Floema is what? Functions, the structure of phloem, unlike xylem

Floema is a special kind of plant tissue. In translation from the Greek language, this term means "bark". Also it is often called a bast. Floema is a tissue through which nutrients are transferred to the organs of plants. What kind of building does she have? How does the transport of nutrients occur? What is different from xylem?

Conductive plant tissues: xylem and phloem

To carry mineral substances and water to different parts of the plant, a conductive tissue is needed . It consists of two types of complex tissues - phloem and xylem.

Xylem is also called wood, and phloem is called a bast. They, as a rule, are in close proximity to one another and form conductive bundles (also called vascular fibrous). According to the mutual arrangement of phloem and xylem, several types of conducting tissues are distinguished:

1. Collaterial (the tissues are adjacent to each other and are equidistant from the axial part of the plant organ).
2. Bicollateral (xylem surrounded by two phloem segments).
3. Concentric (when the xylem surrounds the phloem and vice versa).
4. Radial (when there is an alternation of phloem and xylem in radii).

The structure of phloem

Plant phloem is a special kind of conductive tissue that is necessary for the transfer of nutrients formed as a result of photosynthesis to the organs of the plant where they are used. By type of origin, it is divided into the following types:

• Primary (differentiated from procambium);
• Secondary (formed from cambium).

Their main difference lies in the fact that in the primary phloem there are no heart-shaped tubes. However, their cellular composition is identical.

The phloem consists of the following cell types:

• Sitovidnye (provide the main transfer of substances and do not have cell nuclei);
• Sclerenchyma (serve for support);
• Parenchymal (perform the function of short-range radial transport).

The main feature of the sieve cells is the presence of special pores in the cell walls. Their origin is still unclear. The channels of the sieve elements are lined with callosa (polysaccharide), which can accumulate in them. Callosa can clog the channels of these cells, for example, when the plant is in a resting phase in the winter.

Floam transport

Floema is a tissue through which concentrated solutions of hydrocarbons (mostly sucrose) are formed, formed as a result of photosynthesis. In addition, assimilates and metabolites are transferred, but in a lower concentration. The rate of transport of substances reaches several tens of centimeters within an hour.

The transfer of substances is carried out from the organs, where nutrients are actively formed, to those parts of the plants where they are used or stored. Active transfer of substances occurs to the roots, shoots, forming leaves, reproductive organs, tubers, bulbs, rhizomes.

As a result of the experiments, the scientists found out that transport is carried out from donor organs to those parts of plants that are located closest to them. In addition, the transfer of substances is two-way. Therefore, the plant can accumulate nutrients or expend them in different periods of vegetation.

Floema: Functions

Photosynthesis is carried out in leaf chloroplasts with the participation of sunlight. Its products, water and other solutions of minerals absorbed by plant roots are necessary for the functioning of absolutely all cells. Floema is the tissue that provides their translocation. Solutions flow over the sieve elements from zones with high hydrostatic pressure to areas of its low value. Therefore the main function of phloem is transport.

The difference between phloem and xylem

Despite the fact that xylem and phloem perform similar functions and are in close proximity, they have differences. The movement of substances in the xylem is from the root to the leaves. Moreover, the cells that form this kind of tissue are vascular elements, tracheids, fibers and wood parenchyma. Xylem is necessary for transferring water together with dissolved nutrients.

So, phloem is one of the types of conductive plant tissue. It serves to transfer nutrients from those organs of the plant where they are actively formed, in those parts where they are stored or consumed. Floema is represented by three types of cells - sieve, sclerenchyma and parenchyma. The main transport function is performed by sieve cells with special pores that do not have nuclei.

The transfer of substances can be carried out in two directions, and its speed sometimes reaches several tens of centimeters per hour. Another conductive tissue, similar in function to phloem, is xylem. But the main difference lies in the fact that the xylem only transfers water in one direction (from roots to shoots) with mineral substances dissolved in it.