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Plants. Multicelled , eukaryotic, photosynthetic autotrophs . General characteristics of all plants. Multicellular Eukaryotic Autotrophic – carry out photosynthesis Cell wall composed of cellulose Surplus carbohydrate is stored as starch Alternation of generations
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Plants Multicelled, eukaryotic, photosynthetic autotrophs.
General characteristics of all plants • Multicellular • Eukaryotic • Autotrophic – carry out photosynthesis • Cell wall composed of cellulose • Surplus carbohydrate is stored as starch • Alternation of generations • Gametophyte – cells are (n) • Sporophyte generation – cells are (2n) • Evolved from algae - Chlorophyta
Bryophytes: nonvascular plants • Live in moist environments and absorb water by diffusion • Lack lignin-fortified tissue required to support tall plants on land • Example: mosses and liverworts
Tracheophytes • Have transport vessels: xylem and phloem • Some plants are seedless; reproduce by spores • Ferns • horsetails • Includes the seed plants • Gymnosperms – cone bearing • Various modifications for dry conditions • Cedars, sequoias, redwoods, pines, yews, and junipers • Angiosperms – flowering • Most diverse and plentiful on earth • Daisies, roses, fruits, nuts, grains, and grasses • Subdivided into monocotyledon (monocots) and dicotyledon (dicots)
Strategies that enabled plants to move to land • Cell walls – made of cellulose lend support to the plant whose cells, unsupported by a watery environment must maintain their own shape • Roots and root hairs – absorb water and nutrients from the soil • Stomates – open to exchange photosynthetic gases and close to minimize excessive water loss. • Cutin– waxy coating on leaves that prevents water loss. • Gametes and zygotes of some form within a protective jacket of cells called gametangia to prevent drying out. • Sporopollenin – found in spores and pollen, protects plants in harsh terrestrial environment. • C-4 and CAM plants survive in dry environments • Seeds and pollen have protective coat prevent desiccation. • Gametophyte generation has been reduced.
How Plants Grow – • plants grow through their lives because embryonic tissues called meristem tissues continue to divide • Primary Growth • Zone of cell division - These meristem cells are actively dividing. Located at the tips of roots and the buds of shoots • Zone of Elongation-the plant grows into the soil and up into the air. • Zone of differentiation –cells undergo specialization into meristems that give rise to • Ground meristem– becomes the cortex • Protoderm - becomes the epidermis • Procambium becomes primary xylem and phloem
Secondary growth • Lateral meristem provides secondary growth which is increase in girth. In herbaceous (non-woody) plants, there is only primary growth. In woody plants secondary growth is responsible for the gradual thickening of the roots and shoots formed from earlier primary growth.
Plant tissue – three types • Dermal tissue – covers and protects the plant. It includes endodermis, epidermis and modified cells like guard cells, root hairs, and cells that produce a waxy cuticle. • Vascular tissue – transports water and nutrients around the plant • Ground tissue – most common tissue, functions in support, with thick cell walls and containing lignin.
Vascular Tissue • Xylem- conducts water and minerals from roots throughout the plant; xylem cells are dead at maturity. • Tracheids- long thin cells that overlap and are tapered at the ends. Water passes from one cell to another through pits areas with no secondary cell wall. • Vessel elements – wider, shorter and thinner walled with less tapered ends than tracheids. • Xylem – makes up wood
Phloem – carries sugars from the leaves to the rest of the plant. • Sieve tube members – end walls contain seive plates that facilitate the flow of fluid from one cell to the next. Cells are alive at maturity, but lack nuclei, ribosomes, and vacuoles. • Companion cells – connected to each sieve tube member containing all cell organelles . Nurtures the sieve cell elements
Ground Tissue • Parenchymal cells – look like traditional plant cells. Some contain chlorophyll. When turgid, they help give the plant support and shape. They retain their ability to divide and differentiate into other cell types after the plant has been injured. Entire plants can be cloned form one parenchymal cell.
Collenchymal cells – function to provide support to the growing stem. The “strings” of a stalk of celery consists of collenchymal cells. • Sclerenchymal cells - support the plant • Fibers - long thin and fibrous, usually occuring in bundles. • Sclereids – short and irregular in shape. They make up, tough seed coats and pits, give pear its gritty texture.
Roots – anchors plant, absorbs nutrients, stores food • Epidermis covers the entire surface; modified for absorption. Slender projections (root hairs) greatly increase the absorptive surface area. • Cortex – consists of parenchymal cells contain many plastids for storage of starch and other organic substances. • Stele – (vascular cylinder) consist of vascular tissue surrounded by layers of pericycle, from which lateral roots arise. • Endoderm- The vascular cylinder surrounded by tightly packed layer of cells called endodermis. Each endoderm is wrapped with the Casparian strip. Select what minerals enter the vascular cylinder and the body of the plant.
