23.3 - Recycling within Ecosystems

Question 1

What is decomposition?

Answer 1

• Chemical process where compounds are broken down into smaller molecules
• Essential elements, such as N or C cannot be used directly in organic form, it must be processed to an inorganic form (more usable)

Question 2

Define decomposer and detail their roles.

Answer 2

Decomposer: Organism that breaks down dead organisms to release nutrients back into the ecosystem

• Thus turning organic compounds into inorganic ones (nutrients) available to photosynthetic producers
• Primarily, microscopic fungi, bacteria

Question 3

Define saprobiotic nutrition and explain the roles of saprophytes.

Answer 3

Saprobiotic nutrition: Decomposers obtain energy from dead waste or organic material (saprophytes)

• Saprophytes digest food externally by secreting enzymes onto dead waste or organic material, enzymes break down complex organic molecules to simpler ones, decomposers absorb these
• Decomposers release stored inorganic compounds back to the environment

Question 4

Define detritivores and give their roles

Answer 4

Detritivores: Organism that feeds on decaying material

• They speed up decay process by feeding on detritus – dead & decaying material
• They break the material down into smaller material, increasing SA to allow decomposers to work on them

Question 5

What is the role of nitrogen?

Answer 5

NITROGEN: Used for making aas (then proteins); Nucleic acids in plants & animals

• Animals obtain N from the diet, plants must obtain from the environment
• N_2(g) is abundant in air (78%), plants cannot take it up in this form
• Bacteria play a part in combining nitrogen with other elements so plants can obtain it

Question 6

Describe the process of nitrogen fixation

Answer 6

Nitrogen-fixing bacteria contain the enzyme nitrogenase, combines atmospheric nitrogen with hydrogen to form ammonia that can be taken up by plants (nitrogen fixation)

Question 7

Describe the roles of the 2 bacteria involved in nitrogen fixation

Answer 7

Azotobacter - free living nitrogen fixing soil bacterium

Rhizobium – live in root nodules of leguminous plants (e.g. peas, beans, clover)

• Has symbiotic mutualistic relationship with plant
  
  • Plant gains aas from Rhizobium, produced by nitrogen fixation
  • Bacteria gains carbohydrates produced by photosynthesis, used as energy source

Question 8

What is nitrification and how does it work?

Answer 8

Process by which ammonium in the soul is converted into N-containing molecules (used by plant), nitrifying bacteria (free-living) are involved

Oxidation Reaction

1. Nitrifying bacteria (Nitrosomanas) oxidise ammonium into nitrites (NO₂^-)
2. Nitrobacter oxidise nitrites to nitrates (NO₃^-)

Nitrate ions are highly soluble, hence that is the form which N enters the plant

Question 9

Describe the process of denitrification

Answer 9

• If oxygen is unavailable (e.g. in waterlogged soil), denitrifying bacteria converts nitrates

back to N_2(g)

• Denitrification only occurs in anaerobic conditions

Question 10

What is ammonification?

Answer 10

Process by which decomposers converting N-containing molecules in dead organisms, faeces and urine to ammonium compounds

Question 11

Learn the nitrogen cycle/carbon cycle

Answer 11

See B6.3.1 word document