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PLANT STRUCTURE AND FUNCTION Life - Plants Copyright © 2009 Pearson Education, Inc. Evolution and types of plants Since the earth was once Plants can be placed covered in water, plants under two groups had to make three Vascular- having true adaptations to survive on roots, leaves, and stems land The ability to prevent water loss The ability to reproduce in the absence of water The ability to absorb and transport nutrients Ex. ferns, conifers, flowering plants Nonvascular- not having true roots, leaves, and stems Ex. mosses, liverworts, hornworts Vascular Plants can be divided into two groups Seedless Plants Made up of ferns and plants closely associated with ferns Seed Plants Two types of seed plants Gymnosperms- which includes pine trees, produce seeds that are not encased in fruit Angiosperms- aka flowering plants, produce seeds within a protective fruit The two main groups of angiosperms are the monocots and the dicots Monocots (Ex. Lilies, onions, corn, grasses, wheat) – One cotyledon – Parallel leaf venation – Scattered vascular bundles – Flower parts in 3s or multiples of 3 – Fibrous roots The two main groups of angiosperms are the monocots and the eudicots Dicots—most plants are eudicots (Ex. Trees) – Two cotyledons – Branched leaf venation – Ring of vascular bundles – Flower parts in 4s or 5s (or multiples) – Taproot system A typical plant body contains three basic organs: roots, stems, and leaves Plants absorb water and minerals from soil through roots Plants absorb the sun’s energy and carbon dioxide from the air through shoots (stems and leaves) Plant roots depend on shoots for carbohydrates produced via photosynthesis Plant shoots depend on roots for water and minerals Copyright © 2009 Pearson Education, Inc. A typical plant body contains three basic organs: roots, stems, and leaves Plant roots – Anchor plant – Absorb water and minerals – Store food Plant shoots – Stems, leaves, and reproductive structures – Stems provide support – Leaves carry out photosynthesis Copyright © 2009 Pearson Education, Inc. Terminal bud Leaf Shoot system Blade Flower Petiole Axillary bud Stem Node Internode Root hairs Root hair Taproot Root system Epidermal cell Many plants have modified roots, stems, and leaves Modifications of plant parts are adaptations for various functions – Food or water storage – Asexual reproduction – Protection – Climbing – Photosynthesis Copyright © 2009 Pearson Education, Inc. Many plants have modified roots, stems, and leaves Root modifications – Food storage – Large taproots store starches – Examples include carrots, turnips, sugar beets, sweet potatoes Many plants have modified roots, stems, and leaves Stem modifications – Stolon—asexual reproduction – Rhizomes—storage, asexual reproduction – Tubers—storage, asexual reproduction – Cactus stem—water storage and photosynthesis Many plants have modified roots, stems, and leaves Leaf modifications – Protection – Cactus spine, Thorns – Climbing – Pea plant tendril Three tissue systems make up the plant body Dermal tissue – tightly packed epidermis cells – First line of defense – Waxy layer called cuticle – reduces water loss Three tissue systems make up the plant body Vascular tissue – Composed of xylem and phloem – Xylem transports water from roots to leaves – Phloem transports glucose made in leaves to nonphotosynthetic parts of the plant – Arranged in bundles Ground tissue – Leaf ground tissue is called mesophyll – Bulk of plant body – Food production and storage (because it contains chloroplasts) Review of 3 types of tissues Plant cells and tissues are diverse in structure and function Plants cells have three structures that distinguish them from animals cells – Chloroplasts used in photosynthesis – A large, fluid-filled vacuole – A cell wall composed of cellulose Transpiration Transpiration – water is absorbed through roots (specifically root hairs); as water evaporates from the stomata openings it pulls water up through the plant from a combination of cohesion (water attracted to itself) and adhesion (water attracted to the tree) Transpiration demo PLANT GROWTH Copyright © 2009 Pearson Education, Inc. Primary growth lengthens roots and shoots Plant growth is indeterminate – Growth occurs throughout a plant’s life – Plants are categorized based on how long they live – Annuals complete their life cycle in one year – Biennials complete their life cycle in two years – Perennials live for many years Animal growth is determinate – Growth stops after a certain size is reached Copyright © 2009 Pearson Education, Inc. Primary Growth and Secondary Growth Primary growth is the vertical growth of a plant (shoot growing up and root growing down). Secondary growth is an increase in diameter of roots and shoots (getting thicker). This growth does not occur at all parts of the body like in animals. This is because not all cells in a plant divide. Meristem – small, unspecialized cells that divide continually Meristem There are two types of meristem cells. 1. Apical meristem – located at the tips of roots and shoots Responsible for primary growth 2. Lateral meristem – cells responsible for creating more xylem / phloem and bark Responsible for secondary growth Primary growth allows roots to push downward through the soil and shoots to grow upward Terminal bud Axillary buds Arrows = direction of growth Root tips Secondary growth increases the girth of woody plants Year 1 Early Spring Year 1 Late Summer Year 2 Late Summer Key Dermal tissue system Ground tissue system Vascular tissue system Shed epidermis Primary xylem Vascular cambium Primary phloem Epidermis Cortex Secondary xylem (wood) Cork Cork cambium Secondary phloem Bark Secondary xylem (2 years’ growth) Secondary growth increases the girth of woody plants Vascular cambium produces cells in two directions – xylem produces wood toward the interior of the stem – The xylem is responsible for water transport in plant – Moves water through transpiration – phloem produces the inner bark toward the exterior of the stem – Living tissue of the tree that is responsible for moving sugar throughout the plant Secondary growth increases the girth of woody plants Cork cambium produces the outer bark, which is composed of cork cells Copyright © 2009 Pearson Education, Inc. Secondary growth increases the girth of woody plants Wood annual rings show layers of xylem – In temperate regions, periods of dormancy stop growth of secondary xylem – Rings occur in areas when new growth starts each year The bark (phloem and cork) is sloughed off over time Secondary growth increases the girth of woody plants Part of the Xylem Sapwood transports water Heartwood stores resins and wastes