nutrient cycle

Question 1

How do saprobionts function?

Answer 1

-feed on dead organisms and waste products - a type of decomposed which recycle chemical elements
-secrete enzymes to digest their food externally then absorb the nutrients -extracellular digestion
-during this process organic molecules are broken down into inorganic molecules

Question 2

What is saprophytic nutrition?

Answer 2

The obtaining of nutrients from dead organic matter/ waste using extracellular digestion

Question 3

Describe the process of nitrogen fixation.

Answer 3

• nitrogen gas is turned into nitrogen-containing compounds
  -carried out by nitrogen fixing bacteria such as rhizobium found in root nodules of leguminous plants.
  -converts nitrogen into ammonia
  -the plant then uses this to produce amino acids/proteins
  -mutualistic relationship- the plant is provided with nitrogen compounds and the bacteria is provided with carbohydrates

Question 4

What is a mutualistic relationship?

Answer 4

A type of relationship where both species benefit

Question 5

Describe the process of ammonification.

Answer 5

-saprobionts(bacteria) decompose proteins(from dead organisms/waste) into ammonia

Question 6

Describe the process of nitrification.

Answer 6

-when ammonia ions in the soil are changed into nitrates- which can then be used by plants
-first one type of nitrifying bacteria change ammonia into nitrites
-then another those of nitrifying bacteria convert nitrites into nitrates

Question 7

Describe the process of denitrification.

Answer 7

-nitrates converted into nitrogen gas by denitrifying bacteria - they use nitrates for respiration and produce N2
-this happens under anaerobic conditions

Question 8

What is the impact of lightening on nitrogen?

Answer 8

Can fix nitrogen into nitrogen oxides

Question 9

What is the impact of fertilisers on soil?

Answer 9

Can add nitrogen containing compounds into the soil

Question 10

What is mycorrhizae?

Answer 10

-fungi made up of long thin strands called hyphae, which connect to the plant’s roots
-the hyphae increase the SA - absorption of water and minerals for the plant
-the hyphae in turn obtain organic compounds from the plant such as glucose

Question 11

What is phosphorus used for?

Answer 11

Needed to make biological compounds such as phospholipids, ATP, and DNA

Question 12

Where is phosphorus found?

Answer 12

-found in rock and dissolved oceans in the form of phosphate ions(PO4 3-)

Question 13

What happens to phosphate ions dissolved in water?

Answer 13

Phosphate ions dissolved in water in the soil can be assimilated by plants and other producers

Question 14

Describe the phosphorus cycle.

Answer 14

1)phosphate ions in rocks released into soil by weathering
2)P ions are absorbed by roots and assimilated by the plant such- helped by mycorrhizae
3)P ions transferred through the food chain as animals eat plants etc.
4)P ions are lost from animals in waste products - saprobionts
5)when organisms die, saprobionts decompose P containing compounds which are released into the soil
6)weathering also releases P ions into seas, lakes, and rivers. P ions absorbed by aquatic producers(algae and plants) and then passed along the food chain
7)waste products of seas bjrds(guano) contains high proportion of P ions
-guano returns a large amount of P ions into the soil and is often used as natural fertilisers

Question 15

How do mineral ions become the limiting factor?

Answer 15

-when microorganisms die in a natural ecosystem, they decompose. Microorganisms breakdown and convert compounds into useable compounds for producers to use
-in agricultural ecosystems, large amounts of biomass are harvested or removed, which removes nutrients from the ecosystem(soil).
-unless the mineral ions are replaced, the concentration decreases, which if left could decrease productivity; crop yield/animal product yield would decrease.
-the mineral ions have become the limiting factor

Question 16

What are natural fertilisers?

Answer 16

Made from organic matter, including manure, composted vegetables, crop residues, sewage sludge, bone meal.

Question 17

What are the advantages of natural fertilisers?

Answer 17

-cheap
-improve soil structure, which improves soil’s ability to retain water and aeration of the soil
-reduces erosion
-releases nutrients over a long period of time(can also be a -ve)

Question 18

What are the disadvantages of natural fertilisers?

