Chapter 15: Prokaryotes and Protists The book lumps these VERY DIFFERENT organsims together, simply because they are small, or microscopic Bacteria Archae Protista Major episodes in the history of life Do not memorize these dates, but understand that the timeline is based on fossil and molecular evidence What do you notice? When did Pangaea form? Major episodes in the history of life When is there evidence of the first prokaryotic organisms? Eukaryotic? What is going on here? What can be said about animals, plants and fungi??? Prokaryotes Prokaryotes are diverse and are everywhere, in great numbers! No nucleus or membrane bound organelles 1. Bacteria 2. Archaea Factoid: The number of bacteria in one human s mouth is greater than the total number of people who ever lived. Prokaryotes Bacteria: are classified by their shapes Cocci (spheres), Bacilli (rods) and Spirochetes (spirals). Important decomposers in an ecosystem, also have symbiotic relationships with other organisms, and can cause disease Archaea: similar in shape and size to bacteria, but inhabit extreme environments Thermophiles: heat (have we seen one of these before?) Halophiles: salt Methanogens The prokaryotes demonstrate a wide variety in how they eat or in their nutrition 1
Moving right along to the Protista Protista is the earliest eukaryotic domain Infolding of the plasma membrane and endosymbiosis likely resulted in the first eukaryotic organisms What was endocytosed? Protistans represent a diverse group at the crossroads to all the other Kingdoms Most protists are unicellular, but some are mutlicellular. Some are photsynthetic, some ingest their food, while some absorb nutrients (like fungi) All protists are aquatic, or are dependent on water for survival Protista Diversity -Protozoan (animal-like protists, heterotrophs) Amoebas Flagellates Ciliates -Slime Molds (get food via absorption) -Plant-like protists Euglenas Dinoflagellates Diatoms Green algae Seaweeds: Green, Red, Brown Oh, yeah, I saw a bunch of these protists in the pond water!! From Protists to Plants Moving right along! Green algae are the ancestors to all plants Who, ME? Wow I feel so important! Charophyceans 2
475 million years ago, shallow seas experiences seasonal droughts Envision multicellular, photosynthetic algae living near the shore of lakes, ponds, etc. Natural selection would favor those algae that could withstand occasional drying out Gametes and embryos are particularly sensitive to dessication **Gametangia formation** Gametangia are specialized structures in which gametes and then embryos develop A little bit more about about gametangia For algae, surrounding water ensures gametes and developing offspring stay moist Water also provides dispersal mechanism Plants, however keep gametes/offspring from drying out in the air (so do animals, think about it!!) The move from water to land Plants, by definition are multicellular, photosynthetic organisms with terrestrial adaptations In addition to gametangia, what adaptations would be helpful, if one were to survive on land? The move from water to land Or, what is different about living on land versus water? Where is water? Where are nutrients? Plants have been very creative! Symbiotic set up at roots with fungi! Vascular tissue Xylem, phloem Waxy covering for leaves (cuticle) Lignin (for strength) Stomata Pollen Seeds, etc. Major steps in plant evolution coincide with structural adaptations to living on land What adaptations do you see ocurirng at each major fork in the phylogenetic tree? 3
The 4 major branches of plants One important, early adaptation Bryophytes (mosses) Seedless, vascular plants (ferns) Gymnosperms (Conifers,etc) Angiosperms (flowering plants) Plants and fungi made a pact Fungi help plants with water absorption from the ground Plants throw fungi a bone (some sugar!) Beautiful example of a mutualistic, symbiotic relationship Mycorrhizae Bryophytes (mosses) What can you tell me about mosses? Where do you find them? What do they look like? Seedless, vascular plants (ferns) What can you tell me about ferns? What do they look like, where do they live? Time for climate change! Earth cools down and dries up. Harsh winters ensue Hmmmm, which seedless vascular plants will be the most successful? 4
Gymnosperms (conifers) Pines, firs, spruces, junipers, cedars,redwoods Oldest organisms on earth! Evergreens What is special about their leaf shape? Why do you think that might be? Gymnosperms (conifers) Leaf shape and covering Airborne pollen from male cone travels to ovule at the female cone Fertilization NOTE: Pollen is dispersed by wind, not water Cells that become sperm!! Gymnosperms (conifers) Pollen (containing male gametes) land on ovule containing female gametes Fertilization! (n + n = 2n) Embryo develops into seeds, while partially embedded in parent plant What is a seed? A seed is a plant embryo (2n), and food for the embryo within a protective coat food Water resistant coat Finally, the Angiosperms The flowering plants Their major adaptation is the flower! 250,000 species, provide us with flowers, fruit, vegetables, corn, cotton, rice, etc, Most angiosperms rely on insects or animals to move pollen from male to female plant organs Your e welcome, it was nothing. In the right environmental conditions, seeds can germinate and become a new plant..but you knew that! 5
What is a flower? Pollen landing on stigma (think sticky) Note that ovule is totally surrounded and protected by the ovary Embryo Fertilization at ovule! Seed surrounded by ovary Thick ovary=fruit, note seed inside What is a flower? What is the function of fruit?? In brief, pollen lands on stigma Pollen extends a tube, down towards ovary, deposits sperm at ovule Ovary is protective chamber around an ovule where embryo develops The whole ovule develops into a seed, and the seed is fully enclosed in the ovary Fruit is a thick ovary wall, that surrounds seeds! fruit Plant evolution in 30 seconds Plants evolved from green algae. Major adaptations to land characterize the plant family Almost all plants have a symbiotic relationship with fungi (mycorrhizae) 1. Gametangia and cuticles (Bryophtes: Mosses) 2.Vascular Tisssue (Seedless vascular plants: Ferns) 3.Pollen and Seeds (Gymnosperms: Conifers/Evergreens) 4.Flower and further protection of developing seed in an ovary (Angiosperms) seeds Plant evolution in 30 seconds DON T memorize this!!!! small For all of these, the organism that we readily SEE is 2n, diploid. The haploid (n) part of the plant is the reduced (in size) reproductive structures. big 6
Fungi Fungi are single celled or multicellular organisms that obtain nutrients by absorption (heterotrophs) They secrete digestive enzymes into their environment, and then absorb what they can Fungi (along with bacteria) are important decomposers of any ecosystem Hyphae are branches of cells Mycelium is a mat of tangled hyphae They have a cell wall made of chitin and can digest cellulose! Don t worry about fungal reproduction!!! 7