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Transcript
PLANTS What are plants? Eukaryotic (have a nucleus) Have cell walls made of cellulose Carry out photosynthesis using the pigment chlorophyll a and chlorophyll b Belong to the kingdom Plantae What do plants need to survive Sunlight – make food through photosynthesis Gas Exchange (CO2 and O2) Water and Minerals PHOTOSYNTHESIS 6 CO2 + 6 H2O → C6H12O6 + 6 O2 Carbon dioxide + Water + Light energy → Glucose + Oxygen Plant evolution The ancestor to today’s plants were similar to green algae Plants are divided into 4 major groups Alternation of generations The lifecycle of plants has 2 phases Gametophyte (haploid – N) Sporophyte (diploid – 2N) During evolution – the size of the gametophyte decreased and sporophyte increased Types of plants 1) Bryophytes (Mosses and others) 2) Ferns 3) Gymnosperms -------------- 4) Angiosperms Bryophytes Found in damp places Have specialized reproductive cells that require water for reproduction. Lack vascular tissue – water/nutrient carrying tissue supported by lignin Lack support to grow tall Moss life cycle Seedless vascular plants - Ferns and relatives Have vascular tissue which makes it possible to move fluids through the plant (against gravity) Phloem = carries nutrients Xylem = carries water Do not have seeds – reproduce through spores Reproductive cells need water for fertilization Gymnosperms – cone bearing plants First seed plants – allows the plant to Reproduce without water Protect the embryo in a seed Provide nutrients to the embryo Reproduction occurs through pollination Pollen (the male gametophyte) is transferred to the female cone Gymnospserm lifecycle Angiosperms – flowering plants Reproduce sexually through flowers Ovaries in flowers develop into fruits to help disperse seeds Flowers attract pollinators and reproduction is more efficient than the wind pollination of gymnosperms Monocot vs. dicot Chapter 28 Plant Structure and Function Plants have tissues and organs too!!!!! TISSUES = dermal, vascular and ground ORGANS = Roots, stems and leaves Plant growth Where do plants grow???? Meristems = regions of cells in which mitosis produces new cells that are ready for differentiation Apical meristem = rapidly growing regions at the tip of the stem and roots Meristems All plants tissues arise at meristems (regions of rapidly dividing, undifferentiated cells) Growth in apical meristems at tips of shoots and roots (primary growth) increases length In some plants, growth in lateral meristems (secondary growth) thickens roots and shoots Apical and Lateral Meristems Apical Meristem and Primary Growth Simple Tissue (Ground) Tissue Ground tissue = produces and stores sugars and contributes to the support of the plant Parenchyma = thin cell walls, contain a large vacuole, in leaves have chloroplasts (mesophyll) Collenchyma = thicker cell walls Supports rapidly growing plant parts (make up “strings” of celery) Sclerenchyma = thickest cell walls – resist stretching, cloth, rope, nutshells, seed coats Types of tissue – Dermal Tissue Dermal tissue = the protective outer covering in a plant Epidermis - Usually a single outer layer of cells that secrete a waxy, protective cuticle May contain specialized cells that form stomata for gas exchange Periderm - Replaces epidermis in woody stems and roots Vascular Tissue Vascular tissue = supports the body and transports water and nutrients Xylem- carries water and ions through the plant Consists of two types of cells that are dead at maturity: tracheids and vessel members Lignin-filled secondary walls Phloem conducts sugars, other organic solutes Sieve tubes connect end to end at sieve plates Companion cells load sugars into sieve tubes Flowering Plant Tissues Studying Plant Parts: Tissue Specimens Tissue specimens are cut along standard planes Roots Root Function Support a plant Anchor it to the ground Store food Absorb water from the soil Absorb nutrients from the soil 28.5 Primary Structure of Roots Roots mainly function to provide plants with a large surface area for absorbing water and dissolved mineral ions Support a plant Anchor it Store food Root hairs Fine extensions of root epidermis that increase the surface area for absorption Roots cont. Types of roots Taproot – carrots, beets, dandelions Fibrous root - grasses Root pressure – roots actively pump nutrients into the root. Water moves in by osmosis. This causes a pressure that causes water to move up the plant into the stem Eudicot and Monocot Root Structures Taproot system (eudicots) A primary root and lateral branchings Central vascular cylinder Fibrous root system (monocots) Adventitious and lateral roots Vascular cylinder divides root into cortex and pith Stems Functions of stems Produce leaves, branches and flowers Hold up the leaves to the sun Transport substances throughout the plant Inside the Stem Vascular bundles Multistranded cords of vascular tissues threaded lengthwise through ground tissues of all shoots Two distinct patterns of vascular bundles Tissues in a Buttercup Stem Structure of Wood Seasonal Growth Vascular cambium is inactive in cool winters or long dry spells, and active when warmth or moisture returns In regions where seasonal change is pronounced, alternating bands of early and late wood form “tree rings” Seasonal Growth 