Chapter 13 - Energy + Ecosystems - (13.3) Nutrient Cycles

Question 1

What is the simple sequence of the nutrient cycle?

Answer 1

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

Question 2

What is the role of saprobionts and what are they?

Answer 2

The role of these saprobionts in nutrient cycle cannot be overstimulated.
Saprobionts can be bacteria and fungi.
They are the driving forces that ensure nutrients are released for reuse. Without them, nutrients would be remained locked up as complex molecules and never be used again by plants.

Question 3

Why do living organisms require a source of nitrogen?

Answer 3

Living organisms need nitrogen to manufacture proteins, nucleic acids and other nitrogen-containing compounds.

Question 4

What are the 4 main stages in the nitrogen cycle?

Answer 4

Ammonification, nitrification, nitrogen fixation and denitrification. Each of them involve saprobiotic microorganisms.

Question 5

What is ammonification?

Answer 5

It is the production of ammonia from organic nitrogen-containing compounds.
In nature these compounds include urea (from the breakdown of excess amino acids) and proteins, nucleic acids and vitamins (found in faeces and dead organisms)
Saprobionts feed on faeces and dead organisms materials, releasing ammonia which is when ammonium ions in the soil are formed.
This is when nitrogen returns to the non-living components of the ecosystems

Question 6

What is Nitrification?

Answer 6

Plants use light energy to produce organic compounds. Some bacteria obtain their energy from chemical reactions in involving inorganic ions.
A oxidation reaction occurs from the conversation of ammonium ions to nitrate ions. This releases energy.

Question 7

How is the conversion of ammonium ions to nitrate ions carried out?

Answer 7

It is carried out by free-living soil microorganisms called nitrifying bacteria.

Question 8

How many stages does this occur in and what are the stages?

Answer 8

The first stage is the oxidation of ammonium ions to nitrite ions
The second stage is the oxidation of nitrite ions to nitrate ions

Question 9

What does nitrifiying bacteria require?

Answer 9

It requires oxygen to carry out the two conversations and so they require soil with many air spaces. This is to raise productivity, it is important for farmers to keep soil structure light and well aerated by ploughing.
Having good drainage also prevents the air spaces to be filled with water and therefore prevents air being forced out of the soil.

Question 10

What is nitrogen-fixation?

Answer 10

This is the process by which nitrogen gas is converted into nitrogen-containing compounds. This occurs industrially and also naturally when lighting passes through the atmosphere

Question 11

What are the two main types of microorganisms that help to carry out nitrogen-fixation?

Answer 11

Free-living nitrogen-fixing bacteria: This type of bacteria reduces gaseous nitrogen to ammonia, which they then use to manufacture amino acids.
Nitrogen-rich compounds are released from them when they die and decay.

Mutualistic nitrogen-fixing bacteria : These bacteria live in the roots of plants (nodules) such as peas and beans. This allows the plant to use free nitrogen in the atmosphere and soil.
They obtain carbohydrates from the plant and the plant acquires amino acids from the bacteria.

Question 12

What is Dentification?

Answer 12

This stage is when soils become waterlogged and have low oxygen concentrations, the type of microorganisms present changes.
Fewer aerobic nitrifying bacteria are found and there is an increase in anaerobic denitrifying bacteria.
These convert soil nitrates into gaseous nitrogen. This reduces the availability of nitrogen-containing compounds for plants. For land to be productive. the soils on which crops grow must therefore be kept well aerated to prevent the build-up of denitrifying bacteria.

Question 13

What is the phosphorus cycle?

Answer 13

Phosphorus is an important biological element as it is a component of ATP, phospholipids and nucleic acids.
Life therefore depends on it being recycled constantly.

Question 14

How does the phosphorus cycle differ from the nitrogen and carbon cycle?

Answer 14

The carbon and nitrogen cycle uses the main the reservoir of each element from the atmosphere.
Where as in the phosphorus cycle the main element is in mineral form rather than in the atmosphere.
The phosphorus cycle all together lacks the gaseous phase.

Question 15

What is phosphorus?

Answer 15

It exists mostly as phosphate ions in the form of sedimentary rock deposits.

Question 16

Explain the phosphorus cycle:

Answer 16

These have their origins in the seas but are brought to the surface by geological uplifting of rocks.
The weathering and erosion of the rocks helps phosphate ions to become dissolved and available for absorption by plants which incorporate them in their biomass.
The phosphate ions pass into animals which 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 water or soil.
Some phosphate ions remain in parts of animals, such as bones or shells that are very slow to breakdown.
Phosphate ions in excerta (waste matter) are released by decomposition and dissolved out of rocks, which are further transported by streams and rivers or lakes and oceans where they form sedimentary rocks thus completing the cycle.

Question 17

What are mycorrhizae?

Answer 17

Mycorrhizae are associations between certain types of fungi and the roots of the vast majority of plants.
This relationship is mutualistic.
The plant benefits from improved water + inorganic ion uptake
The fungus receives organic compounds such as sugars and amino acids from the plant.

Question 18

What is the role of mycorrhizae in nutrient cycles:

Answer 18

The fungi act like extensions of the plants root system and vastly increase the total surface for the absorption of water and minerals. The mycorrhizae 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 mycorrhizae plays a part in nutrient cycles because it improves the uptake of relatively scarce ions (eg, phosphates ions)