You Must Know: Taxonomy and Animal Evolution
Bacteria and Archaea
What You Need to Know
1. The key ways in which prokaryotes differ from eukaryotes with respect to genome, membrane-bound organelles, size, and reproduction.
2. Mechanisms that contribute to genetic diversity in prokaryotes, including transformation, conjugation, transduction, and mutation.
Concept: Structural and Functional adaptations contribute to prokaryote success
-Life is divided into three domains: Archaea, Bacteria, and Eukarya. Both domain Bacteria and domain Archaea are made up of prokaryotes.
-The most common shapes of prokaryotes are spheres, rods, and helices; most are about 1-5µm in size. This is perhaps 1/10 the size of a typical eukaryote cell.
-Prokaryotes have no true nuclei or internal compartmentalization. The DNA is concentrated in a nucleoid region and has little associated protein. Relative to eukaryotes, prokaryotes have simple, small genomes.
-In addition to their one major chromosome, prokaryote cells may possess smaller, circular, independent pieces of DNA called plasmids.
-Prokaryotes reproduce though an asexual process called binary fission, and they continually synthesize DNA.
-Outside their cell membranes, most prokaryotes possess a cell wall that contains peptidoglycans. Gram-positive bacteria have simpler walls with more peptigoglycans, whereas gram-negative cells have walls that are structurally more complex.
-Prokaryotes use appendages called pili that adhere to each other or to surrounding surfaces. About half of the prokaryotes are motile, because they possess whiplike flagella.
+Because the flagellum of bacteria is structurally different from the eukaryotic flagellum, this is another example of analogous structures.
Concept: Rapid reproduction, mutation, and genetic recombination promote genetic diversity in prokaryotes
-Three mechanisms by which bacteria can transfer genetic material between each other are:
1. Transformation: in which a prokaryote takes up DNA from its environment.
2. Conjugation: in which genes are directly transferred from one prokaryote to another.
3. Transduction: in which viruses transfer genes between prokaryotes.
-The major source of genetic variation in prokaryotes is mutation.
Concept: A great diversity of nutritional and metabolic adaptations has evolved in prokaryotes.
-Prokaryotes can be placed in four groups according to how they take in carbon and how they obtain energy.
+Photoautotrophs are photosynthetic, and they use the power of the sunlight to convert carbon dioxide into organic compounds.
+Chemoautotrophs also use carbon dioxide as their source of carbon, but they get energy from oxidizing inorganic substances.
+Photoheterotrophsuse light energy to make ATP but most obtain their carbon from an outside source already fixed in organic compounds.
+Chemoheterotrophs get both carbon and energy from organic compounds.
-Obligate aerobes cannot grow without oxygen because they need oxygen for cellular respiration.
-Obligate anaerobes are poisoned by oxygen. Some use fermentation, whereas others extract chemical energy by another form of anaerobic respiration.
-Facultative anaerobes use oxygen if it is available; when oxygen is not available, they undergo fermentation.
-Some prokaryotes can use atmospheric nitrogen as a direct source of nitrogen in a process called nitrogen fixation. They convert N2 to NH4+. You might what to review the nitrogen cycle in the ecology section.
Concept: Molecular systematic is illuminating prokaryotic phylogeny.
-The first prokaryotes that that were classified in the domain Archaea are known as extremophiles and live in extreme environments such as geysers:
1. Extreme halophiles live in saline environments (highly concentrated and with salt).
2. Extreme thermophiles live in very hot environments.
-Other Archaea do not live in extreme environments. Methanogens use carbon dioxide to oxidize H2 and produce methane as a waste product.
Concept: Prokaryotes play crucial roles in the biosphere
-Many prokaryotes are decomposers, breaking down dead corpses, vegetation, and waste products.
-Many prokaryotes are symbiotic, meaning that they form relationships with other species:
1. Mutualism: Both symbiotic organisms benefit.
2. Commensalism: One organism benefits, whereas the other is neither helped or harmed.
3. Parasitism: One organism benefits at the expense of the other.
Concept: Prokaryotes have both harmful and beneficial impacts on humans:
-Some prokaryotes are pathogenic and cause illness by producing poisons.
