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AQA A Level Biology > 3.3.5 Nutrient Cycles > Flashcards

3.3.5 Nutrient Cycles Flashcards

1
Q

Natural ecosystem (not changed by human activity) nutrients are recycled through ___ ___

A

food webs

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2
Q

Many microorganisms (e.g. bacteria and fungi) are ________ (type of decomposer)

A

saprobionts

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3
Q

What do saprobionts do and what does this allow to happen?

A
  • Feed on remains of dead plants & animals & on waste products = break them down
  • Allows chemical elements to be recycled
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4
Q

How do saprobionts digest their food?

A
  • Saprobionts secrete enzymes & digest their food externally, then absorb soluble molecules (nutrients) they need
  • Known as extracellular digestion
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5
Q

What happens during extracellular digestion?

A

Organic molecules are broken down into inorganic ions

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6
Q

What is meant by saprobiotic nutrition?

A

Obtaining nutrients from dead organic matter using extracellular digestion

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7
Q

Some fungi form ___ relationships with roots of plants

A

symbiotic

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8
Q

Relationships between _____ and the ____ of _____ are known as mycorrhizae

A

Relationships between fungi and the roots of plants are known as mycorrhizae

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9
Q

Describe how fungi is connected to the plant’s roots

A

Fungi made up of long, thin strands called hyphae which connect to plant’s roots

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10
Q

What does the fungi’s hyphae help the plant to do?

A
  • Hyphae increase SA of plant’s root system = helps plant to absorb ions from soil that usually are scare (e.g. phosphorus)
  • Also increase uptake of water
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11
Q

Fungi obtain _______ _________ (e.g. glucose) from plants

A

organic compounds

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12
Q

Why do plants and animals need nitrogen?

A

To make proteins and nucleic acids (DNA & RNA)

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13
Q

Why can’t animals and plants use nitrogen from the air?

A

It’s inert

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14
Q

What does the nitrogen cycle show?

A

Shows how nitrogen is converted into usable form & then passed between different living + non-living organisms

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15
Q

Name the 4 stages in the nitrogen cycle

A
  1. Nitrogen Fixation
  2. Ammonification
  3. Nitrification
  4. Denitrification
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16
Q

What is occuring in nitrogen fixation?

A

Nitrogen gas → ammonia

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17
Q

Nitrogen Fixation

State the equation of nitrogen gas turning into ammonia

A

N2 + 6H → 2NH3

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18
Q

Nitrogen Fixation

Describe how nitrogen gas is converted into ammonia

A

Bacteria e.g. Rhizobium turns nitrogen into ammonia

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19
Q

Where are Rhizobium are found?

A

Inside root nodules (growths on roots) of leguminous plants (e.g. peas, beans)

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20
Q

Explain how Rhizobium forms a mutualistic relationship with plants

A

They provide the plant with nitrogen compounds & plant provides them with carbohydrates

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21
Q

Nitrogen Fixation

Name & describe 2 ways other than via bacteria that nitrogen gets into an ecosystem

A
  • Lightining
    • Fixes atmospheric nitrogen
  • Artificial fertilisers
    • Produced from atmospheric nitrogen on industrial scale in Haber process
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22
Q

Describe what occurs in ammonification

A

Nitrogen compounds from dead organisms + animal waste are turned into ammonia by saprobionts via decay, which then forms ammonium ions

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23
Q

Ammonification

How can ammonium ions (NH4+) also be produced?

A

Ammonia can also dissolve in water to produce ammonium ions

24
Q

Describe what occurs in nitrification

A

Ammonium ions in soil are changed into nitrogen compounds which can be used by plants (nitrates)

  1. ammonium ions → nitrites
  2. nitrites → nitrates
25
Q

Nitrification

Describe how first ammonium ions are turned into nitrites

A

Nitrifying bacteria (Nitrosomonas) change ammonium ions → nitrites

26
Q

Nitrification

Describe how then nitrites are turned into nitrates

A

Other nitrifying bacteria (Nitrobacter) change nitrites → nitrates

27
Q

Nitrification

State the equation for: ammonium ions → nitrites

A

NH4+ → NO2-

28
Q

Nitrification

State the equation for: nitrites → nitrates

A

NO2- → NO3-

29
Q

Nitrifying bacteria is known as chemoautotrophs. What is meant by this?

A

Called chemoautotrophs ∵ use chemical energy released from these reactions (nitrification) to live

30
Q

What happens during denitrification?

A

When nitrates in soil → nitrogen gas by denitrifying bacteria

31
Q

Why does denitrifying bacteria use nitrates?

A

To carry out respiration (use NO as source of O) & produce nitrogen gas

32
Q

What kind of conditions does denitrification occur in?

A

Happens under anaerobic conditions e.g. in waterlogged soils

(Bacteria use NO as source of O ∵ of anaerobic conditions)

33
Q

Why are fertilisers used?

