How can the absence of starch in the elaborated sap be explained knowing that it is produced by photosynthesis ?
Your question is most misleading. Starch is not produced by photosynthesis, photosynethesis produces sugars, and when those sugars are in excess, cellular enzymes convert the sugars, mainly glucose, into starch.
Elaborated sap is sugars that were in transport in the phloyem, and excess pressure caused a rupture to form sap flow.
The absence of starch in the elaborated sap can be explained as follows:
1. Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to produce glucose, which is the primary source of energy for plant cells.
2. Glucose is initially stored in the form of starch in plant tissues such as leaves, stems, and roots. Starch serves as a long-term energy storage molecule for plants.
3. However, during the process of translocation, which is the movement of sugars and other nutrients in the plant, glucose is converted into sucrose.
4. Sucrose is a disaccharide composed of glucose and fructose, and it is the primary sugar transported through the phloem vessels in plants.
5. The conversion of glucose to sucrose allows for efficient transport of sugars from areas of high concentration (source, usually leaves) to areas of low concentration (sink, such as developing fruits, roots, or storage organs).
6. Unlike starch, sucrose is a readily available energy source that can be used directly by other plant tissues. Therefore, the elaborated sap, which contains sucrose, is the form in which sugars are transported to various parts of the plant.
7. Since the sap contains sucrose rather than starch, it indicates that the glucose produced by photosynthesis has been converted into sucrose and is being transported to other parts of the plant for growth, development, or storage, rather than being stored as starch.
The absence of starch in the elaborated sap can be explained by understanding the process of photosynthesis and the role of starch in plants.
Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize food from carbon dioxide and water. During photosynthesis, plants convert light energy into chemical energy and produce glucose as a primary product. This glucose can be used by plants for immediate energy needs or it can be stored as starch for future use.
Starch is a complex carbohydrate that serves as the main storage form of glucose in plants. It is synthesized in the chloroplasts of plant cells and stored in specialized structures like roots, tubers, and seeds. Starch molecules are too large to be transported through the phloem, which is responsible for transporting organic nutrients in plants.
Elaborated sap, also known as phloem sap, is the fluid that flows through the phloem tissue in plants. It contains various organic compounds, including sugars, amino acids, hormones, and minerals. However, unlike xylem sap (which primarily contains water and minerals), phloem sap does not usually contain starch.
The absence of starch in the elaborated sap can be explained by the fact that starch is not a mobile form of energy in plants. Starch is typically stored in plant organs like roots, tubers, and seeds, while sugars (such as glucose and sucrose) are the main mobile forms of energy that can be transported through the phloem tissue. Sugars are soluble and can be transported from the photosynthetic organs (such as leaves) to other parts of the plant where energy is needed.
In summary, the absence of starch in the elaborated sap can be attributed to the fact that starch is not readily transported through the phloem tissue. Instead, sugars are the primary form of energy transported through the phloem, while starch serves as a storage form of energy within plant cells.