Plant structure and functions

Category: Education

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Topic : Plant structure and functions Name : Karen Amante and Renz Mariane Mendoza School : Laguna State Polytechnic University


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The Root System ◦ Underground (usually) ◦ Anchor the plant in the soil ◦ Absorb water and nutrients ◦ Conduct water and nutrients ◦ Food Storage :

The Root System ◦ Underground (usually) ◦ Anchor the plant in the soil ◦ Absorb water and nutrients ◦ Conduct water and nutrients ◦ Food Storage

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The Shoot System ◦ Above ground (usually) ◦ Elevates the plant above the soil ◦ Many functions including: - photosynthesis - reproduction & dispersal - food and water conduction Note: the shoot system includes the leaves and the reproductive organs, although these will be covered in more detail separately.

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Monocots Dicots Floral Arrangement 3’s 4’s and 5’s Leaf Venation Parallel Net Vascular Bundles Scattered Ring Habit Herbaceous Herbaceous + Woody Roots Fibrous Taproot Growth Primary Only Primary and Secondary Examples: Grass, Palm, Orchid Oaks, Roses, Sunflowers

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Cell Types in the Plant Body Parenchyma Cells

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PARENCHYMA CELLS Least specialized plant cells Thin and somewhat flexible cell walls Living at maturity Carry on most of the plant's metabolic functions Generally have a large central vacuole Most parenchyma cells have the ability to differentiate into other cell types under special conditions During repair and replacement of organs after injury

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COLLENCHYMA CELLS Thicker primary cells walls (usually with uneven thickness) Living at maturity Role in support of herbaceous plants Example - the "strings" of celery

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SCHLERENCHYMA CELLS Thick secondary cell walls Dead at functional maturity Cannot increase in length - occur in parts of the plant which have quit growing in length Two types - fibers and schlerids Fibers - long, slender cells with a more or less regular secondary cell wall Example - hemp fibers for making rope Schlerids - shorter cells with an irregular shape Example - stone cells in pears and hard nut and seed shells

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TISSUE ORGANIZATION IN ANGIOSPERM Dermal tissue/ Surface/ Protective The dermal tissue is the boundary between the plant and the outside world. It functions in protection against water loss, regulation of gas exchange, secretion, and (especially in roots) absorption of water and mineral nutrients. There are two main types of dermal tissue: epidermis and periderm . The epidermis is usually transparent (epidermal cells lack chloroplasts) and coated on its outer surface with a waxy cuticle that prevents water loss. Epidermal tissue includes several differentiated cell types, including pavement cells, guard cells, and trichomes (epidermal hairs). The other dermal tissue type is the periderm , or bark. It replaces the epidermis of stems and roots once a plant has developed secondary thickening.

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Epidermis The epidermal tissue functions in prevention of water loss and acts as a barrier to fungi and other invaders. Thus, epidermal cells are closely packed, with little intercellular space. To further cut down on water loss, many plants have a waxy cuticle layer deposited on top of the epidermal cells. Trichomes are minute hairs on the epidermis. On leaves these hairs can interfere with the feeding of some herbivores, prevent frost forming on and damaging the leaf, reduce evaporation due to wind, and reflect light. And in locations where plants get most of their water from cloud drip, leaf hairs maximise this process by acting as points of condensation. Hairs on the roots increase the surface area available to the plant for uptake of water and minerals.

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Vascular Tissue Vascular tissue is a complex tissue and characteristic of vascular plants . The two main components of vascular tissue are the xylem and phloem. The vascular tissue in plants is arranged in long, discrete strands called vascular bundles. These bundles include xylem and phloem, as well as supporting and protective cells. It is involved in the transport of water, ions, minerals, and food.

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Xylem Thick secondary cell walls, often deposited unevenly in a coil-like pattern so that they may stretch. Dead at functionally maturity. Involved in conduct of water and ions in the plant. Two types – tracheids and vessels ๐ Tracheids – long, slender cells connected to each other by pits. Found in all vascular plants. ๐ Vessels – shorter, larger diameter cells with completely perforated cell wall ends. Found only in Angiosperm.

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Phloem Involved in transport of sucrose, other organic compounds, and some ions Living at functional maturity ๐ Protoplast may lack organelles and nucleus, End walls connect to each other via sieve-plates Two Types of cells in the phloem – sieve-tube members and companion cells ๐ Sieve-tube members – actual conduit for sucrose transport. ๐ Companion cells – has a nucleus, that may also control the sieve-tube element and may aid in sucrose loading. ● Sieve Plate – it connects sieve-tube to another sieve-tube

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Ground Tissue/Fundamental It comprises the bulk of the primary plant body. Parenchyma, collenchyma , and sclerenchyma cells are common in the ground tissue.

