Bio 108 : How are living organisms classified?
Is an unfamiliar organism a plant, an animal or neither?
What are the identifying characteristics of animals and plants? Why were fungi considered plants for many years?
1. Taxonomy-Classifying organisms. Scientists try to put related organisms together based on common ancestry.
Taxonomy schemes of the past
a. 1960’s--Up unitl 1960, most scientists classified all life as plant or animal.
Plants Animals
b. Robert Whitaker was an important taxonomist
1) Early Whitaker scheme based on mode of nutrition. Photosynthesis is a process of building food.
Plants Animals Fungi
Photosynthesis Living food Dead food
2) 5 category scheme of Whitaker
Plants
Animal
Fungi
Protista (complex cell type, single-celled organisms)
Monera (simple cell type, single-celled organisms)
2. Three domain system (p. 140)
In the early 1990's, Carl Woese discovered a cell type so fundamentally different from other cells, that life's taxonomy was revised to reflect that there are 3 basic cell types, or domains.
Eukarya Bacteria Archaea
a. The domain Eukarya are broken down into the categories (Kingdoms) of
Animalia Plantae Fungi Protista
b. The Domain Bacteria consists of most single-celled organisms on the planet and is made of a simple cell type called a prokaryote.
c. The Domain Archaea are an ancient line of single-celled organisms that are poisoned by oxygen. They survive only in extreme environments like the hot springs at Yellowstone National Park.
3. Photosynthetic organisms (make their own food from non-living material)
a. Most photosynthetic organisms are in the domain Eukarya and kingdom Plantae.
b. The domain bacteria contains some photosynthesizers
Cyanobacteria (also called blue-green) algae such as Oscillatoria or Spirulina
Simple cell type. Starts the food chain in much of the ocean
c. The domain Eukarya and Kingdom Protista also contain many photosynthesizers.
Green algae such as Spirogyra with its spiral patterned chloroplasts. Mostly freshwater species. Algae gave rise to land plants 400 million years ago.
Brown and Red algae: Ocean forms used to make carageenan and algin, thickeners in milkshakes, pudding, ice cream. Sushi wraps.
Euglena: A single-celled organism which is both photosynthetic and motile.
4. Plant kingdom: Here are some of the major divisions (or phylum) in the plant kingdom.
Division or phylum is the next taxonomic level below kingdom. You will see both terms used with plants.
Think of a division (or phylum) as being a basic body plan. For example, in the animal kingdom, the majority of species are in the phylum Arthropoda. Arthropods are characterized by segmented body parts, jointed legs and an exoskeleton. There are four evolutionary lines in this phylum which can be grouped into different classes, a lower level still. 1) insects 2) spiders 3) crabs and 4) trilobites (all extinct). There are more species of insects known (over 1 million) then all the other Plant and Animal species put together!
How many different phyla are there? It depends on who you ask, but an estimate would be:
Kingdom Animal: 33 phyla
Kingdom Plant: 12 divisions (or phyla). The plant divisions are shown in Table 9.1 p. 141
a. Division Bryophyta: Mosses, no vascular system (No water transport)
Spores not seeds. Spores are single-celled reproductive structures. They lack stored food. Like seeds, spores are able to resist harsh, environmental conditions and grow when conditions are favorable.
These are the first land plants. They arose about 400 million years ago. There are about 25,000 species in existence.
b. Division Pterophyta: Ferns differ from mosses since they are vascular plants, which transport water in veins. Why is this an advantage over mosses? 12,000 species exist. Spore producers.
Here is a picture of fern sori, the structure that produces spores.
c. Gymnosperms: There are 4 divisions of gymnosperms (naked seed plants). Recall that seeds contain an embryo (baby plant) and stored food surrounded by a hard, outer coat.
1) Division Cycadophyta. Sago palm, not a true palm, related to plants from dinosaur age
2) Division: Ginkgophyta. Ginkgo biloba, only surviving species. May help memory in Alzheimer’s. Scroll down this page for an overview of all plant divisions except for plants with true fruits, Magnoliophyta.
3) Division Gnetophyta. Genus Ephedra (Mormon tea)
4) Division Coniferophyta
Coniferophyta is the second most abundant plant division after the angiosperms. Much of the land area on Earth is covered with conifers such as the Pacific Northwest of the U.S.. Examples: Evergreen trees (pine, spruce, fir). Some will even grow in Mesa like Canary Island Pine.
d. Angiosperms: Flowering plants
Division Magnoliophyta: All 250,000 species of flowering plants are in this division. This is the most abundant plant division. Angiosperms have flowers which develop into fruits containing seeds. Only plants in this division have their seeds enclosed by the fruit.
5. Classification of a typical organism (see fig. 8.7 p. 134)
Common name: Human Corn plant Bean plant Kingdom Animal Plant Plant Phylum or Division Vertebrate Magnoliophyta Magnoliophyta Class Mammal Monocot Dicot Order Primate Commelinales Fabales Family Hominidae Grass Legume Genus Homo Zea Phaseolus species sapiens mays vulgaris
6. Binomial system (2 names) p. 124-126
Genus and species is the specific name of an organism. Developed by Carol Linnaeus in the 1700’s.
Species: a group of organisms that freely interbreed to produce fertile offspring. This definition works best for animals. Yet, even among animals closely related different species sometimes interbreed, for example, wolves and dogs. In plants, species lines are often more blurred than animals. For example, tangerines and grapefruits can interbreed as shown below.
Organisms in the same genus share many characteristics.
Example:
Orange=Citrus sinensis
Grapefruit=Citrus paradisi
Tangerine=Citrus reticulata
Tangelo=Citrus paradisiXCitrus reticulata
Exercise: Explain why the blurring of species lines is consistent with Darwin's concept of "descent with modification" (i.e. where do new species come from)?
Lecture Notes List Next Lecture
