Chapter 29 Plant Diversity 1 How Plants Colonized Land Concept 29 1 Land plants evolved from green algae Morphological and Molecular Evidence Chapter 29 Plant Diversity 1 How Plants Colonized Land 1 Remember algae are photosynthetic protists Green algae called charophytes are the closest relatives of land plants Plants are multicellular eukaryotic photosynthetic autotrophs as are brown red and certain green algae Plants have cell walls made of cellulose so do green algae Dinoflagellates and brown algae Plants have chloroplasts with chlorophyll a and b as do green algae Euglenids and a few Dinoflagellates Charophytes share four distinctive traits with land plants 4 reasons why they are the closest relative of plants Rings of cellulose synthesizing proteins Distinctive rings of proteins in the plasma membrane that synthesize the cellulose microfibrils of the cell wall Peroxisome enzymes Structure of flagellated sperm Formation of a phragmoplast An enzyme that help minimize the loss of organic products resulting from photorespiration The structure of the sperm closely resembles that of charophyte sperm A group of microtubules known as the phragmoplast forms between the daughter nuclei of a Adaptations enabling the move to land dividing cell Natural selection favors individual algae that can survive periods when they are not submerged in water In charophytes a layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out Derived traits of plants Many of the adaptations that appear to have emerged after land plants diverged from their algal relatives facilitated survival and reproduction on dry land Alternation of Generations and Multicellular Dependent Embryos The life cycles of all land plants alternate between two generations of multicellular organisms gametophytes and sporophytes The multicellular haploid gametophyte produces the eggs and sperm via mitosis of haploid gametes that fuse during fertilization forming diploid zygotes Mitotic division of the zygote produces a multicellular diploid sporophyte Meiosis in a mature sporophyte produces haploid spores reproductive cells that can develop into a new haploid organism Placental transfer cells enhance the transfer of nutrients from the parent to embryo through elaborate ingrowths of the wall surface Embryophytes are the multicellular dependent embryo of land plants Walled spores produced in sporangia Plant spores are haploid reproductive cells that can grow into multicellular haploid gametophytes by Chapter 29 Plant Diversity 1 How Plants Colonized Land 2 The polymer sporopollenin makes the walls of plant spores tough and resistant to harsh Sporangia are a multicellular organ that produces the spores Sporocytes are diploid cells within the sporangium that later become haploid spores via mitosis environments meiosis Multicellular Gametangia Gametangia are gametes produced within multicellular organs Archegonia are female gametangia Antheridia are male gametangia Each egg is fertilized within the archegonium where the zygote develops into an Apical Meristem embryo Though plants cannot move from place to place their roots and shoots can elongate increasing exposure to environmental resources The growth in length is sustained throughout the plant s life by the activity of apical meristem localized regions of cell division at the tips of roots and shoots Outer epidermis protects the body and various types of internal tissues The epidermis in many species has a covering the cuticle which consists of wax and other polymers The cuticle acts as waterproofing helping prevent excessive water loss from the aboveground plant organs while also providing some protection from microbial attack Early land plants lacked true roots and leaves They formed symbiotic associations with fungi similar in structure to beneficial associations observed today Mycorrhizal fungi form extensive networks of filaments through the soil enabling them to absorb nutrients more The fungi transfer nutrients to their symbiotic plant partner a benefit that may have helped plants without Many land plants produce molecules called secondary compounds products of secondary metabolic pathways side branches off the primary metabolic pathways that produce the lipids carbohydrates amino acids and other compounds between plants and fungi effectively than a plant can on its own roots to colonize common to all organisms The Origin and Diversification of Plants One way to distinguish groups of plants is whether or not they have an extensive system of vascular tissue cells joined into tubes that transport water and nutrients throughout the plant body Present day plants have a complex vascular tissue system called vascular plants Plants that do not have an extensive transport system liverworts mosses and hornworts are described as nonvascular plants called bryophytes species Chapter 29 Plant Diversity 1 How Plants Colonized Land 3 Bryophytes share some derived traits with vascular plants such as multicellular embryos and apical meristems while lacking many innovations of vascular plants such as roots and true leaves Vascular plants can be categorized further into smaller clades lycophytes and pterophytes These plants lack seeds which is why collectively the two clades are often informally called seedless vascular plants Seedless vascular plants are paraphyletic Groups of seedless vascular plants are sometimes referred to as a grade a collection of organisms that share a key biological feature Members of a grade do not necessarily share the same ancestry A third clade of vascular plants consists of seed plants which represent the vast majority of living plant A seed is an embryo packaged with a supply of nutrients inside a protective coat Seed plants can be divided into two groups gymnosperms and angiosperms based on the absence or presence of enclosed chambers in which the seed matures Gymnosperms are grouped together as naked seed plants because their seeds are not enclosed in chambers Angiosperms are a huge clade consisting of all flowering plants The seeds develop inside chambers called ovaries which originate within flowers and mature into fruits Concept 29 1 Summary land plants evolved from green algae Morphological and biochemical traits as well as similarities in nuclear and chloroplast genes suggest that charophytes are the closest living relative of land plants A protective layer of sporopollenin and other traits allow charophytes to tolerate