Land Plants Bio 114 (Science, Dr. Hyman, Organisms)
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This 12 page Class Notes was uploaded by Morgan Sawyer on Friday November 13, 2015. The Class Notes belongs to Bio 114 (Science, Dr. Hyman, Organisms) at James Madison University taught by Dr. Oliver Hyman in Fall 2015. Since its upload, it has received 14 views. For similar materials see Biology of Organisms (Bio 114) in Biology at James Madison University.
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Date Created: 11/13/15
Bio114 Lecture Notes week of November 9, 2015 Overview: Why does Meiosis exist? - The paradox of sex - The purifying selection hypothesis - The changing environment hypothesis Protists - What makes something a protest? - Why care about Protists? - How do they reproduce? o Life cycle diversity in Protists - Protists are a type of eukaryote How does each organism reproduce? - Bacteria and archaea are by binary fission - Animals, Plants, and Fungi are both asexual and sexual Why is sex such a rare trait? The Paradox of Sex - Asexual reproduction is more efficient because every individual can produce offspring - All this being equal, sexual reproduction puts organisms at a disadvantage because they do not multiply as efficiently as asexual organisms - Asexual reproduction is much more efficient in making copies of themselves which increase their fitness - “Males are worse than useless”… true because they slow down reproduction So, why does sex exist then? - Sexual reproduction MUST produce some sort of advantage that asexual reproduction does not: o Hypothesis: The purifying selection hypothesis The changing environment hypothesis Purifying Selection Hypothesis - Sex removes bad genes - In mitosis the exact genetic replica’s = “bad” mutations/genes that will be inherited by all offspring of sexual parents. o So the bad gene is continually passed along o Less fit = fewer offspring - In meiosis unique gametes = “bad” mutations/genes NOT inherited by all offspring = competitive advantage o More fit = more offspring o Sex can help population increase fitness by decreasing the changes of inheriting that bad gene Changing-Environment Hypothesis - Offspring that are genetic clones of their parents are unlikely to thrive if the environment changes - Pathogens evolve new ways to infect the host = changing environment - If no sex were to occur there would be no genetic variation so the pathogen would fully be able to take over resulting in the death of the host Evidence for Changing Environment Hypothesis Host - Hypothesis: in environments where pathogens are evolving and are present sexual reproduction by outcrossing is favored - Roundworm: can self or cross fertilize (outcross) - Outcrossing > genetic diversity - Predicts that there is more outcrossing when pathogens are present Protists - What makes something a protist? - Why care about protists? - How do they reproduce? o Life cycle diversity in protists What is a protist? - Any eukaryote that is not a plant, animal or fungus - Most diverse group of eukarya o Uni- or multicellular o Diverse life-cycles o Diverse metabolisms (hetero & photo) o Mobility o Have a nuclei and membrane bound organelles - Tend to live in environments surrounded by water (wet soil, water, other organisms) - Form a paraphyletic group Why care about protists? 1. Ecological significance a. Food chains b. Carbon sinks 2. Agricultural/Economic significance a. Crops, forestry, and fishery pests 3. Evolutionary significance: a. Protists teach us a lot about eukaryotic evolution and how plants and animals evolved 4. Public Health Significance a. Malaria and other human pathogens/parasites Ecological Importance of Protists - Important carbon “sinks” vs. CO2 accumulation in the atmosphere o CO2 is fixed from the air o Eventually C in organisms derives from fixed CO2 sinks to the ocean floor o Carbon is trapped forming rock or petroleum Stops CO2 from leaking back into the atmosphere = carbon sink - Protists take in as much CO2 as all land plants combine! Protists: Agriculture/Economy - Potato Famine - Wiped out the entire potato crop in Ireland in one week - Protists are big in agricultural roles Haploid vs. Diploid Dominate Life Cycle - Human’s are diploid dominate - The only place they are haploid is the sperm and the egg In an animal lifecycle: - The diploid life stage is multicellular - The haploid life stage is unicellular - The gametes are produced by meiosis - Most of the lifecycle is spent in they diploid phase = diploid dominate In contrast, most protists are HAPLOID DOMINATNT – they spend the majority of their life in the haploid phase/life stage Protists and Public Health Plasmodium falciparum (Malaria) is an excellent example of haploid dominate life cycle - Spends most of its life in haploid form (n) Why does this matter? (11/11 Lecture Notes) - Understanding the lifecycle helps us treat the disease/beat the pathogen - Malaria is a haploid dominate cycle - The benefits of targeting life stages in humans vs. mosquitos: o Life stages in humans = mitosis = cause sickness, influences transmission o Life cycle in mosquitos = meiosis = genetic variation - The benefits of targeting mitosis vs. meiosis: o Mitosis = the number of malaria parasites in human = effects sickness and likelihood of transmission o Meiosis = genetic variability of malaria = potential to evolve traits to avoid treatments - How might this influence targets for treatments? o Goal: stop disease symptoms reduce destruction of blood cells = reduce mitosis in human o Goal: reduce the ability of malaria to evolve new traits to avoid treatments reduce meiosis in mosquito Important things to look for in Plasmodium Life Cycle - Diploid phase is in the mosquito during zygote phase (sperm and egg) - The Haploid phase takes place everywhere else in the human and mosquito - Fertilization only occurs in the mosquito - Mitosis takes place in every stage except after fertilization - Meiosis only takes place after fertilization - Variation is introduced only in meiosis (the rest is identical because of mitosis) - Mitosis increases the number of malaria parasites in the human blood steam - Rates of mitosis directly affects the levels of malaria parasites in the human blood stream - Meiosis introduces more genetic variation into the malaria population than mitosis - Higher rates of mitosis will increase the change of malaria being transferred from humans to mosquitoes and vice versa - Higher rates of meiosis will help the malaria parasite evolve to avoid treatments Green Plants (green algae and land plants) Why care about green plants? - Provide us with oxygen - Trees eat out CO2 - Able to grant us with food products (chips, wheat) - Paper products - Plants act as the Brita water filters… they filter out the bad water, clean it, absorb it, and then release it into the atmosphere that is potable What is a green plant? - Member’s of Plantae lineage of eukaryotes - Include Green algae and land plants - All members of Plantae are phototrophic eukaryotes with chloroplasts - Some members of Plantae are protists - Green plants are a monophyletic group - Green plants probably have Synapomorphy that are unique to this group RECALL: If there is a monophyletic group you’ll always have a Synapomorphy Green Algae - Uni and multicellular - Most aquatic - Photosynthetic o Chlorophyll a and b - Green plants are monophyletic - Green algae are paraphyletic - Since all land plants share a single common ancestor this tree supports the hypothesis that was only one successful transition from water to land in plants - The nonvascular plants are the least derives group of land plants - Vascular tissues evolved once - Seeds evolved once - Seed plants likely evolved from a non-vascular plant, which evolved from a nonvascular, which evolved from a green algae, which evolved form a protist Land Plants - Multicellular - Mostly terrestrial - Photosynthetic o Chlorophyll a and b - Three main groups o Non-vascular o Seedless vascular o Seed plants Gymnosperms Angiosperms When did the first land plants evolve? - 500 mya - Based on fossil record - Land plants were the first multicellular organisms that could survive completely exposed to air - Helped enable animals to adapt to terrestrial lifestyles - Before land plants oceans had a huge about of diversity and the land had almost nothing other than prokaryotes and single celled protists Why did it take so long to evolve? - Ozone had to be present in the atmosphere to protect larger multicellular organisms from UV radiation - Oxygen levels had to hit the threshold to keep enough oxygen in the atmosphere to allow there to be any life form on the surface How did land plants evolve? - Fossil and genetic evidence tells us land plants evolved from aquatic green algae - Therefore some aquatic green algae developed traits that helped them to survive on land and reproduce better, passing on “dry- land” genes Advantages of being able to survive on dry land: - Oceans are getting overcrowded so have to compete for sunlight, O2, CO2, and inorganic nutrients - No multicellular life on land yet so no need to compete to sunlight, O2, CO2, and inorganic nutrients What adaptations would aid survival on dry land if you were a plant used to living in the water? - The transition to life on land: o Controlling water loss o Surviving intense sunlight o Growing upright in air o Reproducing without water o Using animals to carry pollen and seeds Overview of “Land Plant” Adaptations FIRST: - Adaptations that arose in ancestry’s of land plants (green algae) but allowed for the transition to land to begin NEXT: - Adaptations found in all land plants (but no ancestors) required to live on land - Adaptations found only in some land plants that allowed plants to be even less dependent on living wet areas of land - Further adaptations of these dry adapted plants reacted to improving dispersals and genetic variation Land Plants ~ Lecture Notes 11/13/15 Characteristics: - Includes seedless vascular plants, nonvascular plants, and seed plants - Are a monophyletic group - Evolved from green algae like ancestor - All have nonvascular tissue - Gained access to more resources like light and minerals by moving to land - First adaptations that arose in aquatic ancestors of green plants and allowed for the transition to land to begin Dry-land adaptations probably first arose in tidal zones - New traits in ancestor of green plants allowed them to grow in more successfully at water’s edge o This allowed for less competition with other plants, which allowed increased survival therefore increasing fitness where it was able to pass on