3.3.5 Nutrient Cycles

Question 1

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

Answer 1

food webs

Question 2

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

Answer 2

saprobionts

Question 3

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

Answer 3

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

Question 4

How do saprobionts digest their food?

Answer 4

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

Question 5

What happens during extracellular digestion?

Answer 5

Organic molecules are broken down into inorganic ions

Question 6

What is meant by saprobiotic nutrition?

Answer 6

Obtaining nutrients from dead organic matter using extracellular digestion

Question 7

Some fungi form ___ relationships with roots of plants

Answer 7

symbiotic

Question 8

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

Answer 8

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

Question 9

Describe how fungi is connected to the plant’s roots

Answer 9

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

Question 10

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

Answer 10

• 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

Question 11

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

Answer 11

organic compounds

Question 12

Why do plants and animals need nitrogen?

Answer 12

To make proteins and nucleic acids (DNA & RNA)

Question 13

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

Answer 13

It’s inert

Question 14

What does the nitrogen cycle show?

Answer 14

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

Question 15

Name the 4 stages in the nitrogen cycle

Answer 15

1. Nitrogen Fixation
2. Ammonification
3. Nitrification
4. Denitrification

Question 16

What is occuring in nitrogen fixation?

Answer 16

Nitrogen gas → ammonia

Question 17

Nitrogen Fixation

State the equation of nitrogen gas turning into ammonia

Answer 17

N₂ + 6H → 2NH₃

Question 18

Nitrogen Fixation

Describe how nitrogen gas is converted into ammonia

Answer 18

Bacteria e.g. Rhizobium turns nitrogen into ammonia

Question 19

Where are Rhizobium are found?

Answer 19

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

Question 20

Explain how Rhizobium forms a mutualistic relationship with plants

Answer 20

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

Question 21

Nitrogen Fixation

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

Answer 21

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

Question 22

Describe what occurs in ammonification

Answer 22

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

Question 23

Ammonification

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

Answer 23

Ammonia can also dissolve in water to produce ammonium ions

Question 24

Describe what occurs in nitrification

Answer 24

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

1. ammonium ions → nitrites
2. nitrites → nitrates

Question 25

Nitrification Describe how first ammonium ions are turned into nitrites

Answer 25

Nitrifying bacteria (*Nitrosomonas*) change ammonium ions → nitrites

Question 26

Nitrification Describe how then nitrites are turned into nitrates

Answer 26

Other nitrifying bacteria (*Nitrobacter*) change nitrites → nitrates

Question 27

Nitrification State the equation for: ammonium ions → nitrites

Answer 27

NH₄⁺ → NO₂^-

Question 28

Nitrification State the equation for: nitrites → nitrates

Answer 28

NO₂^- → NO₃^-

Question 29

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

Answer 29

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

Question 30

What happens during denitrification?

Answer 30

When nitrates in soil → nitrogen gas by denitrifying bacteria

Question 31

Why does denitrifying bacteria use nitrates?

Answer 31

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

Question 32

What kind of conditions does denitrification occur in?

Answer 32

Happens under anaerobic conditions e.g. in waterlogged soils (Bacteria use NO as source of O ∵ of anaerobic conditions)

Question 33

Why are fertilisers used?

Answer 33

* To replace lost minerals = more energy from ecosystem can used for growth * = increases efficiency of energy transfer

Question 34

Describe artificial fertilisers

Answer 34

* Inorganic * Contain pure chemicals (e.g ammonium nitrate) as powders or pellets

Question 35

Describe natural fertilisers

Answer 35

* Organic matter * Include manure, compost vegetables, crop residues & sewage sludge

Question 36

Explain how nutrients are lost when crops are harvested

Answer 36

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

Question 37

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

Answer 37

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

Question 38

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

Answer 38

Leads to fertilisers leaching into water ways & thus eutrophication

Question 39

What is leaching?

Answer 39

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

Question 40

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

Answer 40

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

Question 41

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

Answer 41

∵ phosphates less soluble in water

Question 42

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

Answer 42

having too much of one nutrient

Question 43

Describe how eutrophication occurs (6x)

Answer 43

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

Question 44

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

Answer 44

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

Question 45

Excess CO₂ in atmosphere dissolves in \_\_\_\_

Answer 45

ocean

Question 46

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

Answer 46

* Shells and bones sink to bottom of ocean and form rock such as chalk and limestone * Carbon returns to atmosphere as rocks weather

Question 47

Describe the greenhouse effect

Answer 47

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

Question 48

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

Answer 48

so much longer than

Question 49

When is methane produced?

Answer 49

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

Question 50

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

Answer 50

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

Question 51

Describe the effect of global warming on vectors/pests

Answer 51

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

Question 52

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

Answer 52

* Carbon dioxide taken in as a result of photosynthesis * Carbon is incorporated into compounds in the trees

Question 53

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.

Answer 53

* Plants already have enough nitrate / nitrate no longer limiting * Another named factor is limiting growth e.g. light intensity

Question 54

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

Answer 54

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

Question 55

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)

Answer 55

* Ammonia formed by decay * On nitrogenous waste / nitrogenous compounds