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Class Diagram (Chapters 15- (Chapter 15 (analysis of genes and recombiant…

- - - - rhyniophytes
        
        have an epidermis and cuticle
        
        a cortex of parenchyma
        
        simple bundle of xylem comprised of tracheids with annular secondary walls
        
        earliest fossil of a vascular land plant was the cooksonia
        
        equal dichotomous branching
        
        both branches being equal size and vigor
        
        no leaves
        
        short cylinders
      - zosterophyllophytes
        
        most have smooth surface but others had enations
        
        grew as small bunches
        
        similar to rhyniophytes
        
        3 distinct ways it isn't
        
        xylem was an exarch protostele
        
        sporangia opened transversely along the top edge
        
        sporangia were lateral
        
        small herbs with no secondary growth
      - xylem structure of early vascular plants
        
        siphonostele
        
        occurs in ferns and seed plants
        
        pith is present in the center
        
        endarch prostele
        
        protoxylem is in the center and metaxylem differentiates on the outer edge
        
        center is solid mass of xylem with no pith
        
        this is called a protostele
    - - equinsetophytes
        
        monopodial growth
        
        main trunk, lateral branches, true leaves
        
        umbrella shaped sporangiophore
        
        sister to the ferns
      - ferns
        
        leaf trace diverges from the siphonostele
        
        leaves a small segment of vascular cylinder of parenchymna, called the leaf gap
        
        over 12000 species
        
        almost all are leptosporangiate ferns
        
        first appeared in the Devonian Period
      - monilophytes
        
        horsetail differs from other ferns
        
        woody plants
        
        lignophytes
        
        otherwise known as euphyllophytes
      - origin of megaphylls (euphylls)
        
        webbing
        
        the parenchyma that develops between telomes and even lower branches
        
        telomes
        
        ultimate twigs, those of last dichotomy
        
        sporophyll
        
        a sporangium-bearing, leaf-like structure
        
        evolution is summarized by telome theory
        
        leaves evolved from branch systems and are present in all seed plants, ferns, and equisetophytes
      - trimerophytes
        
        pseudomonopodial branching
        
        single main trunk rather than a series of dichotomies
        
        overtopping is a big issue because of unequal branching
    - - extant genera
        
        isoetes is a genus of 60 species of small plants call quillworts
        
        small corm-like stem that has roots attached below and leaves above
        
        grown in wet muddy areas
        
        selaginella
        
        less common in temperate north america
        
        can be distinguished by a small flap of tissue on the upper surface of the leaves
        
        called the ligule
        
        known as the resurrection plant
        
        plants are smaller and mistaken for moss
        
        microphylls are spirally arranged on their stems
        
        all species have true roots and short upright branches
        
        lycopodium is fairly common in forests of tropical regions
        
        all are homosporous
        
        ground pine or club moss
      - heterospory
        
        many species have remained homosporous, others became heterosporous
        
        extinct and extant lycophytes sporangia are grouped compactly called cones or strobili
        
        this protects them
      - morphology
        
        as wood grew to a larger circumference, cambial cells increased wider tangetially
        
        another important advance was the evolution of true roots
        
        enations in the division Lycophyta are called microphylls for clarity
  - - - trophic levels
        
        energy flow= carbon flow
        
        decomposers- fungi and bacteria that break down remains
        
        secondary consumers- carnivores and some omnivores
        
        primary consumers- herbivores and some omnivores
        
        primary producers- autotrophs
        
        feeding levels
      - species composition
        
        depends on whether the climate is mild or stressful
        
        refers to the number and diversity of a species that coexist in an ecosystem
      - temporal structure
        
        plants change dramatically throughout the season
        
        the changes that an ecosystem undergoes with time constitute
      - physiognomic structure
        
        the physical size and shape of the organisms and their distribution in relation to each other and the physical environment
    - - r- and K- Section
        
        r is the biomic potential
        
        carrying capacity is symbolized by K
      - age distribution (demography)
        
        instrinsic rate of natural increase/ biotic potential- number of offspring produced by an individual in ideal conditions
        
        generation time- the length of time from the birth of one to the birth of its offspring
      - geographic distributions
        
        zones can be established by using chemicals called allelochemics
        
        uniform distributions- type that occurs in orchards or farms
        
        clumped distributions- where the space is too small or large and rarely average
        
        random distribution- no uniform or obvious pattern in the individuals
        
        limiting factor- how the habitat limits the plant from developing and overpopulating
    - - introduction
        
