Plants Tissues, Organs, and Systems
Meristematic cells Specialized cells that are responsible for producing specialized cells, they produce three types of tissue in the body of a plant. Meristematic Cells Dermal tissue Ground tissue Vascular tissue Epidermal cells Carries out tasks transport
Three basic organs evolved: roots, stems, and leaves Reproductive shoot (flower) Terminal bud Node Internode Terminal bud Shoot system They are organized into a root system and a shoot system Leaf Vegetative shoot Blade Petiole Axillary bud Stem Taproot Lateral roots Root system Figure 35.2
A Root Is an organ that anchors the vascular plant Absorbs minerals and water Often stores organic nutrients In most plants The absorption of water and minerals occurs near the root tips, where vast numbers of tiny root hairs increase the surface area of the root Figure 35.3
A stem is an organ consisting of An alternating system of nodes, the points at which leaves are attached Internodes, the stem segments between nodes An axillary bud Is a structure that has the potential to form a lateral shoot, or branch A terminal bud Is located near the shoot tip and causes elongation of a young shoot
Leaves The leaf Is the main photosynthetic organ of most vascular plants Leaves generally consist of A flattened blade and a stalk The petiole, which joins the leaf to a node of the stem
Leaf anatomy Cuticle Sclerenchyma fibers Key to labels Dermal Ground Vascular Stoma Guard cells Stomatal pore Epidermal cell (b) 50 µm Surface view of a spiderwort (Tradescantia) leaf (LM) Upper epidermis Bundlesheath cell Palisade mesophyll Spongy mesophyll Guard cells Cuticle Lower epidermis (a) Xylem Phloem Cutaway drawing of leaf tissues Guard cells Vein Figure 35.17a c Vein Air spaces Guard cells (c) Transverse section of a lilac (Syringa) leaf (LM) 100 µm
Tissue Organization of Leaves The epidermal barrier in leaves Is interrupted by stomata, which allow CO 2 exchange between the surrounding air and the photosynthetic cells within a leaf The ground tissue in a leaf Is sandwiched between the upper and lower epidermis The vascular tissue of each leaf Is continuous with the vascular tissue of the stem
Monocots and dicots Differ in the arrangement of veins, the vascular tissue of leaves Most monocots Have parallel veins Most dicots Have branching veins
In classifying angiosperms Taxonomists may use leaf morphology as a criterion (a) Simple leaf. A simple leaf is a single, undivided blade. Some simple leaves are deeply lobed, as in an oak leaf. (b) Compound leaf. In a compound leaf, the blade consists of multiple leaflets. Notice that a leaflet has no axillary bud at its base. (c) Doubly compound leaf. In a doubly compound leaf, each leaflet is divided into smaller leaflets. Petiole Axillary bud Leaflet Petiole Axillary bud Figure 35.6a c Leaflet Petiole Axillary bud
All the major organs of a plant are made of all three tissue types. Dermal Vascular and Ground tissues Dermal tissue Figure 35.8 Ground tissue Vascular tissue
The dermal tissue system Consists of the epidermis and periderm Ground tissue Includes various cells specialized for functions such as storage, photosynthesis, and support
The vascular tissue system Carries out long-distance transport of materials between roots and shoots Consists of two tissues, xylem and phloem Xylem Conveys water and dissolved minerals upward from roots into the shoots Phloem Transports organic nutrients from where they are made to where they are needed
Like any multicellular organism A plant is characterized by cellular differentiation, the specialization of cells in structure and function Some of the major types of plant cells include Parenchyma Collenchyma Sclerenchyma Water-conducting cells of the xylem Sugar-conducting cells of the phloem
Water-conducting cells of the xylem and sugarconducting cells of the phloem WATER-CONDUCTING CELLS OF THE XYLEM SUGAR-CONDUCTING CELLS OF THE PHLOEM Vessel Tracheids 100 m Sieve-tube members: longitudinal view Pits Companion cell Sieve-tube member Tracheids and vessels Sieve plate Vessel element Vessel elements with partially perforated end walls Tracheids Cytoplasm Nucleus Companion cell 30 m 15 m Figure. 35.9
Meristems generate cells for new Apical meristems organs Are located at the tips of roots and in the buds of shoots Elongate shoots and roots through primary growth Lateral meristems Add thickness to woody plants through secondary growth
An overview of primary and secondary growth Shoot apical meristems (in buds) Primary growth in stems Epidermis In woody plants, there are lateral meristems that add secondary growth, increasing the girth of roots and stems. Vascular cambium Cork cambium Lateral meristems Pith Cortex Primary phloem Primary xylem Apical meristems add primary growth, or growth in length. Figure. 35.10 Root apical meristems Pith Primary xylem Secondary xylem Secondary growth in stems Vascular cambium Periderm Cork Secondary phloem cambium The cork cambium adds secondary dermal tissue. Cortex Primary phloem The vascular cambium adds secondary xylem and phloem.
In woody plants Primary and secondary growth occur simultaneously but in different locations Terminal bud Bud scale Axillary buds This year s growth (one year old) Leaf scar Stem Internode Node One-year-old side branch formed from axillary bud near shoot apex Last year s growth (two years old) Leaf scar Scars left by terminal bud scales of previous winters Figure 35.11 Growth of two years ago (three years old) Leaf scar
Primary growth lengthens roots and shoots Primary growth produces the primary plant body, the parts of the root and shoot systems produced by apical meristems The primary growth of roots Produces the epidermis, ground tissue, and vascular tissue
Primary Growth of Roots The root tip is covered by a root cap, which protects the delicate apical meristem as the root pushes through soil during primary growth Cortex Vascular cylinder Epidermis Key Dermal Ground Vascular Root hair Zone of maturation Zone of elongation Apical meristem Root cap Zone of cell division Figure 35.12 100 m
Organization of primary tissues in young roots Epidermis Cortex Vascular cylinder Endodermis Pericycle Core of parenchyma cells Xylem 100 m (a) Transverse section of a typical root. In the roots of typical gymnosperms and eudicots, as well as some monocots, the stele is a vascular cylinder consisting of a lobed core of xylem with phloem between the lobes. Phloem 100 m (b) Transverse section of a root with parenchyma in the center. The stele of many monocot roots is a vascular cylinder with a core of parenchyma surrounded by a ring of alternating xylem and phloem. Endodermis Pericycle Key Dermal Ground Vascular Xylem Phloem Figure 35.13a, b 50 m
Primary Growth of Shoots A shoot apical meristem Is a dome-shaped mass of dividing cells at the tip of the terminal bud Gives rise to a repetition of internodes and leafbearing Apical meristem Leaf primordia nodes Developing vascular strand Figure. 35.15 0.25 mm Axillary bud meristems
In most monocot stems The vascular bundles are scattered throughout the ground tissue, rather than forming a ring Ground tissue Epidermis Vascular bundles Figure 35.16b 1 mm (b) A monocot stem. A monocot stem (maize) with vascular bundles scattered throughout the ground tissue. In such an arrangement, ground tissue is not partitioned into pith and cortex. (LM of transverse section)
Plant growth Like multicellular animals (like humans) plants can form new cells and tissues, BUT Unlike humans they also regularly form new organs throughout their lives. Plants growth is mainly upward and downward, meaning these areas are where meristematic cells are found. A plant can also grow outward, as its stem becomes wider in a layer meristematic cells called cambium.