Bio Ch 24

Lignin

Chemical that hardens the cell walls of land plants.

Root hair

Extension of a root epidermal cell that collectively increases the surface area for the absorption of water and minerals.

Epidermal tissue

Exterior tissue, usually one cell thick, of leaves, young stems, roots, and other parts of plants.

Bark

External part of a tree, containing cork, cork cambium, and phloem.

Monocot

Flowering plant group; members have one embryonic leaf (cotyledon), parallel-veined leaves, scattered vascular bundles, flower parts in threes or multiples of three, and other characteristics.

Eudicot

Flowering plant group; members have two embryonic leaves (cotyledons), net-veined leaves, vascular bundles in a ring, flower parts in fours or fives and their multiples, and other characteristics.

Perennial

Flowering plant that lives more than one growing season because the underground parts regrow each season.

Shoot apical meristem

Group of actively dividing embryonic cells at the tips of plant shoots.

Shoot system

Aboveground portion of a plant consisting of the stem, leaves, and flowers.

Blade

Broad, expanded portion of a land plant leaf that may be single or compound leaflets.

Axillary bud

Bud located in the axil of a leaf.

Apical meristem

In vascular land plants, masses of cells in the root and shoot that reproduce and elongate as primary growth occurs.

Internode

In vascular plants, the region of a stem between two successive nodes.

Root system

Includes the main root and any and all of its lateral (side) branches.

Mesophyll

Inner, thickest layer of a leaf consisting of palisade and spongy mesophyll; the site of most of photosynthesis.

Endodermis

Internal plant root tissue forming a boundary between the cortex and the vascular cylinder.

Deciduous

Land plant that sheds its leaves annually.

Evergreen

Land plant that sheds leaves over a long period, so some leaves are always present.

Leaves

Lateral appendage of a stem, highly variable in structure, often containing cells that carry out photosynthesis.

Cork cambium

Lateral meristem that produces cork.

Pericycle

Layer of cells surrounding the vascular tissue of roots; produces branch roots.

Casparian strip

Layer of impermeable lignin and suberin bordering four sides of root endodermal cells; prevents water and solute transport between adjacent cells.

Palisade mesophyll

Layer of tissue in a plant leaf containing elongated cells with many chloroplasts.

Spongy mesophyll

Layer of tissue in a plant leaf containing loosely packed cells, increasing the amount of surface area for gas exchange.

Annual ring

Layer of wood (secondary xylem) usually produced during one growing season.

Primary root

Original root that grows straight down and remains the dominant root of the plant; contrasts with fibrous root system.

Cork

Outer covering of the bark of trees; made of dead cells that may be sloughed off.

stomata

Small openings between two guard cells on the underside of leaf epidermis through which gases pass.

Stolon

Stem that grows horizontally along the ground and may give rise to new plants where it contacts the soil—e.g., the runners of a strawberry plant.

Root nodules

Structure on plant root that contains nitrogen-fixing bacteria.

Petiole

The part of a plant leaf that connects the blade to the stem.

Ground tissue

Tissue that constitutes most of the body of a plant; consists of parenchyma, collenchyma, and sclerenchyma cells that function in storage, basic metabolism, and support

Meristem

Undifferentiated embryonic tissue in the active growth regions of plants.

Stem

Usually the upright, vertical portion of a plant that transports substances to and from the leaves.

Phloem

Vascular tissue that conducts organic solutes in plants; contains sieve-tube members and companion cells.

Leaf vein

Vascular tissue within a leaf.

Cuticle

Waxy layer covering the epidermis of plants that protects the plant against water loss and disease-causing organisms.

3. Describe the primary growth of a stem. Describe the cross sections of a herbaceous eudicot, a monocot, and a woody eudicot.

As seasonal growth resumes, the apical meristem at the shoot tip produces new cells that increase the height of the stem. The shoot apical meristem is protected within the terminal bud, where leaf primordia (immature leaves) envelop it. The leaf primordia mark the location of a node; the portion of stem in between nodes is an internode. As a stem grows, the internodes increase in length. In addition to leaf primordia, the three specialized types of primary meristem develop from a shoot apical meristem. These primary meristems contribute to the length of a shoot. The protoderm, the outermost primary meristem, gives rise to the epidermis. The ground meristem produces two tissues composed of parenchyma cells: the pith and the cortex. The procambium produces the first xylem cells, called primary xylem, and the first phloem cells, called primary phloem. In the herbaceous eudicot stem such as a sunflower, the vascular bundles are arranged in a distinct ring in which the cortex is separated from the central pith, which stores water and products of photosynthesis. The cortex is sometimes green and carries on photosynthesis. In a monocot stem, such as a corn stalk, the vascular bundles are scattered throughout the stem, and often the cortex and pith are not clearly distinguishable a woody eudicot stem has an entirely different organization from that of a herbaceous eudicot stem. A woody stem forms three distinct areas: the bark, the wood, and the pith. Vascular cambium occurs between the bark and the wood, which causes woody plants to increase in girth. Cork cambium, occurring first beneath the epidermis, is instrumental in the production of cork in woody plants. The xylem rays and phloem rays that are visible in the cross section of a woody stem. Rays consist of parenchyma cells that permit lateral conduction of nutrients from the pith to the cortex, as well as some storage of food. A phloem ray can vary in width and is a continuation of a xylem ray.

Epidermis

In mammals, the outer, protective layer of the skin; in plants, tissue that covers roots, leaves, and stems of nonwoody organisms.

Fibrous root system

In most monocots, a mass of similarly sized roots that cling to the soil.

