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Transcript
Seed Plant Structure and Function Chapter 23 Seed Plant Overview: • The plant body consists of two basic parts--- the shoot system and the root system • Shoot system is above ground and includes organs such as leaves, buds, stems, flowers, and fruits • The functions of the shoot system include photosynthesis, reproduction, storage, transport, and hormone production • The root system is below ground and includes roots as well as modified stem structures such as tubers and rhizomes • The functions of the root system include anchorage, absorption, storage, transport, and production of certain hormones Seed Plant Overview Cont.: • Seed plants contain 2 types of vascular tissue (xylem & phloem) to help transport water, minerals, & food throughout the root & shoot systems • Plant cells have several specialized structures including a central vacuole for storage, plastids for storage of pigments, and a thick cell wall of cellulose • Plant cells are all box-shaped in appearance Plant Cell Organization • Plant cells are arranged into tissues and tissue systems • A simple tissue is composed of only one type of cell; a complex tissue is composed of more than one cell type. • Plants are composed of specialized cells and tissues • In plants, the formation of new cells, tissues and organs is restricted almost entirely to regions known as meristems Meristems: • There are 3 main types of meristematic tissue in vascular seed plants ---- apical, intercalary, & lateral meristems Meristems: • Apical Meristem occur at the tips of roots and shoots and are responsible for the length-wise extension of the plant body known as primary growth • Cells in apical meristems are produced by mitosis & then differentiate into specialized cells & tissues Intercalary Meristems • Some monocots, such as grasses & bamboo, have intercalary meristems located above the bases of leaves and stems allowing them to regrow quickly after being cut down Growth in Plants • Woody plants have meristem between xylem & phloem to produce wood • Lateral meristems produce outward growth in plants or secondary growth • Lateral meristems are called cambium (cambia, plural) • Vascular cambium makes wood & vascular tissues and cork cambium makes cork & bark • Plants without lateral meristems have only primary, not secondary growth and are called herbaceous plants Specialized Plant Cells: • Plants have 3 basic types of cells --parenchyma, collenchyma, & sclerenchyma • Parenchyma cells are the most abundant & least specialized • Parenchyma are loosely-packed, cube shaped or elongate cells with a large central vacuole & thin cell walls Parenchyma • Parenchyma cells can specialize for various functions (storage, photosynthesis, etc.) • Parenchyma form the bulk of non-woody plants such as the fleshy part of an apple • Collenchyma cells are irregular in shape with thicker cell walls & support the growing parts of plants Collenchyma Collenchyma cell walls are also flexible to support new growth regions of the plant (example: tough strings on a celery stalk) Sclerenchyma • Sclerenchyma cells support non-growing parts of plants because they have thick, rigid, non-stretchable cell walls • Sclerenchyma Cells • Sclerenchyma cells often die at maturity leaving empty, box-like structures • Two types of sclerenchyma cells are fibers & sclereids • Fibers are cells up to 50cm long that usually occur in strands such as linen & flax • Sclerenchyma Fibers • Sclereids have thicker cell walls & come in many shapes • Sclereids may be single cells or groups of cells and give pears their gritty texture & give hardness to peach pits & walnut shells Sclerynchyma Fibers Sclerynchyma Sclereid Fibers Other Plant Tissues & Systems: • Tissues are groups of cells with similar structures & functions • Plants have 3 tissue systems --- ground, dermal, and vascular tissues • Plant tissues make up the main organs of a plant --- root, stem, leaf, & flower • Ground tissue makes up most of the plant's body, dermal tissue covers the outside of the plant, & vascular tissue conducts water & nutrients Dermal Tissue: • Covers the plant body and consists of epidermis in young plants & non-woody plants that is replaced later by periderm in woody plant • Epidermis is made of parenchyma cells in a single layer • Epidermis on stem and leaves prevents water loss by transpiration & produces a waxy material called cuticle Dermal Tissue: Guard Cells surrounding stoma • Openings in the epidermis on the underside of a leaf where gases are exchanged are called stomata (stoma, singular) • Sausage-shaped guard cells are found on each side of the stoma to help open and close the pore to prevent water loss • Dead cork cells replace epidermis in woody stems & roots Ground Tissue: • Ground tissue constitutes the majority of the plant body and contains parenchyma, collenchyma, and sclerenchyma cells • Ground tissue of the leaf (called mesophyll) uses the energy in sunlight to synthesize sugars in a process known as photosynthesis • Spongy Mesophyll of Leaf • Ground tissue of the stem (called pith and cortex) develops support cells to hold the young plant upright • Ground tissue of the root (also called cortex) often stores energy- rich carbohydrates Vascular Tissue: • Vascular tissues transport water and dissolved substances inside the plant and helps support the stem • The 2 types of vascular tissue are xylem & phloem • Xylem carries water and dissolved ions from the roots to stems and leaves • Phloem carries dissolved sugars from the leaves to all other parts of the plant • Xylem has 2 kinds of conducting cells --tracheids & vessel elements Vascular Tissue: • Tracheids are long, narrow sclerenchyma cells with walls and pits for water to move between them • Vessel elements are short, wide sclerenchyma cells without end walls stacked on top of each other • Angiosperms (flowering plants) have tracheids & vessel elements, while gymnosperms (cone bearers) only have tracheids • Phloem moves sap (dissolved sugars & minerals) from source (where they are made) to sink (where they will be used) Phloem Cells Xylem Cells Vascular Tissue: • Phloem is made of cells called sieve tube members and companion cells • sieve tube members are stacked to form tubes called sieve tubes with porous sieve plates between the cells for movement of sugars • Companion cells are along each sieve tube member & help in loading sugar into the sieve tube Root and Shoot system of a plant Root System: • Roots grow underground (subterranean part of the plant) • Roots have 3 main functions --- (1)anchor plants (2) absorb and conduct water & minerals (3) store food • The first root to emerge from the most seeds is called the primary root or taproot & can grow deep to reach water • Taproots may store food (carrot & beet) Root Systems • Monocots have highly branched, roots called fibrous roots that grow near the surface & spread out to collect water • Fibrous roots such as in grasses often help prevent erosion • Adventitious roots grow from a stem or leaf above ground in some plants and serve to prop up or support the plant (corn) • Aerial roots obtain water & minerals from the air & enable the plant to climb (orchids & ivy) Adventitious Roots Arial Roots Taproots Fibrous Roots Structure of the Root: • Root cap covers the apical meristem (growth tissue) at the tip of the root & produces a slimy substance so roots can more easily grow through the ground • Apical meristem replaces cells of the root cap as they are damaged • Epidermis covers the outside of the root & has extensions called root hairs that absorb water & minerals and increase the surface area of the root Structure of the Root: • The core of the root is called the vascular cylinder, contains xylem & phloem • A band of ground tissue called cortex surrounds the vascular cylinder • A single cell layer called endodermis separates the cortex & vascular tissue • Endodermal cells are coated with a waxy layer called the Casparian strip so water is channeled into the vascular tissue • The Pericycle is the outermost layer of central vascular tissue & forms lateral roots Stem Structure & Function: • Adapted to support leaves • Transport water & minerals • Transport sugars (usually sucrose) from Source (where they're made) to Sink (where they're stored) • Movement of sugars is called translocation • Store food and/or water • Tubers (potatoes) underground food storage stems • Stems grow from the tip or apical meristem • Stems increase in circumference by lateral meristems • Leaves are attached to stems at nodes & have lateral buds that can develop into new stems or branches • Internode is space between nodes on a stem • The tip of each stem usually has a Terminal Bud enclosed by specialized leaves called Bud Scales • Vascular Tissue is arranged in bundles with xylem toward the inside & phloem toward the outside • Vascular bundles are scattered throughout monocot stems • Vascular bundles are arranged in rings in dicot stems Stem Structure • Secondary grow (woody growth) occurs in dicots, but less often in monocots • Plants with only primary growth (non-woody) are called herbaceous • Darker wood in the center of a tree trunk is called Heartwood and is composed of old, nonfunctional xylem • New, functional xylem makes up lighter wood in the tree trunk and is called Sapwood • Sapwood gets wider, but heartwood remains the same size • Bark is the protective covering of Woody Plants & consists of Cork, Cork Cambium, and Phloem Translocation of Sugars: • Phloem cells move sugars through a plant • Sugars made in photosynthetic cells are PUMPED into Sieve Tubes by ACTIVE TRANSPORT at the Source • Turgor Pressure Increases as Water enters the Sieve Tube by Osmosis • TURGOR moves the SAP toward the SINKS • Known as the PRESSURE-FLOW HYPOTHESIS Transport of Water: • Transport of Water and mineral Nutrients occurs in the Xylem • Water movement in plants is driven by Transpiration (evaporation of water from leaves & stems) • As water evaporates, more water is pulled into the roots • Transpiration produces a NEGATIVE pressure in the xylem pulling water UPWARD • Water molecules are cohesive (attracted to each other) which also pulls water upward • Water is also adhesive sticking to the walls of the xylem • Known as Cohesion Theory of water movement Leaf Structure & Function: • Flat surfaces helps leaves capture sunlight for photosynthesis • Convert carbon dioxide and water into simple sugars (glucose) • Some leaves store food (onion) and water • Protect (cactus spines) • Used Dyes, Fibers, Fuels, Drugs, Wax, Soap, Spices and Food Leaf Structure & Function: • Attached by a stem-like petiole to the plant • Simple leaves have one blade, while compound leaves have several leaflets • Covered with a single layer of cells called epidermis (upper & lower) • A waxy cuticle prevents water loss • Openings called stomata on the underside of leaves for gas exchange (CO2 & O2) • Two guard cells on either side of the stomata open & close the openings • Two guard cells on either side of the stomata open & close the openings • When guard cells LOSE water, the stoma CLOSE, while the stoma OPEN when guard cells gain water & swell • Stomata are CLOSED during the HOTTEST parts of the day to prevent water loss from leaves • Below the epidermis are 2 types of chlorophyll containing MESOPHYLL cells ---palisade & spongy • PALISADE mesophyll cells are closely packed columnar cells (most photosynthesis occurs here) • SPONGY mesophyll cells are loosely packed with air spaces containing CO2 & O2 • VASCULAR BUNDLES (xylem & Phloem) in the spongy mesophyll appear as VEINS on the surface of the leaf • VENATION is the arrangement of veins in a leaf • Monocots leaves (such as Grasses or Corn Plants) have Parallel Venation • Dicots leaves form a Branched network called Net Venation • In carnivorous plants (Venus Fly Trap), the leaves trap insects for food so the plant can get enough nitrogen (grow in N2 poor soil)