Unit 4: Plant Anatomy

Basic Plant Cell

Cell is smallest unit which exhibits life characteristics Features unique to plant cells are cell wall, chloroplasts, plasmodesmata, large central vacuole Cell wall surrounds cell on outside of the plasma membrane Made of cellulose which gives shape, protection, strength Porous, containing channels called plasmodesmata that enable transport and communication between neighboring cells Plasma membrane regulates specialized movement of substances in and out of cells Cytoplasmic membrane surrounding a large central vacuole is called a tonoplast Vacuoles are membrane-ground sacs involved in plant cell growth and storage of water, enzymes, pigments, ions, and waste proucts Plastids are membrane-bound organelles responsible for photosynthesis, storage of products like starch, and molecule synthesis Chloroplasts are site of phosynthesis, absorbing sunlight using green pigment, chlorophyll, and converting it into chemical energy or glucose Sometimes convert to chromoplasts (such as when fruit ripens) which synthesize and store other pigments giving plants distinctive colors Amyloplasts are responsible for storing glucose molecules produced during photosynthesis by linking them together in long chains of starch Nucleus is genetic control center of cell that contains chromosomes and is surrounded by nuclear envelope Mitochondria generate most of cell's chemical energy ATP 

Osmosis and Turgor Pressure Diffusion is movement of particles from high to low concentration Osmosis - water molecules cross semi-permeaeble membranes moving from more dilute to more concentrated  Hypotonic solutions have lower concentration of solutes relative to cell Hypertonic solutions have higher concentration of solutes compared to cell Isotonic solutions contain the same relative solute concentration as the cell Turgor pressure enables plant to hold itself upright against gravity Allows plants to swell instead of burst with water intake Plant cells with correct internal water pressure are said to be turgid Plants with too little internal water are said to be flaccid or plasmolysed Loss of water from a plant cell is called plasmolysis

