35The Plant Body

35 Vegetative Organs of the Flowering Plant Body

• Flowering plants possess three kinds of vegetative (nonreproductive) organs: roots, stems, and leaves.

35 Vegetative Organs of the Flowering Plant Body

• Most flowering plants belong to one of two major lineages.

• Monocots are generally narrow-leaved flowering plants such as grasses.

• Eudicots are broad-leaved flowering plants such as roses.

• Monocots and eudicots account for 97 percent of the species of flowering plants.

• Most of the remaining species (including water lilies and magnolias) are structurally similar to eudicots.

Figure 35.1 Monocots versus Eudicots

35 Vegetative Organs of the Flowering Plant Body

• The shoot system of a plant consists of the stems and the leaves, as well as flowers.

• Leaves are the main sites of photosynthesis.

• Stems hold and display the leaves to the sun and provide connections for the transport of materials between roots and leaves.

• A node is the point where a leaf attaches to a stem.

• Regions of stem between nodes are the internodes.

• The root system provides support and nutrition.

Figure 35.2 Vegetative Organs and Systems

35 Vegetative Organs of the Flowering Plant Body

• There are two main types of root system: taproot and fibrous root.

• Taproot (many eudicots): a single, large, deep-growing primary root with smaller lateral roots.

• Fibrous root system (monocots and some eudicots): composed of numerous thin roots roughly equal in diameter – holds soil in place very effectively.

35 Vegetative Organs of the Flowering Plant Body

• A bud is an embryonic shoot.

• A stem bears leaves at its nodes, and where each leaf meets the stem, there is a lateral bud.

• At the tip of each stem or branch there is an apical bud, which produces the cells for the growth and development of that stem or branch.

35 Vegetative Organs of the Flowering Plant Body

• A potato is a portion of the plant’s stem, and its “eyes” contain lateral buds = tuber

• The runners of strawberries are horizontal stems.

• In some plant species the leaves are highly modified, such as the thorns of a cactus.

35 Vegetative Organs of the Flowering Plant Body

• Leaves are well adapted for gathering light.

• The blade of a leaf is a thin, flat structure, attached to the stem by the petiole, which holds the leaf at an angle almost perpendicular to the sun.

Figure 35.5 The Diversity of Leaf Forms

A simple leaf has a single blade.

A compound leaf has multiple blades (or leaflets) arranged along an axis or radiating from a central point.

35 Plant Cells

• Plant cells have all the organelles common to eukaryotes.

• Plant cells have additional distinguishing features:

1) chloroplasts (or other plastids)

2) vacuoles

3) cell wall

• Each plant cell has its own primary cell wall. Some plant cells produce a thick secondary wall.

35 Plant Cells

• Plasmodesmata are pore-like structures that pass through primary cell walls, allowing substances to move freely from cell to cell without crossing the plasma membrane.

35 Plant Cells

• Parenchyma cells are the most numerous type of cell in young plants.

• Parenchyma cells usually have thin walls and large central vacuoles.

• The photosynthetic cells in leaves are parenchyma cells filled with chloroplasts.

• Some parenchyma cells store lipids or starch.

• Other parenchyma cells serve as “packing material” and play a vital role in supporting the stem.

35 Plant Cells

• Collenchyma cells are supporting cells that lay down primary cell walls that are thick in the corners.

• Collenchyma cells provide support to leaf petioles, nonwoody stems, and growing organs.

35 Plant Cells

• Sclerenchyma cells are the main supporting cells of a plant.

• There are two types of sclerenchyma cells: elongated fibers and variously shaped sclereids.

• Fibers often organize into bundles.

• Sclereids may pack together very densely.

35 Plant Cells

• The xylem conducts water from roots to above ground plant parts. It contains conducting cells called Tracheids .

• Vessel elements are the water “pipeline” system in flowering plants, also formed from dead cells.

• Vessel elements are generally larger in diameter than tracheids and are laid down end-to-end to form hollow tubes.

35 Plant Cells

• Cells of the phloem are alive when they do their job, unlike those of the xylem.

• The characteristic cell of the phloem is the sieve tube member.

• Cells of the phloem are arranged end-to-end and form long sieve tubes, which transport carbohydrates and other materials.

35 Plant Cells

35 Plant Tissues and Tissue Systems

• A tissue is an organization of cells that work together as a functional unit.

• Tissues are grouped into tissue systems that extend throughout the body of the plant from organ to organ.

• There are three plant tissue systems: vascular, dermal, and ground.

Figure 35.12 Three Tissue Systems Extend throughout the Plant Body

35 Plant Tissues and Tissue Systems

• The vascular tissue system includes the xylem and phloem; it is the conductive or “plumbing” system of the plant – occurs in vascular bundles.

• The phloem transports carbohydrates from photosynthesis from sites of production (sources such as leaves) to sites of utilization (sinks) elsewhere in the plant ( live cells).

• The xylem conducts water and minerals from the roots to above ground plant parts (dead cells).

35 Plant Tissues and Tissue Systems

• The dermal tissue system is the outer covering of the plant.

• All parts of the young plant body are covered by an epidermis, which is a single layer or multiple layers of cells.

• The epidermis contains epidermal cells and other specialized cells such as guard cells.

• The shoot epidermis secretes a layer of wax (the cuticle) which helps retard water loss from stems and leaves.

35 Plant Tissues and Tissue Systems

• The ground tissue system makes up the rest of a plant.

• Ground tissue functions primarily in storage, support, photosynthesis, and the production of defensive and attractive substances.

Cross sections of eudicot leaves.

35 Forming the Plant Body

• In plants, the growth of leaves, flowers, and fruits is determinant (ceases to grow once adulthood is reached).

• In plants the growth of roots and stems is indeterminate and is generated from specific regions of active cell division.

• Plants exhibit regions of: Primary growth – leads to lengthening of the plant

body and organ formation. Secondary growth – growth in the diameter of stems

and roots (wood and bark).

Figure 35.14 A Woody Twig

35 Forming the Plant Body

• The root cap protects the delicate growing area of the root as it pushes through the soil.

• The root cap also detects the pull of gravity and controls the downward growth of roots.

• Tissues of the root are divided into three zones: cell division, cell elongation, and cell differentiation.

Root cap

Root tip

Figure 35.15 Tissues and Regions of the Root Tip

35 Forming the Plant Body

• Cross sections of most tree trunks in temperate zone forests have annual rings.

• Wood consists of secondary xylem.

• Annual rings form due to differential rates of growth in spring (when water is plentiful) and in summer.

• Wood that is no longer conducting water is known as heartwood.

• Sapwood is wood that is actively conducting water and minerals in the tree.

Figure 35.21 Annual Rings

Figure 35.19 Vascular Cambium Thickens Stems and Roots (Part 2)

35 Leaf Anatomy Supports Photosynthesis

• Leaf anatomy is adapted to carry out photosynthesis, limit evaporative water loss, and transport the products of photosynthesis to the rest of the plant.

• The zones in leaf that photosynthesize are the called mesophyll.

• Within the mesophyll is air space through which CO2 can diffuse to the photosynthesizing cells.

Figure 35.23 (a) The Eudicot Leaf

35 Leaf Anatomy Supports Photosynthesis

• Veins supply mesophyll cells with water and minerals, and they transport the products of photosynthesis to the rest of the plant.

• Leaf epidermis: outermost cell layer, covered by a waxy cuticle. Functions to keep water and photosynthetic products in the leaf.

• Guard cells allow controlled gas exchange through pores in the leaf (the stomata).