27.1 Why Do Biologists Study Protists?

• Malaria ranks as one of the world’ s worst infectious diseases.

• Species that produce chemical energy in this way are called primary producers.

• Diatoms and other organisms that drift in the open oceans or lakes are called plankton.

• A food chain describes nutritional relationships among organisms, and thus how chemical energy flows within ecosystems.

• The carbon atoms in carbon dioxide molecules move to organisms on land or in the oceans and then back to the atmosphere, in what researchers call the global carbon cycle.

• A carbon sink is a long term reservoir of carbon.

27.2 How Do Biologists Study Protists?

• Synapomorphy is a shared, derived trait that distinguishes major monophyletic groups, groups that include all the descendants of a common ancestor and only those descendants

• Paraphyletic groups represent some, but not all, of the descendants of a single common ancestor.

• Flagella are organelles that project from the cell and whip back and forth to produce swimming movements.

• Direct sequencing is based on sampling soil or water, analyzing the DNA sequence of specific genes in the sample, and using the data to place the organisms from the sample on a phylogenetic tree.

27.3 What Themes Occur in the Diversification of Protists?

• All eukaryotes alive today have:

  • either mitochondria or genes that are normally found in mitochondria

  • A nucleus and endomembrane system

  • a cytoskeleton.

• Endosymbiosis theory proposes at mitochondria originated when a bacterial cell took up residence inside another cell about 2 billion years ago

• Symbiosis is said to occur when individuals of two different species live in close and prolonged physical contact

• Endosymbiosis occurs when an organism of one species lives inside the cells of an organism of another species.

• Most of the genes from the endosymbiotic bacterium moved into the nuclear genome in what was one of the most spectacular lateral gene transfer events in the history of life

• When phagocytosis occurs, an individual takes in packets of food much larger than individual molecules

• Protists can feed by either

  • ingesting packets of food

  • absorbing organic molecules directly from the environment

  • performing photosynthesis

• A flexible membrane and dynamic cytoskeleton give these species the ability to surround and “swallow” prey using long, fingerlike projections called pseudopodia

• Some protists that live by absorptive feeding are decomposers, meaning that they feed on dead organic matter, or detritus.

• If an absorptive species damages its host, that species is called a parasite.

• Amoeboid motion is a sliding movement observed in some protists.

• A life cycle describes the sequence of events that occur as individuals grow, mature, and reproduce.

• Fertilization is the fusion of two haploid gametes to form a diploid zygote.

• This alternation of multicellular haploid and diploid forms is known as alternation of generations.

• The multicellular haploid form is called a gametophyte, because specialized cells in this individual produce gametes, also haploid, by mitotic cell division.

• The multicellular diploid form is called a sporophyte because it has specialized cells that undergo meiotic cell division to produce haploid cells called spores.

• A spore is a single haploid cell that divides mitotically to form a multicellular, haploid gametophyte.

27.4 Key Lineages of Eukaryotes

• Fungi play a large role as decomposers in many ecosystems due largely to their ability to produce enzymes that break down the cell walls of plants and other organisms.

• Biologists use the name Plantae to refer not just to the commonly named land plants, but to the entire monophyletic group that includes glaucophyte algae, red algae, and green algae as well.

• Some species are capable of bioluminescence, meaning they emit light via an enzyme-catalyzed reaction.

• Sessile means to be permanently fixed to a substrate.