Types of roots • Taproot – single large root that gives rise to lateral branch roots. • Carrots ,beets, turnips • Fibrous root system- highly branching roots; hold soil and minimize erosion. • grasses
Stems • Primary tissue of stems – • Vascular bundles – vascular tissue running the length of the stem in strands • Monocots – vascular bundles scattered • Dicots – vascular bundles arranged in a ring • Ground tissue – • Cortex and pith – parenchymal tissues modified for storage. • Apical meristem– located at the tips of roots and shoots supplying cells for the plant to grow in length.
Secondary Growth in stems • Secondary growth is the product of lateral meristem which replaces the epidermis with a secondary dermal tissue, such as bark which is thicker and tougher. • A second lateral meristem adds layers of vascular tissue • Wood is secondary xylem that accumulates over the years.
The Leaf • Organized to maximize sugar production and minimize water loss • Epidermis covered by a waxy cuticle made of cutin • Guard cells control opening of the stomates • Palisade and spongy mesophyllare found in the inner part of the leaf and are involved in photosynthesis. • Vascular bundles (veins) in the mesophyll carry water and nutrients from the soil to the leaves and also carry sugar from the leaves to the rest of the plant. • Bundle sheath cells – surround the veins and separate them from the rest of the mesophyll.
Stomates • About 90% of the water lost in plants is lost through the stomates. • When guard cells fill with water they become turgid and the stomata open. When plants lose water the guard cells become flaccid and the guard cells close the stomata. • Depletion of CO2 within the air spaces of the leaf, which occurs when photosynthesis begins, triggers the stomates to open.
Increase in potassium ions in the guard cells lowers their water potential, causing water to diffuse into them. • Blue light receptor in a guard cell, stimulates the activity of ATP powered proton pumps in the plasma membrane of the guard cells, which in turn promote uptake of K+ ions. This causes stomates to open. • Stomate opening correlates with active transport of H+ out of the guard cells and into the surrounding epithelial cells. • Lack of water causes the guard cells to lose their turgor become flaccid and close the stomate. • High temperatures close the stomate by stimulating cellular respiration and increasing O2 concentration within the air spaces of the leaf. • Abscisic acid produced in the mesophyll cells in response to dehydration, signals guard cells to close the stomates.
Transport in Plants • Transport of xylem – xylem rises in a plant against gravity and requires no energy. • Root pressure- water flowing into the stele from the soil as a result of high mineral content in the root cells. guttation. • Transpirational pull- pulls fluid up the world’s tallest trees. • Evaporation of water from leaves causes negative pressure tension) to develop in the xylem tissue from the roots to the leaves • Cohesion of water - for each molecule of water that evaporates from a leaf by transpiration, an other molecule of water is drawn in at the root to replace it.
Factors affecting transpiration rate • Humidity level • Wind • Light intensity • Closing stomates
Absorption of Nutrient and Water • Apoplast and symplast- lateral movement of water and solutes • Mycorrhizae – symbiotic structures consisting of the plant’s roots intermingled with hyphae of a fungus. • Rhizobium – symbiotic bacterium living in the nodules of roots of specific legumes and fixes atmospheric nitrogen to a form usable by the plant.
Mycorrhizae Apoplast and symplast
Translocation of Phloem sap • Phloem sap travels around the plant from source to sink • Mature leaves are the primary source of sugar. • Sink stores or consumes sugar – growing roots and fruit. • Storage organs like tubers and roots are the sugar sink in the growing season, but they become the source during the spring when starch is broken down to be used as a sugar source by the rest of the plant.
Plant Reproduction • Asexual Reproduction • Vegetative propagation (clone)- New plant grows form the vegetative part of a plant root, stem, or leaf. • Grafting • Cuttings • Bulbs • runners
Sexual Reproduction in Plants • The Flower is the sexual organ of a plant. • Fertilization begins with pollination • Pollen grain contains • Three monoploid nuclei • One tube nucleus • Two sperm nuclei • Pollen lands on the stigma of the flower • Produces a pollen tube that burrows down the style into the ovary. • Two sperm nuclei travel down the pollen tube into the ovary. The two remaining sperm nuclei enter the ovule through the micropyle. • One sperm fertilizes the egg to become the embryo (2n)
The other sperm nucleus fertilizes the two polar bodies and becomes the triploid (3n) endosperm (food for the growing embryo) • This is called double fertilization because two fertilizations occur. • After fertilization • Ovule becomes the seed • Ripened ovary becomes the fruit • Seed - seed coat, embryo and cotyledon (or endosperm. • Embryo- • Hypocotyl- becomes lower part of stem • Epicotyl- becomes upper part of the stem • Radicle – (embryonic root) first organ to emerge from the germinating seed.
Plant Responses • Hormones – • Auxins • Phototropisms • Apical dominance • Stem elongation • IAA (indoleacetic acid) naturally occuringauxin • Some man made auxins are used as weed killers • Root powder helps roots develop quickly in a cutting • Auxins are produced in the growing tip of a plant and transported downward polar transport)
Plant hormones • Cytokinins • Stimulate cytokinesis and cell division. • Work with auxins to promote growth and cell division. • Antagonistic to auxins with respect to apical dominance. • Delay senescence (aging) by inhibiting protein breakdown. • Produced in roots; travel up plant
