Living things are classified in six kingdoms based on structure. Within prokaryotes, which appeared 3. Within eukaryotes, which evolved 1. Cells are also defined according the need for energy. Autotrophs are "self feeders" that use light or chemical energy to make food.
Superficially, they look a lot like bacteria, and many biologists confused them as bacteria until a few decades ago. But hiding in their genes is a story that modern DNA analysis has recently revealed: archaeans are so different genetically that they belong in their own domain. Many archaean species are found in some of the most inhospitable environments, areas of immense pressure bottom of the ocean , salinity such as the Great Salt Lake , or heat geothermal springs.
Organisms that can tolerate and even thrive in such conditions are known as extremophiles. It should be noted that many bacteria are also extremophiles. For whatever reason, archaeans are not as abundant in and on the human body as bacteria, and they cause substantially fewer diseases. Research on archaeans continues to shed light on this interesting and somewhat mysterious domain. This domain is most familiar to use because it includes humans and other animals, along with plants, fungi, and a lesser-known group, the protists.
Unlike the other domains, Domain Eukarya contains multicellular organisms, in addition to unicellular species. The domain is characterized by the presence of eukaryotic cells.
For this domain, you will be introduced to several of its kingdoms. Kingdom is the taxonomic grouping immediately below domain see Figure 1.
Kingdom Animalia is comprised of multicellular, heterotrophic organisms. This kingdom includes humans and other primates, insects, fish, reptiles, and many other types of animals. Kingdom Plantae includes multicellular, autotrophic organisms. Except for a few species that are parasites, plants use photosynthesis to meet their energy demands. Kingdom Fungi includes multicellular and unicellular, heterotrophic fungi.
Fungi are commonly mistaken for plants because some species of fungi grow in the ground. Fungi are fundamentally different from plants in that they do not perform photosynthesis and instead feed on the living matter of others.
Another misconception is that all fungi are mushrooms. A mushroom is a temporary reproductive structure used by some fungal species, but not all.
Some fungi take the form of molds and mildews, which are commonly seen on rotting food. Lastly, yeast are unicellular fungi. Through their metabolism, these yeast produce CO2 gas and alcohol. The former makes bread rise and the latter is the source for all alcoholic beverages. Figure 3. Plants, animals, fungi and protists are eukaryotes and share the same basic cellular structure.
These cells share many of the same organelles which carry out similar functions. They have membrane-bound organelles and many eukaryotes form complex, multicellular tissues. Bacteria and Archaea are prokaryotes. They are all single-celled organisms that have smaller cells, a simpler design and fewer organelles than eukaryotes.
Their organelles are not contained within membranes and their genetic material is not held within a nucleus. There are two basic types of living things: organisms that obtain energy by producing their own food and organisms that obtain energy by consuming other materials. Animals and fungi are heterotrophs ; they consume other organisms or organic material to provide them with the energy they need.
Some bacteria, archaea and protists are also heterotrophs. Plants are called autotrophs because they make their own food. Plants use water, carbon dioxide and energy from the sun to produce glucose through the process of photosynthesis.
Some types of protists also obtain energy through photosynthesis. Photosynthesizing protists are single-celled organisms, but many of them grow together in colonies to form plant-like structures. They live in fresh water or saltwater. Green algae of are a well-known group of autotrophic protists. Other types of protists that use photosynthesis include:.
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