Plants and Nitrogen
Goals and Objectives:
-
Be able to describe or illustrate the nitrogen
cycle and define ammonification, nitrification, and denitrification.
-
Be able to explain why nitrogen fixation is
purely done by prokaryotes.
-
Be able to describe, in a general sense, the
process of rhizobial infection and nodule formation in legumes.
-
Be able to describe the biochemical reactions
involved in nitrogen fixation by symbiotic bacteria.
-
Be able to describe the process of infection
and nodule development by nitrogen fixing bacteria in legumes.
-
Be able to describe how nitrogen is assimilated
and transported once it has been taken up by the plant in the form of ammonia.
-
Be able to describe how nitrate is assimilated
by plants.
-
Be able to describe how plants cycle nitrogen.
-
Be able to discuss the importance of nitrogen
in agriculture and in plant communities in general.
Study Questions:
-
Most plants obtain their bulk of their
nitrogen from the soil in the form of _____________ or _______________.
-
What is the nitrogen cycle? What three
pools of nitrogen make up the nitrogen cycle?
-
Give a definition for each of the following
and explain where each occurs in the nitrogen cycle.
-
Ammonification
-
Nitrification
-
Denitrification
-
Nitrogen Fixation
-
List the non-biological sources of fixed nitrogen.
-
What does the textbook mean when it says the
"Biological nitrogen fixation is exclusively a prokaryote domain"
page 101.
-
Give a general description of the free-living
nitrogen fixers. (You will not be required to learn the genera).
-
Give a general description of the nodule forming
symbiotic nitrogen fixers. List the three major genera involved
in this process.
-
What other symbiotic nitrogen fixers are mentioned
in the text?
-
Describe the process by which symbiotic nitrogen
fixing bacteria set up infection in legumes.
-
Write the equation for the enzymatic reaction
involving dinitrogenase. You do not need to know the specifics about
how the enzyme works.
-
Compare the cost of nitrogen fixation by the
amount of ATP used and the amount of carbon required to fix a gram of dinitrogen.
-
What does molecular oxygen do to the process
of nitrogen fixation?
-
List the strategies for regulating oxygen
that have evolved.
Skip sections on Hydrogen Production (pages
108-112) and Genetics of Nitrogen Fixation (pages 112-113).
-
Once dinitrogen has been fixed by symbiotic
bacteria, how is the ammonia handled within the plant? (See figure 6.12
on page 114)
-
What are the functions of the following enzymes?
-
Glutamine Synthetase
-
Glutamate Synthase
-
Glutamate Dehydrogenase
-
Aminotransferase (Transaminase)
-
How is nitrogen exported from the nodules?
-
How do plants that do not form nitrogen-fixing
associations take up nitrogen from the soil?
-
How are the enzymes involved in nitrate assimilation
controlled?
-
As plants age, nitrogen is moved from one
place to another. How is nitrogen usually stored in the plant?
What occurs when a plant is under nitrogen stress (too little nitrogen)?
-
How are fertilizers used in agricultural situations
and what are the results or effects of this usage?
-
In natural ecosystems, what controls the availability
of nitrogen to the plant?