        operational habitat
        
        aspects of the habitat that definitely affect a plant
        
        parts of the plant can become migratory, but no whole plant can
        
        seeds, pollen, fruit, spores, and vegetative propagules can move
        
        habitat is a set of conditions in which an organism completes its life cycle
      - biotic components of the habitat
        
        organisms other than plants
        
        fungi and bacteria are pathogenic rather than predatory
        
        frugivores- fruit eating animals that aide in seed dispersal
        
        other plant species
        
        commensal relationship- one benefits and the other one is unaffected
        
        transplant experiments are conducted to see what living condition is better for a plant
        
        niche- adapted to a particular set of conditions
        
        competitive exclusion
        
        species is less adapted is excluded from ecosystem by superior competitors
        
        competition- two organisms do not grow as well together as they do seperately
        
        mutualism- beneficial for both
        
        the plant itself
        
        habitat modification may be beneficial, but it can be detrimental or neutral
        
        by the plant just being in the habitat, it modifies its environment
      - abiotic components of the habitats
        
        nonliving and physical phenomena
        
        disturbances
        
        the soil is enriched by the ash in fire
        
        fire is easily started by the plant debris on the ground and how plants are easily flammable
        
        examples- fires, landslides, avalanches, and floods
        
        latitude and altitude
        
        altitude
        
        high altitude is similar to those at a high latitude
        
        latitude
        
        at the equator plants cannot measure season by photoperiod
        
        Soil Factors
        
        as plants die, they decompose and release nutrients back into the soil
        
        young soil are less diverse than more mature soils
        
        after many years, a thick soil may result in a distinct profile with 3 layers or horizons
        
        b
        
        rich in nutrients and contains both humus and clay
        
        area where materials from a accumulate
        
        the zone of deposition
        
        c
        
        composed mostly of parent rock or rock fragments
        
        a
        
        rainwater washes nutrients from it downward into the next layer
        
        called the zone of leeching
        
        consist of litter and debris
        
        uppermost
        
        the first plants that invade new soil are called pioneers
        
        Climate
        
        between the high and low extremes is the tolerance range
        
        ranges vary greatly from species to species
        
        moisture occurs as rain or snow or as hail
        
        this supplies water but also damages the plant
        
        growing seasons are usually determined by the last, severe killing frost in the spring and the first killing frost of autumn
        
        the average temperature is not as important as the extremes
        
        most species are restricted to certain regions
  - - - plant diseases caused by viruses
      - origin of viruses
      - formation of new virus particles
      - virus metabolism
      - virus structure
    - - Sequencing entire genomes
      - DNA sequencing
      - DNA cloning
      - identifying DNA fragments
      - restriction endonucleases
      - nucleic acid hybridization
    - - mRNA Translation
      - tRNA
      - ribosomes
    - - transcription of genes
      - the structure of genes
      - the genetic code
        
        20 types of amino acids are used in synthesizing proteins but only 4 different nucleotides are present in mRNA
      - protecting the genes
        
        histone proteins hold the most nuclear DNA
        
        most DNA is stored in the nucleus
        
        DNA does not participate in protein synthase
        
        if the storage isn't safe, the DNA can become inaccurate
- - - - other types of roots and root modification
        
        haustorial roots of parasitic flowering plants
        
        root nodules and nitrogen fixation
        
        mycorrhizae
        
        contractile roots
        
        aerial roots of orchids
        
        the root epidermis (velamen) are composed of several layers of large dead cells
        
        many roots are epiphytic(lives by being attached to the branches of trees)
        
        their roots spred along the surface of the bark and often dangle freely in the air
        
        prop roots
        
        buttress roots- plate-like, upper side grows more rapidly so the trees can't be blown over by the wind
        
        act like stabilizers
        
        make contact with soil, transport water and nutrients to the cells
        
        the stem of a monocot can become wider, with more vascular bundles
        
        storage roots
        
        provide long term storage for carbohydrates
        
        roots of strangler figs
      - origin and development of lateral roots
        
        differs than the bud formation in shoots
        
        cells are more densely cytoplasmic with smaller vacuoles and resume mitotic activity
        
        lateral roots are initiated by cell divisions in the pericycle
      - internal structure of roots
        
        mature portions of the root
        
        passage cells- thought to once represent passageways for the absorption of minerals, it is now thought they were slow to develop
        
        the powerful absorption of water and water pressure called root pressure
        
        zone of elongation
        
        zone of maturation/ root hair zone
        
        between the vascular tissue and the endodoermis are the parenchyma cells that make a region called the pericycle
        
