Problem 1
\(A\) vital cycle. Why is the Calvin cycle crucial to the functioning of all life forms?
Problem 2
Be nice to plants. Differentiate between autotrophs and heterotrophs.
Problem 3
Why are the reactions of the Calvin cycle sometimes referred to as the dark reactions? Do they take place only at night, or are they grim, secret reactions?
Problem 4
The Calvin cycle can be thought of as taking place in three stages. Describe the stages.
Problem 5
Match each term with its description. (a) Calvin cycle (b) Rubisco (c) Carbamate (d) Starch (e) Sucrose (f) Amylose (g) Amylopectin (h) \(\mathrm{C}_{3}\) plants (i) \(\mathrm{C}_{4}\) plants (j) Stomata 1\. \(\mathrm{CO}_{2}\) fixation 2\. Storage form of carbohydrates 3\. \(\alpha-1,4\) linkages only 4\. 3-Phosphoglycerate is formed after carbon fixation 5\. The dark reactions 6\. Includes \(\alpha-1,6\) linkages 7\. Required for rubisco activity 8\. Carbon fixation results in oxaloacetate formation 9\. Allow exchange of gases 10\. Transport form of carbohydrates
Problem 6
Suggest a reason why rubisco might be the most abundant enzyme in the world.
Problem 7
In an atmosphere devoid of \(\mathrm{CO}_{2}\) but rich in \(\mathrm{O}_{2}\), the oxygenase activity of rubisco disappears. Why?
Problem 8
Explain why the maintenance of a high concentration of \(\mathrm{CO}_{2}\) in the bundle-sheath cells of \(\mathrm{C}_{4}\) plants is an example of active transport. How much ATP is required per molecule of \(\mathrm{CO}_{2}\) to maintain a high \(\mathrm{CO}_{2}\) concentration?
Problem 9
Glyceraldehyde 3 -phosphate dehydrogenase in chloroplasts uses NADPH to participate in the synthesis of glucose. In gluconeogenesis in the cytoplasm, the isozyme of the dehydrogenase uses NADH. Why is the use of NADPH by the chloroplast enzyme advantageous?
Problem 10
Light and dark talk. Rubisco requires a molecule of \(\mathrm{CO}_{2}\) covalently bound to lysine 201 for catalytic activity. The carboxylation of rubisco is favored by high \(\mathrm{pH}\) and high \(\mathrm{Mg}^{2+}\) concentration in the stroma. Why does it make good physiological sense for these conditions to favor rubisco carboxylation?
