Bags were placed over several leafs of a small poplar tree. In the middle of the
ID: 86607 • Letter: B
Question
Bags were placed over several leafs of a small poplar tree. In the middle of the day radioactive 14 CO2 was placed in one of the bags that surround a full grown leaf. By the middle of the night, very little of the 14 CO2 was detected in the original bag, but it was detected in a bag that covered a small, expanding leaf. Describe the most plausible route the carbon followed in to the plant, from one leaf to another and out of the plant. In describing a possible route include the names of tissues, cells and orangelles. Also in your explanation use the terms sink, source and the terms for any other processes, substances that are necessary for a complete explanation.
Explanation / Answer
Plausible root of CO2 14 is
1. It entered the leaf theough stomata, then travelling through the spaces in mesophyll tissues it crossed the cell membrane of few cells of mesophyll tissue. These are special cells containing chloroplast.
2. CO2 entered choloroplaat and reacted with RUBP compound inside the stroma through the process called dark reaction. This reaction led to conversion of CO2 to glucose molecule.
3. This glucose got converted to starch for easy storage and is part of the same cells where it is manufactured.
4. Accumulation of starch/food in one area of plant is called source region (full grown leaf). From here this food is transferred to the place it's required (small expanding leaf) called sink.
5. This starch is converted to sucrose a disaccharide and is transported from source(mature leaf) to sink( root and other parts needing food) through phloem.
6. The flow of sucrose is mass bulk flow and is supported by osmotic concentration gradient.
7. This sucrose is transported to the other cells of plamt where ot changes to glucose and becomes part of respiratory cycle.
8. Glucose from the cell enters mitochondria and undergoes breakdown to release energy in form of ATP required by the cell. This reaction breaks glucose molecule back onto CO2 which escapes out onto other bag through mesophyll tissue and stomata.
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