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Chapter 24.docx

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Wilfrid Laurier University
Tristan Long

Chapter 24 PlantsWe assume that all plants are photoautotroph but some plants are heterotrophic Heterotrophic plants can feed on neighbouring plants through a sharing of roots Plants can survive in areas where no animal could survive 241 Defining characteristics of land plants Land plants are eukaryotesAlmost all are photoautotroph use light as energy but not all are capable of photosynthesis Cell wall made of cellulose All plants sessilestationary Plant life cycle called alternation of generations life cycle Most animals diploid stage dominates life cycle and produces gametes sperm and egg which are the only things in a haploid stageshort lived until it fuses into the diploid stage Land plants have 2 multicellular stages in their life cycle oOne diploid one haploid oDiploid generation produces spores and is called sporophyte oHaploid generation produces gametes by mitosis and is called gametophyte Miosis forms haploid cells Miosis forms spores not gametes sperm and egg like in animalsSpores single haploid cells with thick cell walls Embryo new sporophyte generation is retained inside gametophyte tissue 24 2 The transition to life on land No plants in the beginning Solar radiation converted much of the oxygen into an ozone layer oLethal dosage of UV rays had kept organisms under waterCyanobacteria were first to adapt to intertidal zonesGreen algae is the ancestor of modern plants oHad cell walls store energy as starch have chlorophyll a and bBecause terrestrial environments pose very different challenges that aquatic environments evolution in land plants produced a range of adaptations crucial to survival Early plants were exposed to higher levels of harmful UV radiation and so gradually they were able to synthesize phenylpropanoids molecules that absorb UV lightConcept fix natural selection doesnt give organisms trying to adapt to the environment what they need The organism that has the trait is then able to reproduce and pass it downGreatest challenge plants had to get over was living on dry land Plants part of kingdom Plantae which has 10 phyla The earliest form had no cuticle to prevent water loss or enough tissue strength to allow them to grow upwards oMade them necessary to stay small and grow close to land oThese plants were poikilohydric meaning they have little control over their internal water contentand dont restrict water loss When moisture levels low they would dry out and when high they would increase meaning they were drought resistant because they could survive drying out Later on plants evolved to have cuticle and stomata pores in cuticle covered surface and so because of this could control water loss oAlso had watertransport tissues that provide support for upright growth Almost all modern day plants form symbiotic associations aka mycorrhizas with certain soil fungi oFungi colonizes the plants roots and grows in the soil beyond the root systemoThe plant provides the fungus with carbon and the fungus provides the plant with increasing amount of soil nutrients
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