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Kingdom PLANTAE Multi-celled / eukaryotic Autotrophic / chloroplast Cell wall - cellulose Kingdom PLANTAE Plant Evolution Plants: Alternation of Generation Gametophyte (n): Haploid, produces eggs and sperms which then unite to form sporophyte Sporophyte (2n): Diploid which goes through meiosis to produce spores which grow into gametophytes Plants: Alternation of Generation Plants: Alternation of Generation - MOSSES Plants: Alternation of Generation - FERNS Plants: Flowers Alternation of Generation Plants: Flowers Most plants are angiosperms, flowering plants Angiosperm seeds protected and dispersed in fruits, which develop from ovaries Plants: Flowering Plants Angiosperms, or flowering plants, are most familiar and diverse plants Two main types of angiosperms Monocots: orchids, bamboos, palms, lilies, grains, and other grasses Dicots: shrubs, ornamental plants, most trees, and many food crops Comparison between dicot and monocot seeds Seed coat Embryonic shoot Embryonic leaves Embryonic root Cotyledons COMMON BEAN (DICOT) Fruit tissue Cotyledon Seed coat Endosperm CORN (MONOCOT) Embryonic leaf Embryonic shoot Sheath Embryonic root Figure 31.11B Plants: Monocots vs Dicots Plants: Flowering Plant Reproduction The angiosperm flower is a reproductive shoot consisting of sepals petals stamen carpels Anther Carpel Stigma Ovary Stamen Ovule Sepal Petal Figure 31.9A Plants: Stamens - male reproductive organs of plants Pollen grains develop in anthers, at the tips of stamens Carpels - female reproductive organs of plants Ovary at the base of the carpel has ovule Life cycle of angiosperm involves several stages Ovary, containing ovule Embryo Fruit, containing seed Seed Mature plant with flowers, where fertilization occurs Seedling Germinating seed Figure 31.9B Figure 31.10 Plants: The ovule develops into a seed After fertilization, ovule becomes seed Fertilized egg inside seed - embryo Other fertilized cell - endosperm, stores food for the embryo Resistant seed coat protects the embryo and endosperm Triploid cell OVULE Zygote Two cells Cotyledons Endosperm Seed coat Shoot Embryo Root SEED Figure 31.11A Seed dormancy is an important evolutionary adaptation in which growth and development are suspended temporarily It allows time for a plant to disperse its seeds It increases the chance that a new generation of plants will begin growing only when environmental conditions favor survival Plant: Asexual Reproduction Asexual reproduction: Bulbs: parts of root split and form new bulb (ex. tulip) Tubers: modified underground stem have buds (ex. potato) Runners: plant stem run above ground (ex. Strawberry) Rhizomes: woody underground stem (ex. Iris) Modified stems include runners, asexual reproduction rhizomes, plant growth and food storage tubers, food storage as starch STRAWBERRY PLANT Runner POTATO PLANT Rhizome IRIS PLANT Rhizome Tuber Taproot Root Figure 31.4B Asexual runners Figure 31.14D Plant: Asexual Reproduction Vegetative propagation: cuttings or bits of tissue increase agricultural productivity But it can also reduce genetic diversity Cutting: cut stem form roots Layering: bent stem touching ground form roots Grafting: stock of one grafted on stem (scion) of another Plants: Shoot and Root System Root system Provides anchorage Absorbs and transports minerals and water Stores food Shoot system Consists of stems, leaves, and flowers in angiosperms Stems: located above ground and support leaves and flowers Leaves: main sites of photosynthesis in most plants Plant: Cell Structure Plants: 3 Tissue Systems Instead of organs, plants have roots, stems, and leaves are made of three tissue systems The epidermis The vascular tissue system The ground tissue system PLANTS: Epidermis and Vascular Tissue The epidermis covers and protects the plant The cuticle is a waxy coating secreted by epidermal cells that helps the plant retain water The vascular tissue contains xylem and phloem It provides support and transports water and nutrients Xy: high (water) Phlo: lo (nutrients) Rise of water: transpiration pull, capillary action, root pressure Phloem transports food molecules made by photosynthesis Figure 32.5B Figure 32.3 Plants: Vascular & Ground Tissue Vascular tissue: Xylem: inside, bring water up; usually dead cells act as tube Phloem: outside bundle, brings nutrients down Pith: storage and structure Cambium: growth tissue – divide into xylem and phloem (2nd growth) The ground tissue system functions mainly in storage and photosynthesis VASCULAR TISSUE SYSTEM Xylem Phloem Epidermis GROUND TISSUE SYSTEM Cortex Endodermis Figure 31.6B These microscopic cross sections of a dicot and a monocot indicate several differences in their tissue systems Figure 31.6C Three tissue systems in dicot leaves Epidermis: stomata (singular, stoma) surrounded by guard cells – regulate opening/closing of stomata Figure 31.6D Ground tissue system of a leaf – mesophyll, site of photosynthesis Figure 31.6D Vascular tissue: xylem and phloem Figure 31.6D Plants: Guard cells control transpiration Guard cells: control transpiration Opening and closing of stomata - adaptation to help plants regulate water content / adjust to changing environmental conditions H2O Guard cells H2O H2O H2O H2O H2O K+ H2O Vacuole H2O H2O H2O Stoma opening Stoma closing Figure 32.4 Plant Growth: Primary vs Secondary Most plants continue to grow as long as they live (as opposed to animals that stop growing) Two types of growth: - primary growth (length) - secondary growth (width) Plants: Primary Growth Growth from tissue meristems Meristems: unspecialized, dividing cells (like our stem cells) Apical meristems: tips of roots and stems and terminal buds ; length growth Primary growth (length growth) new cell productions Terminal bud Axillary buds Arrows = direction of growth Root tips Figure 31.7A Cortex Epidermis DIFFERENTIATION Vascular cylinder CELL DIVISION ELONGATION Root hair Cellulose fibers Apical meristem region Root cap Figure 31.7B Plants: Secondary growth Secondary growth: Increase in a plant's width Lateral meristem (also called cambium): Vascular cambium (located between xylem and phloem) Cork cambium (not in grasses or herbs, but found in woody dicots, ex. oaks) Vascular cambium thickens stem by adding layers of secondary xylem, or wood, next to its inner surface Also produces secondary phloem- tissue of bark Cork cambium produces protective cork cells located in bark Figure 31.8A Plants: Secondary Growth Everything outside vascular cambium – bark Secondary phloem Cork cambium Protective cork cells Woody log result of several years of secondary growth (inside “dead”; outside “growing”) Sapwood Rings Wood rays Heartwood Sapwood Vascular cambium Secondary phloem Bark Cork cambium Cork Heartwood Figure 31.8B Plant: Behavior = Tropism Plant behavior: Phototropism Gravitropism Geotropism thigmotropism Figure 33.1A Phototropism is the bending toward light It may result from auxin moving from the illuminated side to the shaded side of a stem Figure 33.1A Gravitropism is a response to gravity Figure 33.9A Thigmotropism - response to touch Responsible for coiling of tendrils and vines around objects Enables plants to use other objects for support while growing toward sunlight Figure 33.9B Phototropism Shaded side of shoot Light Illuminated side of shoot Figure 33.1B Hormone controls phototropism Light Control Figure 33.1C Tip removed Tip covered by opaque cap Tip covered by transparent cap DARWIN AND DARWIN (1880) Base covered by opaque shield Tip separated by gelatin block Tip separated by mica BOYSEN-JENSEN (1913) Shoot tip placed on agar block. Chemical (later called auxin) diffuses from shoot tip into agar. Agar Control Block with chemical stimulates growth. Offset blocks with chemical stimulate curved growth. Other controls: Blocks with no chemical have no effect. NO LIGHT Figure 33.1D Plants: Hormones Hormones affect: cell elongation cell differentiation Table 33.2 Auxin: stimulates cell division – phototropism and geotropism Positive and negative geotropism (b/c unequal distribution of hormone, unequal growth & root grows faster) Plants: Hormones Cytokinins: promote cell division Produced in actively growing roots, embryos, and fruits Opposite auxin, so plant coordinates growth of root and shoot systems Cytokinins – develop side growth Ex grow branch Auxin – stimulate length growth w/o auxin, plant becomes thicker b/c cytokinins Terminal bud No terminal bud Figure 33.4 Plants: Hormones Gibberellins: stimulate cell elongation and cell division in stems and leaves Gibberellins: can stimulate seed growth Figure 33.5A Gibberellins with auxin - influence fruit development Grapes at right treated with gibberellin, left not Figure 33.5B Plants: Hormones Abscisic acid (ABA) inhibits germination of seeds Ratio of ABA & gibberellins determines whether seed remain dormant or germinate Also “stress hormone” – close stomata when too dry Seeds of many plants remain dormant until ABA inactivated or washed away Ex. flowers grow from seeds after rainstorm in Mojave Desert Figure 33.6 Plants: Hormones Ethylene: triggers fruit ripening Given off as cells age Figure 33.7A Fruit growers use ethylene to control ripening Apple farmers slow down ripening action of natural ethylene Tomato farmers pick unripe fruit and then pipe ethylene into storage bins to promote ripening Plants: Circardian Rhythms Circadian rhythms: internal biological clock controls daily cycles Even in the absence of environmental cues, they persist with periods of about 24 hours But such cues are needed to keep them synchronized with day and night Figure 33.10