A
  • To replace lost minerals = more energy from ecosystem can used for growth
  • = increases efficiency of energy transfer
34
Q

Describe artificial fertilisers

A
  • Inorganic
  • Contain pure chemicals (e.g ammonium nitrate) as powders or pellets
35
Q

Describe natural fertilisers

A
  • Organic matter
  • Include manure, compost vegetables, crop residues & sewage sludge
36
Q

Explain how nutrients are lost when crops are harvested

A
  1. Crops take in minerals from soil as they grow
  2. When crops are harvested, they’re removed from field & ∴ don’t decompose there
  3. ∴ minerals ions they contain (e.g. phosphates and nitrates) = not returned to soil by decomposers in nitrogen or phosphorous cycles
37
Q

Explain how nutrients are lost when animals or animal produces are removed from land

A
  1. Animal eat plants = take in their nutrients
  2. ∴ when removed = nutrients aren’t replaced though their remains or waste products
38
Q

Name an environmental issue that occurs when too much fertiliser is used (more than the plant needs)

A

Leads to fertilisers leaching into water ways & thus eutrophication

39
Q

What is leaching?

A

When water-soluble compounds in soil are washed way (e.g. by rain or irrigation systems) into nearby ponds/rivers

40
Q

Explain why using artifical fertilisers are more likely to result in leaching than natural fertilisers

A
  1. Inorganic ions in chemical fertiliser = relatively soluble
    • Excess minerals = not used immediately are more likely to leach into waterways
  2. VS natural fertilisers = nitrogen and phosphorus are contained in organic molecules that need to be decomposed by microorganisms before they can be absorbed by plants
    • ∴ their release into soil = more controlled & leaching is less likely
41
Q

Why is the leaching of phosphates less likely than the leaching of nitrates?

A

∵ phosphates less soluble in water

42
Q

Using fertilisers also changes the balance of nutrients in the soil and can result in crops dying due to….

A

having too much of one nutrient

43
Q

Describe how eutrophication occurs (6x)

A
  1. Mineral ions leached from fertilised fields stimulate rapid growth of algae in ponds + rivers
  2. Large amounts of algae block light from reaching plants below
  3. Eventually plants die ∵ unable to photosynthesise enough
  4. Bacteria feed on dead plant matter
  5. Increased no. of bacteria reduce oxygen concentration in water by carrying out aerobic respiration
  6. Fish & other aquatic organisms die ∵ not enough dissolved oxygen
44
Q

What causes the short-term fluctuations in the proportions of oxygen and carbon dioxide in the atmosphere?

A

Variations in rates of respiration and photosynthesis

e.g. concentration of CO2 at night is greater than during the day ∵ no photosynthesis occurs, but respiration occurs

45
Q

Excess CO2 in atmosphere dissolves in ____

A

ocean

46
Q

Give an example of parts of organisms that don’t decompose. State what they form and how the carbon is returned to the atmosphere.

A
  • Shells and bones sink to bottom of ocean and form rock such as chalk and limestone
  • Carbon returns to atmosphere as rocks weather
47
Q

Describe the greenhouse effect

A
  1. Sun’s radiation reaches Earth
  2. Some of it is reflected back & some radiated back to Earth by clouds + greenhouse gases that form part of the atmosphere
    • Greenhouse gases absorb heat
  3. Gases trap this heat close to Earth’s surface keeping it warm
48
Q

Carbon dioxide remains in the atmosphere for… ________ …other greenhouse gases

A

so much longer than

49
Q

When is methane produced?

A

When micro-organisms break down organic molecules which organisms are made of:

  • Decomposers break down dead remains of organisms
  • Micro-organism in intestines of primary consumers (e.g. cattle) digest food that’s been eaten
50
Q

Describe how the consequences of global warming could lead to loss of native species

A
  1. It’ll affect niches that are available in a community
  2. ∴ distribution of species will change
  3. Species may be able to migrate & compete for niches
  4. Leads to loss of native species that occupy those niches
51
Q

Describe the effect of global warming on vectors/pests

A

Life cycles and populations of insect pests would change to adapt to changed conditions ∴ tropical diseases could spread towards poles (as they carry pathogens)

52
Q

Explain how the growth of a forest results in a decrease in the carbon content of the atmosphere (2)

A
  • Carbon dioxide taken in as a result of photosynthesis
  • Carbon is incorporated into compounds in the trees
53
Q

Explain why the mass of crop produced stays the same in both fields when more than 40 kg of fertiliser is added. (2)

Fertiliser added is sodium nitrate.

A
  • Plants already have enough nitrate / nitrate no longer limiting
  • Another named factor is limiting growth e.g. light intensity
54
Q

Explain how the change in global mean temperature could decrease the yield of crop plants. Name 4 reasons. (4)

A
  • Increased temperature could decrease yield ∵ not optimum for enzyme action
  • Increase rate of transpiration
  • Increased prediation by insect pests
  • Unpredicated effects on rainfall
55
Q

It is estimated that, each year, a total of 3 × 109tonnes of ammonia are converted to nitrate. Only 2 × 108 tonnes of ammonia are produced from nitrogen gas. Explain the difference in these figures. (2)

A
  • Ammonia formed by decay
  • On nitrogenous waste / nitrogenous compounds

AQA A Level Biology (41 decks)

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