BIO10& Plant&Lecture&Notes& ch.&&17&&117&Plant Kingdom Characteristics of the Plant Kingdom;  eukaryotic,  multicellular,  sexually reproducing organisms  autotroph  feed themselves by photosynthesis Facts about members of this kingdom  the dominant organisms on the surface of the earth  about 263,500 species of plants today  Today’s plants probably came from green algae  Originally all were aquatic organisms not well adapted to living on land Adapting to Terrestrial Living  how to absorb minerals?  how to conserve water?  how to reproduce on land? Plants require relatively large amounts of 6 inorganic minerals:  N  K,  Ca,  Phosphorus,  Mg,  and Sulfur Each of these minerals constitutes 1% or more of a plant’s dry weight Plants must absorb these materials, along with water, through their roots the first plants were symbiotically involved with mycorrhizaeBIO10& Plant&Lecture&Notes& ch.&&17&&118& One of the key challenges to living on land is to avoid drying out  a watertight outer covering called a cuticle  water enters plants only through roots  cuticle prevents water loss to the air  specialized pores called stomata (singular, stoma)  allow passage for H2O through cuticle  found in the leaves and, sometimes, the green portion of stem  allow for the passage of CO2 into the plant for photosynthesis and H2O vapor and O2 to pass out Reproducing sexually on land presented special challenges  as plants could not move, it was necessary for plants to pass gametes from one individual to another  the first plants needed a film of water for a sperm to swim to an egg and fertilize it  later, pollen evolved, providing a means of transferring gametes without drying outBIO10& Plant&Lecture&Notes& ch.&&17&&119&Plant Evolution key evolutionary advances in the evolution of the plant kingdom  Roots  vascular tissue  transports water and nutrients through the plant body and provides structural support  seeds o provide nutrients and protection for the plant embryo until it encounters favorable growing conditions  flowers and fruits o improved the chances of successful mating in sedentary organisms and facilitated dispersal of their seeds Nonvascular Plants  no vascular system  size of the plant limited because all materials had to be transported by osmosis and diffusion  only 2 phyla of living plants completely lack a vascular system  liverworts (phylum Hepaticophyta)  hornworts (phylum Anthocerophyta)  na third phylum of plants has a simple conducting tissue system of soft strands  mosses (phylum Bryophyta)BIO10& Plant&Lecture&Notes& ch.&&17&&120& Vascular Tissues: specialized cylindrical or elongated cells that form a network throughout a plant the earliest vascular plants grew by cell division at the tips of the stem and roots primary growth made plants longer or taller ater vascular plants developed a new pattern of growth in which a ring of cells could divide around the periphery of the plant secondary growth: plant stem increased in diameter Seedless Vascular Plants  2 phyla of living-seedless-vascular plants  ferns (phylum Pterophyta)  in ferns, the sporophyte generation is much larger and more complex than the gametophyte  the leaves are the sporophyte are called fronds  club mosses (phylum Lycophyta)  crucial adaptation to life on land  protects the embryonic plant when it is at its most vulnerable stageBIO10& Plant&Lecture&Notes& ch.&&17&&121& Seed plants produce two kinds of gametophytes, male and female, which develop completely within the sporophyte  male gametophytes are called pollen grains  they arise from microspores  a female gametophyte contains the egg within an ovule  it develops from a megaspore  There is no need for free water in the fertilization process  pollination by insects, wind, or other agents transfers pollen to an ovule  the pollen grain then cracks open and sprouts as a pollen tube, bringing sperm cells directly to the egg All seed plants are derived from a single common ancestor gymnosperms  in these seed plants, the ovules are not completely enclosed by sporophyte tissue at the time of pollination angiosperms  the most recently evolved of all plant phyla,  the ovules are completely enclosed in sporophyte tissue called the carpel at the time of pollinationBIO10& Plant&Lecture&Notes& ch.&&17&&122& Parts of a Seed  Embryo  Endosperm: a source for food for the developing embryo  in some seeds, the endosperm is used up by the embryo and stored as food in structures called cotyledons  Outer Covering: drought resistant How did seeds help plants adapt to land?  Dispersal  facilitates the migration and dispersal into new habitats  dormancy  permits plants to postpone development until conditions are favorable  germination o controls when the plant develops so that it can be synchronized with critical aspects of the plant’s habitat  nourishment o provisions the seed during the critical period just after germination Seeds allow plants to bypass the dry season  Hard seed coats crack when wet by the rains.  Seeds will not germinate during the dry season.BIO10& Plant&Lecture&Notes& ch.&&17&&123& Gymnosperms  Four phyla constitute the gymnosperms  conifers (phylum Coniferophyta) o trees that produce their seeds in cones and most have needle-like leaves  ncycads (phylum Cycadophyta) o have short stems and palmlike leaves  gnetophytes (phylum Gnetophyta) o contains only three kinds of very unusual plants  ginkgo (Ginkgophyta o only one living species, the maidenhair tree, which has fan-shaped leaves The life cycle of conifers is typical of gymnosperms conifers form two types of cones  seed cones contain the female gametophytes  pollen cones contain the pollen grains (male gametophytes)  conifer pollen grains are dispersed by wind to the seed cones  the fertilized seed cones produce seeds, which are also wind-dispersed  the germinated seed will grow into a new sporophyte plantBIO10& Plant&Lecture&Notes& ch.&&17&&124& Rise of the Angiosperms  90% of all living plant species  virtually all