Soil Flashcards
Soil can be divided into 2 groups:
- Organic soil: derived from sedimentation in bogs and marshes
- Mineral soils: derived from rock weathering and other inorganic material
What is the composition of soil?
- Inorganic material matter (40%)
- Organic matter (5%)
- Air and water (50%)
- Living organisms
What are the 4 horizons?
- O horizon: Layer of undecomposed plant material
- A horizon: Surface soil ( Most microbobial acvitity)
- B horizon: Subsoil (
- C horizon : Soil base ( low microbial activity, derived from underlying bedrocks)
Where do most of microbial activity take place?
At the surfaces of soil particles
What is the most important component influencing microbial activity in surface soils?
Water
What is the type of soil retaining the water to the right extent?
Silt
How do we call the soil that surrounds plant roots and receive plant secretion?
Rhizosphere
How do we call an association between a fungi and a plant root?
Micorrhizae
In the top few centimeters, what microorgansim is the most abundant?
Bacteria/archea
What catalysis nitrogen fixation?
Nitrogenase complex
What is Rhizopshere ?
the soil that surrounds plant roots and receive plant secretion
Why is it difficult to do Nitrogen fixation?
Because of the 3 bounds of N2. Only fiew prokaryotes can fix nitrogen .
Exemple of nitrogen fixer free living?
Cyanobacteria, Azobacter, Beijerinckia, Clostridium
Exemple of nitrogen fixer symbiotic?
Rhizobium
How many electrons are needed for nitrogen fixation, and where do they come from?
8, from pyruvate
What inhibits dinitrogenase reductase?
Oxygen
What is the final product of nitrogen fixation and what is it used for?
Ammonia, used to produce a.a. etc.
Ammonia can be used by plants , NH3 dissolves in water to produce ammonium NH4
what do free-living nitrogen fixer especially need?
Soil rich in organic matter, because nitrogen fixation requires a lot of energy
Clostridium is …
anaerobe, aerobe?
Strict anaerobe
Azobacter is…
anaerobe, aerobe?
Strict aerobe
Why is azobacter aerobe, if the enzyme dinitrogen reductase is inhibited by oxygen?
The enzyme is protected by a very high rate of O2 consumption, which keeps the intracellular environment anaerobic.
What is a major nitrogen-fixing organism in nature?
Cyanobacteria
How does cyanoacteria produces ennergy?
by oxygenic photosynthesis, oxygen is produced in the cell
Hoe does cyanobacteria fix nitrogen? Explain with O2…how is it possible?
- Nitrogen fixation occurs in specialized anaerobic cells (heterocyst), which lack Photosystem II (does not produce O2)
- Heterocysts have thick cell wall that slow down diffusion of O2
- The regular cell provide the heterocysts with carbohydrate (pyruvate)
The mutualistic relationship between ________ plants and nitrogen-fixing bacteria is one of the most important symbioses known.
Leguminous
What is a heterocyst, what does it do?
It is a specialized anaerobic cell. Its job is to fix nitrogen…
What nitrogen fixing organism is best known in the symbiosis with a leguminous plant?
Rhizobium
What does the symbiosis (nitrogen fixing bacteria and plant root) lead to?
Formation of nodules
