3.5.4 nutrient cycles

Question 1

what are nitrogen contents and how are they displayed on graphs?

Answer 1

nitrogen content can be used to measure biomass instead of carbon which can be broken down by respiration

logarithmic scale: not equal scale

change in temp leads to a change in biomass of bacteria

Question 2

describe both decomposition and saprobionts definitions

Answer 2

decomposition = the chemical process of hydrolysis (takes in water to break bonds) of complex biological molecules to smaller inorganic molecules or ions

saprobionts = organisms mainly fungi and microorganisms that secrete digestive enzymes onto the dead remains of other organisms hydrolyse the biological molecules in these dead remains and then absorb some of the products of this digestion

rest remains in surroundings and can be absorbed by other organisms

Question 3

what is composting?

Answer 3

organic material

mechanical grinders and choppers

microorganisms

1. mesophilis (10-45 degrees)
2. thermophilis, main active phase (50-65 degrees)
3. curing, temp falls, mesophilis recolonise

Question 4

describe simple nutrient cycle

Answer 4

how a chemical elements moves from an abiotic environment into living organisms and then back into abiotic environments

diagram on notes:
- nutrient in biological molecules in primary producers
- nutrient in biological molecules in primary consumers
- nutrient in biological molecules in secondary consumers
- decomposers

Question 5

what are limitations of the phosphorus cycle?

Answer 5

bacteria = some bacteria convert plants - available phosphate into organic forms that are not available to plants

absorption = inorganic phosphorus can be chemically bound to soil particles, making it unavailable to plants

pH: needs to be soluble to be taken up by plants, dependant on pH
less then pH 4 or more then pH 8 the phosphorus starts to become tied up by other compounds
farmers add phosphorus as fertiliser

Question 6

describe phosphorus cycles

Answer 6

1. rain and weathering
   rocks release inorganic ions
   distributed into soils and water
2. plants then animals
   absorption incorporated into organic molecules eg DNA
3. death and bacteria (excretion and decomposition)
   organic phosphate is available to bacteria
   they break down organic matter to inorganic forms
4. water
   phosphorus in soil can end up in waterways and eventually oceans
5. sedimentation
   phosphorus incorporated into sediments over time

Question 7

what is phosphorus?

Answer 7

main components in DNA, ATP and lipids(phospholipid bilayer)

mostly stored in soil and rocks in forms of PO4 3-

plants absorb directly through roots

diagram on notes

Question 8

what is denitrification?

Answer 8

three processes remove remove nitrogen from atmosphere and pass it through ecosystems

denitrification = reduces nitrates to nitrogen gas, thus replenishing the atmosphere

closes nitrogen cycle

Question 9

what is nitrification?

Answer 9

ammonia can be taken up directly by plants. through roots

most of the ammonia produced by decay is converted into nitrates

bacteria of the genus Nitrosomonas oxidise NH3 to nitrites NO2-
bacteria of the genus Nitrobacter oxidise the nitrites to nitrates NO3-
called nitrifying bacteria, nitrogen is made available to plants

Question 10

what is decomposition?

Answer 10

the plants made by plants enter and pass through food webs like carbohydrates

each tropic level, their metabolism produces organic nitrogen compounds that return to the environment through excretions

finial beneficiaries of these materials are microorganisms of decay

they break down the molecules in excretions and dead organisms into ammonia

Question 11

what is nitrogen fixation?

Answer 11

free living bacteria such as Azotobacter

symbiotic bacteria Rhizobium in root nodules of legumes

legumes = sinbiotic relationship with nitrogen

rhizobium contains an enzyme called nitrogen that converts nitrogen + hydrogen to ammonia

ammonia is used to make amino acids which the legumes can use to make proteins in return for supplying the bacteria with carbohydrates

Question 12

what are the 3 types of fixation?

Answer 12

biological fixation = certain microbes

atmospheric fixation = lightening

industrial fixation = haber process

Question 13

describe nitrogen fixation

Answer 13

nitrogen molecule is inert

to break it apart, atoms can combine with other atoms that require the input of substantial energy

haber process

Question 14

nitrogen cycle diagrams

Answer 14

IMPORTANT DIAGRAM ON NOTES

Question 15

what are the 4 biological processes of the nitrogen cycle?

Answer 15

nitrogen fixation
decompostion
nitrification
denitrification

Question 16

how do plants secure nitrogen in compounds?

Answer 16

plants secure their nitrogen in fixed ie incorporated in compounds

nitrogen ions N03-
ammonia NH3
ammonium NH+4
nitrite NO2-

animals secure nitrogen compounds from plants or animals

plants —— animals, digestion

Question 17

what are nitrogen compounds?

