The Plant Body
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Transcript of The Plant Body
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35The Plant Body
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35 Vegetative Organs of the Flowering Plant Body
• Flowering plants possess three kinds of vegetative (nonreproductive) organs: roots, stems, and leaves.
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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.
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Figure 35.1 Monocots versus Eudicots
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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.
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Figure 35.2 Vegetative Organs and Systems
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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35 Plant Cells
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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.
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Figure 35.12 Three Tissue Systems Extend throughout the Plant Body
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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).
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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.
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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.
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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).
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Figure 35.14 A Woody Twig
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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
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Figure 35.15 Tissues and Regions of the Root Tip
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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.
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Figure 35.21 Annual Rings
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Figure 35.19 Vascular Cambium Thickens Stems and Roots (Part 2)
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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.
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Figure 35.23 (a) The Eudicot Leaf
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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).