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 their roles.

Answer 2

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
• are primarily microscopic fungi, bacteria.
• are saprotrophs.

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

Used for making aas (then proteins) and nucleic acids in plants & animals

• Animals obtain N from the diet, plants must obtain from the environment
• N2(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 (a form of nitrogen that can be taken up by plants).

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)

The bacteria have symbiotic mutualistic relationship with plant (both organisms benefit):

• Plant gains aas from Rhizobium, which are produced by nitrogen fixation.
• Bacteria gains carbohydrates produced by plant in photosynthesis, used as energy source.

Question 8

What is nitrification and the process?

Answer 8

Process by which ammonium compounds in the soil are converted into N-containing molecules that can be used by plants. Nitrifying bacteria (free-living) are involved.

Is an Oxidation Reaction, so only occurs in well-aerated soil. Two steps:

1. Nitrifying bacteria (Nitrosomanas) oxidise ammonium compounds 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 in soil back to N2(g)

Denitrification only occurs in anaerobic conditions. Bacteria use nitrates as a source of energy for respiration and nitrogen gas is released.

Question 10

What is ammonification?

Answer 10

Process by which decomposers convert N-containing molecules in dead organisms, faeces and urine into ammonium compounds.

Question 11

Learn nitrogen and carbon cycle!!

Answer 11

NOW