Question

1.      a) where does the Calvin cycle happen in Sansevieria trifasciata?
         b) summurize the photosynthesis difference between Sansevieria trifasciata and typical C3 plants. what general category does Sansevieria trifasciata plant fit in.

Answer 1

Sansevieria trifasciata is also known as snake plant or mother-in-law's tongue. Now known as Dracaena trifasciata, it is a flowering plant belonging to family Asparagaceae. It is commonly found in tropical forests of West Africa. Other names are Saint George's sword and viper's bowstring hemp. It is a C4 plant.

In C4 plants photosynthesis takes place in the chloroplast of mesophyll cell which is thin-walled. Subsequently, the 4-carbon acid (oxaloacetate, malate, or aspartate) produced is transported to the bundle sheath cell (which is thick-walled). Calvin cycle occurs in the chloroplast of the bundle sheath cell. It protects the Calvin cycle from the process of photorespiration. Photorespiration is a waste process in which rubisco (Calvin cycle enzyme) acts on oxygen rather than on carbon dioxide. Mostly plants belong to the C3 category and cannot avoid photorespiration. C4 plants minimize this wasteful process by separating the process of initial carbon dioxide fixation and the Calvin cycle in space and performing the two processes in two different cells as explained above.

The photosynthesis difference between Sansevieria trifasciata (C4) and typical C3 plants

C3 photosynthesis: The process of the Calvin cycle begins with a 3 carbon compound 3-phosphoglyceric acid (that is why it is called C3 plant). C3 photosynthesis is a one stage process happening in chloroplast organelles acting as a storage center for sunlight energy. This energy is used to combine ATP and NADPH to form sugar molecules. Around 85% of plants come in this category.

C4 photosynthesis: It is a two-stage process producing a 4 carbon compound as an intermediate which on reaching bundle sheath cell (the process is explained above) spits into carbon dioxide and a 3 carbon compound. The carbon dioxide then undergoes the Calvin cycle the same as in C3 photosynthesis. Thus C4 photosynthesis produces a higher concentration of carbon helping plants to survive extreme conditions where low light and water are available.

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