Sucrose and Starch Biosynthesis

Question 1

Photosynthetic pathways

Answer 1

C3 (most common)
C4
CAM

Question 2

Why did CO2 concentrating mechanisms arise in plants?

Answer 2

Reduction in [CO2] ~350 MYA

Question 3

What make C4 more efficient than C3 photosynthesis?

Answer 3

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.

Question 4

What is the kranz anatomy?

Answer 4

structure of cells in C4 plants
bundle sheath cells in centre (contain RuBisCo)
surrounded by ring of mesophyll cells and then the epidermis

Question 5

What does CAM stand for?

Answer 5

Crassulacean acid metabolism

Question 6

Why did the CAM metabolism arise?

Answer 6

Adaptation for desert plants
Allows stomata to be closed in the day
Saves water

Question 7

How does the CAM metabolism work?

Answer 7

Opens stomata at night

Takes in CO2 and stores as malic acid in vacuole

Question 8

What does the CAM metabolism help plants with?

Answer 8

Reduces water loss through stomata by allowing plant not to open stomata during the day.

Question 9

How is CO2 fixed into malic acid?

Answer 9

atmospheric + respiratory CO2 -> bicarbonate ion

bicarbonate ion + phosphoenolpyruvate + PEP carboxylase -> Pi + oxaloacetate

oxaloacetate + NADH -> malate
malate -> malic acid

Question 10

Types of photosynthesis in terms on water usage

Answer 10

CAM

Question 11

Types of photosynthesis in terms of ATP per molecule of CO2

Answer 11

C3

Question 12

What controls gas exchange across leaves?

Answer 12

stomata

Question 13

A decrease in turgor pressure, driven by _______ of K+ closes stomata.

Answer 13

loss

Question 14

An increase in turgor pressure, driven by _______ of K+ opens stomata.

Answer 14

influx

Question 15

What is unusual about guard cells compared to other epidermal cells?

Answer 15

contain chloroplasts

Question 16

Where does starch synthesis occur?

Answer 16

The stroma (chloroplasts)

Question 17

What is start made up of?

Answer 17

Chain of glucose molecules

Question 18

What is starch made from in the plant (to be stored)?

Answer 18

ADP-glucose

Question 19

What are two techniques for studying starch use in plants called?

Answer 19

Starch photography

Autoradiogram

Question 20

What are the point of the process of starch photography?

Answer 20

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.

Question 21

What is the method used to produce an autoradiogram?

Answer 21

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

Question 22

Describe transport in the phloem

Answer 22

bidirectional transport driven by positive pressure

Question 23

Describe transport in the xylem

Answer 23

unidirectional transport root to shoot driven by negative pressure