Nutrient cycles

Question 1

What is the simple process that nutrient cycles follow?

Answer 1

• A nutrient is taken up by producers as simple, inorganic molecules
• The producer incoporates nutrients into complex organic molecules
• When the producer is eaten, the nutrient passes to consumers
• When the producers and consumers die, their complex molecules are broken down by saprobiontic consumers (decomposers) that release the nutrients in their organic form so they can be taken up and used by plants again
• The cycle repeats

Question 2

Describe the importance of the nitrogen cycle?

Answer 2

• Living organisms require a source of nitrogen to manufacture proteins, nucleic acids and other nitrogen containing compounds.
• Although nitrogen makes up 78% of the atmosphere, it can not be taken up directly by plants
• Plants can only absorb nitrogen in the form of nitrate ions (NO3-) by active transport

Question 3

What are the four steps of the nitrogen cycle?

Answer 3

• Ammonification
• Nitrification
• Nitrogen fixation
• Denitrification

Question 4

What are the different ions involved in the nitrogen cycle?

Answer 4

• Ammonia (NH3)
• nitrate ions (NO3-)
• Nitrite (NO2-)
  Nitrogen gas (N2)

Question 5

What occurs during ammonification?

Answer 5

• This is the production of ammonia from organic nitrogen - containing compounds.
• These compounds contain urea (excess amino acids), proteins, nucleic acids and vitamins
• Saprobiontic microorganisms feed on faeces and dead organisms which releases ammonia, returning it to the soil.

Question 6

What is nitrification?

Answer 6

• Plants use light energy to produce organic compounds
• Some bacteria obtain their energy from chemical reactions involving inorganic reactions
• This is an oxidation reaction that releases energy. It is carried out by free living soil microorganisms called nitrifying bacteria
• This conversion of ammonium ions occurs in two stages:
  1. The oxidation of ammonium (NH3) to nitrite ions (NO2-)
  2. The oxidation of nitrite ions to nitrate ions (NO3-)
• Nitrifying bacteria require oxygen to carry out these processes and therefore require soil with many air spaces.
• To raise productivity, soil structure and good drainage is required to increase these conversions

Question 7

What is nitrogen fixation?

Answer 7

• This is the process where nitrogen gas is converted to nitrogen containing compounds. This can be carried out industrially, using the haber process or naturally when lightning passes in the atmosphere
• These processes are carried out in two processes:
  1. Free - living nitrogen bacteria = These bacteria reduce gaseous nitrogen to ammonia, which means they can use it to manufacture amino acids. NItrogen - rich compounds are released from them when they die
  2. Mutualistic nitrogen - fixing bacteria = These bacteria live in nodules on the roots of plants (legumes) such as peas and beans. When converting atmospheric nitrogen into ammonia, these bacteria obtain carbohydrates and sugars from the plant and the plant obtains nitrogen from which they can manufacture amino acids for plant growth.

Question 8

What is denitrification?

Answer 8

• When soils become waterlogged, and have a low oxygen concentrations, the type of microorganisms present changes. Fewer aerobic nitrifying and nitrogen - fixing bacteria are found and there is an increase in anaerobic denitrifying bacteria,
• These anaerobic denitrifying bacteria convert soil nitrates into gaseous atmospheric nitrogen. This reduces the avaliability of nitrogen - containing compounds in plants.

Question 9

Describe the phosphorous cycle?

Answer 9

• Phosphorous is an important biological element as it is a component of ATP, phospholipids and nucleic acids. Therefore, we are dependent on it being recycled
• The main component of the phosphorous cyle is in mineral form rather than in the atmosphere like the nitrogen and carbon cycle

Question 10

Draw a diagram of the phosphorous cycle

Question 11

What are the steps in the phosphorous cycle?