        the bands of altered calls called casparian strips
        
        minerals do not have free access to the vascular tissues because of the innermost layer of the cortical cells called the endodermis
        
        root hairs only function for several days then die and degenerate
        
        root apical meristem
        
        the mitotically inactive central region is known as the quiescent center
        
        their nuclei do not take thymidine and do not become radioactive
        
        root cap
        
        cells are meristemic
      - external structure of roots
        
        structure of individual roots
        
        behind the zone of elongation is the root hair zone
        
        expands the roots surface area
        
        root hairs form only in a part of the root that is not elongating or they would be cut off
        
        many epidermal cells extend out as narrow tricomes
        
        the root of the apical meristem is protected by a thick layer of cells called the root cap
        
        dictyosomes of the root cap cells secrete a complex polysaccharide called mucigel which lubricates passage of the roots
        
        the zone of elongation is just behind the root cap and root apical meristem
        
        cells undergo division and expansion
        
        the root tip is the region here growth in length occurs
        
        organization of root systems
        
        most monocots cannot undergo secondary growth after their stem is formed
        
        adventitious roots are roots that don't develop from the taproot
        
        increase the absorptive and transport capacities of the root system
        
        most monocots and some eudicots have a mass of many similarly sized roots constituting in a fibrous root system
        
        most seed plants have a single prominent taproot and small lateral roots or branch roots comint out
        
        taproot develops from the embryonic root called the radicle
  - - - insect traps
      - leaves with kranz anatomy
        
        has a special metabolism with C4 photosynthesis
      - tendrils
      - bud scales
      - leaves of conifers
      - sclerophyllous foliage leaves
      - succulent leaves
    - - monocots
        
        the primordium is more a cylinder and encircles the shoot apical meristem
        
        are intiated by the expansion of the root meristem, like eudicots
      - basal angiosperms and eudicots
        
        at the base of the meristem, cells interior to the protoderm grow outward, forming a protrusion known as a leaf primordium
        
        extends upward as a narrow cone, growing so rapidly that it becomes taller than the shoot apical meristem
        
        this initiates the lamina, that grows a small leaf which develops a mature plant
        
        this increases thickness, establishing the bulk of the midrib
    - - petiole
        
        some species can bear two small flaps of tissue at its base calles stipules, which serve various functions
        
        leaf traces branch from from stem vascular bundles and diverge toward the petiole
        
        can be both small and large
      - vascular tissues
        
        many fibers are arranged in a sheath (called a bundle sheath) around vascular tissues
        
        midrib (midvein)
        
        lateral veins
        
        involved in conduction
        
        minor veins
        
        release water from xylem and load sugar into pholem
        
        between the palisade parenchyma and the spongy mesophyll
      - mesophyll
        
        some have a layer of palisade parenchyma along both leaf surfaces
        
        in the lower portion of the leaf is the spongy mesophyll
        
        open, loose aerenchyma that permits carbon dioxide to diffuse rapidly away from stomata into all of the leaf's interior
        
        upper surface of most leaves is a layer of cells called the palisade parenchyma (mesophyll)
        
        separated slightly so each cell has the most surface exposed to intercellular spaces
        
        main photosynthetic tissue of most plants
        
        ground tissues interior to the epidermis
      - epidermis
        
        contain a coating of cutin and sometimes wax
        
        often hairy
        
        large fat tabular in both stem and leaf
        
        must allow the entry of carbon dioxide
        
        must be waterproof but translucent
        
        flat, thin foliage leaves have a large surface area through which water can be lost
        
        can be a serious problem if the soil is so dry the roots cannot replace the water
        
        this is called transpiration
    - - leaf blade
        
        compound leaf has a blade divided into several individual parts
        
        has many small blades (leaflets)
        
        each attached by a petiolule
        
        this is attached to an extension of the petiole, the rachis
        
        simple leaf base has a blade of one part
      - lamina
        
        flat, light harvesting portion
        
        also known as the leaf blade
      - ventral face #
        
        also known as the adaxial side
        
        smooth
        
        upper side
      - petiole
        
        abscission zone
        
        leaf scar is the corky part in the fall that protects the area the leaf fell off
        
        involved in cutting off the leaf when its useful life is over
        
        some plants do not have petiole
        
        they form a sheathing leaf base
        
        this makes the leaf called a sessile leaf instead of a petiolate
        
        holds the blade out to the sun
        
        also known as the stalk
      - dorsal side
        
        also known as the abaxial side
        
        large veins protrude like backbones
        
        lower side
  - - - Crassulacean Acid Metabolism
        
        not efficient- the total amount of carbon dioxide is so small that it may be totally used in the C3 metabolism after just a few hours of sunlight
        
