Question

The radio labelled carbon in carbon dioxide supplied to potato plants in an experiment was seen in the tuber eventually. Trace the movement of the labelled carbon dioxide.

Answer 1

Entry to the plant

The radiolabeled carbon in carbon dioxide enters the leaf through the stoma.

Mesophyll cells (source)

The carbon dioxide is then fixed in the mesophyll cells of the leaf through the process of the Calvin cycle of photosynthesis. The carbon is found in the glucose molecule that is formed. Polymerisation of glucose molecules takes place to form starch. These starch granules are found in the stroma of the chloroplast.

Companion cell

Starch is then converted to sucrose and enters the companion cell of the phloem. through the process of active transport.

Sieve tube

Radiolabelled carbon in sucrose is now transported by active transport from the companion cell to the sieve tube. The radiolabeled sucrose now travels downwards in the sieve tube.

Tuber cells

The sucrose now gets unloaded into the sink i.e the cells of the tuber where it is stored as starch.