) feed on faeces and dead organisms materials, releasing ammonia.
• This ammonia forms ammonium ions in the soil.
• This is where nitrogen returns to the non-living component of the ecosystem.

Question 9

Describe the process of nitrification (nitrogen cycle)

Answer 9

• Free living nitrifying bacteria oxidise ammonium ions to nitrate ions and this releases energy.
• This conversion occurs in two stages:
  1) Oxidation of ammonium ions to nitrite ions (NO2-)
  2) Oxidation of nitrite ions to nitrate ions (NO3-)
• These bacteria require aerobic conditions.

Question 10

How do farmers increase the productivity by encouraging the action of free living nitrifying bacteria

Answer 10

They aerate the soil

Question 11

Describe the process of nitrogen fixation (nitrogen cycle)

Answer 11

• Nitrogen fixation is the process by which nitrogen gas is converted into nitrogen containing compounds.
• This is carried out by microorganisms, by which there are two main types:
  1) Free living nitrogen fixing bacteria= These bacteria reduce gaseous nitrogen to ammonia which they then use to manufacture amino acids. Nitrogen-rich compounds are released from them when they die and decay.
  2) Mutualistic nitrogen-fixing bacteria= These bacteria live in nodules on the roots of plants such as peas and beans. They obtain carbohydrates from the plant and the plant acquires amino acids from the bacteria.

Question 12

Describe the process of denitrification (nitrogen cycle)

Answer 12

• Aenaerobic denitrifying bacteria convert soil nitrates into gaseous nitrogen.
• This reduces the availability of nitrogen containing compounds for plants.

Question 13

What sort of conditions allow denitrifying bacteria to thrive

Answer 13

Anaerobic conditions such as when soils become waterlogged and have a low oxygen concentration.

Question 14

Does the phosphorus cycle have a gaseous phase

Answer 14

No

Question 15

Describe the phosphorus cycle

Answer 15

• Phosphorus exists mostly as phosphate ions (PO4 3-) in the form of sedimentary rock deposits.
• These deposits have their origins in the sea but are brought to the surface by the geological uplifting of rocks.
• The weathering and erosion of these rocks dissolves phosphate ions which makes them available for plants to absorb.
• These phosphate ions pass into animals that feed on the plants.
• Excess phosphate ions are excreted by animals and may accumulate in waste material such as guano formed from the excretory products of some sea birds.
• On the death of plants and animals, decomposers such as certain bacteria and fungi break them down releasing phosphate ions into the water or soil.
• Some phosphate ions remain in parts of animals that are slow to break down.
• Phosphate ions in excreta, released by decomposition and dissolved out of rocks are transported by streams and rivers into lakes and oceans where they form sedimentary rocks thus completing the cycle.

Question 16

What are micorrhizae

Answer 16

• Associations between certain types of fungi and the roots of the vast majority of plants.
• The fungi act like extensions of the plants root system and vastly increase the total surface area for the absorption of water and minerals.

Question 17

What role do micorrhizae play in nutrient cycles

Answer 17

• The micorrhiza acts like a sponge and so holds water and minerals in the neighbourhood of the roots.
• This enables the plant to better resist drought and to take up inorganic ions more readily.
• The micorrhiza plays a part in nutrient cycles by improving the uptake of relatively scarce ions such as phosphate ions.
• This is a mutualistic relationship (between plants and mycorrhizal fungi): the plant benefits from improved water and inorganic ion uptake while the fungus receives organic compounds such as sugars and amino acids.