13.3 Nutrient Cycles

Question 1

How does energy enter an ecosystem

Answer 1

Via sunlight and leaves as heat

Question 2

Describe the basis of a simple nutrient cycle

Answer 2

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

Question 3

What are nitrogen ions used for

Answer 3

Proteins

Nucleic acids

Question 4

How is the majority of nitrogen taken up

Answer 4

Taken up by plants through the soil. These ions are absorbed via active transport through the routes

Question 5

What other way can nitrogen be taken up

Answer 5

The atmosphere contains 78% nitrogen, but only a small proportion of organisms can use this

Question 6

What is the problem with nitrate ions and soil

Answer 6

Nitrate ions are very soluble and easily leach into the soil deep enough the plant roots cannot reach them

Question 7

How are nitrate concentrations restored in natural ecosystems

Answer 7

By recycling the nitrogen-containing compounds

Question 8

How are nitrate concentrations restored in agricultural ecosystems

Answer 8

By using fetilisers

Question 9

Why is release of nitrate ions by decomposition important in natrual ecosystems

Answer 9

Because there are few nitrate ions available from other sources

Question 10

What are the 4 stages of the nitrogen cycle

Answer 10

1. Ammonification
2. Nitrification
3. Nitrogen fiaxtion
4. Denitrification

Question 11

What does each 4 stages of the nitrogen cycle involve

Answer 11

Saprobiontic microorganisms

Question 12

What is ammonification

Answer 12

The production of ammonia from organic nitrogen-containing compounds

Question 13

What compounds can be used to produce ammonia

Answer 13

Urea
Proteins
Nucleic acids
Vitamins

Question 14

Describe the process of ammonification

Answer 14

Saprobiontic organisms, mainly fungi and bacteria, feed on faeces and dead organisms material, releasing ammonia, which then forms ammonium ions in the soil. This is where nitrogen returns to the ecosystem

Question 15

What is nitrification

Answer 15

The obtainment of energy from chemical reactions involving inorganic ions. Example is the conversion of ammonium ions to nitrate ions in an oxidation reaction

Question 16

Describe the process of nitrification

Answer 16

1. Oxidation of ammonium ions to nitrate ions (NO2-)

2. Oxidation of nitrate ions to nitrite ions (NO3-)

Question 17

What carries out the process of nitrification

Answer 17

Nitrifying bacteria that live in the soil

Question 18

What do nitrifying bacteria require to carry out the conversion of ammonium ions to nitrite ions

Answer 18

Oxygen. Therefore soil is required to have air spaces

Question 19

How do farmers ensure air spaces in soil

Answer 19

1. Keeping soil structure light and well aerating it by ploughing
2. Good drainage to prevent air spaces filling with water

Question 20

What is nitrogen fixation

Answer 20

The process by which nitrogen gas is converted into nitrogen-containing compounds

Question 21

What are the 2 types of nitrogen fixating microorganisms

Answer 21

1. Free living nitrogen fixing bacteria

2. Mutualistic nitrogen fixing bacteria

Question 22

What is free living nitrogen fixing bacteria

Answer 22

These bacteria reduce gaseous nitrogen into ammonia, which they use to manufacture amino acids

When they die and decay the nitrogen rich compounds are released into the soil

Question 23

What is mutualistic nitrogen-fixing bacteria

Answer 23

These bacteria live in nodules on the roots of plants such as peas and beans

They obtain carbs from the plant and the bacteria obtain amino acids from the mutualistic nitrogen fixing bacteria

Question 24

How does denitrification occur

Answer 24

When soils become waterlogged, and have a low oxygen concentration, the type of microorganism present changes.

There are fewer nitrifying and nitrogen-fixing bacteria present and more anaerobic denitrifying bacteria.

Question 25

Why are anaerobic denitrifying bacteria bad

Answer 25

Because they reduce the availability of nitrogen-containing compounds for plants by converting soil nitrates into gaseous nitrogen

Question 26

For land to be productive in terms of nitifying and nitrogen-fixing bacteria presence what must occur

Answer 26

The soil must be kept well aerated to prevent build up of denitrifying bacteria

Question 27

What is phosphorus used in

Answer 27

ATP

Phospholipids

Nucleic acids

Question 28

Where is the main resevoir of phosphorus ions

Answer 28

Mineral form than in the atmosphere. The P cycle completely lacks a gaseous form

Question 29

How does phosphorous exist

Answer 29

As phosphate ions (PO43-) in the form or sedimentary rock deposits

Question 30

Where are sedimentary rock deposits found and what happens to them

Answer 30

They are primarily found in the seas and are brought to the surface by geological lifting

Question 31

Describe the phosphate nutrient cycle

Answer 31

1. The weathering and erosion of sedimentary rock deposits help phosphate ions to become dissolved and available for absorption by plants which incorporate them into their biomass
2. The phosphate ions pass into animals which feed on the plants
3. Excess phosphate ions are excreted by animals and many accumulate in waste material, such as that from sea birds
4. On the death of plants and animals, decomposers such as bacteria and fungi break them down - releasing phosphate ions into the water or soil. Some ions remain in parts of animals, like bones or shells, that are slow to break down
5. 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 32

What are mycorrhizae

Answer 32

Associations between certain types of fungi and the roots of a vast majority of plants

Question 33

What do the fungi act as in mycorrhizae

Answer 33

Extensions of the root system, increasing the total surface area for the absorption of vitamins and minerals in the neighbourhood of the roots.

Question 34

How do mycorrhizae play an important role in nutrient cycles

Answer 34

By improving the uptake of relatively scarce ions such as phosphate ions

Question 35

How is the mycorrhizal relationship mutualistic

Answer 35

because the plant benefits from improved water and inorganic ion uptake, while the fungus receives organic compounds such as sugars and amino acids from the plant.