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AQA A Level Biology Paper 2 > Topic 5.4 - Nutrient Cycles > Flashcards

Topic 5.4 - Nutrient Cycles Flashcards

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1
Q

What is a saprobiont?

A

A microorganism that decomposes dead biomatter.

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2
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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3
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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4
Q

What happens during extracellular digestion?

A

Organic molecules are broken down into inorganic ions

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5
Q

What is meant by saprobiotic nutrition?

A

Obtaining nutrients from dead organic matter using extracellular digestion

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6
Q

Some fungi form ___ relationships with roots of plants

A

symbiotic

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7
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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8
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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9
Q

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

A

organic compounds

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10
Q

Why do plants and animals need nitrogen?

A

To make proteins and nucleic acids (DNA & RNA)

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11
Q

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

A

It’s inert

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12
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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13
Q

Name the 4 stages in the nitrogen cycle

A
  1. Nitrogen Fixation
  2. Ammonification
  3. Nitrification
  4. Denitrification
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14
Q

What is occuring in nitrogen fixation?

A

Nitrogen gas → ammonia

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15
Q

Nitrogen Fixation

State the equation of nitrogen gas turning into ammonia

A

N(2) + 6H → 2NH(3)

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16
Q

Nitrogen Fixation

Describe how nitrogen gas is converted into ammonia

A

Bacteria e.g. Rhizobium turns nitrogen into ammonia

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17
Q

Where are nitrogen-fixing bacteria found?

A

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

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18
Q

Explain how nitrogen-fixing bacteria form a mutualistic relationship with plants

A

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

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19
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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20
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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21
Q

Ammonification

How can ammonium ions (NH(4)+) also be produced?

A

Ammonia can also dissolve in water to produce ammonium ions

22
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
23
Q

Nitrification

Describe how first ammonium ions are turned into nitrites

A

Nitrifying bacteria (Nitrosomonas) change ammonium ions → nitrites

24
Q

Nitrification

Describe how then nitrites are turned into nitrates

A

Other nitrifying bacteria (Nitrobacter) change nitrites → nitrates

25
Q

Nitrification

State the equation for: ammonium ions → nitrites

A

NH(4)+ → NO(2)-

26
Q

Nitrification

State the equation for: nitrites → nitrates

A

NO(2)- → NO(3)-

27
Q

What happens during denitrification?

A

When nitrates in soil are converted to nitrogen gas by denitrifying bacteria

28
Q

Why do denitrifying bacteria use nitrates?

A

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

29
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 because of anaerobic conditions)

30
Q

Why are fertilisers used?

A
  • To replace lost minerals = more energy from ecosystem can used for growth
  • = increases efficiency of energy transfer
31
Q

Describe artificial fertilisers

A
  • Inorganic
  • Contain pure chemicals (e.g ammonium nitrate) as powders or pellets
32
Q

Describe natural fertilisers

A
  • Organic matter
  • Include manure, compost vegetables, crop residues & sewage sludge
33
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 & therefore they don’t decompose there
  3. Therefore minerals ions they contain (e.g. phosphates and nitrates) = not returned to soil by decomposers in nitrogen or phosphorous cycles
34
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. Therefore when removed, nutrients aren’t replaced though their remains or waste products
35
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

36
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

37
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
    • therefore their release into soil is more controlled & leaching is less likely
38
Q

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

A

∵ phosphates less soluble in water

39
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

40
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 because they are 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 because not enough dissolved oxygen
41
Q

Excess carbon dioxide in atmosphere dissolves in ____

A

ocean

42
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
43
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
44
Q

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

A

so much longer than

45
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
46
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
47
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)

48
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
49
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
50
Q

Describe the importance of phosphorus to organisms

A

Phosphate molecules are used in important biological molecules such as ATP and nucleic acids. Phosphate groups are also often added or removed to enzymes to control their activity and therefore different cellular processes.

51
Q

Describe the phosphorus cycle

A

AQA A Level Biology Paper 2 (16 decks)

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