-Antibiotics are chemicals that can kill prokaryotes. They are not effective against viruses. Many bacterial plasmids contain resistant genes to different antibiotics.
-Prokaryotes are used by humans in many diverse ways:
a. Bioremediation, removing pollutants from soil, air, or water. This includes treating sewage, cleaning up oil spills, and precipitating radioactive materials.
b. Symbionts in the gut, manufacturing vitamins, and digesting foods.
c. Gene cloning and producing transgenic organisms.
d. Production of cheese and yogurt and other products.
Protists
You Must Know
1. Protists are no longer considered a kingdom! This may contradict what you learned in previous biology classes.
2. How chloroplasts and mitochondria evolved through endosymbiosis.
Concept: Most Eukaryotes are single-cell organisms
-Protist is now a term used to refer to eukaryotes that are neither plants, animals,nor fungi. Biologists no longer consider Protista a kingdom because it is paraphyletic. Some protists are more closely related to plants, fungi, or animals than to other protists.
a. Group I consisting of 3 species (A, B, C) and the common ancestor is a clade—a monophyletic group—a group consists of ancestral species and all of its descendents.
b. Group II is paraphyletic, meaning that it consists of an ancestral species and some of its descendents (missing G)
c. Group III is polyphyletic, it includes species from two or more common ancestors. :
-Protists vary in structure and function more than any other group of eukaryotes. Here are some general commonalities but even these are NOT TRUE for ALL Groups:ar
a. Most are unicellular.
b. Most use aerobic metabolism and have mitochondria.
-According to the current theory, mitochondria and chloroplasts evolved through endosymbiosis. They were originally unicellular organisms engulfed by other cells that ultimately became organelles of the host cell.
-Protists can be divided into three categories: photosynthetic (plant-like) algae, ingestive (animal-like)protozoans, and absorptive (fungus-like) organisms.
-Most protists are aquatic and are important constituents of plankton. Many other protists live as symbionts in other organisms.
-Protists are such a diverse group that their classification is constantly changing and undergoing revision. However, here are some common protists:
1. Giardia intestinalis (always treat your water….)
2. Trichomonas viginalis (STD)
3. Trypanosoma ssp. (Sleeping sickness and Changas’ disease)
4. Euglena
5. Dinoflagellates (Cause red tides… many bioluminescent)
6. Plasmodium (malaria)
7. Ciliates
8. Amoeba
9. Golden Algae
10. Diatoms
11. Brown Algae
12. Oomycetes (water molds—cause potato blight)
13. Red Algae (used in some sushi wraps)
14. Green Algae (Closest relative to land plants)
15. Slime Molds
An Introduction to Animal Diversity
You Must Know:
1. The Characteristics of Animals
2. The Stages of Animal Development
3. How to sort the Animal phyla based on symmetry, development of a body cavity, and the fate of the blastopore.
Concept: Animals are multicellular, eukaryotes with tissues that develop from embryonic layers.
-Animals have the following characteristics:
1. Multicellular Heterotrophs.
2. Most have muscle and nervous tissue.
3. Most reproduce sexually, with a flagellated sperm and a large egg uniting to form a diploid zygote. The diploid stage dominates the life cycle.
-Zygote: Fertilized Egg
-Cleavages: Successive mitotic cell divisions without cell growth between cycles.
-Blastula: A hollow ball of cells surrounding a cavity called the Blastocoel.
-Gastrula: A blastula is “punched or pushed in”, the embryonic tissue layers will form.
-Ectoderm: The outer tissue layer
-Endoderm: The inner tissue layer
-Blastopore: The opening into the gastrula; it will become the mouth in protostomes and the anus in deuterostomes.
-Archenteron: The blind pouch formed by gastrulation.
-Some animals have larvae, an immature form distinct from the adult stage that will undergo metamorphosis.
-Animals share Hox genes, a unique homeobox-containing family of genes that play important roles in development.
