unit 7 plants ch. 23 roots, stems, & leaves. seed plant structure 3 of the principal organs of...
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Unit 7 Plants
Ch. 23 Roots, Stems, & Leaves
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Seed Plant Structure
• 3 of the principal organs of seed plants are roots, stems, & leaves
• The root system of a plant absorbs water & dissolved nutrients
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Seed Plant Structure
- A stem has a support system for the plant body, a transport system that carries nutrients, & a defense system
that protects the plant against predators & disease
- Leaves are the plant’s main photosynthetic systems
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Plant Tissue Systems
• Plants consist of 3 main tissue systems: dermal tissue, vascular tissue, & ground tissue
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Dermal Tissue
• The outer covering of a plant, that consists of a single layer of epidermal cells
• The outer surfaces are often covered with thick waxy layer to protect against water loss & injury
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Vascular Tissue
• Contains several types of specialized cells
• Xylem consists of tracheids & vessel elements
• Phloem consists of sieve tube elements & companion cells
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Vascular Tissue - Xylem
• All seed plants have a type of xylem cell called a tracheid, cells that resist water pressure
• Vessel elements - wide cells that form hollow tubes, which water can move through freely
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Vascular Tissue - Phloem
• Sieve tube elements - main cells in phloem, form tubes through which materials, like sugars & other foods, are carried in a watery stream
• Companion cells - phloem cells that surround sieve tube elements, help movement of substances in & out of the phloem
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Ground Tissue
• Cells that lie between dermal & vascular tissues
• Consists mainly of parenchyma - cells that are packed with chloroplasts & are the site of most of a plant’s photosynthesis
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Ground Tissue
• Collenchyma - cells that have strong, flexible cell walls that help support larger plants (makes up “strings” of a stalk of celery)
• Sclerenchyma - rigid cell walls that make ground tissue tough & strong
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Plant Growth & Meristematic Tissue
• Meristems - clusters of tissue that are responsible for continuing growth throughout a plant’s lifetime
• Meristematic tissue - undifferentiated cells, they have not yet become specialized for specific functions, such as transport
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Plant Growth & Meristematic Tissue
• Apical meristem - group of undifferentiated cells that divide to produce increased length of stems & roots
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Plant Growth & Meristematic Tissue
• Differentiation - cells develop into mature cells with specialized structures & functions
• As cells differentiate, they produce each of the tissue systems of the plant: dermal, ground, & vascular tissue
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Types of Roots
• The 2 main types of roots are taproots, found mainly in dicots, & fibrous roots, found mainly in monocots
• Taproot - primary root– Ex.) carrots, dandelions, beets, etc.
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Types of Roots
• Fibrous roots - roots that branch to such an extent that no single root grows larger than the rest– Ex.) grass
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Root Structure & Growth
• A mature root has an outsider layer, the epidermis, & a central cylinder of vascular tissue
• Between these 2 tissues, lies a large area of ground tissue
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Root Structure & Growth
• Root hairs - tiny cellular projections that penetrate the spaces between soil particles & produce a large surface area through which water can enter the plant
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Root Structure & Growth
• Cortex - spongy layer of ground tissue just inside the epidermis
• Endodermis - another layer of cells that completely encloses the root’s vascular subsystem in a region called the vascular cylinder
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Root Structure & Growth
• Root cap - protects the root as it forces its way through the soil
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Root Functions
• Roots anchor a plant in the ground & absorb water & dissolved nutrients from the soil
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Stem Structure & Function
• Stems have 3 important functions: they produce leaves, branches, & flowers; they hold leaves up to the sunlight; & they transport substances between roots & leaves
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Stem Structure & Function
• Nodes - where leaves are attached
• Internode - regions between the nodes
• Buds - contain undeveloped tissue that can produce new stems & leaves
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Monocot & Dicot Stems
• In monocots, vascular bundles are scattered throughout the stem
• In dicots & most gymnosperms, vascular bundles are arranged in a cylinder
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Monocot & Dicot Stems
• Vascular bundles - contains xylem & phloem tissue
• Pith - the parenchyma cells inside the ring of vascular tissue
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Primary Growth of Stems
• Primary growth - growth occurring only at the ends of a plant
• Its produced by cell divisions in the apical meristem, & takes place in all seed plants
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Secondary Growth of Stems
• Secondary growth - method of growth where stems increase in width
• In conifers & dicots, secondary growth takes place in lateral meristematic tissues called the vascular cambium & cork cambium
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Secondary Growth of Stems
• Vascular cambium - produces vascular tissues & increases the thickness of stems over time
• Cork cambium - produces the outer covering of stems
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Formation of Wood
• Heartwood - older xylem near the center of the stem that no longer conducts water
• Sapwood - surrounds heartwood, active in fluid transport
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Formation of Bark
• Bark - includes all of the tissues outside the vascular cambium, includes: phloem, the cork cambium, & cork
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Leaf Structure
• The structure of a leaf is optimized for absorbing light & carrying out photosynthesis
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Leaf Structure
• Blades - flattened section, attached to the stem by a thin stalk - petiole
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Leaf Functions
• A leaf can be considered a system specialized for photosynthesis
• Subsystems of the leaf include tissues that bring gases, water, & nutrients to the cells that carry out photosynthesis
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Leaf Functions
• Guard cells - specialized cells in the epidermis that control the opening & closing of stomata (air spaces) by responding to changes in water pressure
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Leaf Functions
• Plants keep their stomata open just enough to allow photosynthesis to take place, but not so much that they lose an excessive amount of water
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Leaf Functions
• Transpiration - the loss of water through its leaves