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UNIT 11 – BOTANY Chapters 22 – 24 22.1: What is a Plant? Characteristics of Plants • Plants are eukaryotes with cell walls containing cellulose • Plants carry out photosynthesis – Need sunlight, CO2, H2O, & minerals History & Evolution of Plants • Ancestors of modern plants were waterdwelling organisms similar to algae • Early land plants were centimeters tall – Grew close to the ground to obtain water • Plant evolution: – Became more resistant to drying out – Capable of conserving water 22.2: Seedless Plants Green Algae • Fossil evidence suggests green algae were the first plants • Algae are in fresh or salt water, or moist areas on land – Most are single-celled – Some form multicellular colonies Mosses & Other Bryophytes • Bryophytes—a group of plants that lack vascular tissue – Includes mosses, hornworts & liverworts • Vascular tissue—tissues in plants that carries water & nutrients • Mosses & bryophytes are small so they can draw up water – Are found only in damp environments 22.3: Seed Plants The Importance of Seeds • Seed—plant embryo and a food supply covered in a protective coating • Seeds enabled plants to survive in many environments on dry land • Seed plants are divided into two groups: – Gymnosperms—have seeds in cones (pines & fir trees) – Angiosperms—have seeds in flowers (most plant species) • The male gamete of plants is carried in a pollen grain • Pollination—transfer of pollen grain to female ovule • Embryo of plant contained within the seed is protected by the seed coat • Seeds can survive drought, cold/heat – Embryo begins growing when conditions are right 22.4: Flowering Plants Angiosperm Diversity • Angiosperms reproduce using flowers – Flower develops into fruit to protect seeds • Monocot—angiosperm with one seed leaf – Ex: grasses, lilies, corn • Dicot—angiosperm with two seed leaves – Ex: roses, tomatoes, oak trees • Woody plants—have thick cell walls in stems to support plant – Ex: trees, shrubs • Herbaceous plants—do not have woody stems or tissues – Ex: dandelions, daisies 23.2: Roots • Plant vascular tissues consist of long, slender cells – Xylem—vascular tissue that carries water – Phloem—vascular tissue that carries nutrients & carbohydrates Root Structure & Growth • Root systems in plants: – Taproot—large primary root (trees, carrots) – Fibrous root—many roots branching from base of plant (grasses) Root Anatomy • Dermal tissue – Epidermis protects root – Root hairs absorb nutrients • Ground tissue – Water & minerals move through cortex • Vascular tissue – Contains xylem & phloem in the vascular cylinder • Root cap covers & protects root tip 23.3: Stems Stem Structure & Function • Stems produce leaves, branches & flowers • Stems transport substances throughout the plant using xylem & phloem • Growing stems contain nodes where leaves are attached • Buds—produce new stems & leaves • Vascular bundle—clusters of xylem & phloem in a stem • Dicots have vascular bundles arranged in a ring • Monocots have vascular bundles scattered throughout the stem 23.4: Leaves Leaf Structure & Function • Leaves carry out photosynthesis • Blade—thin, flattened portion of leaf – Attached to stem by the petiole • Epidermis of leaves covered by a waxy cuticle to limit water loss • Xylem & phloem bundled in veins of leaf • Underside of leaf has stomata—small openings for gas & water exchange – Allows for transpiration—loss of water through the leaves Gas Exchange & Homeostasis • Leaves take in CO2 & give off O2 during photosynthesis • Plants maintain homeostasis by keeping stomata open enough for photosynthesis while not losing water – Guard cells—open & close stomata 24.1: Flowers The Structure of Flowers • Flowers bring male & female gametes together for reproduction • Sepals enclose the flower bud • Petals are the colored portion of the flower • Stamen—male parts of the flower – Anthers—on tip of stamen; contain pollen grains • Carpel—female parts of the flower – Ovary—base of carpel; contains ovules • Pistil—tubelike structure leading from ovary; guides pollen to ovule – Stigma—sticky end of pistil 24.2: Fruit & Seeds Seed & Fruit Development • Ovaries thicken to produce fruit that encloses seeds • Fruits may be fleshy (ex: strawberries) or tough & dry (ex: peanuts) Seed Dispersal • Dispersal by animals – Seeds enclosed in sweet, fleshy fruit are eaten by animals – Seeds in animals’ feces grow in new areas – Dry fruits with burs or hooks catch on animal’s fur • Dispersal by wind & water – Seeds dispersed by wind are contained in lightweight fruits – Seeds dispersed by water are contained in fruits that float 24.3: Plant Hormones Hormones • Hormones—chemical signals produced by organisms that affect the growth, activity & development of cells & tissues • Plant hormones control development of cells, tissues, & organs • Auxins—hormones that stimulate cell elongation & growth of new roots – Auxins collect on shaded side of stem – Cells on shaded side lengthen the stem towards the light Tropisms & Rapid Movements • Phototropism—plant grows toward light • Gravitropism—plant bends upright; roots grow downward • Thigmotropism—plants respond to touch • Some plants have rapid leaf movements (ex: Venus flytrap)