20–2 Animal-like Protists: Protozoans Copyright Pearson Prentice Hall

20-2 Animal-like Protists: There are four phyla of animal-like protists: zooflagellates sarcodines ciliates Sporozoans Animal-like protists are classified by their means of movement. Copyright Pearson Prentice Hall

Phylum Zoomastigina: Zooflagellates Animal-like protists that swim using flagella are called zooflagellates. Flagella are long, whiplike projections that allow a cell to move. Most zooflagellates have one or two flagella, although a few species have many. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Zooflagellates Zooflagellates usually absorb food through their cell membranes. They live mostly in water environments, such as lakes and streams, where they absorb nutrients from decaying organic material. Some live within the bodies of other organisms, taking advantage of the food from the larger organism. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Zooflagellates Most zooflagellates reproduce asexually by mitosis and cytokinesis. Some zooflagellates may reproduce sexually using meiosis to produce gametes. When gametes from two organisms fuse, a genetically diverse organism is formed. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Sarcodines Phylum Sarcodina: Sarcodines Sarcodines are animal-like protists that have pseudopods. Pseudopods are temporary cytoplasmic projections used for feeding or movement. Amoebas are the best known sarcodines. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Sarcodines Amoebas Amoebas are flexible, active cells with thick pseudopods that extend out of the central mass of the cell. Cytoplasm streams into the pseudopod, and the rest of the cell follows. This type of locomotion is known as amoeboid movement. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Sarcodines Amoebas surround food and engulf it in a food vacuole. A food vacuole is a small cavity in the cytoplasm that temporarily stores food. Food is digested and nutrients are passed to the cell. Waste stays in the vacuole until it is released outside the cell. Amoebas reproduce by mitosis and cytokinesis. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Sarcodines Structures of an Amoeba Contractile vacuole Pseudopods Nucleus Sarcodines use pseudopods for feeding and movement. The amoeba, a common sarcodine, moves by first extending a pseudopod away from its body. The organism’s cytoplasm then streams into the pseudopod. Amoebas also use pseudopods to surround and ingest prey. Food vacuole Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Sarcodines Foraminiferans Abundant in warmer regions of the oceans. Secrete shells of calcium carbonate. Their shells accumulate at the ocean floor and form huge deposits. The white chalk cliffs of Dover, England are deposits of foraminiferan skeletons raised above sea level due to geological processes. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Sarcodines Heliozoans (“sun animals”) Thin spikes of cytoplasm supported by microtubules project from their silica shells. They look like the sun’s rays, giving them their name. Copyright Pearson Prentice Hall

Phylum Ciliophora: Ciliates Ciliates use cilia for feeding and movement. Cilia are short hairlike projections that propel a cell. The internal structure of cilia and flagella are identical. The beating of cilia propels a cell rapidly through water. Found in fresh and salt water. Most are free living, and do not exist as parasites or symbionts. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Ciliates Paramecia  One type of ciliate is a paramecium. In a paramecium, the cilia are grouped into rows and bundles, and beat in a regular pattern. The cell membrane is highly structured. Trichocysts are bottle-shaped structures found just below the surface of the cell membrane used for defense. When in danger, the paramecium releases these stiff projections to protect the cell from predators. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Ciliates Paramecia have two types of nuclei, like most ciliates: The macronucleus keeps multiple copies of most genes that the cell needs in its day-to-day existence. The micronucleus contains a copy of all of the cell's genes. A paramecium may contain one or more micronuclei. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Ciliates Cilia sweep food particles into the gullet, an indentation in one side of the organism. The gullet traps the particles and forces them into food vacuoles. The food vacuoles fuse with lysosomes which contain digestive enzymes. Once the material in the food vacuole is digested, the waste material empties through the anal pore. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Ciliates In fresh water, water moves into the paramecium by osmosis. Excess water is collected in contractile vacuoles and emptied into canals arranged in a star-shaped pattern around contractile vacuoles. Contractile vacuoles are cavities in the cytoplasm that are specialized to collect water. Once full, they contract, pumping water out of the organism. This helps to maintain homeostasis. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Ciliates Structures of a Paramecium Ciliates use hairlike projections called cilia for feeding and movement. Ciliates, including this paramecium, are covered with short, hairlike cilia that propel them through the water. Cilia also line the organism’s gullet and move its food—usually bacteria—to the organism’s interior. There, the food particles are engulfed, forming food vacuoles. The contractile vacuoles collect and remove excess water, thereby helping to achieve homeostasis, a stable internal environment. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Ciliates Conjugation  Ciliates reproduce asexually by mitosis and cytokinesis. When placed under stress, paramecia may engage in conjugation, which allows them to exchange genetic material with other individuals. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Ciliates Two paramecia attach themselves to each other. Meiosis produces four haploid micronuclei, three of which disintegrate. The remaining micronucleus in each cell divides again. Macronucleus Micronucleus MEIOSIS During conjugation, two paramecia attach themselves to each other and exchange genetic information. The process is not reproduction because no new individuals are formed. Conjugation is a sexual process, however, and it results in an increase in genetic diversity. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Ciliates The two cells exchange one micronucleus from each pair. The macronuclei disintegrate, and each cell forms a new macronucleus from its micronucleus. Exchange of micronuclei Macronuclei disintegrate During conjugation, two paramecia attach themselves to each other and exchange genetic information. The process is not reproduction because no new individuals are formed. Conjugation is a sexual process, however, and it results in an increase in genetic diversity. New macronuclei form Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Ciliates Conjugation is not a form of reproduction because no new individuals are formed, but it is a sexual process. In large populations, conjugation helps produce and maintain genetic diversity. Genetically identical paramecia form During conjugation, two paramecia attach themselves to each other and exchange genetic information. The process is not reproduction because no new individuals are formed. Conjugation is a sexual process, however, and it results in an increase in genetic diversity. Copyright Pearson Prentice Hall

