Botany (the Study of Plants) General Plant Review All plants are: Eukaryotic Autotrophic Multicellular Cell Walls with cellulose Chloroplasts w/ chlorophyll a, b, and carotenoids May have waxy cuticle to prevent water loss. Stomata allow gas exchange. Plants probably evolved from green algae (charophytes) Chloroplast similarity Biochemical similarities Cell Wall similarities Plant Reproduction Alternation of Generations – plants grow a separate, haploid organism to produce gametes; the same plant exists in two different forms during its life, although sometimes it’s hard to differentiate between the forms Multicellular Sporophyte – (2N) Mitosis Meiosis Zygote (2N) Unicellular fertilization Spores (N) Unicellular Gametes (egg & sperm) Multicellular Gametophyte (N) Evolutionary Trend – early plants displayed the gametophyte (n) as the dominant structure, modern plants show the sporophyte as dominant (2n) (Ex: Moss is HAPLOID, but Oak Trees are DIPLOID) zygote GREEN ALGA BRYOPHYTE FERN GYMNOSPERM ANGIOSPERM Classifying Plants Plants can be divided into 2 major categories based on their characteristics: Nonvascular Plants Do NOT have specialized tissues to transport water and nutrients Instead, these plants transport water from cell-to-cell by osmosis Vascular Plants Have specialized tissues to transport water and nutrients in plants Xylem – carries water upward from roots Phloem – carries nutrients and carbohydrates produced by photosynthesis Nonvascular Plants (Bryophytes) Short with no specialized tissues to transport water Major types: Mosses Liverworts Hornworts Nonvascular Plants/ Bryophytes Mosses Have rhizoids that anchor them to the ground (instead of roots) Depend on water for fertilization The sperm must swim to the egg Therefore, nonvascular plants must live in MOIST environments Gametophyte is the dominant phase of the life cycle Moss/ Bryophyte Life Cycle Zygote grows, mature develops into a sporophyte sporophyte while still attached to gametophyte. zygote Diploid Stage Fertilization Meiosis Haploid Stage Spores germinate. sperm- producing structure male gametophyte egg- producing female structure gametophyte Vascular Plants/Tracheophytes Have specialized tissues to transport water and nutrients in plants called Xylem & phloem Vascular plants (tracheophytes) can be divided into 2 categories: Seedless vascular plants (spores) Seed (vascular) plants Seedless Vascular Plants Ferns – A Close Up Diploid sporophyte is the dominant stage Have rhizomes, which are underground stems Fronds: large “leaves” where spores develop Develop spores in sporangia on underside of fronds Reproduce using spores A sorus (plural: sori) is a cluster of sporangia Fern Life Cycle Sporophyte still attached to gametophyte sorus zygote rhizome Diploid Stage fertilization meiosis Haploid Stage Spores Spores develop are egg released sperm mature gametophyte Spore germinates Seed (Vascular) Plants Have true roots, leaves, and stems Have the ability to form seeds, which are used for reproduction Seed plants are the most dominant group of photosynthetic organisms on land There are 2 types of seed (vascular) plants: 1. gymnosperms (cones) 2. angiosperms (flowers) Seed (Vascular) Plants Gymnosperms = “cone bearers” “naked seeds” – not enclosed in ovaries Bear seeds directly on the surfaces of cones Cones = sporophyte structures that produce gametophytes (seeds) Coniferous trees are the major example Pines, junipers, spruces, etc. section through one surface view of one cone scale ovule (houses two ovules) Pine Life Cycle ovule surface view of one cone scale (houses a pollen-producing sac) mature sporophyte seed section through a coat pollen-producing sac zygote seeding embryo Diploid seed fertilization meiosis pollen tube Haploid microspores eggs form sperm- megaspores producing cell pollination form female gametophyte Seed (Vascular) Plants Angiosperms = flowering plants Seeds are enclosed by an ovary Flowers are reproductive organs Evolutionary advantage attract pollinators Flowering plants contain ovaries Ovaries surround and protect seeds Ovary develops into a fruit after pollination & helps with seed dispersal when eaten Examples: Maple trees, tulips, grass sporophyte Flowering Diploid Plant Life Double fertilization Meiosis Meiosis Haploid mitosis Cycle without microspores pollination cytoplasmic division two sperm enter ovule female gametophyte Evolutionary Tree for Plants Nested monophyletic groups flowering green zygophytes, charophytes bryophytes lycophytes horsetails ferns cycads ginkgos conifers gnetophytes plants algae related groups seed plants euphyllophytes embryophytes (land plants) vascular plants (closely related groups) Transport in Vascular Plants