Lecture 6 - N and Phosphorous

Question 1

What is N needed for in plants?

Answer 1

N is needed to make AA, proteins and other cellular constituents.

Question 2

What does N deficiency cause?

Answer 2

Stunted growth and chlorotic leaves from chlorophyll damage.

Question 3

What proportion of air is N?

Answer 3

78% of air is N.

Question 4

Why is making biologically available N difficult?

Answer 4

Because N2 is a triple bond, pretty hard to break.

Question 5

What’s the Haber process reaction?

Answer 5

N2 + 3H2 -> 2NH3

Question 6

What temperature and pressure is required in the Haber Process.

Answer 6

Temperatures between 300-600c and high pressures of 20-80MPa.

Unfortunately however, this has a relatively low yield.

Question 7

What proportion of global energy is used for the Haber process?

Answer 7

A surprisingly high 2%.

Question 8

What % of Ammonia is used to make fertiliser?

Answer 8

85%

Question 9

How many tons of oil make 1 tonne of fertiliser?

Answer 9

2 tons per 1 ton of fertiliser.

Question 10

Why is symbiosis useful for plants in terms of N usage?

Answer 10

Microorganisms help breakdown N2, pretty beneficial to plants and the microorganisms get some carbohydrates as a reward.

Question 11

Why is reduction of nitrate to ammonia important?

Answer 11

Because it also provides N, typically found in the soil.

Question 12

What amount of Mt per annum do nitrate reduction and N2 fixation give per year.

Answer 12

20k Mt per year for nitrate reduction.

200K Mt per year for N2 fixation.

Question 13

What’s the three main issues with the haber reaction?

Answer 13

1 It’s super sensitive to oxygen

Question 14

What do rhizobia bacteria do?

Answer 14

Rhizobia form an infection thread, which means they form an invagination of theplasma membrane in root hairs. A tube is formed and they can enter.

Question 15

In legumes for every 100C fixed in leaves, how much goes to the nodules?

Answer 15

1/3 of C goes to the nodules.

Of this third, 5C grown and maintance. 12C production of NADH/ATP to fix N and 15C for assimilation of NH3.

Question 16

Name two other ways plants can get C.

Answer 16

Parasitism.

Carnivorousness.

Question 17

Is NH3 toxic to plants?

Answer 17

Yes, increased sensitivity to low temperature and necrosis.

Question 18

How much micrograms m3 of ammonia can a plant tolerate per year, day and hour.

Answer 18

75m3 per year on average.

However 600 per 24 hours and 10k per hour is the tolerance limits.

Question 19

What is the glutamate synthase cycle?

Answer 19

A cycle that converts ammonia to glutamate.

Question 20

What is glutamate the raw material for?

Answer 20

Production of amino acids and chlorophyll.

Question 21

What is P needed for?

Answer 21

Growth, photosynthetic capacity/rate, phospholipids etc.

Question 22

What % of Phorphorous is used as fertiliser

Answer 22

98%

Question 23

How do we get phosphate back?

Answer 23

Takes millions of years :(

Question 24

How much Mt of phosphate ends up in the oceans per year and how much of it is used and wasted.

Answer 24

21. 5Mt of phosphate ends up in the ocean every year.

2. 5Gt used by oceanic life, 19Mt completely wasted.

Question 25

What % of P is at Morroco?

Answer 25

51%, sadly P use is increasing too.

Question 26

How can these phosphate issues be dealt with?

Answer 26

Phosphate may be applied more efficiently.
80-90% of P applied as fertiliser bound to soil and biologically unavailable :(

Fertiliser directly delivers as little as 1-5% of plant P demand.

Also can try help recycle phosphate.

Question 27

Give two biological adaptations for increasing phosphate uptake.

Answer 27

1 Cluster roots - really densely packed proteoid roots which massively increase root surface area.

Question 28

What type of acid to cluster roots also produce?

Answer 28

Citric acid.

Question 29

What does citric action cause in reactions?

Answer 29

Citric acid swaps the carbohydrate and citric acid for the phosphate, releasing the phosphate into the soil which then can be taken up by the roots.

Question 30

What alternatives to phosphate may some plants show?

Answer 30

Galactolpiids and sulpholipid membranes may be used instead.

Also reduced protein production

Question 31

How may a plant produce lower protein?

Answer 31

Preventing young leaves photosynthesising.

Having few ribosomes, so produce proteins more slowly.