Each plant consists of three main parts: roots, stem and leaves. They are interconnected by conductive tissues and ensure normal growth and development of the body. But this only applies to evolutionarily more progressive plants. Lower organisms such as mosses, lichens and algae cannot boast a high level of development, which means that their body is much simpler. For example, rhizoids perform root functions in them. What are rhizoids in algae, mosses and other primitively developed organisms? What is their evolutionary significance?
What are rhizoids? Definition
Rhizoids are threadlike parts of lower plants that are one or more cells and serve as the root. Often they are colorless, short (their length can be limited to a few millimeters) and not too durable.
What are the differences between root and rhizoids?
- There are no conductive tissues in rhizoids. Osmosis and the flow of water into the body - this is one of the most important functions of the roots of the plant. If there are no xylem and phloem in the underground structures, they cannot be considered true roots.
- A big difference in the dimensions of the roots and rhizoids. If the former can reach tens of meters in length and a meter in width, then rhizoids are small, sometimes even microscopic formations.
- The root is a combination of a huge number of cells and tissues. Rhizoids, in turn, can be formed by several or even one cell, which depends on the functions.
However, one similarity can be seen right away: both the root and the rhizoids perform the function of anchoring - holding the plant's body in the soil. But even here you can make a reservation that the root copes with this function much more efficiently than rhizoids.
And yet, rhizoids are a kind of predecessor of true roots. These formations in the process of evolution gave rise to a new type, therefore they are of great importance in terms of the development of fauna, and also attract the interest of botanists. This is what rhizoids are in biology.
Rhizoid Functions
The importance of these structures in biology is not limited to a large role in the evolutionary process. Rhizoids also perform some functions related to supporting the growth and development of mosses, lichens, algae. Among them:
- Retention of the main part of the plant in the soil or at the bottom of the reservoir, if we are talking about algae.
- Gas exchange and loosening of the soil.
- Avoid getting excess water, too large drops of moisture.
- Water absorption.
These are the most common functions that rhizoids of algae and mosses can perform.
Types of Rhizoids
Not all underground structures of mosses and algae are alike. Even among such simple formations, specialization is observed depending on functions and structure. What are rhizoids and what are they in nature?
Rhizoids can be smooth (simple) and reed. The first are ordinary underground structures that serve to attach, sustain the plant and maintain its immobility.
Reed rhizoids differ in that their diameter is slightly smaller, the walls are thinner and wavy. Inside such formations there are outgrowths resembling papillae or tongues, where their name comes from. The function of such rhizoids is the flow of water by the capillary method, which is facilitated by such an unusual form.
Also, when studying “felt” from rhizoids, one can also find intermediate variants of these structures, which incorporate the features of both smooth and reed analogues. This is what rhizoids are in terms of structural diversity.
Which organisms can rhizoids be found in?
Previously, mosses and algae belonged to lower plants, since their structure was evolutionarily less developed than that of spore and seed plants. Rhizoids are also observed in all representatives of the kingdom of lichens, since this organism is a symbiotic relationship between algae and fungi. By the way, some representatives of fungi also form rhizoids.
Not all mosses possess these subterranean structures. For example, sphagnum, which lives in wetlands, absorbs water throughout the surface of the body, respectively, in this case, the formation of rhizoids is not necessary. All sphagnum mosses have the same situation.
What is the difference between rhizoids and rhizomoids?
We learned what rhizoids are and what role they played in the evolutionary process for the entire biological world. However, there are intermediate underground structures that stand on the evolutionary ladder between the rhizoids and the rhizome. We are talking about rhizomoids - another type of root structure of more developed organisms than mosses or algae.
Rhizomoids are a precursor to the rhizome of ferns and plunders. They are formed by interweaving several rhizoids at once so closely as if it were one continuous structure. However, they are not true roots for the same reason as rhizoids of mosses, algae and lichens. Now it is clear what rhizoids are and what is their difference from rhizoids.