Kingdom Protista
What is a Protist? There is much debate about this very diverse group of organisms. Scientists have been arguing for years over how best to classify these organisms. Eventually the protists may be divided into many separate kingdoms. For now, we will consider the protists as a single kingdom. A protist is any organism that is not: a plant, an animal, a fungus or a prokaryote.
Most protists are, unicellular but a few are colonial and a few are. multicellular Protists are eukaryotes that are not members of the kingdoms: Plantae, Animalia, or Fungi. The range and variety of organisms in this kingdom is huge. It is thought that this group may contain over 200,000 different species.
Because most protists are unicellular they are considered the simplest eukaryotic organisms, but their cells are extremely complex. They must carry out within a single cell all the basic functions performed by specialized cells, such as: digestion, gas exchange, circulation and excretion.
In multicellular organisms, essential biological functions are carried out by organs. Unicellular protists carry out the same essential functions, but they do so using subcellular organelles, rather than with multicellular organs.
One way to classify the protists is according to....the way they obtain their nutrition. Some protists are, heterotrophic some are, autotrophic and some are. mixotrophs Mixotrophs are capable of combining photosynthesis and heterotrophic nutrition. Classification of Protists The heterotrophs are called animal-like protists. The photosynthetic autotrophs are called plant-like protists. A few obtain their food by external digestion and are called fungus-like protists.
Protists can be divided into three categories: Protozoa: Ingestive animal-like protists Algae: Photosynthetic plant-like protists Slime Molds: Absorptive, fungus-like protists.
The protists were the first eukaryotic cells, and they evolved 1.5 billion years ago.
The evolution from prokaryotes to the first eukaryotes was one of the big evolutionary transitions, second in importance only to the origin of life.
One theory is that larger, more complex cells evolved partly as a result of certain prokaryotes taking up residence inside other cells. These prokaryotes that began to live inside other cells became the mitochondria of that cell. This theory is referred to as. endosymbiosis The first eukaryotes acquired mitochondria by...engulfing aerobic prokaryotes.
Chloroplasts were formed by a similar fashion. Nonphotosynthetic prokaryotes captured and trapped photosynthetic prokaryotes and these became the chloroplasts inside the cell.
The Evidence They are the appropriate size to be descendants of bacteria. Chloroplasts and mitochondria contain their own DNA. The DNA is a single, circular molecule of DNA like the one found in the bacteria. Many of the enzymes contained in the cell membrane of bacteria are found in mitochondria and chloroplast membranes. Mitochondria and chloroplasts contain ribosomes that resemble those of the bacteria. Mitochondria and chloroplasts carry out their own replication by a splitting process similar to binary fission.
Both of these (mitochondria and chloroplasts) are types of symbiosis known as endosymbiosis. Endosymbiosis: A hypothesis about the origin of the eukaryotic cell, maintaining that the forerunners of eukaryotic cells were symbiotic associations of prokaryotic cells living inside larger. prokaryotes Mitochondria originated as symbiotic, aerobic bacteria.
THE PLANT-LIKE PROTISTS: THE ALGAE
Algae are a very diverse group of protists. They range in size from microscopic single-celled organisms to large multicellular seaweeds. All of the algae are. autotrophs They are, eukaryotic have, chloroplasts and make their own food by. photosynthesis
Algae are producers in the food chain. They are responsible for much of the atmospheric oxygen. They are classified by color. They all contain chlorophyll, but the green chlorophyll may be masked by other pigments. There are green algae, red algae, brown algae, golden brown, and yellow algae.
In the past, the algae were classified as plants and placed in the Kingdom Plantae. Algae lack the specialized tissues that are found in the true plants. They are now classified as protists and are no longer a part of the plant kingdom for the following reasons: Algae lack vascular tissue that is found in the true plants. Algae lack true roots, stems and leaves.
Algae are divided and classified into several phyla, based on the following characteristics: 1. Their color: RED BROWN GOLDEN GREEN All algae contain chlorophyll a, which is required for photosynthesis. Some phyla have accessory pigments that give them a characteristic color.
These algae consist of a single cell. Most unicellular algae are aquatic and compose the phytoplankton of aquatic ecosystems. Phytoplankton are the...unicellular, photosynthetic organisms in aquatic ecosystems that form the foundation of aquatic food chains. The phytoplankton produce almost half of the world s carbohydrates and are the major producers of oxygen in the atmosphere.
Colonial algae have a structure that consists of..groups of cells acting in a coordinate manner.
