You should know...
Animal-like Protists
Around 65,000 kinds of animal-like Protists have been known and studied. They are more usually called Protozoan (Greek: proto = first; zoa = animals). Their characteristics are unicellular and heterotrophic.
Body Characteristics
Protozoan characteristics include size and shape, as well as body structure and function.
Size and shape
Protozoans are microscopic in size, around 10 to 200 microns (µm). Their cell shape is quite variable; some are fixed, while others are changeable. Most Protozoan have some sort of motion appendage, such as pseudopodia (fake foot), cilia (soft hair), or flagella (whip-hair). Some also have a protective shell.
Structure and function
Basically, Protozoa are composed of a cell membrane, cytoplasm, food vacuole, contractile vacuole, and nucleus. The cell membrane acts as a protective barrier and regulates food and gas exchange. A food vacuole is formed by ingesting or 'swallowing' molecules using the cell membrane or a spesific structure called cytostome (cell's mouth). The digested products of the food vacuole then enter the cytoplasm by diffusion. Food remains are exported through thr cell membrane by the vacuole. The contractile vacuole is a pump that excretes liquid food remains out of the cell by controlling and expanding, hence its name. The nucleus function is to control cell metabolic activity.
Life Styles
Protozoans are heterotrophic. They prey on bacteria, other Protists, and organic waste. As a bacterial predator, Protozoa play important role in controlling bacteria population in the wild.
Habitat
Protozoans are solitary or form colonies in a diverse range of habitats. Most of them live freely in ocean or freshwater, such as gutters, ponds, or rivers. Other live inside the soil. Some live symbiotically inside the bodies of animals or humans.
Reproduction
Most Protozoan reproduce asexually by binary fission. Cell division is started by karyokinesis (nuclear division) followed by cytokinesis (cytoplasm division). Those that reproduce sexually do so by combining gametes cells or vegetative. Sexual reproduction by the union of vegetative nuclear is called conjugation.
In their life cycle, several Protozoans can produce inactive form of cells called a cyst. A cyst is covered by a polysaccharide capsule that protects the Protozoan from unfavorable environments, such as droughts. Once conditions are favorable again for example when food and water available, the cyst will break apart and new protozoa are alive again.
Classification
There are more than 60,000 species of protozoan already identified. They are classified into four groups based on their method of motility; Rhizopoda, Ciliata, Flagellata, and Sporozoa.
Fungus-like Protists
Fungus-like Protists are the group of water and slime molds. The fungus-like characteristics have structure to produce spores, heterotrophic, parsitic, or act as decomposers. As decomposers, they produce enzyms that break down or convert organic materials from dead organisms and absorb them in the form of inorganic materials.
Water Molds (Oomycota)
There are 580 known kinds of water molds that act as decomposers in aquatic habitats. Most of them are free-living and obtain their nutrients from the remains of dead plants in ponds, lakes, and water streams. Some live inside dead tissue of plants, and some others are parasites of other aquatic organisms, for example Saprolegnia. It attaches itself to fish or other aquatic organisms. Saprolegnia has layers of membrane.
There are also other water molds that are pathogenic to plants, for example white molds (Plasmopara viticola) that grow in colonies on grapes. Another example is the wilting and rotting potato plants and tomato plants that is caused by the water mold Phytophthora infestans.
Water molds can reproduce sexually or asexually. It reproduce asexually by forming sporangium at the tip of their hyphae structures (filament or thread). Sporangium will be filled by flagellated spores (zoospores) that will be released when they mature. When spores fall on an optimal environment, they grow to become new mycelium.
Sexual reproduction occurs by the meeting of male and female gametes. Gametes are produced by differenttiated hyphae. Male gametes are produced by antheridium, and female ones by oogonium. Fertilization between gametes produces diploid zygotes that grow into thick-walled spore which then will grow into new mycellium.
Slime Molds (Myxomycota)
All slime molds produce free-living cells during part of their life cycle. These cells are called amoeboid because of their resemblance to Amoeba. Like the real Amoeba, slime molds are phagocytic predators because slime molds can ingest bacteria, pests, spores, and other organic components.
During times of low food availability, hungry cells combine themselves together to form a slimy mass. This mass migrates to a new environment with more favorable conditions to support their growth. The mass motion is derived from the acculumulative force of contraction from each single cells. An example of a slime molds is Dictyostellium discoideum.
Protists
Protists are a group of eukaryotic organisms, either unicellular or multicellular, and have not yet shown real tissue differentiation. The member differ from one another in morphology and how they live. There are those with fungi, animal, or plant characteristic.
Fungus-like Protists (molds) are parasitic molds or predatory molds that produce spores. Parasitic molds are unicellular, aquatic decomposers. Predatory molds or phagocytes are slime molds which are aggregates of migrating cells that form a spore-like structure.
Animal-like Protists cover all non-photosynthetic Protozoan, for example Rhizopoda and Sporozoa. Protozoans are parasitic and unicellular predators.
Plant-like Protists are unicellular and photosynthetic; some also have flagella (tail like cellular structure used for movement). Most of these Protists live freely or in a colonies in open seas and other aquatic regions. They are imortant members of Phytoplankton. Phytoplankton are the producers of the aquatic habitats. Other plant-like Protists are golden, red, green, and brown algae.
Protista
