3. Nutrient cycles in natural ecosystems

Question 1

define saprobionts

Answer 1

feeds on remains of dead plants and animals using extracellular digestion to break down the remains

Question 2

define saprobiotic nutrients

Answer 2

obtaining nutrients from dead organic matter using extracellular enzymes

Question 3

what are mycorrhizae

Answer 3

where some fungi form symbiotic relationships with plant roots

Question 4

outline fungis symbiotic relationship with plants

Answer 4

• fungi are made from hyphae
• these connect to the plants roots increasing the surface area
• this helps plants absorb ions and increase water intake
• in turn the fungi obtains organic compounds such as glucose from a plant

Question 5

how much of the atmosphere is made up of nitrogen

Answer 5

78%

Question 6

name two uses for nitrogen’s within organisms

Answer 6

• to make proteins
• to make nucleic acids

Question 7

what do plants and animals need in order to use nitrogen

Answer 7

bacteria to convert it into nitrogen containing compounds first

Question 8

what does the nitrogen cycle show

Answer 8

how nitrogen is converted into usable forms and passed down food chains and a non-living environment

Question 9

name the four stages of the nitrogen cycle

Answer 9

1. nitrogen fixation
2. ammonification
3. nitrification
4. denitrification

Question 10

outline stage one of the nitrogen cycle

Answer 10

1. Nitrogen Fixation:
   - nitrogen gas is turned into nitrogen containing compounds
   - carried out by bacteria such as Rhizobium
   - it turns nitrogen into ammonia, which are turned into ammonium ions which can be used by the plant
   - the bacteria receives carbs in return

Question 11

where is rhizobium found

Answer 11

inside root nodules

Question 12

outline stage two of the nitrogen cycle

Answer 12

2. Ammonification
   - nitrogen compounds from dead organisms are turned into ammonia by sapbriobionts
   these form ammonium ions

Question 13

outline stage three of the nitrogen cycle:

Answer 13

3. Nitrification:
   - when ammonium ions in the soil are converted into nitrogen compounds
   - nitrifying bacteria change ammonium ions into nitrites
   - then Nitrobacter changes nitrites into nitrates

Question 14

outline stage four of hte nitrogen cycle

Answer 14

4. Denitrification:
   - nitrates in the soil are converted into nitrogen gas via denitrifying bacteria
   - happens in anaerobic conditions
   - they use nitrates in the soil to carry out respiration and produce nitrogen gas.

Question 15

name reasons for plants and animals to need phosphorus?

Answer 15

to make DNA, phospholipids and ATP

Question 16

where is phosphorus found

Answer 16

found in rocks and dissolved in the ocean in the form of phosphate ions

Question 17

define assimilation

Answer 17

where phosphate ions in the ocean can be absorbed and used to make more complex molecules by producers

Question 18

outline the phosphurus cycle

Answer 18

• weathering releases phosphate ions from rocks into the soil
• phosphate ions are taken into the root and are assimilated
• ions travel through the food chain due to consumers eating dead plant matter, absorbing phosphate ions
• when plants and animals die, saprobionts are involved in breaking down the organic compounds
• this releases phosphate ions into the soil so it can be assimilated by plants
• weathering of rocks dissolved phosphate ions into the sea to be picked up by algae and passed down the food chain to birds
• waste produced by birds is high in phosphate ions, and can be used as a natural fertiliser

Question 19

what can increase the rate of assimilation

Answer 19

mycorrhizae