Answer 11

• Phosphorous exits mainly as phosphorous ions (PO43-) in the form of sedimentary rock deposits. They have their origins but are brought to the surface by the uplifting of rocks.
• The weathering and erosion of these rocks helps phospahte ions to become dissolved and so avaliable for absoprtion by plants which incoporate them into their biomass
• The phosphate ions pass into animals which feed from these plants. Excess phosphate ions are excreted and accumulate in the waste
• On the death of these plants and animals, decomposers such as bacteria and fungi break them down into water and soil
• Some phosphate ions may remain in parts of animals such as bones and shells
• Phosphate ions in exterta are released by decomposistion and dissolved out rocks, then are transported by streams and rivers, lakes and then oceans where they form sedimentary rocks, completing the cycle

Question 12

What are mycorrihaze?

Answer 12

• Mycorrihaze are associtations between certain types of fungi and the roots of the vast majority of plants.
• Fungi act like extensions of the plants roots system and increase the surface area for the absorption of water and minerals

Question 13

How do Mycorrihaze facillitate the uptake of water and inorganic ions by plants?

Answer 13

• Mycorrihaze act as sponges and hold water and minerals in the neighbourhood of the roots
• This enables the plant to resist drought and take up inorganic ions easier
  -The Mycorrihaze play a part in the nutrient cycles by improving the uptake of relatively scarce ions such as phosphate ions

Question 14

How is the relationship of Mycorrihizal relationship mutualistic?

Answer 14

• Plants benefit from improved water and inorganic ion uptake
• Fungus recieve organic compounds such as sugars and amino acids from the plant

Question 15

Why do we need fertilisers?

Answer 15

• All plants require nitrates from the soil. Much food production is intensive in order to achieve maximum yield from crops and animals
• Intensive food production makes a large demand on the soil because mineral ions are continually being taken up by crops being grown on it
• In natural ecosystems, the minerals are returned by decomposers (saprobionts)
• In agricultural systems, the crop is harvested and transported for consumers. Therefore the urine, feeces and dead remains of the consumers are rarely returned to the same area of land. This means mineral ion concentrations will fall and not be replenished, this is a limiting factor and reduces productivity

Question 16

What are organic and artificial fertilisers?

Answer 16

Organic = Consists of dead and decaying remains of plants and animal wastes such as manure and bonemeal

Artificial Fertilisers = These are mined from rocks and deposists and then are converted into different blends for a particular crops. These contain three elements such as nitrogen, phosphorous and potassium

Question 17

How do fertilisers increase productivity?

Answer 17

• plants require nitrates for growth as they can use It for essential components such as amino acids,ATP and nucleotides in DNA
• This also increases the rate of photosynthesis and improve productivity

Question 18

What are the detrimental effects of nitrogen - containing fertilisers?

Answer 18

1. Reduces Species diversity = This is because nitrogen - rich soils favor the growth of grass, nettles and other rapidly growing species.
2. Leaching = This may lead to polution of water houses
3. Eutrophication = This is caused by leaching of fertilisers

Question 19

What is the process of leaching?

Answer 19

• This is the process of which nutrients are removed from the soil.
• Rainwater can dissolve any soluble nutrient such as nitrate ions and carry them deep into the soil, however leached nitrates may find their way into water courses such as streams and rivers which may turn into freshwater lakes
• This can have a harmful effect as a high nitrate ion concentrations in drinking water.
• This can prevent efficient oxygen transport in babies and has been linked to stomach cancer in humans.
• Leached nitrate ions can cause eutrophication also

Question 20

What is the process of eutrophication?

Answer 20

• In most lakes and rivers there is a naturally low concentration of nitrate and nitrate ions so nitrate ions are a limiting factor for plant and algal growth
• As nitrate concentrations increase as a result of leaching, plants and algae will grow
• Algae grows mostly at the surface of water, causing upper layers of water to be populated with algae. This is called an algal bloom
• The dense layer of algae absorbs light, preventing it from penetrating to lower depths
• Light then becomes a limiting factor for aquatic plants so they eventually died
• Saprobiontic plants feed on the dead organisms and require oxygen for respiration, this now becomes a limiting factor
• This reduces oxygen levels for aerobic respiration of aerobic organisms such as fish which then die
• This reduces competition for anaerobic organisms which then reduces competition for anaerobic organisms which then further decomposes dead material