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A dichotomous key is an organized set of couplets (always sets of two statements) of mutually exclusive characteristics that provides a logical and linear method to identify anything of interest. Dichotomous keys begin with general characteristics and proceed to couplets indicating progressively specific characteristics. In biology, scientists use dichotomous keys to identify unknown organisms. Generally there are two types of dichotomous keys: bracketed and indented.
Bracketed keys are numbered; the number of the first statement is followed with a period and the second statement of the couplet is followed with a prime symbol (′). Variations of the methods exist; for example, instead of period and prime, “a” and “b” may be used. In a bracketed key, leads (a lead is each statement on one line) direct you to the couplet that is indicated by the lead selected, usually another set of couplets designated by a number, or the name of a species.
1.Flowers red ...... 2
1′Flowers not red ..... 3
2.Plant herbaceous ....... Species A
2′Plant woody ........ Species B
3.Leaves simple ......... Species C
3′Leaves compound ........ Species D
Indented keys: The numbering in indented keys can be similar to that of bracketed keys; however, sometimes indented keys are not numbered at all, and successive couplets are indented. The difference between bracketed and indented keys is the way the couplets are organized. In an indented key, instead of proceeding to the lead number indicated by the lead (which may not necessarily be the next couplet) as in a bracketed key, couplets may be subdivided until a species name is given.
1. Flowers red
2. Plant herbaceous ........ Species A
2′ Plant woody ......... Species B
1′ Flowers not red
3. Leaves simple...... Species C
3′ Leaves compound ........ Species D
•Always read both choices, even if the first seems to be the logical one at first.
•Be sure you understand the meaning of the terms involved. Do Not Guess.
•When measurements are given, use a calibrated scale. Do Not Guess.
•Because living things are always somewhat variable, do not base your conclusion on a single observation. Study several specimens to be sure your specimen is typical.
Why are dichotomous keys considered to be artificial?
The hypothetical animals used in this exercise are called Caminalcules and were constructed by J. H. Camin at the University of Kansas in the 1960's.
who began classifying organisms in the 18th century, that there was a uniformly accepted method for the classification of organisms; it was this system that led to the field of modern taxonomy.
The field in which scientists group organisms based on their evolutionary relationships
shared derived traits
is deciding on homologous traits. Some traits that appear to be homologous may in fact be analogous traits
which are traits that are similar phenotypically, but have different origins. One of the best examples of this would be the wings of an insect and the wings of a bird. The wings of these two groups of organisms were derived independently of each other (insects are arthropods and birds are chordates) and even though they perform the same basic function, grouping these two organisms together based on presence of wings would lead to an erroneous group.
discovered the structure of the DNA molecule
scientists that study taxonomy and phylogenetics
an interpretation of the evolutionary relationships between organisms,
and they are usually depicted as phylogenetic trees
is the ancestor of all of the organisms that are represented by the tips.
a tip can represent any taxon (domain, kingdom, phylum, class, etc.) but the smallest groups represented by tips are usually species.
Tips that arise from the same branch
is a taxon that is known to be closely related to the rest of the taxa in the phylogeny, but shares less in common with the rest of the taxa than the rest of the taxa do with each other.
epresent the point where one taxon or group of taxa diverges from another taxon or group of taxa. Finally, a branch represents groups of organisms through time. Branches often represent the evolution of various characteristics (adaptations).
are defined as shared derived characteristics (traits) that are not present in distant taxa. For instance, in the figure above, the two sister taxa may share a synapomorphy that is not present in the root ancestor or in the outgroup.
These characteristics are considered to be ancestral and may be shared with other groups of organisms outside of the phylogeny as well.
try to avoid cases where synapomorphies are derived more than once.
Tree of Life determined by Carl Woese, the ancestors of the Bacteria diverged earlier than the ancestors of the Archaea and Eukarya.
Bacteria and Archaea form the group traditionally known as?
based on the fact that they lack a nucleus and other organelles and have cell walls made up of different chemicals than the cell walls of the eukaryotes
Pseudopeptidoglycan, polysaccharide, glycoprotein, or protein
Only in certain types
Microscopy and Culturing methods
its plasma membrane is surrounded by a peptidoglycan-rich cell wall
the plasma membrane is surrounded by a thin peptidoglycan-poor cell wall, which is in turn surrounded by a lipid bilayer.
Gram staining technique, Gram-positive bacteria stained what color?
purple because the stain interacts with peptidoglycan,
Gram-negative bacteria is stained what color?
pink, because the lipid bilayer prevents the stain from interacting with the peptidoglycan.
single cell on a solid agar surface may grow to an observable mass of homogenous cells called a colony in a short time. Colony morphology (shape, size, color) is species-specific and does not change unless growth conditions change or a mutation occurs. Therefore, colony morphology is useful for characterization and identification of microorganisms.
