Topic 5.4 - Nutrient Cycles

Question 1

What is a saprobiont?

Answer 1

A microorganism that decomposes dead biomatter.

Question 2

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

Answer 2

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

Question 3

How do saprobionts digest their food?

Answer 3

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

Question 4

What happens during extracellular digestion?

Answer 4

Organic molecules are broken down into inorganic ions

Question 5

What is meant by saprobiotic nutrition?

Answer 5

Obtaining nutrients from dead organic matter using extracellular digestion

Question 6

Some fungi form ___ relationships with roots of plants

Answer 6

symbiotic

Question 7

Describe how fungi is connected to the plant’s roots

Answer 7

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

Question 8

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

Answer 8

• 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 9

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

Answer 9

organic compounds

Question 10

Why do plants and animals need nitrogen?

Answer 10

To make proteins and nucleic acids (DNA & RNA)

Question 11

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

Answer 11

It’s inert

Question 12

What does the nitrogen cycle show?

Answer 12

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

Question 13

Name the 4 stages in the nitrogen cycle

Answer 13

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

Question 14

What is occuring in nitrogen fixation?

Answer 14

Nitrogen gas → ammonia

Question 15

Nitrogen Fixation

State the equation of nitrogen gas turning into ammonia

Answer 15

N(2) + 6H → 2NH(3)

Question 16

Nitrogen Fixation

Describe how nitrogen gas is converted into ammonia

Answer 16

Bacteria e.g. Rhizobium turns nitrogen into ammonia

Question 17

Where are nitrogen-fixing bacteria found?

Answer 17

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

Question 18

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

Answer 18

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

Question 19

Nitrogen Fixation

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

Answer 19

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

Question 20

Describe what occurs in ammonification

Answer 20

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

Question 21

Ammonification

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

Answer 21

Ammonia can also dissolve in water to produce ammonium ions

Question 22

Describe what occurs in nitrification

Answer 22

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

1. ammonium ions → nitrites
2. nitrites → nitrates

Question 23

Nitrification

Describe how first ammonium ions are turned into nitrites

Answer 23

Nitrifying bacteria (Nitrosomonas) change ammonium ions → nitrites

Question 24

Nitrification

Describe how then nitrites are turned into nitrates

Answer 24

Other nitrifying bacteria (Nitrobacter) change nitrites → nitrates

Question 25

Nitrification State the equation for: ammonium ions → nitrites

Answer 25

NH(4)+ → NO(2)-

Question 26

Nitrification State the equation for: nitrites → nitrates

Answer 26

NO(2)- → NO(3)-

Question 27

What happens during denitrification?

Answer 27

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

Question 28

Why do denitrifying bacteria use nitrates?

Answer 28

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

Question 29

What kind of conditions does denitrification occur in?

Answer 29

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

Question 30

Why are fertilisers used?

Answer 30

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

Question 31

Describe artificial fertilisers

Answer 31

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

Question 32

Describe natural fertilisers

Answer 32

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

Question 33

Explain how nutrients are lost when crops are harvested

Answer 33

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

Question 34

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

Answer 34

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

Question 35

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

Answer 35

Leads to fertilisers leaching into water ways & thus eutrophication

Question 36

What is leaching?

Answer 36

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

Question 37

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

Answer 37

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

Question 38

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

Answer 38

∵ phosphates less soluble in water

Question 39

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

Answer 39

having too much of one nutrient

Question 40

Describe how eutrophication occurs (6x)

Answer 40

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

Question 41

Excess carbon dioxide in atmosphere dissolves in \_\_\_\_

Answer 41

ocean

Question 42

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 42

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

Question 43

Describe the greenhouse effect

Answer 43

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 44

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

Answer 44

so much longer than

Question 45

When is methane produced?

Answer 45

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 46

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

Answer 46

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 47

Describe the effect of global warming on vectors/pests

Answer 47

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 48

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

Answer 48

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

Question 49

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

Answer 49

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

Question 50

Describe the importance of phosphorus to organisms

Answer 50

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.

Question 51

Describe the phosphorus cycle

Answer 51