C.6 The nitrogen and phosphorus cycles

Question 1

What is the nitrogen cycle?

Answer 1

The biogeochemical cycle where nitrogen is converted into various chemical forms

Question 2

What is unable to be used by plants and animals?

Answer 2

Nitrogen

Question 3

What does chemoautotrophic bacteria convert nitrogen into?

Answer 3

Compounds that can be assimilated by plants and animals

Question 4

What are the four components of the nitrogen cycle?

Answer 4

Nitrogen fixation
Ammonification
Nitrification
Dénitrification

Question 5

What is the first stage of the nitrogen cycle?

Answer 5

Nitrogen fixation

Question 6

What is nitrogen fixation?

Answer 6

The conversion of inert nitrogen gas into ammonia

Question 7

What catalyses the conversion of nitrogen into ammonia?

Answer 7

The enzyme nitrogenase

Question 8

What produces nitrogenase?

Answer 8

Nitrogen-fixing bacteria in the soil

Question 9

When does ammonia become ammonium?

Answer 9

When mixed with water

Question 10

What does Rhizobium supply ammonia to plants in exchange for?

Answer 10

Carbohydrates

Question 11

How can ammonia be produced from organic sources of nitrogen?

Answer 11

When broken down by decomposers

Question 12

In ammonification, what happens as a plant or animal decays?

Answer 12

Saprotrophs will decompose organic materials to produce ammonia

Question 13

What does ammonification release?

Answer 13

Ammonium ions into the soil which can be absorbed by plants

Question 14

What is nitrification?

Answer 14

The conversion of ammonium ions into nitrites and nitrates by nitrifying bacteria in the soil

Question 15

What converts ammonium ions into nitrites?

Answer 15

Nitrosomonas

Question 16

What do nitrobacters convert?

Answer 16

The nitrites into nitrates

Question 17

What do nitrosomonas and nitrobacter reactions require?

Answer 17

Oxygen

Question 18

If the reaction needs oxygen, what must the soil be?

Answer 18

Well aerated to ensure a rich supply of nitrites and nitrates

Question 19

Why do nitrates and nitrites function as a predominant source of nitrogen for plants?

Answer 19

As they are easier for plants to assimilate

Question 20

What is dentrification?

Answer 20

A chemical reduction process that converts nitrates into nitrogen gas

Question 21

What carries out dentrification?

Answer 21

Denitrifying bacteria

Question 22

When does denitrification occur?

Answer 22

In the absence of oxygen

Question 23

What can be used instead of oxygen as an electron acceptor during cellular respiration?

Answer 23

Nitrates

Question 24

When will nitrates be used during cellular respiration instead of oxygen?

Answer 24

In oxygen poor condition

Question 25

What is reduced when nitrates are used instead of oxygen?

Answer 25

The availability of nitrates to plants

Question 26

When does waterlogging occur?

Answer 26

When the soil becomes inundated with water through flooding or irrigation with poor drainage

Question 27

How does waterlogging impact the nitrogen cycle?

Answer 27

By reducing the levels of nitrates and nitrites in the soil

Question 28

Through which process does waterlogged soil lose nitrates and nitrites?

Answer 28

Denitrification and leaching

Question 29

Where will there be a build up of water when rainfall exceeds evaporation?

Answer 29

Within porous soil

Question 30

What happens as water drains downwards through the soil?

Answer 30

Soluble minerals are removed with it

Question 31

What does continual leaching do to the upper layers of soil?

Answer 31

Impoverishes them

Question 32

What does the continual leaching do to the lower bedrock?

Answer 32

Concentrates dissolved minerals in the lower bedrock

Question 33

Where is leaching most common?

Answer 33

In highly porous soils

Question 34

Where is leaching least common?

Answer 34

In textured soils

Question 35

What does a reduction in nitrogen availability within the soil mean for plants?

Answer 35

That they are unable to access sufficient quantities of nitrogen from the soil via their roots

Question 36

How are insectivorous plants able to obtain nitrogen in low nutrient environments?

Answer 36

By feeding on invertebrates

Question 37

What is an example of an insectivorous plant?

Answer 37

Venus fly trap

Question 38

What happens when the insect is trapped in the plant?