        second metabolic adaption that improves conservation of water while permitting photosynthesis
      - water
        
        photorespiration
        
        an energy-wasting process where phosphoglycolate is broken down to two molecules of carbon dioxide
        
        most plants keep their stoma open during the day, permitting entry of carbon dioxide, but water is lost
      - leaf structure
        
        standard structure palisade parenchyma above and spongy mesophyll below
        
        excellent for absorbing carbon dioxide but bad for conserving water
      - light
        
        duration
        
        number of hours that sunlight is available
        
        quantity
        
        light intensity or brightness
        
        quality
        
        refers to the colors or wavelengths it contains
      - Disorder is increasing (entropy)
    - - Pigment
        
        accessory pigments are molecules that absorb wavelengths not absorbed by chlorophyll a
        
        sometimes absorb light to protect light-sensitive substances
        
        any material that absorbs certain wavelengths specifically and therefore have a certain color
      - https://www.youtube.com/watch?v=sQK3Yr4Sc_k
      - photoautotrophs are organisms that gather light and use it to assimilate smalll inorganic molecules into their own tissues
        
        Heterotrophs are organisms that cannot do this but instead take in organic molecules and respire them
      - anabolic metabolism
        
        storage compounds
        
        long term storage (starch and lipids)
        
        intermediate term storage (sugar glucose and disaccaride sucrose
        
        short term storage (ATP and NADPH)
      - stroma reactions
        
        also known as dark reactions or calvin/benson cycle
        
        ATP and NADPH interact with carbon dioxide and produce carbohydrate
      - light- dependent reactions
        
        electromagnetic radiation spectrum
        
        treated as a set of particles called quanta or photons
        
        encompasses gamma rays, x-rays, ultraviolet light, infrared light, microwaves and radio waves
    - - reducing power
        
        the tendency to accept or donate electrons varies greatly and is known as a molecule's redox potential
        
        reduced compounds contain hydrogen
        
        hydrogen gives electrons away reducing its partner's partial positive charge
        
        oxidized compounds contain a lot of oxygen
        
        oxygen pull electrons away from an atom and raise that atom's partial positive charge
        
        oxidation reaction- one that increases the positive charge
        
        reduction reaction- reduces positive charge on an atom
        
        oxidized means that an atom does not carry as many electrons as it could
        
        when electrons are added to an atom, it becomes reduced
      - electron carriers
        
        plastoquinones
        
        have a long hydrocarbon tail, so they are hydrophobic
        
        after they pick up two electrons, they bind to two protons
        
        only carries to sites that are close
        
        plastocyanin
        
        small proteins that carries electrons on metal atoms
        
        cytochromes
        
        only carries to sites that are close
        
        intrinsic membranes
        
        small proteins that contain a cofactor (heme)
      - energy carriers
        
        ATP is recycled repeatedly, thousand times per second
        
        3 methods by which ADP can be phosphorylated to ATP
        
        oxidation phosphorylation
        
        last stages of respiration, ADP is phosphorylated to ATP
        
        substrate-level phosphorylation
        
        organisms that don't have the necessary organelles or pigments respire some of the high-energy compounds they have consumed or imported by phloem
        
        photophosphorylation
        
        light energy in photosynthesis
        
        it is converted to ADP and phosphate by metabolic reaction, but the phosphate can be reattached with a high-energy bond by the reactions of photosynthesis or respiration
        
        2 ways to transport energy from energized pigments into endergonic reactions
        
        allow energized pigments to make one or several smaller, less energetic intermediates that can be moved and controlled easily
        
