Information about Mycorrhizae
- Benefit plant by increasing absorption of phosphorus, zinc, manganese, and copper
- Fungi benefit by receives carbohydrates and vitamins from the host
- Endomycorrhizae: penetrate root cells. Hyphae penetrate root tissue cells forming highly branched structures called arbuscules and occasionally swellings called vesicles.
- Arbuscules – associate w/ plasma membranes and are thought to aid transfer of materials between environment and cells by increasing surface area
- Ectomycorrhizae: surround the roots. A highly branched network of hyphae (Hartig Net) forms around the root epidermal and cortex cells.
Why does transpiration have to occur? What generic strategies have been developed to limit transpiration?
- The major route for water loss in plants is through the stomata, and there are about 12,000 stomata per square inch of leaf. The stomata cannot remain closed because CO2 is required to perform photosynthesis. Every time CO2 is let in via stomata transpiration occurs, thus transpiration is a necessary evil.
- Also transpiration is the basis for the TTCA model of water transport in plants.
- Plants have developed various strategies to try and deal with transpiration including trichomes, the cuticle, stomatal crypts in xerophytes, CAM plants, and most importantly guard cells.
What is the normal transpiration rate? Describe the specific ways that plants perform stomatal regulation.
- A leaf is kept from wilting by having a transpiration stream that flows at a rate of 75cm/min within xylem vessels. Guard cells control the photosynthesis/transpiration compromise (close stomata if rate is too high, open stomata if rate is too low)
- Stomata are controlled through various mechanisms including…
- Osmosis: K+ redistribution and water potential changes cause guard cells to swell and open when gaining water; “shrink” and close when losing water
- Blue light photoreceptor triggers ATP driven proton pumps which trigger the K+ influx as described above.
- Decrease in CO2 within air spaces
- Biological rhythms
What are the two methods of water transportation within a root (between/within)?
- Apoplastic: transportation through areas outside of the plant cells. Found in areas of the cell walls and dead tissues of the xylem.
- Symplastic: transportation through the cytoplasm of cells via that plant’s plasmodesmata.
Give information about the plant endocrine system, incl. mechanisms of action, types of cellular responses, and major hormone categories.
- Hormones (chemical messengers) function to coordinate growth & development and mediate response to external cues (affect division, elongation, gene expression, and differentiation of cells)
- Hormones are produced in a variety of locations, and are active even in small amounts (not used in their mechanisms, so they can continue to affect another cell)
- Hormones work by signal transduction pathways: ligand (substance that binds to a receptor), target tissue (tissue equipped with receptors specific to a particular ligand)
- Hormone sequence of action: reception, signal transduction, cellular response
- Examples of cellular responses: Altering gene expression (protein synthesis regulation), activating or deactivating enzymes (protein kinase enzymes), changing the properties of membranes (permeability to ions)
- Cellular response may differ based on hormone concentration, developmental state of tissue, interplay of two or more hormones, tissue type
- Major hormone categories: Auxins, Cytokinins, Gibberellins, Ethylene, Abscisic Acid
Auxin – Produced where? Function? Other information?
- Manufactured in apical bud meristem, young leaves, and seed embryo
- Major stimulator of shoot elongation, root growth (Callus tissue), Apical dominance, fruit development, and inhibition of fruit/leaf abscission
- Has been used to create seedless fruits
- Stimulates vascular cambium (secondary growth)
- Used to prevent pre-harvest drop of fruit (makes cells in the abscission zone less sensitive to ethylene)
- Functions in vascular tissue differentiation
- Synthetic auxins: (2,4-D) – herbicidal compound (mechanism unknown). Agent orange (South Vietnam)
Cytokinins – Produced where? Function? Other information?
- Synthesized in the roots and then transported via xylem
- Stimulates axillary bud production and lateral shoot formation (more roots -> increase cytokinin -> stimulates axillary buds -> more lateral branches)
- Delays leaf senescence (yellowing and eventual death)
- Can produce anti-aging properties, may work by inhibiting protein breakdown, stimulating protein synthesis, etc.
