<unk>  have conventionally been regarded as simple plants within the study of botany. All are Eukaryota, though Chromophyta have Bacterial (see Blue-green<unk>  characteristics and some authorities consider them all to be Protists, however this view is now considered to be outdated. They may still be included in the<unk>  as plants. Some authors often include the blue-green<unk>  (Cyanophyta) but note that they are not eukaryote.<unk>  do not represent a single evolutionary direction or line but a level of organization that may have developed several times in the early history of life on Earth.
The protists are traditionally considered more animal-like (see Protozoa).
The prokaryotic forms, referred to as blue-green<unk>  are only half-algae with a mixture of bacterial characteristics. However, they are quite distant from the bacteria and are referred to by some as Cyanochloronta. All other forms belong as true eukaryota<unk>  within the study of Botany, they have a nucleus enclosed within a membrane. The protoctists are defined by some as eukaryotic microorganisms with the exception of animals and plants and including fungi and<unk> , slime moulds and other obscure eukaryotes. There is still some disagreement on some of these matters.<unk>  range from single-cell organisms to multicellular organisms, some with fairly complex differentiated form and (if marine) called seaweeds. All lack leaves, roots, flowers, seeds and other organ structures that characterize higher plants (vascular plants). They are distinguished from other protozoa in that they are photoautotrophic although this is not a hard or vast distinction as some groups contain members that are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy, or phagotrophy. Some unicellular species rely entirely on external energy sources and have reduced or lost their photosynthetic apparatus.
All<unk>  have photosynthetic machinery ultimately derived from the cyanobacteria, and so produce oxygen as a byproduct of photosynthesis, unlike non-cyanobacterial photosynthetic bacteria. It is estimated that<unk>  produce about 73 to 87 percent of the net global production of oxygen - which is available to humans and other animals for respiration.
Algae
Biofilm
Speculum
Striae
Elementary particle
Dermatophyte
Clavicle
Ovum