Transport Within Plants Water and minerals absorbed by roots are drawn upward in the xylem to the shoots Sugar produced by photosynthesis is exported from leaves to other organs via the phloem Transport can be passive or active Short- and Long-Distance Transport in Plants Water and sugars move differently in plants, depending on whether they’re going a short or a long distance Ie. – walking down the street or taking an airplane across the world Short-Distance Transport 1. Simple diffusion/osmosis substances in one cell move out of one cell, across the cell wall, and into another cell 2. Plasmodesmata Plasmodesmata are connections between the cytoplasm of adjacent plant cells Substances move between cells through these openings Long-Distance Transport Over long distances, these 3 processes (simple diffusion, apoplast,& symplast) take too long Water and solutes move through xylem and phloem by bulk flow, the movement of a fluid driven by pressure Transpiration Transpiration is the evaporation of water from leaves and other parts of the plant; it causes a pull that brings more water up through the xylem An average maple tree loses more than 200L of water per hour during the summer! Unless this water is replaced by water absorbed by the roots, leaves will wilt and die (Cohesion-Tension Theory) Transpiration works through a combination of evaporation, water potential, adhesion, and cohesion to pull water up the xylem The Photosynthesis- Transpiration Compromise Exposing leaves to the sun and opening stomata (cellular “holes” in the underside of the leaf) to allow for gas exchange helps photosynthesis, but causes transpiration to occur at a faster rate. Plants balance the loss by controlling when stomata are open. Mechanism for Stomatal Opening & Closing Guard cells open and close stomata by changing shape using ion and hormone signals based on plant stress. Plant Structure, Growth, & Development The Diversity of Angiosperms Angiosperms (flowering plants) can be divided into 2 major categories: Monocots – have one seed leaf (cotyledon) Dicots – have 2 seed leaves (cotyledons) Monocots Monocots have only 1 cotyledon (seed leaf) Examples of monocots: Corn, wheat, lilies, orchids, palms Dicots Dicots have 2 cotyledons (seed leaves) Examples of dicots: Roses, clover, tomatoes, oaks, daisies Woody vs. Herbaceous Plants Angiosperms can also be subdivided into woody (produce wood) and herbaceous (do not produce wood) plants Woody plants are made of cells with thick cell walls that support the cell body Examples: trees, shrubs, vines Herbaceous plants do not produce wood as they grow, and instead have smooth stems Examples: dandelions, sunflowers Plant Life Spans The lifespan of plants, however, is genetically determined Annuals – complete their life cycle in 1 year Examples: marigolds, cucumbers (lots of garden plants) Biennials - complete their life cycle in 2 years Year 1: germinate & grow roots Year 2: grow stems & leaves, produce flowers & seeds Examples: evening primrose, celery Perennials – live for more than 2 years Examples: Maple trees, grasses, palm trees Plant Structure Plants are made up of a root system and a shoot system The Root System What do roots do? Anchor the plant in the soil Absorb minerals and water Store food Types of root systems Fibrous root system Found mostly in monocots Taproot system Found mostly in dicots How do roots grow? Roots grow down from the tip in a region called the apical meristem, where the cells are dividing quickly The Shoot System The shoot system consists of: vegetative shoots (which bear leaves) floral shoots (which bear flowers) Stems have 3 important functions: Producing leaves, flowers (reproduction), branches Holding leaves up to the sunlight for photosynthesis Transporting substances between roots and leaves How do stems grow? Primary growth Increase in length Occurs by cell divisions in apical meristem (at top of shoot) Secondary growth Increase in width Occurs by cell divisions in the lateral meristems (outward growth) The Shoot System: Leaves Leaves are the primary photosynthetic organs of most vascular plants Most leaves have a flattened blade and a petiole, which is the stalk that attaches the leaf to the stem Tissues in Plants All 3 plant organs (root/stem/leaf) have dermal, vascular, and ground tissue systems Dermal Tissue System Outer protective covering, similar to our skin Protects the plant from water loss and disease The cuticle is a waxy coating that helps to prevent water loss Tissue Systems in Plants Vascular Tissue System Carries out long-distance transport of materials within the plant Xylem and phloem are examples of vascular tissues Ground Tissue System Pith (inside vascular tissue) and