Compare the size and shape of the domains Bacteria and Archaea. Why do you think they were grouped in the same kingdom by earlier biologists?
Root nodules form when the roots of plants, typically legumes like beans, peas, clovers, etc., are inoculated with nitrogen-fixing bacteria Nitrogen-fixing bacteria have the ability to take atmospheric nitrogen (N2), which most organisms are not able to use as a nutrient, and through a series of physiological processes convert it to ammonia (NH3), which is used by plants as an essential nutrient to make pigments and proteins along with other nitrogenous compounds.
Why does grass often appear greener in areas where clover grows?
you just practiced the pure culture technique developed by a German physician, Robert Koch, about 100 years ago.
Each colony contains a cluster of cells originated from a single cell when you first streaked it during last lab period.
number of different species present
how equally individuals are distributed among the different species present
when there are many species present and individuals are distributed equally among them (i.e. all species are equally represented and the abundance of one species does not “swamp” the others numerically)
if many species are present and they are equal or nearly equal in their abundance.
are composed of only a few species, or if there are many species, only a few are abundant (i.e. a few species dominate).
community stability (i.e. the ability of a community to resist or recover from a disturbance) or as a measure of community maturity.
The most widely used measure of species diversity is the Shannon Index (referred to below as H-prime or H′The most widely used measure of species diversity is the Shannon Index (referred to below as H-prime or H′), which incorporates richness (number of species) and evenness (relative abundance of species) into its calculation.
The larger the value of H′, the greater?
H′ = -Σ^S (pi ln pi)
look at paper for more information
Species richness (S) refers to the number of different species encountered. It is simply determined by counting the number of different species present in the sampled area. The larger the value of S, the greater the species richness.
S = the number of different species
Species evenness (J) refers to the distribution of individuals among species. It is determined by considering how closely a set of observed species abundances is to the highest possible diversity (Hmax) given the same number of species. The larger the value of J, the more evenly individuals are distributed among the species present.
Protists are not a true clade, as they make up several distinct eukaryotic lineages (i.e., they are not a monophyletic group). However, tradition keeps the study of all of these different groups of organisms together.
Protozoans are all unicellular and heterotrophic—they ingest their food just like animals do. Although generally found in freshwater habitats, there are some marine, damp terrestrial, and endosymbiotic protozoans. The four main groups of protozoans are distinguished from each other based on their mode of locomotion.
Ciliated protozoans move by beating in unison the many small cilia that line their unicellular bodies. Paramecium is a classic example of a ciliated protozoan.
What is the relationship between the oral cavity, the gullet, and the food vacuoles?
Flagellated protozoans move by beating their few, long, whip-like flagella. One example of a flagellated protozoan is Trichonympha, the protist that lives mutualistically in the guts of termites and enables them to break down cellulose and lignin and therefore to digest wood.
Amoeboid protozoans move by means of cytoplasmic extensions known as pseudopodia. The classic example of an amoeboid protozoan is of course Amoeba.
Spore-forming protozoans exhibit an entirely parasitic life cycle. They are transferred from one human host to another by means of a vector. Plasmodium is an example of a spore-forming protozoan. It is the organism responsible for the disease malaria. Mosquitoes are the vectors that transfer Plasmodium.
Where exactly are these Plasmodium protozoans located?
Like fungi, slime molds are heterotrophs that feed on dead organic matter. They are terrestrial organisms, often found in shady, moist locations. There are two main types of slime molds, but in lab we will only look at one type—the plasmodial slime molds (do not confuse plasmodial slime molds with Plasmodium, the flagellated protozoan discussed above).
what is the representative plasmodial slime mold
Physarum; is a very well-studied organism in biology (much like Drosophila) and is a representative plasmodial slime mold. The live specimen you are observing is in what is called the plasmodial, or feeding, stage.
Do you think Physarum should be classified as multicellular, unicellular, or perhaps something different entirely?
Algae are considered plant-like in that they are autotrophic—they produce their own food through the process of photosynthesis. However, unlike plants, algae are aquatic, some of which are freshwater and some of which are marine. Many algae are unicellular, while many are multicellular. The unicellular algae are often collectively referred to as phytoplankton, which form the bases of aquatic food chains. Multicellular algae are more commonly known as seaweeds.
Euglenoids are unicellular freshwater algae. Euglena is the classic example.
What function is served by the red eye spot (also known as the stigma)?
What about the contractile vacuole?
