Photosynthesis and Partitioning

Question 1

What is a source?

Answer 1

Provides assimilates. e.g. green photosynthesising leaves.

Question 2

What is a sink?

Answer 2

Uses assimilates. e.g. flowers, seeds, developing leaves.

Question 3

How much solar energy is outside of the spectrum so cannot be used by plants?

Answer 3

51.3%

Question 4

How is energy lost?

Answer 4

Energy lost by reflection
NPQ- energy dissipated as heat
Carbohydrate synthesis loss

Question 5

What is photorespiration?

Answer 5

Carbon or O2 is fixed into sugars.
Wasted energy

Question 6

What is the reaction of photorespiration, and what do the products do?

Answer 6

RuBisCO + O2 ~> 2 phosphoglyolate + 3 phosphoglycerate

2 phosphoglycolate: Useless, costs energy to turn it into something useful
3 phosphoglycerate: Stores energy

Question 7

What is non photochemical quenching (NPQ)?

Answer 7

Photosynthetic proteins absorb excess energy and dissipate it as heat.
Done by the Xanthophyll cycle.

Question 8

What is the Xanthophyll cycle?

Answer 8

Violaxanthin ~> Antheraxanthin ~> Zeaxanthin
Done by light stress

Question 9

What does Zeaxanthin do?

Answer 9

Protects lipid membranes
Stimulates NPQ

Question 10

What is partitioning?

Answer 10

Fewer assimilates go to roots, stems and tillers and more go into growth and grain filling

Question 11

What did the sugar beet ten year breeding programme do to the ratio of AGM : BGM and Marc : Sugar

Answer 11

AGM : BGM
1:2 ~> 1:2.8
Marc : Sugar
1:3 ~> 1:3.8

Question 12

What is sink strength determined by?

Answer 12

Determined by genetics
Also by biotic and abiotic stresses.

Question 13

What is SWEET11?

Answer 13

A group of sugar transporters.
Expressed heavily in developing grains