It is believed by many scientists that the green algae gave rise to the land plants. Evidence supporting this theory includes: a) Both groups of organisms have chloroplasts that contain chlorophylls a and b. b) Both store their food as starch. c) Both have cell walls composed of cellulose.
Plant- Like Protists Unicellular Algae 20-3
Although these types of unicellular protists are motile, they are considered plant-like because they are autotrophic. Diatoms Dinoflagellates Euglena
Diatoms are unicellular algae that have.. a unique glass-like wall made of silica. The wall consists of two parts that overlap like a shoebox and its lid. The walls are able to withstand great pressure and offer protection from the crushing jaws of predators.
Most reproduce by binary fission. Sexual reproduction is not common. There are over 100,000 different species.
They are the major component of phytoplankton, making them very important producers in both freshwater and salt water ecosystems. They are an essential source of nutrition for microscopic heterotrophs such as protists and invertebrates. As producers, they release an abundance of oxygen into the atmosphere.
They have two flagella that make them spin in the water as they move. The dinoflagellates are characterized by cells that are.reinforced by cellulose plates.
Dinoflagellates are abundant components of both marine and freshwater plankton, forming the basis of the food chain. Many are photosynthetic. Others are mixotrophs or heterotrophs.
Some dinoflagellates bloom in the ocean and create red tides. They have an abundance of carotenoids turning the water a reddish color. They produce toxins which can kill fish and invertebrates in the area. Some species can produce bioluminescence, a display of light that can be seen at night.
Euglenophytes are flagellated, unicellular algae that exhibit both plant-like and animal-like characteristics.
A euglenoid has a pocket at one end of the cell from which.one or two flagella emerge. A familiar euglenoid is Euglena. Euglena are. mixotrophs In sunlight they are, autotrophic but when sunlight is unavailable, they can become, heterotrophic absorbing nutrients from their environment.
Label the structures of the Euglena: 1 Cell membrane 2 Pellicle 3 Flagella 4 Contractile vacuole 5 Nucleus 6 Chloroplast 7 Eyespot
Euglena have both plant and animal characteristics: Animal like Characteristics: a) They are highly motile and move with a flagella. b) They can take in food through the cell membrane. c) There is no cell wall. Plant like Characteristics: a) They have chloroplasts and carry out photosynthesis.
The eyespot is red and is sensitive to light. Euglena seek out bright areas. The cell is also sensitive to touch, heat and chemicals.
Pellicle: There is no cell wall. Transparent protein bands beneath the plasma membrane that provide strength and flexibility.
Contractile vacuoles help to rid the cell of excess water. They swell with water and contract when full to send the water out of the cell.
Euglena reproduce asexually only by: binary fission.
20-2 THE ANIMAL-LIKE PROTISTS: THE PROTOZOANS
Protozoa means "first animals". They perform all the processes of multicellular organisms such as digestion, excretion, and respiration except that in the protozoa all processes take place inside a single cell.
Most are heterotrophic and obtain their nutrients by ingesting small molecules or cells. These particles are digested inside food vacuoles. A food vacuole is..a membrane-bound sac that contains digestive enzymes. They may live in ponds, streams, oceans, mud, soil, in or on certain plants and animals. Some species live as parasites inside the body cavity of certain worms, termites, and humans.
They make up zooplankton and form the basis of the food chain in aquatic environments. They can cause diseases such as..malaria, African sleeping sickness, and dysentery. All are capable of asexual reproduction, usually by binary fission. A few species can reproduce sexually by conjugation.
The protozoa are generally classified into four groups based on their method of movement. Methods of movement include: Pseudopodia (Sarcodines) Cilia (Ciliates) Flagella (Zooflagellates) No movement (Sporozoans)
This group includes hundreds of species of amoebas. The amoeba is a shapeless mass of protoplasm surrounded by a plasma membrane. The amoeba moves by pseudopodia or "false feet".
The oxygen necessary for life diffuses through the cell membrane from the water. Wastes pass out in the same way. Water enters the ameba by osmosis. If the ameoba did not have a way of getting rid of the excess water, it would burst. Contractile vacuole: When this vacuole fills up with water, it contracts and expels the excess water.
Food Getting and Digestion Amoeba eat algae or other protozoans. The particle of food is surrounded by the pseudopodia and engulfed into the cell by phagocytosis. The food is digested by enzymes in the food vacuole. The digested food is absorbed by the cytoplasm and used as a source of energy. The wastes are excreted through the cell membrane.
