How can the absence of starch in the elaborated sap be explained knowing that it is produced by photosynthesis ?
To explain the absence of starch in the elaborated sap, let's break down the process of photosynthesis and how it affects starch production.
During photosynthesis, plants convert light energy into chemical energy in the form of glucose. Glucose is synthesized in plant cells through a series of complex reactions, and it serves as the main source of energy for the plant. However, glucose is not directly transported throughout the plant.
Once glucose is synthesized in the leaves through photosynthesis, it is either used immediately for energy or converted into starch for storage. Starch is a complex carbohydrate made up of glucose molecules, and it serves as a reserve energy source for the plant. Starch is commonly stored in specialized structures like roots, tubers, and seeds.
Elaborated sap, also known as phloem sap, is the fluid that flows through the phloem tissue in plants. It contains sugars, amino acids, hormones, and other organic compounds that are required for the growth and metabolism of the plant. The movement of elaborated sap through the phloem is facilitated by a process called translocation.
In the case of elaborated sap, it primarily consists of sucrose (a disaccharide made up of glucose and fructose) and other sugars rather than starch. The reason for the absence of starch in the elaborated sap can be explained by the fact that starch is mainly stored in parenchyma cells, while the phloem consists of specialized cells called sieve elements and companion cells.
Sieve elements do not have the necessary machinery to synthesize or store starch. Instead, they rely on companion cells for energy supply. The companion cells adjacent to the sieve elements actively load sucrose into the phloem sap, which is then transported throughout the plant to provide energy for growth and other metabolic processes.
Therefore, the absence of starch in the elaborated sap can be explained by the different functions and cellular composition of the phloem and storage tissues in plants. While starch is produced and stored in specialized parenchyma cells, the elaborated sap mainly consists of sucrose and other sugars that are actively loaded into the phloem for transportation.