Concept: Animals can be characterized by “body plans”
-No symmetry: The sponges
-Radial Symmetry: occurs in jelly fish and other organisms, in which any cut through the central axis of the organism would produce mirror images.
-Bilateral Symmetry: occurs in lobsters, humans and many other organisms. These animals have a right side and a left side, and a single cut would divide the animal into two mirror image halves. There is also a dorsal (back) side, ventral (belly) side, and anterior (head) and posterior (tail) ends.
-Cephalization is the concentration of sensory equipment at one end (usually the anterior, or head end) of an organism.
-Acoelomates, such as flatworms, have no cavities (body cavities) between their alimentary canal and the outer wall of their bodies.
-Pseudocoelomates are triploblastic animals (animals with three tissue layers) with a cavity formed from the mesoderm and endoderm.
-Coelomates possess a true coelom. This is a body cavity filled with fluid, and this space separates an animal’s digestive tract from the outer body wall. The coelom forms from tissue derived from mesoderm only.
Functions of the body cavity: See Figure on previous page
1. Cushion suspended organs.
2. Act as a hydrostatic skeleton
3. Enable internal organs to grow and move independently.
Protostomes and Deuterostomes differ in three major ways: See Figure below to summarize the differences:
As you study the figure on the following page consider: Animals in which phylum
1. Lack symmetry and true tissue?
2. Show radial symmetry and are diploblastic?
3. Have three tissue layers but lack a body cavity?
4. Show bilateral symmetry and have a pseudocoelom?
5. Have a true coelom and are protostomes?
6. Have a true coelom and are deuterostomes?
If you can group the animal phyla based on the characteristics above, you are ready for the most common type of animal questions you will see on the AP Biology Exam!
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Invertebrates
You Must Know
1. The traits from the figure on the previous page which are used to divide the animals into groups.
2. Examples of unique traits for each phyla discussed.
3. The evolution of systems for gas exchange, respiration, excretion, circulation and nervous control.
General Information
Invertebrates are animals that lack backbones. Ninety-five percent of all know species are invertebrates. Before we begin to look at them, remember that taxonomy is in flux due to the new molecular data. An outline of animal diversity and classification follows.
Subkingdom Parazoa: (Lacking True Tissues)
-The sponges, once placed in a single phylum, Porifera, are now in the phyla Calcarea and Silicea. The main characteristics of all sponges.
-Sponges are sessile (anchored to the substrate) and lack true tissues. They are diploblastic (their body consists of only two layers of cells).
-Sponges have no muscles or nerves. The body of a sponge looks like a sac with holes in it. Water is drawn in through the pores into the spongocoel and flows out through the osculum through the movement of the flagellated choanocytes.
-Spicules comprise a skeletal framework.
Subkingdom Eumetazoa: (Animals with true tissues)
-Radially symmetrical animals
--All animals except for the Parazoa belong to the clade Eumetazoa, they are animals with true tissues
a. Members of Phylum Cnidaria exist in polyp (vase-like, like a sea anemone) and medusa (like a jelly fish) form.
b. They have radial symmetry, a central digestive compartment known as a gastrovascular cavity, and cnidocytes (cells that function in defense and the capture of prey). Examples of cnidarians are hydras, jellyfish, and corals.
Bilateral symmetrical animals
1. Acoelomates (animals without a body cavity)
-Phylum Plathelminthes (flatworms) Planaria, Tapeworms…
+Flattened bodies with cephalization (sense organs on the anterior end)
+Excretion by flame bulbs and protonephridia
+No specialized organs for gas exchange or circulation
+Gastrovascular cavity with a single opening.
Pseudocoelomates
-Phylum Nematoda (round worms)—Ascaris and C. Elegans
+Cylindrical bodies with tough cuticle
+Complete alimentary canal; no circulatory system
Coelomates
-Phylum Mollusca (Soft-bodied animals) Snails, clams, squids….
+Muscular foot for movement, visceral mass containing most organs, and a mantle, which secretes a shell
+Open circulatory system. This means that the circulatory fluid (hemolymph) is not always contained within vessels but sometimes circulates through body sinuses called the hemocoel.
