Lecture 9: Photosynthetic Pathways

Question 1

Photorespirations

Answer 1

Positively correlated with:
-Light 
-Temperature (and water)
Negatively correlated with
-CO2

Question 2

C4 pathway

Answer 2

• Spatial separation of C-fixation steps, includes additional steps
• CO2 concentrated at site of carboxylation in bundle sheath
• Phosphenolpyruvate
• PEP carbocylase only fixes CO2
• 1st product is 4C oxaloacetate
• Decraboxylations malate in bundle sheath cell
• CO2 is 10 times higher in bundle sheath than in atmosphere

Question 3

Morphology

Answer 3

• Kranz anatomy: wreath-like arrangement of bundle sheath cells
• Oxygenase activity of rubisco effectively eliminated in c4 bundle sheath cells

Question 4

Daily Fluctuations in CO2 exchange as a function of available radiation

Answer 4

• C4 plants can use even the most intense radiaiton for photosynthesis
• C3 plants reach light saturation at lower light intensity
• Sciophytes (shade-loving) adapted to dim light rake up more CO2 than heliophytes (sun-loving) in early morning and late evening
• Heliophytes utilize full sunlight more efficiently than sciophytes

Question 5

Nitrogen and Photosynthetic Machinery

Answer 5

Relationships between nitrogen content and

• (a) chlorophyll content
• (b) Rubisco aciticity in Triticum aestivum

Question 6

Nitrogen Use Efficiency

Answer 6

-Overall C4 plants have low N rewuirements contain 1/3-1/6 amount of N found in C3 plants, yet maintain same or greater photosynthetic rates
-High NUE, maximum photosynthetic rate per gram if nitrogen in the leaf
-Relationship between photosynthetic capacity and N content in leaves:
A) C3 crip plnats (wheat and rice)
C) C3 grasses and herbs
D)Deciduous trees and shrubs
E) evergreen trees and schlerophyllous shrubs

Question 7

Geographical Distributions

Answer 7

• C4 taxa are found in warm to temperate environments and are uncommon in cool th cold climate
• Mainly inhabit warm, grassland eosystem (maize, Millet, sorghum, sugarcane)