Chromalveolata

Some tiny living things live in water.

Many look like big plants. They can make food from sunlight. This helps them grow. Some can be bad for us. One kind caused a big famine. It made potato plants sick.

Other kinds are very good. They make the air we breathe. Some help make ice cream thick. These tiny things are everywhere in the sea.

Scientists once thought a group called Chromalveolata was one big family. They believed these tiny things all came from one ancestor. Most members use chlorophyll c to make food from light. This is a special part used for making energy.

Today, many experts disagree. They think these groups are not one single family. Instead, they are split into different groups. One large group is called SAR. It includes Stramenopiles, Alveolata, and Rhizaria. Another group is called Hacrobia. It includes Haptophyta and Cryptophyta.

These living things do many jobs in nature. Some can be harmful. A water mold once caused a great famine in Ireland. It made potato plants sick.

Other kinds are very helpful. Diatoms make much of the oxygen we breathe. Brown algae, like kelp, make big underwater forests.

People even use brown algae to make ice cream thick. Diatoms have shells that people use in toothpaste. These tiny things help our whole world work.

Scientists once studied a huge group of living things called Chromalveolata. This group was part of a major way to classify all eukaryotes. For a long time, experts thought these organisms shared one single ancestor. They believed this ancestor had a special way of making food. This happened through a process called secondary endosymbiosis. In this event, a red alga and a bikont came together. This helped the group develop parts called plastids. These plastids use chlorophyll c to turn light into energy.

How these groups work is very diverse and complex. Most members are autotrophic, which means they make their own food. They use chlorophylls a and c to do this work. Many also use extra pigments to help catch light. Some members, like water molds, have lost this ability. Each subgroup has its own unique physical features. Alveolata have tiny sacs called alveoli in their cells. Haptophyta have a structure called a haptonema. Cryptophyta use something called an ejectisome. Stramenopiles are known for having two different flagella.

History shows how our understanding of these groups has changed. Thomas Cavalier-Smith first proposed a related group called Chromista in 1981. He later suggested the name Chromalveolata for these organisms. In 2005, this group was seen as one of six major groups. However, scientists began to have doubts very quickly. Papers in 2008 showed that the group might be split up. By 2012, most experts agreed the group was not monophyletic. This means they do not all come from one single branch.

There are many important names and numbers in this study. The original subgroups were Cryptophyta, Haptophyta, Stramenopiles, and Alveolata. Today, we use new names like the SAR group. SAR includes Stramenopiles, Alveolata, and the Rhizaria. Another group called Halvaria includes Stramenopiles and Alveolata. Some scientists also studied a group called Hacrobia. This group was thought to include Haptophyta and Cryptophyta. Recent studies show Haptophyta might actually be closer to the SAR group.

These tiny organisms connect to many things in your daily life. Some can be very harmful to plants and animals. A water mold called Phytophthora infestans caused the Irish potato blight. This led to the Great Irish Famine. On the helpful side, diatoms produce much of our oxygen. They also take in carbon dioxide from the air. You might even eat them in your favorite treats. Brown algae provide a thickener called algin for ice cream. Diatoms have shells used in toothpaste and reflective paint.

Chromalveolata was once considered a major supergroup of eukaryotes. In a 2005 classification, it was seen as one of six primary groups. This group was a refinement of the kingdom Chromista. Thomas Cavalier-Smith first proposed Chromista in 1981. He later suggested the name Chromalveolata to describe these organisms. Scientists believed they all descended from a single event called secondary endosymbiosis. This event involved a red alga and a bikont. This process gave the organisms plastids that contain chlorophyll c.

The mechanism behind the group's origin is quite specific. Through secondary endosymbiosis, a host cell swallowed a red alga. This allowed the descendants to use specific light-harvesting tools. Most members are autotrophic, meaning they produce their own food. They use chlorophylls a and c to perform photosynthesis. Many also use accessory pigments to capture light. However, some groups have lost this ability. For example, ciliates and water molds do not photosynthesize. Despite these differences, most share similar glyceraldehyde 3-phosphate dehydrogenase proteins.

Chromalveolates are incredibly diverse in their physical structures. There are four original subgroups: Cryptophyta, Haptophyta, Stramenopiles, and Alveolata. Each subgroup has unique features that set it apart. Alveolata possess tiny sacs called alveoli. Haptophyta have a structure known as a haptonema. Cryptophyta use an organelle called an ejectisome. Stramenopiles, also called Heterokontophyta, have two different flagella.

Because they are so varied, they lack many common morphological traits. The only shared features are their plastid origins and cellulose in most cell walls.

The history of this classification has changed significantly due to new research. While it was a major group in 2005, doubts arose quickly. In 2006, a review noted a lack of evidence for several major eukaryote groups. By 2008, two different papers published phylogenetic trees that split the group up. These studies suggested the group was not monophyletic. Monophyletic means all members come from one single common ancestor. By 2012, a scientific consensus emerged that Chromalveolata is not a single, unified group.

Today, scientists use new names to describe these related organisms. The Stramenopiles and Alveolata are often grouped together as Halvaria. When the Rhizaria are added to this, they form the SAR group. Another grouping called Hacrobia was used for Haptophyta and Cryptophyta. However, recent studies have split Hacrobia apart. Some analyses show Haptophyta are sister groups to the SAR group. Others suggest Cryptophyta are more closely related to the Archaeplastida, which includes plants.

These organisms play massive roles in our global ecosystems. Some can be very destructive to humans and nature. Dinoflagellates can cause red tides that kill fish and poison oyster harvests. Apicomplexans include the genus Plasmodium, which causes malaria in animals. Water molds can also cause serious plant diseases. The water mold Phytophthora infestans caused the Irish potato blight. This event led to the Great Irish Famine.

Many chromalveolates are vital for life on Earth. Diatoms are major photosynthetic producers. They produce much of the oxygen we breathe and absorb carbon dioxide. Brown algae, like kelp, create underwater forest habitats for marine life. These organisms also provide products we use every day. We use algin from brown algae as a thickener in ice cream. Diatoms have siliceous shells used in toothpaste and reflective paint. This material is known as diatomaceous earth.