Chapter 8

Question 1

The process of converting N2
into forms that plants can use
(NH3)

Answer 1

N-fixation

Question 2

The process that causes the strong two-atom N molecules found in the atmosphere to break apart so they can combine with the other atoms

Answer 2

N-fixation

Question 3

Major N-fixation processes

Answer 3

1. Artificial/Industrial Fixation
2. Lightning/Atmospheric Fixation
3. Biological Fixation

Question 4

N-fixing organisms contain an enzyme _______ which combines with N2 and a fixation occurs in a series
of steps that reduces N2 to NH3

Answer 4

Nitrogenase

Question 5

The N-fixing organisms also requires __.

Answer 5

Co

Question 6

refers to microorganisms fixing N while growing in association with host plant

Answer 6

Symbiotic N fixation

Question 7

is carried by free living bacteria and blue green in the soil or water

Answer 7

non-symbiotic N-fixation

Question 8

This is extremely energy expensive requiring __ ATP molecules for each N molecule fixed

Answer 8

16 ATP

Question 9

What are the host plants

Answer 9

Legumes:
- Peas, clovers, beans, lupins, ipil-ipil, soybeans, peanut, kudzu
Non-legumes (nodulated):
- Alders and Gunnera
Non-legumes (non-nodulated):
- Bahia, azolla, and sugarcane

Question 10

Bacteria
Peas-
Clovers-
Beans-
Lupins & Ipil-ipil-
Soybeans-
Alders-
Gunnera-
Bahia grass-
Azolla-
Sugarcane-

Answer 10

Bacteria
Peas- rhizobium leguminosarum bv. viceae

Clovers- rhizobium leguminosarum bv. trifoli

Beans- rhizobium leguminosarum bv. Phaseoli

Lupins & Ipil-ipil- rhizobium leguminosarum bv. loti

Peanut & kudzu- Brady rhizobium sp.

Soybeans- rhizobium fredii or Brady rhizobium japonicum

Alders- Frankia

Gunnera- Nostoc

Bahia grass- azotobacter

Azolla- Anabaena azollae

Sugarcane- acetobacter

Question 11

In what part of plants body N-fixation occurs?

Answer 11

root
nodules

Question 12

• even if a strain is able to infect a legume, the nodules formed may not be able to fix nitrogen

Answer 12

Ineffective

Question 13

• strains induce nitrogen-fixing nodules

Answer 13

Effective

Question 14

“Each nodule contains __________ of Rhizobium”

Answer 14

Thousand

Question 15

irregular shaped bodies called _________ _________.

Answer 15

bacteroids (Y-shaped)

Question 16

Active and effective nodules are greater than _ mm and concentrate around the ___ ____.

Answer 16

Active and effective nodules are greater than 2 mm and concentrate around the tap root

Question 17

Factors affecting N-fixation

Answer 17

1. Status of available mineral N in the soil solution
2. Proper strain of bacteria
3. Soil pH/acidity
4. Low levels of P, Mo, and Ca will affect N-fixation
5. Any growth factors