Cortex

In plants, ground tissue bounded by the epidermis and vascular tissue in stems and roots; in animals, outer layer of an organ, such as the cortex of the kidney or adrenal gland.

Node

In plants, the place where one or more leaves attach to a stem.

Complex tissue

In plants, tissue composed of two or more kinds of cells (e.g., xylem, containing tracheids and vessel elements; phloem, containing sieve-tube members and companion cells).

Sieve-tube member

Member that joins with others in the phloem tissue of plants as a means of transport for nutrient sap.

Root apical meristem

Meristem tissue located under the root cap; the site of the majority of cell division in the root.

5. List five differences between monocots and eudicots.

Monocots One cotyledon Flower parts in threes or multiples of three Pollen grain with one pore Usually herbaceous Usually parallel venation Scattered bundles in stem Fibrous root system Eudicots Two cotyledons Flower parts in fours or fives or multiples of four or five Pollen grain with three pores Woody or herbaceous Usually net venation Vascular bundles in a ring Taproot system

Herbaceous stem

Nonwoody stem; herbaceous plants tend to die back to ground level at the end of the growing season.

1. Contrast the structure and function of parenchyma, collenchyma, and sclerenchyma cells. These cells occur in what type of plant tissue?

Parenchyma [Gk. para, beside, and enchyma, infusion] cells are the most abundant and correspond best to the typical plant cell. These are the least specialized of the cell types and are found in all the organs of a plant. They may contain chloroplasts and carry on photosynthesis (chlorenchyma), or they may contain colorless plastids that store the products of photosynthesis. Collenchyma cells are like parenchyma cells except they have thicker primary walls. The thickness is uneven and usually involves the corners of the cell. Collenchyma cells often form bundles just beneath the epidermis and give flexible support to immature regions of a plant body. The familiar strands in celery stalks (leaf petioles) are composed mostly of collenchyma cells. Sclerenchyma cells have thick secondary cell walls impreg- nated with lignin, which is a highly resistant organic substance that makes the walls tough and hard. Most sclerenchyma cells are nonliving; their primary function is to support the mature regions of a plant. Two types of sclerenchyma cells are fibers and sclereids. Although fibers are occasionally found in ground tissue, most are in vascular tissue, Xylem contains two types of conducting cells: tracheids and vessel elements (VEs), which are modified sclerenchyma cells

Pith

Parenchyma tissue in the center of some stems and roots.

Sclerenchyma

Plant tissue composed of cells with heavily lignified cell walls; functions in support.

Collenchyma

Plant tissue composed of cells with unevenly thickened walls; supports growth of stems and petioles.

Parenchyma

Plant tissue composed of the least-specialized of all plant cells; found in all organs of a plant.

Root cap

Protective cover of the root tip, whose cells are constantly replaced as they are ground off when the root pushes through rough soil particles.

Periderm

Protective tissue that replaces epidermis; includes cork, cork cambium.

Rhizome

Rootlike underground stem.

2. Contrast the structure and function of xylem and phloem.

Xylem transports water and minerals from the roots to the leaves, and phloem transports sucrose and other organic compounds, usually from the leaves to the roots. Both xylem and phloem are considered complex tissues because they are composed of two or more kinds of cells. Xylem contains two types of conducting cells: tracheids and vessel elements (VEs), which are modified sclerenchyma cells. Both types of conducting cells are hollow and non- living, but the vessel elements are larger, may have perforation plates in their end walls, and are arranged to form a continuous vessel for water and mineral transport. The elongated tracheids, with tapered ends, form a less obvious means of transport, but water can move across the end walls and side walls because there are pits, or depressions, where the secondary wall does not form. In addition to vessel elements and tracheids, xylem can contain sclerenchyma fibers that lend additional support as well as parenchyma cells that store various substances. Vascular rays, which are flat ribbons or sheets of parenchyma cells located between rows of tracheids, conduct water and minerals across the width of a plant. The conducting cells of phloem are specialized parenchyma cells called sieve-tube members that are arranged to form a continuous sieve tube (Fig. 24.7). Sieve-tube members contain cytoplasm but no nuclei. The term sieve refers to a cluster of pores in the end walls, which is known as a sieve plate. Each sieve-tube member has a companion cell, which contains a nucleus. The two are connected by numerous plasmodesmata, and the nucleus of the companion cell may control and maintain the life of both cells. The companion cells are also believed to be involved in the transport function of phloem. Sclerenchyma fibers also lend support to phloem.

4. Describe the structure and organization of a typical eudicot leaf.

a typical eudicot leaf of a temperate zone plant. At the top and bottom are layers of epidermal tissue that often bear trichomes, protective hairs often modified as glands that secrete irritating substances. These features help deter insects from eating the leaf. The epidermis characteristically has an outer, waxy cuticle that helps keep the leaf from drying out. The cuticle also prevents gas exchange because it is not gas permeable. However, the lower epidermis of eudicot and both surfaces of monocot leaves contain stomata that allow gases to move into and out of the leaf. Water loss also occurs at stomata, but each stoma has two guard cells that regulate its opening and closing, and stomata close when the weather is hot and dry. The body of a leaf is composed of mesophyll [Gk. mesos, middle, and phyllon, leaf] tissue. Most eudicot leaves have two distinct regions: palisade mesophyll, containing elongated cells, and spongy mesophyll, containing irregular cells bounded by air spaces. The parenchyma cells of these layers have many chloroplasts and carry on most of the photosynthesis for the plant. The loosely packed arrangement of the cells in the spongy layer increases the amount of surface area for gas exchange.