Protists

Characteristics of diatoms:

• All species are unicellular or colonial coccoid algae. None are free-living flagellates.
• The only flagellate cells produced are the male gametes (= sperm, spermatozoids) of 'centric' diatoms. These have a single forward-pointing flagellum, which bears mastigonemes.
• The relative proportions of the chlorophylls and fucoxanthin produce a yellow-brown or greenish-brown colour in the plastids.
• Most have a large central vacuole or pair of vacuoles.
• Cells (especially during stationary-phase) often accumulate large quantities of lipids and fatty acids; polyphosphate bodies are also present and sometimes take the form of discrete spherical or complex 'volutin' granules, one per vacuole.
• Secretion of extracellular polymeric material (usually polysaccharides) is common, as stalks, pads, capsules, tubes, chitin fibres, or trail material from locomotion.
• All cells (except the gametes and endosymbiotic diatoms) possess a bipartite cell wall comprising two overlapping halves.
• Each half-wall itself consists of a large end-piece, the 'valve', and several or many narrow bands or segments, which together form the 'girdle'.
• The cell wall is almost always heavily silicified.
• Cell wall elements (valves, girdle bands, and auxospore scales and bands) are formed intracellularly, in special membrane-bound 'silica deposition vesicles' associated very closely with the cell membrane; they are not secreted from the cell until they are complete.
• New wall elements are always produced within the confines of an existing cell wall. As a result, average cell size usually decreases with successive mitotic divisions during the life cycle.
• Size is restored via the formation and expansion of a special cell, the auxospore, which is usually a zygote. The basic shape of each diatom species is largely created during the expansion of the auxospore, but is often modified during subsequent mitotic cell divisions.
• During vegetative mitoses, the nucleus always lies to one side of the cell immediately beneath the girdle, at the edge of the hypotheca.
• Mitosis is open, the nuclear envelope breaking down before metaphase; the spindle is a narrow cylinder, persistent at telophase, consisting of two interdigitating half-spindles, each associated with a polar plate.
• The chromosomes bunch closely around the cylindrical spindle at metaphase, becoming impossible to separate and count.
• Cytokinesis occurs through cleavage.
• The life cycle is strictly diplontic: as far as is known, all vegetative cells of all species are diploid, and all mitoses take place in the diploid phase. However, haploids have occasionally been grown in culture in a few species.
• They occur just about everywhere in aquatic and damp terrestrial habitats, providing that photosynthesis is possible.
• They are amazingly diverse, with hundreds of genera and perhaps 200,000 species.

(from tolweb.org)

The 5 characteristics of all living things are:

1. It must grow until it can reproduce.
2. It must consume, transform and store energy. (food, air, etc...) It must grow by absorbing energy in its environ.
3. It must move from the outside (walking, hunting, eating, etc. ...) and/or inside (blood circulation, digestion, etc. ...)
4. It must be able to reproduce (to create entities similar to itself)
5. It must be able to detect the properties of its environment and act appropriately.