Protista. A World in a Drop of Water. 50 m. Figure 28.1. A World in a Drop of Water. Even a low-power microscope Can reveal an astonishing menagerie of organisms in a drop of pond water. The Diversity of Protists. Morphological Diversity Organelles
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Protista A World in a Drop of Water
50 m Figure 28.1 A World in a Drop of Water • Even a low-power microscope • Can reveal an astonishing menagerie of organisms in a drop of pond water
The Diversity of Protists • Morphological Diversity • Organelles • Divide a Large Cell into Compartments • Structures for Support and Protection • Nutrition • Photoautotrophs • Heterotrophs • Mixotrophs • Habitat • Fresh water • Marine • Reprodution • Sexual and Asexual • Variation in Life Cycles
Endosymbiosis in Eukaryotic Evolution • considerable evidence • protist diversity has its origins in endosymbiosis • plastid-bearing protists • Evolved into red algae and green algae • Red algae and green algae • underwent secondary endosymbiosis • they were ingested • Diversity of plastids produced by secondary endosymbiosis
The Endosymbiosis Theory Symbiosis occurs when individuals of two different species live in physical contact Endosymbiosis occurs when an organism of one species lives inside an organism of another species.
Supporting Data Mitochondria and chloroplasts are about the size of an average bacterium. Both organelles replicate by fission, as do bacteria, and have their own ribosomes to manufacture their own proteins. Mitochondria and chloroplasts have genes that code for the enzymes needed to replicate and transcribe their own genomes. Both organelles have double membranes, consistent with the engulfing mechanism.
Impacts on Human Healthand Welfare The most spectacular crop failure in history, the Irish potato famine, was caused by a protist: Phytophthora infestans.
Malaria Malaria, the world's most chronic public health problem, is caused by Plasmodium
Ecological Importance of Protists Protists represent just 10% of the total number of named eukaryotic species and have relatively low diversity but are extraordinarily abundant.
Primary Producers. Species that produce chemical energy by photosynthesis Diatoms rank among the leading primary producers in the oceans abundant Production of organic molecules in the world’s oceans responsible for almost half of the total carbon that is fixed on Earth.
Protists Play a Key Role in Aquatic Food Chains Bacteria and photosynthetic protists are primary producers in the aquatic food chain A food chain describes nutritional relationships among organisms.
Plankton and Phytoplankton Plankton Small organisms that live near the surface of oceans or lakes drift along or swim only short distances Phytoplankton photosynthetic species of plankton organic compounds producedare the basis of food chains in freshwater and marine environments
Protists Act as Carbon Sinks Play key role in the global carbon cycle Could help reduce global warming Carbon sink a long-lived carbon reservoir.
Themes in the Diversification of Protists Several general evolutionary themes tie together the diversity of eukaryotes. The key to understanding the protists is to recognize that a series of important innovations occurred, often repeatedly, as eukaryotes diversified.
Morphological Diversity Metabolism inside the eukaryotic cell can outstrip the cell's transport and exchange capabilities because as cells get larger, the surface area/volume ratio decreases.
Organelles Divide a Large Cell into Compartments Eukaryotes solve the problem of size by dividing their cell volume into compartments
The Evolution of Multicellularity Eukaryotic cells have many internal compartments with distinct, specialized functions. After ingesting a bacterium, for example, a Paramecium surrounds it with an internal membrane, forming a compartment called a food vacuole. When the food has been digested and nutrients have diffused out of the food vacuole, the vacuole merges with the plasma membrane at the anal pore and expels waste molecules The cytoskeleton supports and organizes the interior of the cell, including the organelles
The Evolution of Multicellularity Differentiation of cell types is a crucial criterion for defining multicellularity. In contrast, colonial growth defines groups of cells that all perform the same function
Structures for Supportand Protection Protists have a complex intracellular structure many have a rigid internal skeleton or a hard external structure that provides support or protection, or both shell test
Ingestive Feeding Some protists are large enough to surround and ingest other protists through engulfment by long, fingerlike projections called pseudopodia
Species that feed by beating their cilia to create water currents often attach themselves to a substrate and collect food by sweeping particles into their mouths Organisms that filter food out of water in this way are called filter feeders, or suspension feeders.
Absorptive Feeding Absorptive feeding occurs when nutrients are taken up directly from the environment. Decomposers feed on dead organic matter, or detritus. Parasites live inside other organisms and absorb their nutrition directly from the environment inside their host, causing damage to the host (Figure 28.16).
Photosynthesis A wide variety of protists are photosynthetic. The major photosynthetic groups of protists are distinguished by the pigments they contain and many live symbiotically with animals or other protists.
Key Lineages of Protists Excavata • Excavata - Diplomonadida • Excavata - Parabasalida Discicristata • Discicristata - Euglenida Alveolata • Alveolata - Ciliata • Alveolata - Dinoflagellata • Alveolata - Apicomplexa
Key Lineages of Protists Stramenopila (Heterokonta) • Stramenopila - Oomycota • Stramenopila - Diatoms • Stramenopila - Phaeophyta (Brown Algae) Cercozoa • Cercozoa - Foraminifera Plantae • Rhodophyta (Red Algae) Amoebozoa • Myxogastrida (Plasmodial Slime Molds)
Evaluating Molecular Phylogenies Current phylogenetic tree based on sequence data Eight major lineages of eukaryotes Paraphyletic they do not constitute all the descendants of a single common ancestor
Excavata • Are adapted to anaerobic environments • Lack plastids • Mitochondria that lack • DNA • an electron transport chain • citric-acid cycle enzymes • Diplomonads (e.g., Giardia) • two nuclei • lack a cell wall • reproduce asexually • Parabasalids (e.g., Trichomonas) • lack a cell wall • reproduce asexually (some also reproduce sexually) • feed by engulfing
5 µm (a) Giardia intestinalis, a diplomonad (colorized SEM) Figure 28.5a Diplomonads • Diplomonads • Have two nuclei and multiple flagella
Parabasalids • Parabasalids include trichomonads • Which move by means of flagella and an undulating part of the plasma membrane Flagella Undulating membrane 5 µm (b) Trichomonas vaginalis, a parabasalid (colorized SEM) Figure 28.5b
Discicristata Euglenids lack an external wall reproduce asexually most ingest bacteria or other small cells have flagella with a unique internal structure Clade includes predatory heterotrophs photosynthetic autotrophs pathogenic parasites
Kinetoplastids • Kinetoplastids • Have a single, large mitochondrion that contains an organized mass of DNA called a kinetoplast • Include free-living consumers of bacteria in freshwater, marine, and moist terrestrial ecosystems