+Excretion by nephridia
+Classes include Polyplacophora (chitons), Gastropoda (snails and slugs), Bivalvia (clams and oysters), and Cephalopoda (squids and octopuses)
-Phylum Annelida: Segmented Worms (Earthworms and Leeches)
+Internal and external segmentation
+Excretion by metanephridia in each segment
+Closed digestive system with specialized regions (the crop, gizzard, esophagus, and intestine)
+Brainlike central ganglia with a ventral nerve cord
+Closed circulatory system
Phylum Arthropoda: Jointed legged animals (Insects, arachnids, crustaceans)
+Exoskeleton of chitin, which must be molted to grow
+Jointed appendages
+Open circulatory system
+Various organs for gas exchange including gills, book lungs, tracheal systems
+Ventral nerve cords
+Insects undergo metamorphosis during development.
---Incomplete metamorphosis: egg, nymph, adult (grasshoppers)
---Complete metamorphosis: egg, larva, pupa, adult (butterfly)
Deuterostomia
-The clade Deuterostomia contains a diverse array of organisms, from sea stars to chordates. All have radical cleavage and share common developmental processes. There are two main phyla:
+Phylum Echinodermata (Spiny-skinned animals) Examples: starfish…
--Larvae have bilateral symmetry; adults radiate from center—often five spokes.
--Have a thin skin covering an exoskeleton
--Have a water vascular system. This is a network of internal canals that branch into tube feet used for moving, feeding, and gas exchange.
Phylum Chordata includes two invertebrates subphylums.
Vertebrates
You Must Know
1. The four chordate characteristics
2. Traits which distinguish each of the following groups: Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Bird, and Mammalia.
3. Adaptations the allowed animals to move onto land.
4. How the three classes of mammals differ in their reproduction
Concept: Chordates have a notochord and a dorsal, hollow nerve cord
-Vertebrates derive their name from the vertebrae, a series of bones which make up the backbone. In the majority of vertebrates, vertebrae enclose the spinal cord and have assumed the roles of the notochord.
-Vertebrates are members of the phylum Chordata.
-There are four characteristics of all chordates. Note that some of these are only present during embryonic development
1. A notochord—a long, flexible rod that appears during embryonic development between the digestive tube and the dorsal nerve cord. This is not the spinal cord or vertebral column! These are often confused.
2. A dorsal, hollow, nerve cord formed from a plate of ectoderm that rolls into a hollow tube. Recall that other phyla you have studied such as annelids and arthropods, had a ventral nerve cord.
3. Pharyngeal clefts—grooves that separate a series of pouches along the side of the pharynx. In most chordates (but not tetrapods, the critters with four legs), the clefts develop into slits that allow water to enter and exit the mouth without going through the digestive tract.
4. A muscular tail posterior to the anus.
-Lampreys are the oldest lineage of vertebrates. They are jawless parasitic fish with a skeleton of cartilage.
Concept: Gnathostomes are vertebrates that have jaws
-The jaws of vertebrates evolved from the modification of the skeletal parts that had once supported the pharyngeal (gill) slits.
+Class Chondrichthyes have flexible endoskeletons composed of cartilage, possess streamlined bodies, are denser that water, and will sink if they stop swimming. Some examples are sharks and rays.
+Class Osteichthyesare the bony fishes; these are the most numerous of all vertebrate groups. They have a bony endoskeleton, are covered in scales, and possess a swim bladder from buoyancy control. Some examples of trout and salmon.
Concept: Tetrapods are gnathostomes that have limbs and feet
Class Amphibia members include frogs, toads, salamanders and newts
+Gas Exchange can occur across their thin, moist skin, though many members have lungs.
+Some, such as frogs, have an aquatic larval stage with gills and metamorphosis to an adult stage with lungs.
+They have external fertilization and external development in an aquatic environment. Eggs lack a shell.
+As larvae, amphibians have a two-chambered heart (one atrium, one ventricle), while the adult stage generally has three chambers (two atria, one ventricle)
Concept: Amniotes tetrapods that have a terrestrially adapted egg