Answer 18

-extremely bulky and must be applied in relatively large amounts
-difficult to spread, requires heavy machinery to handle the manure
-weed seeds and fungal spores may be present in the manure - introducing pests to the food chain
-sewage may contain heavy metals such as lead, zinc, and nickel

Question 19

What are artificial fertilisers?

Answer 19

They’re inorganic- contain lure chemicals in the form of powders or pellets

Question 20

What are the advantages of using artificial fertilisers?

Answer 20

-exact compositor of ions is known, which can be matched to the need of the crop
-quick release of minerals for periods of maximum growth
-concentrated so less can be applies - impacts on transport costs
-easy to apply
-soluble so that mineral ions are immediately available(links to a -ve)

Question 21

What are the disadvantages of using artificial fertilisers?

Answer 21

-soluble so leads to leaching
-does not improve soil structure

Question 22

How do fertilisers increase productivity?

Answer 22

-the minerals likely to be in short supply - nitrates, phosphates and potassium(NPK), which are required for growth
-phosphates and nitrates are used to produce amino acids, ATP, and nucleotides in DNA, all of which are needed for growth
-potassium is needed for some active transport which helps maintain the balance of negative and positive ions inside and outside cells
-photosynthesis and active transport both rely on an adequate supply of potassium
-where fertilisers have been provided, sufficient NPK ions have been provided(in most cases)
-plants develop earlier, grow taller and have a greater leaf area - all increase the rate of photosynthesis and thus increases crop productivity
-increase in productivity increases the amount of crop produced which decreases the cost of food.

Question 23

What is leaching?

Answer 23

When water-soluble compounds in the soil are washed away

Question 24

What does it mean if artificial fertilisers are soluble?

Answer 24

-inorganic ions in artificial fertilisers are relatively soluble
-therefore, excess minerals that are not immediately used are more likely to be leached into waterways

Question 25

True or false: leaching is more likely to occur if the fertiliser has been applied before heavy rainfall.

Answer 25

True

Question 26

Why are natural fertilisers less likely to be leached?

Answer 26

-natural fertilisers are less likely to leach because the NPK are contained in organic molecules that must be broken down by microorganisms before they can be absorbed by plants. This means NPK release is more controlled. -phosphates are less likely to leach than nitrates because phosphates are less soluble in water

Question 27

What is eutrophication caused by?

Answer 27

Caused by excess nutrients entering a body of water which increases the nutrient conc. in the water

Question 28

Describe the process of eutrophication.

Answer 28

1)in most lakes and rivers there is naturally a very low conc. of nitrate and so nitrate ions are a limiting factor for plants and algal growth 2)as nitrate conc. increases, because of leaching, it ceases to be a limiting factor, so plants and algae growth increases 3)algae mostly grows at the surface, so the upper layers of the water become densely populated with algae- called ‘algal bloom’ 4)this dense surface layer of algae absorbs light and ore vents light from penetrating to lower depths 5)light is now the limiting factor for growth of plants and algae at the lower depths so they eventually die 6)the lack of dead plants and algae is no longer a limiting factor for the growth of saprobiotic bacteria so these population too grow, using the dead organisms as food 7)saprophytes require oxygen for respiration, creating an increased demand for oxygen 8)oxygen levels decrease and further nitrates are released from decaying organisms 9)oxygen is now the limiting factor for the populations of aerobic organisms, such as fish, which die when oxygen supplies are depleted 10)less aerobic organisms so the populations of anaerobic organisms rise due to lack of competition 11)anaerobic organisms further decompose dead material, releasing more nitrates and some toxic wastes such as hydrogen sulphide, which makes the water putrid.

Question 29

What are the mark points for eutrophication?

Answer 29

-nitrates from fertilisers leach/run off into rivers/lakes -growth of algae blocks sunlight -increasing competition for light -reduced photosynthesis -plants die, increasing food availability for saprobionts -saprobionts aerobically respire(to decompose dead organic matter) -less oxygen for aerobic organisms such as fish, which die.

Question 30

How do fertilises affect biodiversity?

Answer 30

-reduce biodiversity -nitrogen rich soils favour the growth or grasses, nettles, and other rapidly growing species, which outcompete many other species which die as a result -species rich hay meadows only survive when the nitrate conc. are low enough to allow other species to compete with the grasses -this has knock on effects on the biodiversity of insects and animals