Algae are a diverse group of organisms that use photosynthesis to produce food. They are not clearly organized into different tissue types like plants. Algae can be divided into subgroups based on pigments used for photosynthesis. Green algae are thought to be the ancestors of land plants. Red algae are mostly marine and have been around for nearly 2 billion years. Brown seaweed is a diverse group ranging from diatoms to kelp algae. Cyanobacteria are ancient and may have been the first organisms to use photosynthesis. Algal blooms can be harmful to other aquatic life. Algae can be eaten and used for food additives, agar, and biofuels.
Algae (singular seaweed) are a large group of different organisms that use photosynthesis to produce food. Although some forms are large and multicellular, they differ from plants in that their cells are not clearly organized into different tissue types with different functions. This group includes a wide variety of organisms that are not always closely related to each other: similarities in shape are often due to parallel evolution, where different organisms have adapted in similar ways to fill similar niches. They are described as polyphyletic, meaning that not all group members share the same common ancestor.
By modern definition, all algae are eukaryotes, which means that the DNA in their cells is contained within a membrane-enclosed nucleus. Organisms whose cells do not have a nucleus are prokaryotes. Eukaryotes also include plants, fungi and animals. Prokaryotes include bacteria and archaea. Algae can be divided into numerous subgroups, mainly based on the types of pigments they use for photosynthesis.
Green algae
These forms use the green pigment chlorophyll to photosynthesize and are thought to be the ancestors of land plants. Some authorities include them in the plant kingdom, while others prefer to consider them as a separate category of life. They can be unicellular or multicellular, and some types live in colonies or form long filaments made up of many cells. A number of unicellular types are able to move independently using flagella – long, whip-like structures used by many microorganisms for locomotion. Green algae are found in a wide variety of habitats, including freshwater, sea, soil, tree trunks and wetland walls, but most are aquatic.
Land plants are thought to have evolved from a type of green algae, possibly around 500 million years ago. They contain the same types of chlorophyll and other pigments as land plants. There are further similarities: For example, chlorophyll is contained in structures called chloroplasts, and many types store sugars in starch granules, as do land plants.
Red algae
Also known as rhodophyta, these were among the first eukaryotic organisms on the planet and their signatures have been found in rocks nearly 2 billion years old. They are mostly marine organisms and include many types of algae, as well as a number of unicellular species. Their red color comes from the pigments phycoerythrin and phycocyanin, which they use for photosynthesis. These pigments absorb blue light, which reaches further below the ocean surface than the red light trapped by chlorophyll, allowing rhodophytes to photosynthesize at greater depths. This group also includes coralline algae, which build shells made of calcium carbonate of their own and can form coral reefs.
Brown seaweed
The correct scientific name for this group is chromista. It’s an extremely diverse group, with its members ranging from diatoms — microscopic single-celled forms with silica shells — to “kelp” algae — large, multicellular organisms that can grow up to 164 feet (50 meters) long. They use a different type of chlorophyll than that used by plants for photosynthesis and often have additional pigments, such as fucoxanthin, which gives many of these organisms a brown color. Diatoms are an important part of phytoplankton, producing a large amount of the planet’s oxygen through photosynthesis and forming the basis of many marine food chains. Kelp algae can form extensive “forests” on the seabed, which are of great ecological importance.
The cyanobacteria
Today these microorganisms are considered bacteria; however, they are still sometimes referred to by their old name, “blue-green algae”. They differ mainly in that they are prokaryotes, like all bacteria, but they can produce their own food by photosynthesis. Cyanobacteria are a very ancient group and may have been the very first organisms to use photosynthesis. Many experts think that, in the distant past, some single-celled non-photosynthesizing organisms may have incorporated cyanobacteria in a symbiotic relationship, and that these bacteria may have become the chloroplasts seen in algae and plants today.
fioriture algali
From time to time, in certain locations, a species of algae may experience a population explosion, resulting in a so-called “algal bloom”. These can occur on coasts and in freshwater lakes. It is not always possible to establish the cause, but it often appears to be due to agricultural runoff containing fertilizers that stimulate increased growth and multiplication. Algal blooms are often harmful to other aquatic life and occasionally to animals and even humans. The sheer number of algae can severely reduce the oxygen content of the water, and some species produce toxins that can kill or harm other organisms.
it is used
Different types of algae can be eaten, especially among red algae. Seaweeds also provide a number of important food additives and agar, a type of gel used for culturing microorganisms. Another potential use is in the production of biofuels. The organisms are fast-growing and undemanding in terms of conditions and nutrient requirements, and therefore can provide a cheap and efficient way of accumulating biomass for fuel.
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