        ATP is usually involved, but sometimes other "relatives" (such as guanosine triphosphate) enter
        
        allow the pigments to enter into every reaction necessary
        
        energy enters the biological world through photosynthesis
- - - - xylem
        
        control of water transport by guard cells
        
        water transport through xylem
        
        some water lost directly through the cuticle is transcuticular transpiration
        
        water lost is transstomatal transpiration
        
        properties of water
        
        liquid water is said to be cohesive
        
        if it interacts with other substances it is adhesive
      - pholem
        
        sinks- sites that receive transported pholem sap and are extremely diverse
        
        sources- sites from which water and nutrients are transported
    - - the wall and intercellular spaces is called the apoplast of the plant
      - all of the protoplasm of one plant can be considered one continuous mass, referred to as the symplast
      - transfer cells
      - motor cells
        
        are located along the midrib, and when they are shrunken, pressure causes them to be appressed
        
        the location of flexure is either the entire midrib or the point at which the petiole attaches to the lamina or stem
      - guard cells
        
        somewhat shrunken and little internal pressure, are in hydraulic equalibrium with surrounding cells
        
        the opening and closing of the stomatal pores are based on short-distance intercellular transport
    - - the point at which the protoplast has lost just enough water to pull slightly away is called incipient plasmolysis
      - measured in unites of pressure, usually megapascals (MPa) or bars
      - can be decreased
        
        elevated
        
        reducing pressure
        
        cooled
      - can be increased many ways
        
        elevated
        
        put under pressure
        
        heated
      - the free energy of water
    - - active transport
        
        most membranes have membrane-bound molecular pumps that use the energy of ATP to force molecules across the membrane
        
        can happen even if the type of molecule is extremely concentrated on the receiving side
      - osmosis
        
        water molecules can pass through all membranes, but their movements are more rapid if the membrane has protein channels called aquaporins
        
        3 types
        
        differentially or selectively permeable
        
        allow only certain substances to pass through
        
        hydrophilic molecules can cross only if the membranes have a special protein channels
        
        all lipid/ protein cell membranes are differentially permeable
        
        completely impermeable
        
        do not allow anything to pass through them and have little biological significance
        
        freely permeable
        
        allows all solutes to diffuse through and have little biological significance
        
        diffusion through a membrane
      - diffusion
        
        random movement of particles in solution causes them to move from areas of high concentration to low concentration
        
        simplest method
  - - - Fermentations of Alcoholic Beverages
        
        produces ethanol
        
        one of many types of alcohol
        
        other types are isopropyl alcohol andmethyl alcohol,
        
        classified as a depressant
        
        ethanol builds up concentration of
        
        Three types of beverages
        
        spirits
        
        type of spirit depends on the initial fermented material
        
        molasses and agave- rum and tequila
        
        grain- whiskeys, vodka and gin
        
        beverages with ethanol content above 20%
        
        this is obtained by adding ethanol or be distilled
        
        distillation is done by boiling the solution and having vapors be chilled in condensed to create a new liquid
        
        wine
        
        extra ethanol can be added to become a fortified wine
        
        white wines have no skins mixed in
        
        red wines and rose wines have skins mixed in
        
        has resveratrol
        
        fermentation continues as long as sugar is present and the concentration of ethanol has not reached lethal levels (18-20%)
        
        made by fermenting fruit juices rich in sugar
        
        beer
        
        different variations are a result of the malting process
        
        grains are moisten to germinate
        
        sake
        
        20-22% final concentration
        
        also known as rice wine
        
        made by fermenting starchy cereal grains
        
        Sugars present in fruits can be fermented immediately, but starches in seeds and tubers must be depolymerized before it can be fermented
        
        produced by the anaerobic respiration of glucose by yeasts
      - Fermentations of amino acids and other amino acids that contain sulfur or nitrogen
        
        produce odiferous compounds
        
        isobutyric acid
        
        ammonia
        
        putrescine
        
        cadaverine
        
        hydrogen sulfide
    - - various prokaryotes use various reduced compounds as sources of electrons and energy, other prokaryotes use various highly oxidized compounds as electron acceptors
        
        oxygen not present
        
        Fermentation
        
        bacteria ferments diverse substrates such as numerous sugars and organic acids
        
        this results in products like ethanol, lactate, propionate, acetate,acetone,methanol,and carbon dioxide.
      - hydrogen respiration
    - - respiratory quotient
        
        ratio of carbon dioxide liberated to oxygen consumed
        
        glucose RQ=1.0
      - anaerobic respiration
        
        glucose breaks down during glycolysis
        
        occurs in the cytosol and plastids
        
        The NADH shuttle
        
        Obligate anaerobes
        
        strictly use no oxygen
        
        Definition- respiration without oxygen (also called fermentation)
        
        example- bacteria
      - Definition- process that breaks down complex carbon compounds into simpler molecules and simultaneously generates the adenosine triphosphate (ATP0 used in other metabolic processes
- - - - vascular bundles
        
        are collateral, contains both xylem and phloem strands
        
        arranged in one ring surrounding the pith, a region of parenchyma similar to the cortex
      - vascular tissues
        