Phylum Sporozoa: Sporozoans Sporozoans do not move on their own—they are parasitic. Sporozoans are parasites of a wide variety of organisms, including worms, fish, birds, and humans. Many sporozoans have complex life cycles that involve more than one host. Sporozoans reproduce by sporozoites. A sporozoite can attach itself to a host cell, penetrate it, and then live within it as a parasite. Copyright Pearson Prentice Hall

Animal-like Protists and Disease Some animal-like protists cause serious diseases, including malaria and African sleeping sickness. Copyright Pearson Prentice Hall

Animal-like Protists and Disease Malaria Malaria is one of the world’s most serious infectious diseases, killing up to 2 million people each year. The sporozoan Plasmodium, which causes malaria, is carried by the female Anopheles mosquito. When infected red blood cells burst, the release of parasites into the bloodstream produces severe chills and fever, the symptoms of malaria. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Malaria Drugs like chloroquinine are effective against some forms of the disease, but many strains are now resistant. Vaccines are currently available, but only partially effective. The current best means of control involve controlling the mosquitoes that carry it. Copyright Pearson Prentice Hall

Animal-like Protists and Disease A female Anopheles mosquito bites a human infected with malaria and picks up Plasmodium gamete cells. Animal-like protists can cause serious diseases, including malaria. The bite of an Anopheles mosquito can transmit Plasmodium sporozoites. Once in the human body, Plasmodium infects liver cells and red blood cells and multiplies. Copyright Pearson Prentice Hall

Animal-like Protists and Disease The sexual phase of the Plasmodium life cycle takes place inside the mosquito. Gametes fuse to form zygotes, meioses occurs, and sporozoites are produced and migrate to salivary gland. Animal-like protists can cause serious diseases, including malaria. The bite of an Anopheles mosquito can transmit Plasmodium sporozoites. Copyright Pearson Prentice Hall

Animal-like Protists and Disease Infected mosquito bites another human, injecting saliva that contains Plasmodium sporozoites. Animal-like protists can cause serious diseases, including malaria. The bite of an Anopheles mosquito can transmit Plasmodium sporozoites. Plasmodium sporozoites Copyright Pearson Prentice Hall

Animal-like Protists and Disease Sporozoites infect liver cells and multiply asexually. Plasmodium sporozoites Liver Animal-like protists can cause serious diseases, including malaria. The bite of an Anopheles mosquito can transmit Plasmodium sporozoites. Once in the human body, Plasmodium infects liver cells and red blood cells and multiplies. Copyright Pearson Prentice Hall

Animal-like Protists and Disease Infected liver cells burst, releasing Plasmodium cells called merozoites that infect red blood cells. Plasmodium sporozoites Liver Animal-like protists can cause serious diseases, including malaria. The bite of an Anopheles mosquito can transmit Plasmodium sporozoites. Once in the human body, Plasmodium infects liver cells and red blood cells and multiplies. Merozoites Liver cells burst Copyright Pearson Prentice Hall

Animal-like Protists and Disease Merozoites reproduce asexually inside red blood cells. Merozoites Once in the human body, Plasmodium infects liver cells and red blood cells and multiplies. Red blood cells Copyright Pearson Prentice Hall

Animal-like Protists and Disease Infected red blood cells burst, releasing merozoites that infect other red blood cells. Some cells release gametes that can infect mosquitoes. Merozoites Animal-like protists can cause serious diseases, including malaria. The bite of an Anopheles mosquito can transmit Plasmodium sporozoites. Once in the human body, Plasmodium infects liver cells and red blood cells and multiplies. Red blood cells Copyright Pearson Prentice Hall

Animal-like Protists and Disease Other Diseases Caused by Protists African sleeping sickness Amebic dysentery Giardia Copyright Pearson Prentice Hall

Ecology of Animal-like Protists Many animal-like protists are essential to the living world. Some live symbiotically within other organisms. Some recycle nutrients from dead organic matter. Some live in water, where they are eaten by tiny animals, which in turn serve as food for larger animals. Copyright Pearson Prentice Hall

Ecology of Animal-like Protists Some animal-like protists are beneficial to other organisms. The protist Trichonympha lives within the digestive systems of termites. It breaks down cellulose, allowing termites to digest wood. Copyright Pearson Prentice Hall