Answer 17

all life requires nitrogen compounds eg proteins and nucleic acids

air is 79% nitrogen (N2) is the major reserve of nitrogen

most organisms cannot use nitrogen in this form

Question 18

what are the advantages of mycorrihizae?

Answer 18

increase SA for nutrient absorption as well as water + phosphates, nitrates

thick root sheath/ shield = protection from soil pathogens

increased nutrient absorption of plant = faster growth

carbohydrates from plant to mycorrhizae = photosynthesis

some plants cannot take up to certain phosphate ions without mycorrhizae

Question 19

what is the structure of mycorrihizae?

Answer 19

fungi survives as spores

they germinate and spread thread like hyphae, grow into root tissues

once established they extent out from root surface into surround soil

Question 20

describe mycorrhizae

Answer 20

myco = fungus
rhiza = roots

symbiotic relationship between fungi and plant roots
arbuscular mycorrhiza most common

highly specific to the plant species and have evolved with them

response is usually mutualistic

Question 21

fertilisers overview

Answer 21

IMPORTANT ON NOTES

Question 22

what are natural fertilisers?

Answer 22

eg animal manure

do less harm to environment

contain main elements found in organic fertilisers

present in organic compounds such as urea, cellulose, lipids

cannot make use of organic materials in the soil, roots can only take up inorganic

Question 23

what are inorganic fertilisers?

Answer 23

most commonly used fertilisers

contain nitrate, phosphate + potassium ions

NPK fertilisers

inorganic fertilisers are very effective, can calculate exact amounts

undesirable effects on environment

nitrate and ammonium ions are very solvable

Question 24

how does use of fertilisers lead to reduced species diversity?

Answer 24

NPK fertilisers favour the growth of grasses, nettles and rapidly growing species

meadows often how low nitrogen levels in the soil

leaching = excess fertiliser dissolving into rain than into rivers

Question 25

what are the consequences of using fertilisers?

Answer 25

1. reduced species diversity
2. leaching
3. eutrophication

Question 26

how do fertilisers increase productivity

Answer 26

nitrates :

needed for dna and proteins, both for plant growth

plants develop earlier and taller

increased rate of photosynthesis + crop productivity

Question 27

what are the two types of fertilisers?

Answer 27

1. natural fertilisers
   dead and decaying plants, slurry = decomposing bedding, good fertilisers
2. artificial fertilisers
   mined from rocks and blended to give the right mix of nutrients
   npk - nitrogen, phosphorus, potassium
   haber process

Question 28

describe the process of eutrophication

Answer 28

1. In most lakes and rivers there is naturally very low concentration of nitrate and so nitrate ions are a limiting factor for plant and algal growth.
2. As the nitrate ion concentration increases as a result of leaching, it ceases to be a limiting factor for the growth of plants and algae whose populations both grow.
3. As algae mostly grow at the surface, the upper layers of water become densely populated with algae. This is called an ‘algal bloom’.
4. This dense surface layer of algae absorbs light and prevents it from penetrating to lower depths.
5. Light then becomes the limiting factor for the growth of plants and algae at lower depths and so they eventually die.
6. The lack of dead plants and algae is no longer a limiting factor for the growth of saprobiontic bacteria and so these populations too grow, using the dead organisms as food.
7. The saprobiontic bacteria require oxygen for their respiration, creating an increased demand for oxygen.
8. The concentration of oxygen in the water is reduced and nitrates are released from the decaying organisms.
9. Oxygen then becomes the limiting factor for the population of aerobic organisms, such as fish. These organisms ultimately die as the oxygen is used up altogether.
10. Without the aerobic organisms, there is less competition for the anaerobic organisms, whose populations now rise.

11 The anaerobic organisms further decompose dead material, releasing more nitrates and some toxic wastes, such as hydrogen sulphide, which makes the water putride.

Question 29

what is leaching?

Answer 29

Leaching is the process by which nutrients are removed from the soil.

Rainwater will dissolve any soluble nutrients, such as nitrate ions, and carry them deep into the soil, eventually beyond the reach of plant roots. The leached nitrate ions find their way into watercourses, such as streams and rivers, that in turn may drain into freshwater lakes.

Here they may have a harmful effect on humans if the river or lake is a source of drinking water. Very high nitrate ion concentrations in drinking water can prevent efficient oxygen transport in babies and a link to stomach cancer in humans has been suggested. The leached nitrate ions are also harmful to the environment as they can cause eutrophication.