Plant Organ Anatomy

Tissue systems Meristematic & permanent tissue Primary growth (length) and secondary growth (width) occur from addition of new tissue via mitotic cell division All plants have primary cell walls which are flexible and can expand as the cell grows Some plants have secondary cell walls which contain lignin, are inflexible, and provide structural support Meristematic tissue cells are totipotent (are able to differentiate into the entire variety of mature cell types) and are undifferentiated or incompletely differentiated Miotic cell division occurs here Apical, lateral, or intercalary Once formed, continue as meristematic or become permanent tissue  Small cells with thin walls and dense cytoplasm with small vacuoles Large, dense nuclei contain chromatin and is located centrally Meristems can form from other injured cells & aid wound healing Apical meristems or primary meristems give rise to primary plant body located at tips of stems and roots enabling plant to extend in length  plant shoot system originates here as leaf and bud primordia, more complex than SAM Lateral meristems are secondary meristems because they're responsible for secondary growth or increase in girth and thickness in a maturing plant Not all plants exhibit secondary growth Intercalary meristems occur at base of leaf blades and at nodes Enables a leaf blade to increase in length from the base Permanent tissue cells are no longer actively dividing but are differentiated into cells with distinct functions ground, epidermal, and vascular May be living or dead, thin or thick-walled Meristems produce cells that differentiate or specialize and become permanent to take on specific roles and can no longer divide Dermal tissues cover and protect plant Outermost covering Water regulation, protection, gas exchange Epidermis is a single layer of cells covering and protecting underlying tissue Bark is a tough, waterproof outer layer of cork cells that protect woody plants from damage Epidermal cells are the most numerous and least differentiated of the cells in the epidermis with thin walls, no chloroplasts, and alive at maturity. They secrete a waxy cuticle The following features have specialized guard cells Stomata are openings through which the uptake of carbon dioxide and release of oxygen and water vapor can occur on the epidermis of aerial ports of plant the guard cells on each stoma or pore shrink and swell to control exchange and water loss They have chloroplasts, are the only epidermal cells capable of photosynthesis Trichomes are hair-like structures on surface of leaves and stems that develop from epidermal cells reduce loss of water from shoot system by decreasing flow of air over plant surface Can increase solar reflectance to protect against UV & overheating Glandular trichomes can store & exude compounds that defend against herbivory Root hairs are tiny hair-like extensions of root epidermis that absorb water and mineral nutrients in the soil Increase root surface to access most amount of soil Vascular tissue transports water, minerals, sugars to different parts Consists of xylem and phloem - long distance transport Lie adjacent to each other and are arranged in distinct strands called vascular bundles which run up and down the stem The vascular bundle includes the phloem and xylem strands, meristematic tissue called vascular cambium sandwiched in between that creates new vascular tissue allowing secondary growth Xylem conducts water and minerals from roots to leaves via transpiration (loss of water from stomata of plant) Composed of tracheids, vessel elements, xylem parenchyma, and xylem fibers Tracheids and vessel elements are dead at maturity & have thick cell wells of lignin, joined end to end to form hollow tube for water flow pits in side of walls allow water to move from one cell to another In growing tissue, lignified part of cell wall is in rings or helix allowing extension In nonexpanding parts, cell wall forms as netlike or pitted structure for mechanical support Xylem parenchyma are the only living cells in xylem involved in storage Xylem fibers are sclerenchyma cells in between vessels and tracheids for mechanical support Phloem tissue are composed of companion cells, sieve tube elements, phloem parenchyma, phloem slerenchyma Living at maturity  Conduct dissolved sugars and organic molecules in process called translocation that transports products of photosynthesis  to parts where energy is needed or stores Sieve tubes are main conducting channels of phloem and contain cytoplasm but no nucleus Companion cells are special type of parenchyma cell found alongside sieve tubes that provide energy used during translocation Sieve tubes & companion cells not lignified Pholem Parenchyma - storage Phloem Sclerenchyma - mechanical support Ground tissue serves as site for photosynthesis, provides a supporting matrix for vascular tissue, and helps store water and sugars Derived from ground meristem tissue and makes up most of plant body Metabolism, support and defense    Three types mainly differing on wall structure Ground Parenchyma cells are living cells making up bulk of soft internal tissue, commonly called pith Thin, flexible cell walls Large water filled vacuoles Storage and metabolism May contain sugars, organic acids, defense compounds, and starch                                Ground Collenchyma are living cells that are long and narrow with unevenly thick extensible cell walls composed of cellulose and pectin Found in strands or sheets beneath epidermis (young stems, petioles, leaf veins) Provide flexible support to actively growing regions Sclerenchyma cells take over role of mechanical support when growth is complete Ground Sclerenchyma cells are typically dead, providing structural support and protection to non-growing regions Cell walls are hard and rigid due to deposition of lignin Classified as sclereids or fibers based on shape Fibers are elongated with tapering ends and often occur in bundles contribute more than half the volume of woody tissue and are found in all stems & leaves that are hard and tough Sclereids are shorter with more abundant and elaborate pitting Found in structures like seed coats, walnut shells, peach pits

Tissue Arrangements

Stems Epidermis of stem has distinct cuticle exuded by aerial dermal cells Vascular bundles arranged throughout Monocots have scattered vascular bundles without meristematic vascular cambium Dicots have vascular bundles arranged in a ring with distinct line of vascular cambium seperating xylem from phloem Outer ground tissue of dicot stem is the cortex, inner tissue is pith

Roots Epidermis of a root will vary from epidermis of shoots because it won't have cuticle since it needs to absorb soil water Cortex is composed of parenchyma cells loosely packed for aeration Storage of extra sugar as starch Endodermis is innermost layer of cortex with tightly packed cells with waterproof band known as Casparian strip that regulates flow of water into xylem Pericycle is a layer of cells just within the endodermis containing meristematic cells where lateral roots emerge from Stele is the cluster of vascular tissue at the center of the root  In dicots, will appear as an X In monocots, will form a ring around pith (parenchyma cells similar to the cortex)

Leaves Epidermis of leaves will have distinct cuticle as well as an upper and lower epidermal layer Stomata mostly on underside of the leaf to protect from dust and debris and keep sheltered from direct light so water loss is limited Dicot leaves appear different from monocots in that they have distinct palisade and spongy mesophyll (middle leaf) cells Palisade cells will be rectangular, filled with chloroplasts, occur just below the upper epidermis Main photosynthesizers in leaf Spongy cells are smaller and irregular occuring closest to lower epidermis, large air pockets ensure space for gas exchange Monocot leaves have regularly occurring vascular bundles that can be seen in cross section due to parallel venation Reticulate venation of dicots means a cross section will only capture a few veins perfectly across so their vascular bundles will appear more irregular and scattered