        not a circulatory system
        
        phloem
        
        carries sugar to the fruits and into the storage organs of perennial plants
        
        pick up sugar from where it is abundant and transport it to where it is needed
        
        xylem
        
        passes through dead cells not alive
        
        water and minerals enter in the roots and pushed upwards through the leaves and stems
        
        vessel
        
        tracheids
      - cortex
        
        fit together compactly
        
        composed of photosynthetic parenchyma and sometimes collenchyma
        
        interior to the epidermis
      - epidermis
        
        encrusted in cutin (a fatty substance that makes the wall impermeable to water)
        
        single layer of living parenchyma
        
        outermost surface of an herbaceous stem
    - - tubers are like rhizomes that grow for a short period of time to store nutrients (like a potato)
      - rhizomes are fleshy horizontal stems that allow a plant to spread underground
      - corms are vertical, thick stems that have thin leaves
      - bulbs are short shoots that have thick, fleshy leaves
      - phyllotaxy is the arrangement of leaves on a stem
      - terminal bud is the extreme tip of each stem
      - bud scales are the small, corky, waxy stuff that is covering the bud
      - axillary bud is a miniature shoot with a dormant apical meristem and several young leaves
      - leaf axil is the stem area just above the point where a leaf attaches
      - internodes are the regions between the nodes
      - nodes are where leaves are attached
      - shoot is the stem plus the leaves
      - stem is an axis
    - - sclerenchyma
        
        mechanical
        
        short sclereids
        
        long fibers
        
        conducting
        
        can develop from parenchyma cells
        
        both walls are elastic, meaning they can be deformed but pop back to their original shape
        
        has a thick primary and secondary wall
      - collenchyma
        
        require more glucose for their production
        
        present as a layer under epidermis or as bands located next to vascular bundles, making the tips stronger
        
        is found near shoot tips (vines for grapes)
        
        is claylike, able to be reformed and deformed with pressure
        
        primary wall that remains thin in some areas but thick in others (mostly the corners)
      - parenchyma
        
        transfer cells
        
        has large, extensive plasma membrane capable of holding numerous molecular pumps
        
        mediate short distance transport of material
        
        glandular cells
        
        transport large quantities of sugar and minerals into themselves, transform them metabolically and transport them out
        
        contain few chloroplasts and large amounts of dictyosomes and endoplasmic reticulum
        
        are also parenchyma cells
        
        secrete nectar, fragrences, mucilage, resins. and oils
        
        chlorenchyma
        
        thin walls to allow light and carbon dioxide to pass through
        
        have numerous chloroplasts
        
        parenchyma cells involved in photosynthesis
        
        active metabolically and some remain alive after they mature
        
        most common
        
        parenchyma tissue is a mass of parenchyma cells
        
        cells have only primary walls that remain thin
- - - - do not completely surround the egg
- - - - the substitution for meiosis
  - - - has air pores that open to the exterior of the aerenchyma
      - body is sometimes referred to as a thallus
        
        a body without leaves, roots, or stems
    - - leaves defined in 3 rows
      - have two rounded lobes with no midrib and no conducting tissue
      - gametophore resembles moss
- - - - absorbs sugars, minerals, and water
  - - - these occur in the same gametophore in bisexual species
      - archegonia
        
        eggs occur in the megagametangia
      - antheridia
        
        sperms are produced in the microgametangia
      - protonema
        
        long chlorophyllous cell that undergoes mitosis and produces a system of similar cells
    - - rhizoids are at the base of the stem
        
        lack chloroplasts
        
        small, multicolor trichome-like structures that penetrate the surface of a substrate
      - majority of mosses lack hydroids and leptoids
      - leptoids
        
        cells that resemble sieve cells
        
        most common in species that have hydroids
      - composed of cells called hydroids
        
        are elongated cells that loose their cytoplasm when mature
        
        conduct water and dissolved minerals
    - - the surface layer is the only diffence from the underlying layers
        
        the stem tissues are called the cortex
        
        the difference is the outside cells are slightly narrower
        
        is not called the epidermis
      - most steams are slender and have little tissue differentation
      - most grow from a apical meristem that contains a prominent apical cell
      - most have leaves, but they are not homologous with those of vascular plants
        
        this is because they are part of a gametophyte and not a sporophyte
      - The leafy stems of many moss plants grow together
        
        in cool wet areas, they grow more open and loose
        
        also known as gametophores