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Apical Meristems ๐ Located at the tip of roots and shoots ๐ supply cell for the plant to increase in length Lateral Meristems ๐ located near the periphery of the plant, usually in a cylinder ๐ supply cells for the plant to increase in girth

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The Zone of Cell Division- Primary Meristem ๐ Protoderm – outer most primary meristem – produces cell which will become dermal tissue. ๐ Ground meristem – central primary meistem – produces cell which will become ground tissue. ๐ Procambium – innermost primary meristem – produces cell which will become vascular tissue. The Zone of Elongation ๐ Cells elongate up to ten times their original length ๐ This growth pushes the root further downward into the soil The Zone of Maturation ๐ Region of the root where completely functional cells are found

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Root Anatomy- Dicot Roots Epidermis ๐ Dermal tissue ๐ Protection of the root Cortex ๐ Ground tissue ๐ Storage of photosynthetic products ๐ Active in the uptake of water and minerals

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Endodermis ๐ cylinder once cell thick that forms a boundary between the cortex and the stele ๐ even more distinct than dicot counterpart ๐ contains the casparian strip Pericycle ๐ found just inside of the endodermis ๐ responsible for the formation of lateral roots Vascular Tissue ๐ Forms an X – shaped pattern in very center of root

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Root Anatomy - Monocot Roots Epidermis ๐ Dermal tissue ๐ Protection of the root Cortex ๐ Ground tissue ๐ Storage of photosynthetic products ๐ Active in the uptake of water and minerals

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Endodermis ๐ cylinder once cell thick that forms a boundary between the cortex and the stele ๐ even more distinct than dicot counterpart ๐ contains the casparian strip Vascular Tissue ๐ Forms a ring near center of plant Pith ๐ Center most region of root

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Primary Growth of Shoots Apical Meristem ๐ Dome-shaped mass of dividing cells at tip of terminal bud ๐ Gives rise to three primary mersitems : protoderm , ground meristem , and procambium just as root apical meristem ๐ Leaves arise as leaf primordia on the flanks of apical meristem

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Axillary Meristems ๐ Regions of meristematic tissue left behind from apical meristem ๐ Dormant, but have the ability to become activated and form a branch (i.e. becomes the branch's apical meristem ) ๐ Note difference between how shoots forms a branch versus how a root forms a branch ๐ This is do to the position of the vascular tissue in a root vs. the vascular tissue in a shoot ๐ Subtended by a leaf

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Secondary Growth Lateral Meristems add girth by producing secondary vascular tissue and periderm Secondary Plant Body - tissue produced mersitems involved in secondary growth Vascular Cambium - secondary growth meristem which produces xylem and phloem Cork Cambium - secondary growth meristem which produces cork, a tough substance that replaces the epidermis

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Vascular Cambium Secondary growth begins with the initiation of the vascular cambium, a cylinder of meristematic tissue that produces additional xylic and phloic tissues. The cells that eventually form the vascular cambium come from two sources, the procambium in the vascular bundles and the interfascicular parenchyma cells between vascular bundles.

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The Cork Cambium and the Production of Periderm During secondary growth, the epidermis produced by primary growth splits and falls off the stem It is replaced by a new protective tissues produced by the cork cambium A cylinder meristematic tissue that initially forms from the outer cortex of the stem Cork cambium produces cork cells, which form exterior to the cork cambium As cork cells mature, they secrete suberin (a waxy substance) in their cell walls and then die

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Cork cells function as a barrier to protect the stem from physical damage and from pathogens The cork cambium + the cork are known as the periderm The "bark" of the tree consists of the periderm + the phloem Unlike the vascular cambium which can grow in diameter via multiplicative growth, the cork cambium is fixed in size. After a few weeks, the cork cambium loses meristematic ability Expansion splits the original periderm New cork cambium then forms deeper in the cortex of the stem Eventually no more cortex remains, so the cork cambium then forms from parenchyma cells of the secondary xylem

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The Monocot Stem - A Stem Lacking Secondary Growth Monocot stems differ from dicot stems in that they lack secondary growth No vascular cambium nor cork cambium Stems usually uniform in diameter Scattered vascular bundles (not in a ring like dicot stems)

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BY : Karen Mae A. Amante Renz Mariane Mendoza August 29, 2011

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School: Laguna State Polytechnic University

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