3.5.4 Nutrient Cycles

Question 1

In which form do plants need nitrogen?

Answer 1

Most organisms can not use nitrogen gas so they must secure their nitrogen in its fixed form

Question 2

What are the fixed forms of nitrogen?

Answer 2

Nitrate ions: NO3 (2- charge)
Ammonia: NH3
Ammonium: NH4 (+1 charge)

Question 3

What are the four nitrogen processes? (No explanation)

Answer 3

Nitrogen fixation
Decomposition
Nitfrification
Dentrification

Question 4

What is nitrogen fixation?

Answer 4

Forming fixed compounds from nitrogen gas

Question 5

What is decomposition it terms of the nitrogen cycle?

Answer 5

The breaking down of compounds into ammonia

Question 6

What is nitrification?

Answer 6

The oxidation of ammonia into nitrates

Question 7

What is dentrification?

Answer 7

The reducing of nitrates into nitrogen gas

Question 8

What is biological fixation?

Answer 8

Fixation by microbes

Question 9

What is atmospheric fixation?

Answer 9

Fixation by lightning where the energy combines with oxygen

Question 10

What is industrial fixation?

Answer 10

Fixing of nitrogen during the Haber process

Question 11

What is Rhizobium?

Answer 11

A symbiotic bacteria which fixes nitrogen and takes sugars produced by the plant
Contains an enzyme called nitrogenase that converts nitrogen and hydrogen to ammonia

Question 12

How do animals secure their nitrogen?

Answer 12

From plants through feeding

Question 13

What is responsible for decomposition in the nitrogen cycle?

Answer 13

Microorganisms

Question 14

What are the types of nitrifying bacteria?

Answer 14

Genus Nitrosomes: oxidises NH3 to nitrites

Genus Nitrobacter: oxidises nitrites to nitrates

Question 15

Out of the phosphorous and nitrous cycles, which is faster?

Answer 15

Nitrous

Question 16

What are the effects of a low concentration of phosphorous?

Answer 16

It reduces plant growth and slows soil microbial growth

Question 17

Are soil microorganisms sinks or sources in terms of the phosphorous cycle?

Answer 17

They can act as both

Question 18

How can fertiliser run-off damage local water sources?

Answer 18

Large amounts of phosphate lead to growth of algea
Algea die quickly
Decomposers break it down
These microorganisms use a lot of oxygen
Oxygen levels decrease in the water
Other organisms die

Question 19

How do animals absorb phosphates?

Answer 19

By eating plants or plant-eating animals
When animals die, phosphates return to the soil or oceans during decomposition
Then phosphorous ends up in sediments or rock formations
Seabirds eat phosphorous-containing fish

Question 20

What is mineralisation?

Answer 20

When organic phosphorous compounds are mineralised by a wide range of organisms

Question 21

What is assimilation?

Answer 21

When microorganisms assimilate phosphorous which enters in the composition of several macromolecules in the cell
Some microorganisms can store phosphorous in special granules

Question 22

What is the solubility of phosphorous controlled by?

Answer 22

The pH and the presence of Ca / Mg / Fe / Al ions

Question 23

What are natural fertilisers?

Answer 23

Materials derived from animal parts or residues

e.g. manure, seaweed and compost

Question 24

What are artificial fertilisers?

Answer 24

Man - made fertilisers

Question 25

Why are fertilisers needed?

Answer 25

To achieve the high crop yields demanded by developed worlds

Question 26

What do fertilisers contain?

Answer 26

Minerals, such as nitrogen, potassium and phosphorous

Question 27

What is the function of nitrogen in fertilisers?

Answer 27

Increases the plant’s capacity to produce new stems / flowers / fruit
Increases the speed of growth

Question 28

What is the function of phosphorous in fertilisers?

Answer 28

Helps plants to produce oils and starch which is helpful for forming large and strong root systems
Helps the plant to develop chlorophyll which allows more photosynthesis

Question 29

What is the function of potassium in fertilisers?

Answer 29

Aids in the building of protein
Fights off diseases
Essential for photosynthesis

Question 30

How are artificial fertilisers different from natural fertilisers?

Answer 30

Artificial fertilisers add nutrients to the plant whereas natural fertilisers feed the microorganisms and the plant

Question 31

What is groundwater contamination?

Answer 31

Nitrogen fertilisers break down into nitrates and easily travel through the soil
This creates an accumulative effect
This increases plant life which takes up a lot of oxygen and starves fish and crustaceans

Question 32

What is the effect of repeated fertiliser on soil?

Answer 32

Reduces the fertility of the soil, making it barren after time

Question 33

What is the process of eutrophication?

Answer 33

Excess nutrients enter waterways
Nutrients promote plant growth
An algae bloom occurs
Algae die and are decomposed by bacteria
The decomposition of algae requires oxygen
This causes a drop in oxygen levels
Therefore fish and other aquatic life die

Question 34

What are acidifying processes?

Answer 34

The addition of nitrogen
Loss of nitrogen due to leaching or run - off
Production of organic acids from decaying matter
Removal of alkaline products such as hay

Question 35

What is leeching?

Answer 35

The process of water carrying away soluble material when the upper layer of the soil does not absorb all the water

Question 36

What happens when leaching removes too much nitrate from the soil?

Answer 36

The pH drops too far and becomes overly acidic

Question 37

What does soil acidity alter?

Answer 37

Soil microbes

Question 38

What is the effect of a high salt content in the soil?

Answer 38

It limits the ability of seeds to germinate so controlled leaching can reduce salt content

Question 39

What is the process of acidification?

Answer 39

Acidification limits plant species
Which leads to weaker root systems
Which leads to erosion
The wind then removes more topsoil