Answer 38

Digestive enzymes are released that allow it to absorb nutrients from the insect

Question 39

How are insectivorous plants baited to attract insects?

Answer 39

By nectar

Question 40

What does the phosphorus cycle show?

Answer 40

How different forms of phosphorus are transitioned within the environment

Question 41

What do certain rocks contain high levels of?

Answer 41

Phosphate

Question 42

Where can the phosphate released from rocks end up?

Answer 42

Into the soil and water

Question 43

How do rocks that contain phosphate lose it to the soil and water?

Answer 43

Chemical weathering

Question 44

Why do organisms require phosphates?

Answer 44

To synthesise nucleic acids, membranes and ATP

Question 45

When are phosphates returned to the soil?

Answer 45

Upon the decomposition of plant and animal remains

Question 46

What does the phosphorous cycle not include?

Answer 46

A gaseous component

Question 47

Why is the rate of turnover in the phosphorus cycle much lower than other cycles?

Answer 47

Because it doesn't have a gaseous component

Question 48

What are the two rates which are slower due to the fact there is no gaseous component in the phosphorus cycle?

Answer 48

Rate or turnover and replenishment

Question 49

How can phosphates be removed from the lithosphere?

Answer 49

Via mining

Question 50

What can phosphates be converted into?

Answer 50

Phosphate based fertilisers

Question 51

Why is turning phosphate into fertilisers good?

Answer 51

It allows phosphates that otherwise remain inaccessible in buried rock to become available for plant use

Question 52

Why are fertilisers good for plants?

Answer 52

It increases their productivity by increasing plant access to phosphate

Question 53

What happens to the phosphates that comprise part of the plants biomass when the crops are harvested?

Answer 53

They are lost from the phosphorus cycle

Question 54

What does using fertiliser in one site cause in another?

Answer 54

The depletion of phosphorus reserves

Question 55

What is the continued production of phosphate based fertilisers depleting?

Answer 55

Global phosphorus reserves

Question 56

What is contradictory about the demand for fertiliser but turnover in the phosphorus cycle?

Answer 56

Demand for fertiliser is high but turnover in the phosphorus cycle is low

Question 57

What are phosphate minerals classed as?

Answer 57

Non-renewable resource

Question 58

When is it predicted for phosphates to become severely restricted?

Answer 58

Within 50 - 100 years

Question 59

What is the problem with the possible future restriction of phosphates?

Answer 59

It would greatly limit the crop yield

Question 60

What is eutophication?

Answer 60

The enrichment of an ecosystem with chemical nutrients

Question 61

In eutrophication, how can nutrients be introduced?

Answer 61

Via leaching from soil by rainfall or released as part of sewage

Question 62

Where is eutrophication common?

Answer 62

Around agriculture lands where using fertilisers are prevalent

Question 63

What happens when there is an increase in nutrient supplies within waterways?

Answer 63

An algal bloom occurs but then they die. There is an increase in decomposers which results in increased oxygen demand by bacteria. Saprotrophs consume all available oxygen cleaning out the water supply. It also reduces oxygen production by seaweed

Question 64

What will stress the survival of marine organisms in eutrophication?

Answer 64

The reduced oxygen production of seaweeds

Question 65

What can eutrophication potentially lead to within the ecosystem?

Answer 65

A reduction in biodiversity

Question 66

What is the bulk of soil made up of?

Answer 66

A mixture of organic matter, rock and mineral particles

Question 67

What does the relative proportion of components of soil determine?

Answer 67

Soil type

Question 68

What can soil testing kits be used to identify ?

Answer 68

Nutrients Soil ph texture water content

Question 69

How do soil testing kits test for nutrients?

Answer 69

Chemical reagents produce colour changes when testing for N, P and K

Question 70

How do soil testing kits test for soil pH?

Answer 70

Colour changes can be used to identify the acidity or alkalinity of a soil sample

Question 71

How can soil testing kits test for texture?

Answer 71

Soil can be separated into layers according to particle size

Question 72

How can soil testing kits test for water content?

Answer 72

Electrical meters can determine water quantities based on the soils capacity to transmit an electrical current

Question 73

Why do gardeners and farmers need to test their soil for the different components?

Answer 73

To determine the viability of the soil for planting purposes

Question 75

Why do nitrates and nitrites function as a predominant source of nitrogen for plants?