Sucrose and Starch Biosynthesis Flashcards
Photosynthetic pathways
C3 (most common)
C4
CAM
Why did CO2 concentrating mechanisms arise in plants?
Reduction in [CO2] ~350 MYA
What make C4 more efficient than C3 photosynthesis?
PEP carboxylase is an efficient enzyme, works well at lower [CO2]. Concentrates CO2 into C4 compounds in mesophyll cells and then around RuBisCo in bundle sheath cells.
What is the kranz anatomy?
structure of cells in C4 plants
bundle sheath cells in centre (contain RuBisCo)
surrounded by ring of mesophyll cells and then the epidermis
What does CAM stand for?
Crassulacean acid metabolism
Why did the CAM metabolism arise?
Adaptation for desert plants
Allows stomata to be closed in the day
Saves water
How does the CAM metabolism work?
Opens stomata at night
Takes in CO2 and stores as malic acid in vacuole
What does the CAM metabolism help plants with?
Reduces water loss through stomata by allowing plant not to open stomata during the day.
How is CO2 fixed into malic acid?
atmospheric + respiratory CO2 -> bicarbonate ion
bicarbonate ion + phosphoenolpyruvate + PEP carboxylase -> Pi + oxaloacetate
oxaloacetate + NADH -> malate
malate -> malic acid
Types of photosynthesis in terms on water usage
CAM
Types of photosynthesis in terms of ATP per molecule of CO2
C3
What controls gas exchange across leaves?
stomata
A decrease in turgor pressure, driven by _______ of K+ closes stomata.
loss
An increase in turgor pressure, driven by _______ of K+ opens stomata.
influx
What is unusual about guard cells compared to other epidermal cells?
contain chloroplasts
Where does starch synthesis occur?
The stroma (chloroplasts)
What is start made up of?
Chain of glucose molecules
What is starch made from in the plant (to be stored)?
ADP-glucose
What are two techniques for studying starch use in plants called?
Starch photography
Autoradiogram
What are the point of the process of starch photography?
Remove all starch by keeping plant in the dark for 48hr.
Place photographic negative on the leaf and illuminate.
Remove all chlorophyll with warm methanol (80%).
Rinse in water and stain with iodine solution.
What is the method used to produce an autoradiogram?
CO2 with carbon-14 applied to leaf
Radioactive label goes to the roots and young leaves, those tissues that are actively growing but not producing the required sucrose (sink tissues). Radioactivity is exported by mature source leaves
Describe transport in the phloem
bidirectional transport driven by positive pressure
Describe transport in the xylem
unidirectional transport root to shoot driven by negative pressure
