Question

g The first phase of the Calvin cycle is the (a)_____ phase. During this phase, a single CO2 molecule located in the (b)______ of the chloroplast gets fixed with (bonds with) a CO2-acceptor molecule called (c)_____ . This is a (d)_____ (number)-carbon molecule, which becomes an unstable 6-carbon molecule once it is carboxylated by CO2. This unstable molecule immediately splits into (e)______ (number) 3-carbon molecules called (f)_____ , which are the products of this phase of the Calvin cycle.

Answer 1

a) Carbon fixation phase

b) stroma

c) Ribulose bisphosphate (RuBP)

d) 5-carbon molecule

e) two carbon molecules

f) glycerate-3-phosphate (GP)

Explanation:

In the Calvin cycle (also named C3 cycle or Calvin-Benson cycle), the CO2 is reduced in a cyclic process, where the first stable reaction product is 3-phosphoglyceric acid (3-PGA), a 3-C molecule, and the CO2 acceptor molecule is Ribulose bisphosphate (i.e., Ribulose 1, 5-diphosphate). The CO2 enters the chloroplast by passing through the stomata and diffusing into the stroma of the chloroplast, which is the site where sugar is synthesized. The Rubisco enzyme or RuBP carboxylase catalyzes the first step of the cycle (i.e., the attachment of CO2 to RuBP). The result of this reaction is an unstable 6C molecule, which breaks down into two 3C molecules named glycerate-3-phosphate (GP).