its traits to its offspring This was because they were able to survive in tidal zones when no one else could o Which allowed natural selection for “dry adapted” plants - Chlorophyll b was presented in ancestors of green plants and aided in the transition to land What adaptations would aid in survival on dry land if you were a plant used to living in the water? - Need to gather light for photosynthesis - Light is different under deep vs. shallow water vs. on land o Some photosynthetic pigments are better at absorbing light on land vs. under water o Light availability differs with depth so the longest rays are the most advantageous to aquatic photosynthetic algal cell Different kinds of chlorophylls absorb different wavelengths of light - Most photosynthetic organisms have chlorophyll A o Chlorophyll A evolved first, in bacteria - Chlorophyll A is best at absorbing light through water - Chlorophyll B is present in green algae. o Improves light absorption in shallow water and on land o Evolved from A o Bacteria doesn’t have it o Advantageous and key to being on land - Green algae and land plants have chlorophyll a and b, most of their prokaryote and protist ancestors only have chlorophyll a Transition to Land (Part 1): How did plants adapt to dry conditions with intense sunlight? - Main obstacles to surviving on dry land: o Water loss (from evaporation) o Standing upright o Getting water from soul to rest of plant - Solutions: o Cuticle and stomata o Vascular tissue o Vascular tissue Respective to main obstacles Preventing water loss - Problem: o On land plant cells can lose a ton of water by evaporation o Gets released and sucked out of the plant - Solution: o Waxy Cuticle – reduces water loss from plant cells Cuticle - Acts as a sealant - It is a layer of wax/fat (nonliving) covering epidermis and secreted by epidermis o Epidermis is a single later of cells covering the entire plant body - Works as a sealant covering the above-ground part of plants and dramatically reduces water loss to surrounding air - To reduce water loss in hot and/or dry areas, thickened cuticle Downsides to cuticle: Reduces CO2 intake - It is a trade off because it becomes harder for the CO2 to enter in the cuticle when waxy while with no waxy cuticle it becomes easy to diffuse across the membrane Solution to reduced CO2 intake - STOMATA o Acts as trap doors in the epidermis/cuticle that enable CO2 to get in o Stoma is an opening (pore) surrounded by guard cells o Hole in the bottom of the epidermis that allows for CO2 to enter Guard Cells can Change Shape - Trade off because water can get out of the stomata if its open to long - You want the stoma to be open when high water is available and closed with low water is available o If a lot of water is available it doesn’t matter if it’s loosing water it just wants CO2 o In general, having stomata open in the night instead of daytime would reduce water loss o In general, more stomata should be open in the day because the Calvin Cycle requires CO2 and can only occur when the light-dependent reactions of photosynthesis are producing ATP - TAKE HOME: together, cuticle and stomata allow land plants to keep photosynthesizing without drying out o Helped plants move onto land o Movement of land couldn’t have happened without the stomata and cuticle Why is standing upright important? - Reduces competition if you are able to stand up right - They get better access to light What does a plant need to grow tall? - A way to get water from soil to parts of plant not in direct contact with water - A way to get sugar from sites of photosynthesis to other parts of plant (ex. Trunk doesn’t get light) - Stronger structural supports - VASCULAR TISSUE – gets water, sugar, and provides support Adaptation that evolved in vascular plants to support height - Vascular tissue – transports water and sugar through taller plant - Lignin – strongest part of vascular tissues, provides structural support Where is the vascular tissue? - Found in bundles running through roots, stems, and leaves Two types of vascular tissue forming continuous pathway in center of rooms and shoots: - Xylem – carries water and dissolved nutrients from soil/roots up to rest of plant - Phloem – carries sugars and other substances from and up from source to sink (leaves to roots and roots to leaves) How is water moved through the xylem from the roots to the leaves? - It sucks o Uses capillary action of water What causes the pull of water up the plant? - Warm air causes water to evaporate out of stomata in leaves at top of plant - This results in a lower pressure at the top of the plant - Water moves from high to low pressure (roots to shoots). Only works because of cohesive and adhesive properties of water Result of transpiration - Delivery of water and dissolved minerals from roots to leaves - Cools the plant - Entirely driven by the suns energy and cohesive properties of water o No ATP is requires from the plant Sugar transport is more complicated 1. Sugars and other nutrient move up and down the plant through phloem (from source to sinks) 2. Driven by concentration gradients of sugar between different cells play a role (aka facilitated and active transport across cell membranes) ACTIVE TRANSPORT: which means sugar transport can require ATP
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