Soil

Question 1

Soil can be divided into 2 groups:

Answer 1

• Organic soil: derived from sedimentation in bogs and marshes
• Mineral soils: derived from rock weathering and other inorganic material

Question 2

What is the composition of soil?

Answer 2

• Inorganic material matter (40%)
• Organic matter (5%)
• Air and water (50%)
• Living organisms

Question 3

What are the 4 horizons?

Answer 3

• 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)

Question 4

Where do most of microbial activity take place?

Answer 4

At the surfaces of soil particles

Question 5

What is the most important component influencing microbial activity in surface soils?

Answer 5

Water

Question 6

What is the type of soil retaining the water to the right extent?

Answer 6

Silt

Question 7

How do we call the soil that surrounds plant roots and receive plant secretion?

Answer 7

Rhizosphere

Question 8

How do we call an association between a fungi and a plant root?

Answer 8

Micorrhizae

Question 9

In the top few centimeters, what microorgansim is the most abundant?

Answer 9

Bacteria/archea

Question 10

What catalysis nitrogen fixation?

Answer 10

Nitrogenase complex

Question 11

What is Rhizopshere ?

Answer 11

the soil that surrounds plant roots and receive plant secretion

Question 12

Why is it difficult to do Nitrogen fixation?

Answer 12

Because of the 3 bounds of N2. Only fiew prokaryotes can fix nitrogen .

Question 13

Exemple of nitrogen fixer free living?

Answer 13

Cyanobacteria, Azobacter, Beijerinckia, Clostridium

Question 14

Exemple of nitrogen fixer symbiotic?

Answer 14

Rhizobium

Question 15

How many electrons are needed for nitrogen fixation, and where do they come from?

Answer 15

8, from pyruvate

Question 16

What inhibits dinitrogenase reductase?

Answer 16

Oxygen

Question 17

What is the final product of nitrogen fixation and what is it used for?

Answer 17

Ammonia, used to produce a.a. etc.

Ammonia can be used by plants , NH3 dissolves in water to produce ammonium NH4

Question 18

what do free-living nitrogen fixer especially need?

Answer 18

Soil rich in organic matter, because nitrogen fixation requires a lot of energy

Question 19

Clostridium is …

anaerobe, aerobe?

Answer 19

Strict anaerobe

Question 20

Azobacter is…

anaerobe, aerobe?

Answer 20

Strict aerobe

Question 21

Why is azobacter aerobe, if the enzyme dinitrogen reductase is inhibited by oxygen?

Answer 21

The enzyme is protected by a very high rate of O2 consumption, which keeps the intracellular environment anaerobic.

Question 22

What is a major nitrogen-fixing organism in nature?

Answer 22

Cyanobacteria

Question 23

How does cyanoacteria produces ennergy?

Answer 23

by oxygenic photosynthesis, oxygen is produced in the cell

Question 24

Hoe does cyanobacteria fix nitrogen? Explain with O2…how is it possible?

Answer 24

• 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)

Question 25

The mutualistic relationship between ________ plants and nitrogen-fixing bacteria is one of the most important symbioses known.

Answer 25

Leguminous

Question 26

What is a heterocyst, what does it do?

Answer 26

It is a specialized anaerobic cell. Its job is to fix nitrogen…

Question 27

What nitrogen fixing organism is best known in the symbiosis with a leguminous plant?

Answer 27

Rhizobium

Question 28

What does the symbiosis (nitrogen fixing bacteria and plant root) lead to?

Answer 28

Formation of nodules