- Structurally similar to the purine adenine (a nitrogenous base)
- Work by stimulating cell division and regulation of cell differentiation (Promote cytokinesis)
Gibberellins – Produced where? Function? Other information?
- Produced in root and bud apical meristem, young leaves and embryos
- Functions in shoot elongation through division and cell elongation (causes growth in dwarf mutants)
- Stimulates fruit growth without fertilization (commercial use allows for seedless grapes)
- Signals seeds to break dormancy and to germinate (ex. water soaked into the seed -> release of GA).
Ethylene – Produced where? Function? Other information?
- Synthesized in most tissues in response to stress (especially in ripening fruits and/or leaf senescence)
- Promotes fruit ripening and abscission of fruit/leaves
- In fruit ripening, seems to play a role in promoting chlorophyll degradation, formation of other pigments, digestion of pectin (middle lamella), synthesis of sugars from a variety of other nutrients
- Leaf, flower, and fruit abscission (Ethylene triggers enzymes that break down cell walls in petiole)
Abscisic acid (ABA) – Produced where? Function? Other information?
- Produced by seed early during development, causes an increase in seed storage proteins
- Helps prevent early germination (corn mutants less responsive to ABA germinate while still on the cob)
- The rinsing of ABA from a seed helps trigger germination
- Water stress triggers ABA synthesis in mature leaves – leads to closure of stomata (therefore involved in regulation of transpiration)
What is a tropism? Describe the various tropisms
- Tropisms: growth response that curves the plant organ toward or away from stimuli (toward = positive, away = negative)
- Mechanism of tropisms: elongation of cells on OPPOSITE side of the organ
- Phototropism: curving of shoot towards light. Sensation of light is tied to the shoot tip, special blue light photoreceptor (cryptochrome). Function via auxin redistribution (migrates from light side to dark side of root tip, then to internode below which causes growth)
- Gravitropism: shoots grow against gravity (negative), roots growth with gravity (positive). Sedimentation of amyloplasts within cells used as an indicator of gravity for cells
- Thigmotropism: response to touch that allows roots to navigate around rocks, and tendrils to wrap around other structures. Cells touching surface slightly shorten, other side elongates.
- Movements in response to a mechanical stimulus: turgor movements (controlled by water efflux following ions), plants drop suddenly after touch. Venus flytrap; scientists unsure of how the mechanism works.
Define systematics. What is the goal? What criteria is used?
- The science of evolutionary history (naming / classifying an organism through evolution)
- The goal of systematic is to find all branches of the phylogenic tree of life
- Comparative anatomy, physiology, embryology, and comparative molecular techniques (eg DNA, RNA, protein) are used together in systematic and taxonomy.
Define taxonomy, describe its origins, current rules, and other information.
- Taxonomy: identifying, naming, and classifying a species
- Species: a group of organisms capable of interbreeding and creation of viable offspring (some exceptions)
- Developed initially by Carolus Linnaeus (1700s) it used polynomial naming (a brief sentence describing a species). This was replaced with the current binomial system; a generic name and a specific epithet (Genus Species). The generic name alone refers to an entire genera, but the specific epithet alone means nothing. Subspecies (varieties) may consist of 3 names.
- Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species. These are grouped to reflect phylogeny (proper ancestral history)
What is phylogeny? Describe the various groups that can be formed when classifying taxa.
- Phylogeny: (evolutionary history) characteristics of organisms are products of their evolutionary past. Studies in phylogeny result in diagrams (“family tree”).
- Monophyletic groups: created by looking for shared unique features among organisms.
- A monophyletic taxon contains ALL members who descended from a common ancestor (none are excluded)
- Natural taxa: taxa where all members have shared ancestry, and correctly reflect the ancestral past of that group.
