Nutrient Cycles 3.5.4 ( Energy transfers in and between organisms 3.5)

Question 1

What percentage of the air is nitrogen

Answer 1

78%

Question 2

Why do we need a cycle of nitrogen

Answer 2

Plants and animals can’t obtain nitrogen through gas exchange , part of the reason being , nitrogen contains a triple bond which is very hard to break

Question 3

Why are microorganisms needed in the nitrogen cycle

Answer 3

To break the nitrogen triple bond and convert nitrogen gas into nitrogen containing substances that plants and animals can absorb

Question 4

Which biological molecules contain nitrogen

Answer 4

Proteins
ATP
Nucleic acids ( DNA , RNA , FAD , NAD , NADP )
urea
chlorophyll
amino acids

Question 5

What are the 4 key processes for The nitrogen cycle ?

Answer 5

1) ammonification
2) nitrification
3) nitrogen fixation
4) dentrification

Question 6

what does the term nitrogen fixing mean

Answer 6

turning nitrogen gas into a nitrogen containing compound

Question 7

Where does nitrogen - fixing happen directly in a plant

Answer 7

In the root nodules of leguminous plants

Question 8

Why does nitrogen - fixing happen directly in a leguminous plant

Answer 8

The root nodules contain bacteria which is able to convert nitrogen gas from the atmosphere into a nitrogen containing compound e.g ammonium or nitrates

Question 9

What is it called when nitrogen - fixing directly happens in a plant

Answer 9

Symbiotic relationship: where both the bacteria and plant are gaining benefit from coexisting together

Question 10

How do the nitrates get into the animals

Answer 10

Animals eat the plants

Question 11

What are denitrifying bacteria within the soil

Answer 11

Bacteria that are able to convert nitrates back into nitrogen gas in the atmosphere

Question 12

Why is denitrification not favoured in agriculture

Answer 12

• denitrification causes to lose nitrogen and nitrogen containing compounds from the soil

Question 13

When does denitrification happen

Answer 13

• Only takes place if you don’t have enough oxygen in the soil
• this is because denitrification is anaerobic

Question 14

How could the soil not have enough oxygen

Answer 14

• if the soil is waterlogged and flooded because that means it’s not going to be as much oxygen because it’s been displaced by water

Question 15

what process does nitrification undergo

Answer 15

oxidation

Question 16

when does nitrification occur

Answer 16

contains aerobic bacteria so only works if there’s oxygen available

Question 17

Explain the role of saprobionts in recycling chemical elements

Answer 17

• Decompose organic compound- proteins in organic matter
• By secreting enzymes for extracellular digestion
• Absorb soluble needed nutrients and release mineral ions

Question 18

what is mycorrhizae

Answer 18

Symbiotic association between fungi and plant roots

Question 19

Explain the role of mycorrhizae

Answer 19

• Fungi act as an extension of plant roots to increase surface area of root system
• To increase rate of absorption of water and inorganic ions
• In return , fungi receive organic compounds e.g. carbohydrates

Question 20

Describe the role of bacteria in nitrogen fixation

Answer 20

• Nitrogen gas (N2) converted into ammonia which forms ammonium ions in soil
• By nitrogen - fixing bacteria

Question 21

Describe the role of bacteria in ammonification

Answer 21

• Nitrogen containing compounds e.g. proteins from dead organisms / waste are decomposed
• Converted to ammonia which forms ammonium ions in soil
• By saprobionts

Question 22

describe the role of bacteria in nitrification

Answer 22

• ammonium ions in soil converted into nitrites then nitrates , via a two step oxidation reaction
  • for uptake by plant root hair cells by active transport
• By nitrifying bacteria in aerobic conditions

Question 23

describe the role of bacteria in denitrification

Answer 23

• Nitrates in soil converted into nitrogen gas
• By denitrifying bacteria in anaerobic conditions

Question 24

suggest why ploughing (aerating ) soil increases its fertility

Answer 24

• More nitrification
• Less denitrification

Question 25

give examples of biological molecules that contain phosphorus

Answer 25

Phospholipids
DNA or RNA
ATP or ADP
NADP

Question 26

Describe the phosphorus cycle

Answer 26

1) phosphate ions in rocks released into soils by erosion
2) Phosphate ions taken up by producers e.g. plants and incorporated into their biomass
• rate of absorption increased by mycorrhizae
3) Phosphate ions transferred through food chain
4) some phosphate ions lost from animals in waste products
5) Saprobionts decompose organic compounds releasing phosphate ions

Question 27

Explain why fertilisers are used

Answer 27

• To replace nitrates / phosphates lost when plants are harvested and livestock removed
  • those removed from soil and incorporated into biomass can’t be released back into the soil through decomposition by saprobionts
• So improve efficiency of energy transfer - increase productivity / yield

