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basic plant organs

-the plant body contains three basic organs:
-roots, stems, and leaves
-each of these organs are composed of different tissues
-the organ structure correlates nicely with function
-plants must draw water and minerals from soil and water and CO2 from the environment
-plant root and plant shoot cannot survive without one another


root system

-anchors the plant in soil
-absorbs ad transports minerals and water
-stores food
-near the root tips there is an abundance of root hairs
-increases surface area


shoot system

-made of stems and leaves
-also reproductive structures such as flowers
-stems: generally above ground
-support leaves and flowers
-nodes: point at which leaves are attached
-internodes: portions of the stem between the nodes
-leaves: main photosynthetic organs
-composed of a flattened blade and a stalk called a petiole which joins the leaf to the node of the stem


two types of buds

terminal buds
axillary buds



terminal buds: at the apex tip of the growing stem
-has developing leaves and a compact series pf nodes and internodes
axillary buds: these are within the angle between the leaf and the stem
-usually dormant
-hormones produced by the terminal buds inhibit their growth-this is called apical dominance
-concentrating resources toward growing taller increases the plants exposure to sunlight, important when vegetation is dense
-under some conditions the axillary buds begin to grow and removing the terminal bud often stimulates the growth of the axillary bud


3 modified root stems

horizontal stem (runner)


horizontal stems

grows along the ground surface
-allows plant to reproduce asexually
ex) strawberry plant



horizontal stems that grow either right below or along the surface of the soil
-they store food and may also spread and form new plants
-potato plants have rhizomes which end in enlarged structures called tubers which are specialized for storage (the potato)



underground shoots which contain swollen leaves for food storage


modified leaves




the tips are coiled around a stem
-this helps the plant to climb such as in a grapevine



spines of a cactus are a modified leaf that protects against being eaten by animals


three main plant tissues

-tissue: group of cells with common structure, function or both
tissue system: composed of one or more functional units within a plant
-the plant root system, stem and leaf are all made of three tissue systems:
1. dermal tissue
2. vascular tissue
3. ground tissue
-three tissue systems have different arrangements in different organs


dermal tissue system

-forms an outer protective covering
-first line of defense against physical damage and infectious organisms
-consists of:
-epidermis: single layer of tightly packed cells
-cuticle: waxy outer covering atop the epidermis, protects against waste loss


vascular tissue

-composed of xylem and pholem tissues
-provides support and long distance transport


ground tissue

-not dermal or vascular
-accounts for the bulk of a young plant
-fills the space between the vascular tissue and the epidermis
-ground tissue internal to the vascular tissue is the pith
-ground tissue external to the vascular tissue is the cortex
-this system functions in support, storage and photosynthesis
-endodermis: is the inner layer of the cortex
-a cylinder that is one cell layer thick
-a selective barrier that determines which materials can pass between the rest of the cortex and the vascular tissue


ground tissue/ vascular tissue

-water and minerals absorbed from the soil enter through the epidermis
-vascular cylinder: vascular tissue in the center of the root
xylem cells: of dicot radiate from the center like spokes of a wheel
-ring of xylem cells found in root of monocot
-phloem cells of dicot fill the wedges between the spokes
-ring of pholem cells found in root of monocot
-the region between the vascular cylinder and the epidermis consists entirely of cortex
-the cortex cells store food and starch and take up minerals that have entered the root via the epidermis


eudicots and monocots have different stem arrangements

-both have vascular tissues arranged in vascular bundles
-monocot stem has vascular bundles scattered throughout the ground tissues
-eudicot stem has vascular bundles arranged in a ring
-unlike root a eudicot stem has both a cortex region and a pith region
-cortex fills the region between the vascular ring and the epidermis
-pith fills the center of the stem and is often vital for food storage
-monocot stems are not divided into pith and cortex


eudicot leaf tissue arrangement

-pores called stomata interrupt the epidermis
-these allow Co2, exchange between the air and the photosynthetic cells within the leaf
-each of the stoma is boarded by two guard cells which regulate the size of the stromata opening
-ground tissue of the leaf is called mesophyll and is sandwiched between the upper and lower epidermis
-consists predominately of photosyntheic parenchymal cells
-chloroplasts are located within these cells
-cells of the lower mesophyll are loosely arranged with air spaces allowing O2 and CO2 to circulate


leaf vascular tissue

-eudicots and monocots have vascular tissue is the leaf made up of a network of veins
-each vein has a vascular bundle composed of xylem and phloem
-the xylem and phloem arw in close contact with the lead photosynthetic organs
-this ensures that photosynthetic tissues are supplied with water and mineral nutrients from the soil and that the sugars made by photosynthesis are transported to the rest of the plant
-the vascular structure also behaves as a skeleton, maintaining the leaf shape


unique plant structures

-three structures distinguish plants from other eukaryotes
-chloroplasts: the site of photosynethesis
-a central vacuole: contains fluid to help maintain the cell shape
-a cell wall made from cellulose, a carbohydrate which surrounds the plasma membrane
-many plant cells have two cell walls
-the first is called the primary cell wall and is laid down first
-a more rigid secondary cell wall is laid down second between the plasma membrane and the primary cell wall
-the middle lamella is sticky layer that holds the primary cell walls of adjacent cells together
-pits are regions where the cell wall is relatively thin allow the migration of water between adjacent cells
-plasmodesmata are channels of communication and circulation between adjacent plant cells


five types of plant cells

1. parenchymal cells
2. collenchyma cells
3. sclerenchyma cells
4. water-conducting cells
5. food conducting cells


parenchymal cells

-most abundant cell type
-have only primary cell walls which are thin and flexible
-preform most metabolic plant function
-aerobic respiration
-food storage
-most can divide and differentiate into other types of plant cells


collenchyma cells

-also do not have secondary cell walls
-have unsually thickened primary cell walls
-provide flexible support in parts of the plant that are still growing
-young stems and petioles often have collenchyma cells just below their surface
-these cells remian alive and elongate as stems and leaves grow


sclernchyma cells

-have thick secondary walls
-strengthened with lignin the primary component of wood
-mature cells cannot elongate and thus are found in regions of the plant that have stopped growing
-most are dead at maturity
-these cells form a rigid cell skeleton to support the plant
-there are two types of cells: fibers and sclerids
1. fibers: are long and slender and often arranged in bundles
2. sclereids: shorter than fiber cells, have thick irregular and very hard secondary walls
-cells responsible for hardness of nutshells


water conducting cells

-two types in angiosperms: tracheids and vessel elements
-both types have rigid, lignin containing secondary cell walls
-tracheids: long, thin cells with tapered ends
vessel elements: wider, shorter, and less tapered
-chains of both these cell types form tubers by over lapping their end
-carries water from the roots to the stems and leaves as part of the xylem tissue
-these tubers are hollow and the cells dead when they are mature-only thier cell walls remain
-rigid, thick walla allow these cells to function in support


food conducting cells

-sleve-tube members are arranged end to end like xylem forming tubes
-remian alive at maturity but lose most organelles ( not nucleus and ribosomes)
-allows more room for the transport of materials
-end walls have sleeve plates containing pores that allow fluid to flow from cell to cell
-companion cells are alongside each sleeve-tube cell (at least one) connected by plasmodesmata and function to supply the cell with proteins


summary of plant cell types

-plant cells are grouped into tissues:
-xylem tissue functions to transport water and dissolved minerals upward from the root
-phloem contains sieve-tube members that transport sugars from leaves/storage tissues to other parts of the plant
-the vascular tissue system, the dermal and ground tissue systems make up each plant organ (leaf, root, ect)