Biology is a fascinating science of nature. Learning new facts about cells and organisms, you are surprised at the wise and complex structure of living beings. Consider one of the secrets of their structure, concerning color and its change.
What are chromatophores in biology
The cells of living beings contain various organelles (organelles) with different functions. Chromatophores are cell organelles located in the cytoplasm and give it color. You can call all cell organelles that have color like this, but this term was assigned to colored bodies in algae cells. Similar formations in higher plants are called chlorophyll grains and chloroplasts.
Sometimes chromatophores are called algal chloroplasts. But it should be noted that fish cells containing a color pigment are also often called a chromatophore, although they have nothing to do with plants. It is also found in some other animals and photosynthetic bacteria.
There is another way to explain what a chromatophore is. In their structure, chromatophores are plastids. As you know, plastids are called organelles of plant cells, which have a smooth membrane on the outside and a membrane inside that forms outgrowths. Leukoplasts, chromoplasts and chloroplasts are plastids. In turn, the chromatophore, as a formation similar to the chloroplast, also refers to plastids.
Chromatophore functions
In algae, chromatophores are involved in photosynthesis, while in fish and animals they only give and change color.
Inside the plasma body of the chromatophore (endoplasm), the kinoplasm (the inner layer of the organoid) containing the color pigment moves.
Shape of chromatophores
Their shape varies, but the most common are star-shaped, disc-shaped, branched and the like. However, these forms are characteristic only for a cell in a state of activity, expansion, called expansion.
In plants, these organelles are usually green, although other colors may occur. Animals can have any color.
Algae overview
Algae are unicellular and multicellular, there are also colonial forms. Some have no membrane in the cell, but only a compacted layer of protoplasm. This allows the 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 minerals - lime, silica.
Algae cells may have one or several nuclei, or may not have a formed nucleus at all. Then the protoplast has a noticeable color, and its center is not colored.
Some representatives of algae have coloringthe pigment is contained in chromatophores, which usually contain pyrenoids (dense bodies with a high content of proteins), and starch reserves are deposited 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 features of chromatophores in spirogyra and some other algae
In algae, the chromatophore is usually involved in nutrition, as it is a participant in the process of photosynthesis and, accordingly, the formation of nutrients. What is the shape of an algal chromatophore?
- Spirogyra has a chromatophore in the form of a ribbon that spirals around the cell walls.
- Ulotrix, like Spirogyra, which is a filamentous multicellular algae, contains a ring-shaped chromatophore.
- Zignema chromatophores - in the form of stellate bodies.
- Chromatophores found in diatoms look like grains, plates, and so on, and contain brown pigments, which gives the algae a yellowish, yellowish-brown or brown color.
- Blue-green algae do not have chromatophores as such. Their color pigments are evenly distributed in the protoplasm, bypassing only the central part. It should be noted that 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 the water reticulum, the cells have dissected chromatophores located near the walls and many pyrenoids in them.
Euglena green chromatophore performsfunction of photosynthesis, participating in the process of nutrition, like many other algae.
When there is no light, this amazing creature is able to eat like an animal, processing organic matter dissolved in water. If the euglena lives in the dark for a long time, then chlorophyll disappears from its chromatophores, making it capable of photosynthesis and giving color. 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). Both names are used.
They are involved in color change under the influence of external factors. The ectoplasm of the chromatophore, which determines its shape, is attached by solid formations - fibrils; it is involved in the regulation of metabolic processes, and can also contact 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.
Thus, many species of animals are known that are capable of mimicry - changing color depending on the background and surrounding objects. Slow color changes are characteristic of the caterpillars of some butterflies and a number of arachnids. In cephalopods, amphibians, reptiles and crustaceans, there is a rapid change in color, carried out by moving pigment grains in chromatophores. The range of colors can be varied. For example, one of the African frogs can changecolor to white, yellow, orange, brown, grey, red, pink and others. The same color change mechanism is used by all known chameleons.
Chromatophores in fish
Unlike other animals, the change in color 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 like gobies or flounders can mimic the look of the ground exactly. In this case, the main role belongs to the nervous system. The fish perceives the ground pattern with the help of the eyes, and this picture, transforming into nerve signals, enters the nervous "network", from where signals go to the melanophore nerve endings. Color change occurs unconsciously, with the help of sympathetic nerves.
Hormonal action is noticeable during spawning - the period when the fish are ready to breed. Sexually mature males under the influence of hormones acquire an attractive coloration for females. It becomes brighter when the female comes into view. Here, the mixed action of the hormonal and nervous systems is manifested: when the male sees the female, the signal goes through the optic nerves to the nervous system, and then to the chromatophores, which, expanding, make the color brighter.
It should be noted that, in addition to melanophores, fish also have other chromatophores - guanophores. However, they can be classified as chromatophores formally, becausethat instead of pigment grains, they contain the crystalline substance guanine, which gives the fish a brilliant silver color. From melanophores, xanthophores and erythrophores are sometimes also isolated.