Dinoflagellates & Diatoms?
Dinoflagellates are unicellular marine algae. They are responsible for several unique marine phenomena that you will learn about in lecture. Diatoms are unicellular algae that occur in both marine and freshwater habitats. Diatoms are unusual in that their cell wall is made up of silica (glass), which is impermeable. Therefore, diatoms are lined with many pores for the transport of materials across the cell wall.
are unicellular algae that occur in both marine and freshwater habitats. Diatoms are unusual in that their cell wall is made up of silica (glass), which is impermeable. Therefore, diatoms are lined with many pores for the transport of materials across the cell wall.
Brown & Red Algae?
Brown algae and red algae are both multicellular and marine.
Two different types of brown algae are kelps and rockweeds. Kelps are the largest of all protists. They grow in large kelp forests near to shore, to depths of about 200 feet. Rockweeds grow in mats that can be seen draped over rocks in the intertidal zone. Although they look quite different from one another, they actually share many structures in common. THALLUS NO XYLEM AND PHLOEM
Red algae are found deeper in the ocean than any other seaweed, but they are commonly encountered at shallow depths as well.
Green algae are a diverse group. There are unicellular and multicellular examples, as well as colonial organisms. Some green algae are freshwater and some are marine (some are also technically terrestrial, but we won’t see these until later in the course). In lab, we will look at a colonial freshwater example, as well as multicellular freshwater and marine examples.
Volvox is a colonial freshwater alga. Being colonial is somewhat intermediate between being unicellular and multicellular. Although each of the cells in the colony are identical (no division of labor or specialization) and could live independently of one another, they exist as an aggregation of cells.
move by rotating/rolling around in the aquatic environment
Codium is a multicellular marine green alga. It is commonly found in the intertidal zone. Observe the demonstration specimens set up in the lab room, and draw them in your notebook. Codium is commonly called dead man’s fingers.
Spirogyra is a multicellular freshwater green alga. he ribbon-shaped, helically-arranged structures that appear to run the length of the filaments are organelles that you are familiar with, though they don’t generally appear this way. They have chloroplasts
Hepaticophyta (Liverworts)- function of the pores is for gas exchange. GAMETOPHYTE, gemme cup
Gemmae are small groups of cells that liverworts produce for asexual reproduction. Gemmae are
disseminated when water droplets fall onto the cups
The mosses are a group of plants with which you are probably familiar. You will often see large numbers of mosses during the rainy season in California. Look at the moss macroscopically as well as using a dissecting scope.
green fuzzy= (n)
slender stalks= (2n) produce spores
Seedless Vascular Plants
As their name implies, seedless vascular plants now possess vascular tissue (xylem and phloem), but they still do not possess seeds (or pollen). Vascular tissue enables these plants to develop true roots, stems, and leaves and reach a taller height than nonvascular plants, but the dependence on water keeps them lower to the ground than the seed plants. The sporophyte generation is the dominant generation in the seedless vascular plants (as well as in all of the seed plants).
Nonvascular plants are so named due to their lack of vascular tissue. Water-conducting xylem and photosynthate-conducting phloem are absent, which keeps these plants from reaching a large size. They do not possess seeds and therefore rely on water to transport their sperm, which also keeps them low to the ground. In nonvascular plants, the gametophyte generation is dominant over the sporophyte generation.
Nonvascular plants names
Lycophyta (Club Mosses)
Psilotophyta (Whisk Ferns)
Seed Plants—Gymnosperms names
Seed Plants—Angiosperms names
Anthophyta (Flowering Plants)
Lycophyta (Club Mosses)- the structure that enables it to stand is vascular tissue. strobili contains the spores, this is gametophyte (2n) but selaginella is sporophyte (n).
Psilotophyta (Whisk Ferns) it differs from other plants because it is sporophyte (n) dominate the sporangia is not on the tip but the "nodes" and "branches"
Psilotophyta (Whisk Ferns) sporophyte dominant strobili found on the tip, does photosynthesis on the stem
Pteridophyta (Ferns) The ferns are the first plants you will see today with large leaves. Ferns are incredibly diverse with a huge number of species (over 12,000).
the sori are on the underside of the lead,
Sori are often covered by an indusium, which is a protective structure. As the sporangia within the sori (and the spores within the sporangia) mature, the indusia will dry up and expose the sori, enabling the spores to be released.
vascular plants that of course possess seeds (and pollen grains). This evolutionary development freed plants from their reliance on water to disperse their gametes, as gametes are now dispersed with the pollen grains by wind. Seeds provide much benefit as well (namely, protection of and nutrients for the developing embryonic plant).
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