composite restoration that was matching in shade ,after one week it became much lighter..the reason could be:
- ...........light started photoinitation
- absorption water
- shade selected after rubber dam.
Forms of absorption:
Water can be absorbed practically through any plant surface, but in the case of terrestrial plants almost all of the water is absorbed through the roots and only a small portion through the aerial organs. Water is absorbed primarily by radical hairs and other root zones, and then transported to the aerial part must be done through the xylem tissues.
The xylem is the most important tissue in the transport of water, it is formed by several different types of living and non-living cells, among which the tracheal elements can be indicated, through which practically all the transport of the water is carried out, The fibers and living parenchymal cells are also found in the xylem.
Tracheal elements:
The tracheal elements (tracheas and tracheids) constitute the conductive system of water and are the cells most directly related to the transport of water in the plant. Both are more or less elongated, have lignified secondary walls and are dead during their functional phase. There is no cytoplasm inside that prevents the passage of liquid, which facilitates the efficient transport of water in relatively large quantities. The apical walls are perforated, typical characteristics of both the trachea and tracheid cells. In the most evolved vessels the walls of the ends may be totally missing, so there is no obstacle that opposes the passage of water through the cell.
If we take a large number of tracheal cells and splice them at their ends, we will obtain a long tube-shaped structure. This is exactly the arrangement they find in the cells that form the vessels, joined together by their end walls, and form what is called a vessel or xylem conduit. The tissues of the xylem tissue form a network of ducts that extend through all the regions of the plant, and bring to all living cells an easily accessible water supply, being of primary importance to the plant, not only to maintain its turgidity , but also for the transport of other substances (for example mineral elements) that can be carried from one cell to another by the movement of water.
The set of vessels is the main route by which water is transported in the angiosperms.
However, there are no vessels in the conifers, and in this group it is the tracheids that constitute the main route of water circulation. These tracheids are long fusiform cells, provided with sharp angled and perforated end walls. These tracheid end walls overlap, and thus constitute a continuous path for the movement of water. Of course, the movement of water in a group of tracheids is much less direct and encounters a much greater resistance than in a trachea system.
Although the tracheas and tracheids are oriented in the plant in a vertical direction and the movement of water takes place predominantly in this direction, there is also a certain lateral movement.
The lateral walls of the tracheas and tracheids are perforated in numerous pits, pores through which water can pass.
Forms of absorption:
Water can be absorbed practically through any plant surface, but in the case of terrestrial plants almost all of the water is absorbed through the roots and only a small portion through the aerial organs. Water is absorbed primarily by radical hairs and other root zones, and then transported to the aerial part must be done through the xylem tissues.
The xylem is the most important tissue in the transport of water, it is formed by several different types of living and non-living cells, among which the tracheal elements can be indicated, through which practically all the transport of the water is carried out, The fibers and living parenchymal cells are also found in the xylem.
Tracheal elements:
The tracheal elements (tracheas and tracheids) constitute the conductive system of water and are the cells most directly related to the transport of water in the plant. Both are more or less elongated, have lignified secondary walls and are dead during their functional phase. There is no cytoplasm inside that prevents the passage of liquid, which facilitates the efficient transport of water in relatively large quantities. The apical walls are perforated, typical characteristics of both the trachea and tracheid cells. In the most evolved vessels the walls of the ends may be totally missing, so there is no obstacle that opposes the passage of water through the cell.
If we take a large number of tracheal cells and splice them at their ends, we will obtain a long tube-shaped structure. This is exactly the arrangement they find in the cells that form the vessels, joined together by their end walls, and form what is called a vessel or xylem conduit. The tissues of the xylem tissue form a network of ducts that extend through all the regions of the plant, and bring to all living cells an easily accessible water supply, being of primary importance to the plant, not only to maintain its turgidity , but also for the transport of other substances (for example mineral elements) that can be carried from one cell to another by the movement of water.
The set of vessels is the main route by which water is transported in the angiosperms.
However, there are no vessels in the conifers, and in this group it is the tracheids that constitute the main route of water circulation. These tracheids are long fusiform cells, provided with sharp angled and perforated end walls. These tracheid end walls overlap, and thus constitute a continuous path for the movement of water. Of course, the movement of water in a group of tracheids is much less direct and encounters a much greater resistance than in a trachea system.
Although the tracheas and tracheids are oriented in the plant in a vertical direction and the movement of water takes place predominantly in this direction, there is also a certain lateral movement.
The lateral walls of the tracheas and tracheids are perforated in numerous pits, pores through which water can pass.
Water absorption by roots:
Practically the plants realize all the water absorption through the radical system and mainly by the region of the roots where the absorbent hairs are.
The water that penetrates the absorbent hairs and other cells of the root epidermis, does so by the effect of a diffusion pressure gradient. Regularly, the diffusion pressure deficit of the root cells is greater than that of soil dissolution, whereby water penetrates the roots from the soil.
As the concentration of solutes in the cells increases or the turgor pressure decreases, the cell diffusion pressure deficit will increase and as a result the water absorption will increase.
We can affirm that most of the water absorption takes place through an osmotic mechanism (passive absorption). However, some researchers estimate that there may be some active, non-osmotic absorption, which requires a metabolic energy expenditure; so much so that the theories that explain water absorption are often called passive absorption theories and active absorption theories.
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