Reproduction They reproduce: asexually by simple cell division. They reproduce: sexually by conjugation
Diseases caused by Sarcodines: Many people become infected with a species of Entamoeba which causes the disease known as ameobic dysentery. These amoeba live in the intestine where they absorb food from the host. The host may experience severe diarrhea and bleeding from damage caused to the intestinal wall.
Cilia are..short, hair like projections that line the cell membrane. The cilia beat in synchronized waves across the surface of the cell. Ciliates are a large, varied group of protists named for their use of cilia to move and feed.
Label the structures of the Paramecium: 1 Contractile vacuole 2 Oral groove 3 Mouth 4 Gullet 5 Food vacuole 6 Anal pore 7 Micronucleus 8 Macronucleus 9 Cilia 10 Trichocyst
The paramecium moves with cilia, which are hair like structures arranged in rows. They beat back and forth to cause movement. The Paramecium has a definite shape and size. It does not change shape like the ameba. The Paramecium has two nuclei: a) Macronucleus: This is the large nucleus. This nucleus regulates nutrition and activities of the cell. b) Micronucleus: This is the small nucleus. This nucleus functions only during reproduction.
The paramecium has the pellicle under the cell membrane. A pellicle consists of bands of protein that provide support to the cell membrane. Food Getting: a) The oral groove is lined with cilia, which force food particles into the mouth. b) The mouth opens into the gullet. c) When the end of the gullet becomes full, it breaks off and becomes a food vacuole where the food is digested. d) The wastes pass out of the cell through the anal pore. Oxygen enters through the cell membrane by diffusion.
Trichocysts are found just under the cell membrane. Trichocysts are used for defense. When a paramecium is confronted by danger, the trichocysts release stiff projections that protect the cell. Sensitivity a) The paramecium has no specialized sense organs, but they are sensitive to touch, heat, chemicals, and light. b) Except when feeding, they swim constantly. When they bump into something, they reverse, and swim off in another direction. This kind of trial and error response is called the avoiding reaction.
Reproduction Asexual by binary fission. Sexual by conjugation. Two paramecia exchange micronuclei, and then continue to divide by fission. They have exchanged genetic information.
The 2500 species found in this group are characterized by the presence of one or more flagella. Flagella are.. long, hair like structures that whip back and forth propelling the cell through the water. This group contains some of the most primitive of the protozoa. The Zooflagellates
The Trypanosomes are flagellates that cause African sleeping sickness. Early symptoms are headache and fever. Advanced symptoms are coma and death. Trypanosomes are found in the blood of jungle animals and are transmitted to man by the bite of the tsetse fly.
Trypanosomes evade the host s immune system with a bait and switch tactic. The surface of the trypanosome is coated with millions of copies of a single protein. Just as the host s immune system learns to recognize this pathogen and launch an attack, new generations of the trypanosome switch to another surface protein with a different molecular structure. These frequent changes in the surface protein prevent the host from developing immunity.
Found in the bloodstream Characteristics include: 1. No method of movement. 2. Reproduce asexually by spores. 3. Always are parasitic. 4. They live by absorbing food from the cells of the host. 5. Cause malaria in man. 6. Requires two hosts: man and the Anopheles mosquito.
Life cycle of the Malarial Parasite, Plasmodium: 1. Mosquito bites a human who has malaria. 2. The plasmodium from the human enters the stomach of the mosquito. 3. Plasmodium travels to the salivary glands of the mosquito. 4. Mosquito bites another human and the plasmodium enters the bloodstream of man. 5. Plasmodium enters the red blood cells where they produce spores. Since they live inside the red blood cell, they are hidden from the host s immune system. Infected red blood cells burst, releasing the spores to infect other red blood cells. 6. Healthy mosquito bites a malaria victim and the cycle continues.
Both the Plasmodium and the Anopheles mosquito have become resistant to drugs and pesticides. In recent years there has been a resurgence of malaria, killing 2 million people a year.
These organisms have unique life cycles that set them apart from the algae, the protozoa, and the fungi. They are. eukaryotic, multicellular, heterotrophic organisms with very little tissue specialization. Water Mold Slime Mold The fungus-like protists include the: slime molds and the water molds.
SLIME Slime molds are typically found growing on damp soil, rotting logs, or decaying leaves. MOLDS They appear as glistening masses of slime that may be white, red or yellow.
They spend part of their life in a mobile, amoebalike feeding form, engulfing organic materials, and part of their life in a stationary reproductive stage. The slime molds play a key role in the recycling of organic material.