28.7 Tree Rings and Old Secrets The number and relative thickness of a tree’s rings hold clues to environmental conditions – such as annual rainfall – during its lifetime Tree rings are used to date archaeological ruins, study ecology, and provide evidence about wildfires, floods, landslides and glaciers Historical Evidence Settlements in North Carolina (1587) and in Virginia (1610) experienced severe drought Leaves Anatomy of a Leaf Stomata (next slide) Mesophyll – where photosynthesis occurs Cuticle – waxy cover to protect/prevent water loss All leaves are metabolic factories where photosynthetic cells produce sugars – but they vary in size, shape, surface specializations, and internal structure Mesophyll – Photosynthetic Ground Tissue Mesophyll=Photosynthetic parenchyma with air between cells CO2 diffuses in and oxygen diffuses out through stomata Plasmodesmata connect adjacent cells Single layer or double layer (palisade and spongy mesophyll) Veins – The Leaf’s Vascular Bundles Veins Vascular bundles in leaves, strengthened with fibers, containing xylem and phloem Two distinct patterns Eudicots: Large veins branch into networks of smaller veins Monocots: Veins of similar size run parallel to the leaf axis Leaves – stomata Stomata – openings in the leaf that allow CO2, water, and O2 to diffuse in and out of the leaf Guard cells = cells that surround the stomata and regulate their opening and closing Homeostasis and stomata Plants keep stomata open just enough so that gas exchange can occur for photosynthesis but not so much that they lose too much water When water is abundant water flows into the leaf. This increases water pressure in the guard cells and opens them. When water is scarce, pressure decreases and the stomata close Water transport in plants Transpiration = water loss from a plant through its leaves Water leaves through open stomata Dry cell walls pull water from deeper in the leaf and pulls water from the roots, stem and leaf through xylem Water “sticks” to water (cohesion) and other molecules (adhesion) Even small trees can lose 100L of water/day What conditions increase transpiration??? Hot Dry Wind How does water move up the plant? Capillary action – the tendency of water to rise in a thin tube 29 Reproduction in flowering plants Parts of a flower Sepals = enclose the flower before the bud opens and protects the flower Petals = attract pollinators to the flower often brightly colored inside the sepals Parts of a flower (cont.) Parts of a flower Stamen = male parts of the flower Anther – produce pollen Filament – a stalk that holds up the anther Carpels Stigma (pistil) = female parts of the flower – sticky structure designed to capture pollen Style – a stalk that holds up the stigma Angiosperm gamete production Angiosperm lifecycle Fruit and seed development Fruit = a thickened ovary wall that encloses seeds Seed Dispersal = Animals = seeds with tough coats are encased in a sweet fleshy fruit Apples, grapes Wind = lightweight fruits that allow them to be carried in the air Dandelions Water = buoyant fruits that allow them to float coconuts Seed Dormancy and Germination Dormancy = the embryo is alive but not growing Germination = growth of the plant embryo following dormancy Advantages of Dormancy Allows for long distance dispersal Allows seeds to germinate in ideal growth conditions Some seeds only germinate under extreme conditions Some pine cones remain sealed until the high temps generated by forest fires cause the cones to open Plant Hormones Hormones = chemical signals produced by an organism that affect the growth, activity, and development of cells and tissues Auxin – stimulate cell elongation and growth of roots Produced in the shoot apical meristem and transported When light hits a part of a plant, auxins build up in the shaded region, causing the plant to bend toward the light Growth of lateral buds is inhibited by auxin (if you cut off the top of a plant, the lateral buds grow more quickly. Cytokinins Cytokinins = hormones produced in the growing roots and developing fruits and seeds. Often produce effects opposite of auxins Stimulate cell division Interact with auxins to balance root and shoot growth Stimulate regeneration of tissues damaged by injury Giberellin, abscisic acid, ethylene Giberellins Found in meristems of shoot, root, and seed embryo Stimulate growth, promote germination Abscisic Acid Found in terminal buds and seeds Inhibits cell division Promotes seed dormancy Ethylene Found in fruit tissues and aging leaves and flowers Stimulates fruits to ripen Causes plants to seal off and drop leaves Tropisms Tropism = plants response to environmental stimuli Phototropism – tendency of a plant to grow toward light Gravitropism – response of a plant to gravity Thigmotropism – response of a plant to touch Rapid responses Some plants can also adjust quickly to their environment Venus fly trap Mimosa (folds leaflets in a few seconds when touched) Response to seasons How do plants know when to flower, drop leaves, etc? Photoperiod = the number of hours of light/dark a plant receives (pigment phytochrome) Winter Dormancy Deciduous plants turn off photosynthetic pathways Transport materials from leaves to roots Seal off leaves Chlorophyll breaks down allowing other pigments to be seen (brown, yellow, etc.)
