Nutrient Cycles

Question 1

Explain the role of saprobionts in recycling chemical elements

Answer 1

Decompose protein, urea, DNA in dead matter

By secreting enzymes for extracellular digestion

Absorb soluble needed nutrients and release phosphate ions

Question 2

Mycorrhizae

Answer 2

Symbiotic association between fungi and plant roots

Question 3

Explain the role of mycorrhizae

Answer 3

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

Question 4

Biological molecules that contain nitrogen

Answer 4

Amino acids

DNA

Chlorophyll

ATP

NAD

Question 5

Role of bacteria in nitrogen fixation

Answer 5

Nitrogen gas converted into ammonia which forms ammonium ions in soil

By nitrogen fixing bacteria

Question 6

Role of bacteria in ammonification

Answer 6

Protein, urea, DNA from waste are decomposed

Converted to ammonia which forms ammonium ions in soil

By saprobionts which secrete enzymes for extracellular digestion

Question 7

Role of bacteria in nitrification

Answer 7

Ammonium ions in soil converted into nitrites then nitrates by 2 step oxidation reaction

For uptake by plant root hair cells by active transport

By nitrifying bacteria in aerobic conditions

Question 8

Role of bacteria in denitrification

Answer 8

Nitrates in soil converted to nitrogen gas

By denitrifying bacteria in anaerobic conditions

Question 9

Why does adding air to soil increase its fertility

Answer 9

more nitrification

less denitrification

Question 10

Biological molecules that contain phosphorus

Answer 10

Phospholipids

DNA

ATP

RuBP

Question 11

Describe the phosphorus cycle

Answer 11

Phosphate ions in rocks released into soils by erosion

Phosphate ions taken up by producers and incorporated into their biomass

Rate of absorption increased by mycorrhizae

Phosphate ions transferred through food chain

Some phosphate ions lost from animals in waste products

Saprobionts decompose organic compounds in dead matter releasing phosphate ions

Question 14

Why are fertilisers used

Answer 14

To replace nitrates and phosphates lost when plants are harvested and livestock are removed

Those removed from soil and incorporated into biomass cant be released back into the soil through deomposition by saprobionts

So improve efficiency of energy transfer which increases productivity

Question 15

Difference between artifical and natural fertilisers

Answer 15

Artificial - Contain inorganic compounds of nitrogen, phosphorus and potassium

Natural - Organic ions released during decomposition by saprobionts

Question 16

Key environmental issues arising from use of fertilisers

Answer 16

Phosphates dissolve in water leading to leaching of nutrients into lakes

Leading to eutrophivation

Question 17

Process of eutrophication

Answer 17

Rapid growth of algae in pond so light blocked

Submerged plants die as they cannot photosynthesise

Saprobionts decompose dead plant matter using oxygen in aerobic respiration

So less oxygen for fish to aerobically respire leading to their death

Question 18

Explain the key advantages of using natural fertiliser over artificial fertiliser

Answer 18

Less water soluble so less leaching → eutrophication less likely

Organic molecules require breaking down by saprobionts → slow release of nitrate/phosphate