Biology is a fascinating science about nature. Learning new facts about cells and organisms, one wonders at the wise and complex structure of living things. Consider one of the secrets of their structure regarding color and its changes.
What are chromatophores in biology
The cells of living things contain various organoids (organelles) that have different functions. Chromatophores are organelles of a cell located in the cytoplasm and giving it a color. You can call it all the organelles of a cell that have color, but this term has been fixed for colored bodies in algae cells. Similar formations in higher plants are called chlorophyll grains and chloroplasts.
Chromatophores are sometimes called algal chloroplasts. But it should be noted that fish cells containing color pigment are also often called a chromatophore, although they have nothing to do with plants. It also occurs in some other animals and photosynthetic bacteria.
It is possible to explain in a different way what the chromatophore is. In their structure, chromatophores are plastids . As you know, plastids are called organoids of plant cells that have a smooth membrane on the outside and a membrane inside, forming outgrowths. Leukoplasts, chromoplasts and chloroplasts are plastids. In turn, the chromatophore as a formation similar to chloroplast also belongs to plastids.
Chromatophore functions
In algae, the chromatophores participate in photosynthesis, while in fish and animals they only attach and change color.
Inside the plasma body of the chromatophore (endoplasm) there is a movement of the kinoplasm (the inner layer of the organoid) containing the color pigment.
The shape of the chromatophores
Their form is different, but most often there are stellate, disc-shaped, branched and the like. However, these forms are characteristic only of a cell in a state of activity, expansion, called expansion.
In plants, these organoids are usually green, although other colors may also occur. Animals can have any color.
Algae Overview
Algae are unicellular and multicellular; there are also colonial forms. Some lack a membrane in the cell, and there is only a compacted layer of protoplasm. This allows algae to change shape. In other algae, the shell is dense, with a high content of cellulose, and in some it is even saturated with mineral substances - lime, silica.
Algae cells can have one or several nuclei, or they may not have a nucleus at all. Then the protoplast has a noticeable color, and its center is not colored.
In some representatives of algae, the coloring pigment is contained in chromatophores, in which pyrenoids (dense bodies with a high content of proteins) are usually found, and starch deposits are stored around the pyrenoids. The type of nutrition of most algae is autotrophic (due to the energy of light penetrating through the water column).
What are the characteristics of the chromatophores in spirogyra and some other algae
In algae, the chromatophore is usually involved in nutrition, since it is a participant in the process of photosynthesis and, accordingly, the formation of nutrients. What shape does the alga chromatophore have?
- Spirogyra has a chromatophore in the form of a ribbon, which coils in a spiral at the cell walls.
- Ulotrix, like spirogyra, which is a filamentous multicellular alga, contains a chromatophore in the form of a ring.
- Zygnema chromatophores are in the form of star-shaped bodies.
- The chromatophores found in diatoms have the appearance of grains, plates, and so on, and contain brown pigments, which gives the algae a yellowish, yellowish-brown or brown color.
- Blue-green algae have no chromatophores as such. Color pigments are evenly distributed in the protoplasm, bypassing only the central part. It should be noted that the blue-green algae are actually colonies of cyanobacteria.
- In unicellular representatives of protococcal algae, the chromatophore has one pyrenoid. In more developed colonial forms, such as a water mesh, the cells have dissected chromatophores located at the walls and many pyrenoids in them.
In euglena, the green chromatophore performs the function of photosynthesis, participating in the nutrition process, as in many other algae.
When there is no light, this amazing creature is able to eat like an animal, processing organics dissolved in water. If euglena lives in the dark for a long time, then chlorophyll disappears from its chromatophores, making it capable of photosynthesis and colorizing. In this case, it loses color.
Chromatophores in animals
In animals, chromatophores are melanophores (not to be confused with human melanocytes, these are completely different cells). Use both names.
They participate in discoloration under the influence of external factors. The chromatophore ectoplasm, which determines its shape, is attached by solid formations - fibrils; it is involved in the regulation of metabolic processes, and can also come into contact with the nervous system, as a result of the receipt of signals from which the chromatophore begins to function differently. Of all the chromatophores, only melanophores have nerve endings.
So, many types of animals are known that are capable of mimicry - a change in color depending on the background and surrounding objects. Slow color changes are characteristic of the tracks of some butterflies and a number of arachnids. In cephalopods, amphibians, reptiles, and crustaceans, a rapid change in color occurs by moving pigment grains in chromatophores. The range of colors in this case can be varied. For example, one of the African frogs can change color to white, yellow, orange, brown, gray, red, pink and others. The same mechanism for changing colors and the well-known chameleons.
Chromatophores in fish
Unlike other animals, the color change of fish is due to a change in the number of chromatophores. This happens not only under the influence of nerve signals, but also with the participation of hormones. Most likely, it depends on the specific situation, and under different conditions, either nervous or hormonal regulation occurs.
Fish such as gobies or flounders can exactly copy the look of the soil. In this case, the main role belongs to the nervous system. The fish perceives the soil pattern with the help of the eyes and this picture, transforming into nerve signals, enters the nervous "network", from where the signals to the nerve endings of the melanophore come. Color change occurs unconsciously, with the help of sympathetic nerves.
The hormonal action is noticeable during spawning - the period when the fish are ready for breeding. Under the influence of hormones, sexually mature males acquire an attractive color for females. She becomes brighter when the female appears in sight. Here the mixed effect of the hormonal and nervous system is manifested: when the male sees the female, the signal enters through the optic nerves into the nervous system, and then to the chromatophores, which, expanding, make the color brighter.
It should be noted that, in addition to melanophores, fish have other chromatophores - guanophores . However, they can be classified as chromatophores formally, because instead of pigment grains they contain the crystalline substance guanine, due to which a shiny silver color appears in the fish. Xanthophores and erythrophors are also sometimes isolated from melanophores.