Question 28

Describe the difference between artificial and natural fertilisers

Answer 28

Natural :
• Organic e.g. manure , compost
• Ions released during decomposition by saprobionts

Artificial :
• Contain inorganic compounds of nitrogen , phosphoric and potassium

Question 29

Explain the key environmental issue arising from use of fertilisers

Answer 29

• Phosphates / nitrates dissolve in water , leading to leaching of nutrients into lakes / rivers etc
• This leads to eutrophication :
1) Rapid growth of algae in pond / river (algae bloom) so light is blocked
2) So submerged plants die as they cannot photosynthesise
3) So saprobionts decompose dead plant matter , using oxygen in aerobic respiration
4) So less oxygen for fish to aerobically respire , leading to their death

Question 30

Explain the key advantage of using natural fertiliser over artificial fertiliser

Answer 30

• Less water soluble so less leaching -> eutrophication less likely
• Organic molecules require breaking down by saprobionts ~> slow release of nitrates / phosphate etc

Question 31

EQ : suggest one source of phosphate in the lake (1)

Answer 31

fertilisers

Question 32

EQ : Name the type of bacteria which convert
(i) nitrogen in the air into ammonium compounds
(ii) nitrites into nitrates (2)

Answer 32

(i) nitrogen - fixation bacteria
(ii) nitrifying bacteria

Question 33

EQ: Other than spreading fertilisers , describe and explain how one farming practice results in addition of nitrogen - containing compounds to a field (2)

Answer 33

• Growing leguminous plants
• They have nitrogen fixing bacteria

Question 34

EQ) Describe and explain how one farming practice results in the removal of nitrogen - containing compounds from a field (2)

Answer 34

• Harvesting the crop
• This removed nitrogen containing compounds

Question 35

EQ : explain how including leguminous plants in a crop rotation reduced the need to use artificial fertilisers (2)

Answer 35

• They contain nitrogen fixing bacteria
• They can still add nitrogen even when crop has been harvested

Question 36

EQ: Application of very high concentrations of fertilisers to the soil causes plants to wilt . Explain why (2)

Answer 36

Changed water potential ( more negative )
Plants lose water by osmosis

Question 37

EQ : In autumn when there is no crop , farm land may be used to grow mustard . The mustard absorbs nitrates which otherwise can leach out of the soil at this time of year . The mustard is ploughed back into the soil just before sowing of the main crop in spring .
Nitrogen compounds in the mustard plants are made available for the main crop after ploughing in the spring . Describe the role of microorganisms in this process . (5)

Answer 37

• Mustard plant would contain amino acids
• Amino acids get broken down by saprobionts into ammonium ions
• Nitrifying bacteria converts ammonium ions to nitrate ions
• Nitrates can be absorbed by roots of plants to be used

Question 38

EQ : Explain why it is important for the farmer to reducing leaching of nitrates (2)

Answer 38

• Can cause health problems
• Leads to eutrophication

Question 39

EQ : Plants absorb a number of other nutrients from the soil including phosphates . Describe why phosphates are needed by a growing plant . (4)

Answer 39

To produce phosphate containing compounds such as :
- ATP
- DNA
- RNA
- FAD
-NAD
- phospholipids
- cell membrane

Question 40

EQ : A large lake is surrounded by fields . These fields are separated from each other by hedges . 100 years ago the lake was a habitat for many plants , invertebrate and fish . Today the lake has no fish and few plants or invertebrate. Explain how increased use of inorganic fertilisers on the fields may have led to these changes (5)

Answer 40

• Leaching in the lake will occur
• Causing algae bloom
• Sunlight is blocked
• Plants can’t photosynthesise
• Plants die
• Decomposed by sapbrobionts using oxygen in respiration
• Less conc of oxygen for fish to aerobically respire
• Fish + invertebrate die

Question 41

EQ : Famers who grow wheat sometimes have a field fallow for a year by not growing a crop in it . The concentration of nitrate ions in the soil decreases when a field is left fallow .
When grass is grown in a field , fewer nitrate ions are lost than when the field is left with bare soil . Explain why (1)

Answer 41

• Nitrate ions can be leached off in soil , so less leaching in a field

Question 42

EQ : A crop of leguminous plants such as clover may be grown in the field and then ploughed in . Explain why less fertiliser would be needed for the wheat crop in the following year (2)

Answer 42

• Clover contains nitrogen fixing bacteria
• When added , decomposed nitrate ions released into the soil

Question 43

EQ : One environmental issue arising from the use of fertilisers is eutrophication . Eutrophication can cause water to become cloudy .
You are given samples of water from three different rivers.
Describe how you would obtain a quantitive measurement of their cloudiness (3)

Answer 43

•Use of calorimeter
• measure absorbance of light
• Same volume of water
• Same wavelength of light