Kingdom Protista

Topics: Protist, Algae, Eukaryote Pages: 9 (1554 words) Published: November 11, 2012
Kingdom Protista: Characteristics
Mostly unicellular, eukaryotic cells
Reproduce asexually or sexually by conjugation
Exhibit all three modes of nutrition
Ultimately spawned all multicellular kingdoms
Very diverse kingdom
Difficult for taxonomists to agree on classification Diverse Modes of Nutrition
Use diverse modes of nutrition
Ingest food
Absorb nutrients from surroundings
Protists that ingest food are typically predators
Use extensions of cell membrane called psuedopods to surround and engulf prey item
Diverse Modes of Nutrition
Protists that absorb nutrients directly from the surrounding environment can be Free-living types in the soil that decompose organic dead matter Parasites that live inside the bodies of other organisms, sometimes harming the host Diverse Modes of Nutrition

Some protists have photosynthetic organelles called chloroplasts Photosynthetic protists are abundant in oceans, lakes, and ponds Free floating
Mutually beneficial associations with other organisms: solar energy captured by the protist is used by host, which shelters and protects the protist Diverse Modes of Nutrition
Photosynthetic protists are collectively known as algae Single-celled, non-photosynthetic protists are collectively known as protozoa Diverse Modes of Reproduction
Most protists reproduce asexually by mitotic cell division Some also reproduce sexually
Two individuals contribute genetic material to an offspring that is genetically different from either parent Occurs during certain time of year or circumstances (e.g. a crowded environment or a food shortage) Protist Reproduction Asexual Sexual (a) (b)

Effects on Humans
Positive impact - ecological role of photosynthetic marine protists (algae) capture solar energy and make it available to the other organisms in the ecosystem release oxygen gas

Negative impact - many human and plant diseases are caused by parasitic protists Major Groups of Protists
Protist classification is in transition
Genetic comparison reveals evolutionary history of organisms Genetic, instead of physical features now separate protist species into different lineages Some physically dissimilar species are now placed in a common lineage

The Excovates
Lack mitochondria
Two major groups
Diplomonads: have two nuclei and move about by means of multiple flagella Parabasalids: live inside animals
Mutually beneficial relationships with other species Parabasalid inhabits gut of termite
Termite delivers food to parabasalid, which digests and releases nutrients to termite Parabasalids
Harms host species
Trichomonas vaginalis causes the sexually transmitted disease trichomoniasis Trichomonas inhabits urinary and reproductive tracts, using flagella to move through them Causes vaginal itching and discharge in females

The Euglenozoans
Have distinctive mitochondria
Two major groups
Single-celled, fresh-water protists
Lack a rigid outer covering
Best known example is Euglena
Moves by whipping single flagellum
Some euglenids photosynthetic, others absorb/engulf food Euglenids
Photoreceptor (eyespot) found in some euglenoids
Provides for a way to sense location of...
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