- Artifical taxa: taxa that do not correctly reflect the ancestral past of that group. Can come in two forms; paraphyletic and polyphyletic
- Polyphyletic: taxa where members descended from more than one ancestral line, and may only resemble each other because of similar evolutionary pressure.
- Paraphyletic: A group that does not include one or more descendants of a common ancestor (one or more are excluded).
Describe the two approaches to phylogeny.
- 1: Looking at similarities and grouping according to the degree of similarity
- Cladistics: Looking for shared UNIQUE features.
Describe cladistics in detail.
- The goal is to understand the evolutionary relationships present among organisms.
- Focuses more specifically on shared characteristics that are unique (eg. Presence/absence of flowers)
- Cladograms are created in an attempt to show groups that share a common ancestor.
- CLADOGRAMS DO NOT IMPLY THAT A SPECIFIC GROUP EVOLVED INTO ANOTHER.
Give general information and statistics about prokaryotic organisms
- 90% of the total weight of living organisms in the sea are prokaryotic
- 1 gram of soil may contain 2.5 billion Bacteria
- 30% of feces weight is from Bacteria
- Prokaryotic cells are at least 3.5 billion years old
- Can exists in all locations (from ice wastelands to boiling hot springs) – very versatile
- They are the primary decomposers and photosynthetic operators for the earth’s ecosystems
- Their success is most likely related to their quick reproduction and metabolic diversity (can survive on almost anything)
- Archaea and Eubacteria are examples that represent two DIFFERENT evolutionary lineages
- Typical features of prokaryotes include lacking a nucleus and organelles, have a single circular chromosome, containing a plasmid (an extra chromosomal piece that can replicate independently of the cell’s chromosome), and containing ribosomes
Describe the structure of a prokaryote, including shapes.
- Plasma membrane: composed of a phospholipid bilayer that many contain important enzyme complexes like the electron transport chain of respiration
- Cell wall: 2 types in Eubacteria - Gram positive (retains crystal violet dye, has a thick layer of peptidoglycan) and Gram negative (does not retain crystal violet dye, has a thinner layer of peptidoglycan with an additional outer membrane). Walls of archaea do not contain peptidoglycan.
- Peptidoglycan:a protein/sugar material which links sugar chains with peptide bonds.
- All bacteria with a few exceptions (Mycoplasmas) are surrounded by a cell wall.
- Flagellum: does not contain microtubules and is not membraned.
- Fimbriae: short, rigid, and “spiky” they are theorized to provide anchorage
- Pili: acts as a tunnel between prokaryotes that functions in conjugation.
- 3 shapes: rod or bacillus (pleural bacilli) is stick-like, coccus (pleural cocci) is spherical, and spirillum (pleural spirilla) are long and curvy
Describe reproduction and gene exchange in prokaryotes.
- Binary fission: a type of asexual reproduction that produces clone populations, represented by the formula Nf = (Ni)2n where n is the generation # and N is the number of bacteria
- There is a large amount of mutants produced during binary fission which gives an evolutionary advantage through adaptability.
- Recombination (gene exchange) mechanisms allow genes to be passed between different bacteria
- Conjugation: the transfer of DNA across a pilus
- Transformation: DNA is absorbed from the environment
- Transduction: viruses move DNA between bacteria
Describe method of feeding for bacteria?
- Most are hetertrophic, but can be autotrophic
- Saprophytic heterotrophs: decomposers (sapro = rotten), most common
- Photosynthetic autotrophs: use chlorophyll pigments to gain energy from light
- Chemosynthetic autotrophs: oxidize various inorganic compounds (H2S) to make energy (don’t need light)
What is the global significance of bacteria?
- Ecosystem: Earth’s recyclers, Nitrogen fixation, Atmospheric gas production, decompositions of toxic substances
- Disease: human and plant disease (some are highly destructive)
- Commercial: antibiotics, vinegar, amino acids, enzymes, yogurt, etc