1. 23–1 Specialized Tissues in Plants
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Seed Plant Structure
Seed Plant Structure
What are the three principal organs and tissues of seed plants?
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Seed Plant Structure
The three principal organs of seed plants are roots, stems, and leaves.
These organs perform functions such as the transport of nutrients, protection, and coordination of plant activities.
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Plant Tissue Systems
What are the three main tissue systems of plants?
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Plant Tissue Systems
Plants consist of three main tissue systems:
dermal tissue
vascular tissue
ground tissue
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Seed Plant Structure
Leaf
Stem
Vascular plants consist of roots, stems, and leaves. Each of these organs contains dermal tissue, vascular tissue, and ground tissue.
Root
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Dermal Tissue
Dermal Tissue
The outer covering of a plant consists of epidermal cells.
Epidermal cells make up dermal tissue.
The outer surfaces of epidermal cells are covered with a thick waxy layer, known as the cuticle. The cuticle protects the plant against water loss and injury.
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Vascular Tissue
Vascular Tissue
Vascular tissue forms a transport system that moves water and nutrients throughout the plant.
Vascular tissue is made up of xylem, a water-conducting tissue, and phloem, a food-conducting tissue.
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Vascular Tissue
Cross Section of a Stem
Vascular tissue is made up of xylem and phloem. Xylem tissue conducts water from the roots to the rest of the plant. Phloem tissue conducts a variety of materials, mostly carbohydrates, throughout a plant. Photo Credit: Ray F. Evert, University of Wisconsin
Xylem
Phloem
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Ground Tissue
Ground Tissue
Cells that lie between dermal and vascular tissues make up the ground tissues.
The three kinds of ground tissue are:
parenchyma
collenchyma
sclerenchyma
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23–2 Roots
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Seed Plant Structure
Roots:
absorb water and dissolved nutrients.
anchor plants in the ground.
protect the plant from harmful soil bacteria and fungi.
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Types of Roots
The two main types of roots are:
taproots, which are found mainly in dicots, and
fibrous roots, which are found mainly in monocots.
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14. Root Structure and Growth
The root’s surface is covered with cellular projections called root hairs. Root hairs provide a large surface area through which water can enter the plant.
Root hairs
A root consists of a central vascular cylinder surrounded by ground tissue and the epidermis. Root hairs along the surface of the root aid in water absorption.

15. 23–3 Stems
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16. Stem Structure and Function
What are the three main functions of stems?
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17. Stem Structure and Function
Stems have three important functions:
they produce leaves, branches and flowers
they hold leaves up to the sunlight
they transport substances between roots and leaves
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18. Monocot and Dicot Stems
The arrangemnet of tissues in a stem differs among seed plants.
How do monocot and dicot stems differ?
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19. Monocot and Dicot Stems
Monocot Stems
Vascular bundles are scattered throughout the ground tissue.
Epidermis
Vascular bundles
Ground tissue
In a monocot, vascular bundles are scattered throughout the stem. Photo Credit: ©Ed Reschke/Peter Arnold, Inc.
Monocot
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20. Monocot and Dicot Stems
Dicot stems have vascular bundles arranged in a ring-like pattern.
Vascular bundles
Epidermis
In a dicot, vascular bundles are arranged in a ring. Photo Credit: ©Ed Reschke/Peter Arnold, Inc.
Cortex
Pith
Dicot
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21. 23–4 Leaves
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Seed Plant Structure
Leaves:
are a plant’s main photosynthetic systems.
increase the amount of sunlight plants absorb.
Adjustable pores conserve water and let oxygen and carbon dioxide enter and exit the leaf.
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23. Leaf Structure
Leaf Structure
How does the structure of a leaf enable it to carry out photosynthesis?
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24. Leaf Functions
Leaf Functions
Most leaves consist of a specialized ground tissue known as mesophyll.
Leaves absorb light and carry out most of the photosynthesis in a plant. Some of the most important manufacturing sites on Earth are found in the leaves of plants. The cells in plant leaves are able to use light energy to make carbohydrates.
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25. The air spaces connect with the exterior through stomata.
Leaf Functions
The air spaces connect with the exterior through stomata.
Stomata are porelike openings in the underside of the leaf that allow carbon dioxide and oxygen to diffuse into and out of the leaf.
Leaves absorb light and carry out most of the photosynthesis in a plant. Some of the most important manufacturing sites on Earth are found in the leaves of plants. The cells in plant leaves are able to use light energy to make carbohydrates.
Stoma
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26. Each stoma consists of two guard cells.
Leaf Functions
Each stoma consists of two guard cells.
Guard cells are specialized cells that control the opening and closing of stomata by responding to changes in water pressure.
Leaves absorb light and carry out most of the photosynthesis in a plant. Some of the most important manufacturing sites on Earth are found in the leaves of plants. The cells in plant leaves are able to use light energy to make carbohydrates.
Guard cells
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27. When water pressure within guard cells is high, the stoma open.
Leaf Functions
When water pressure within guard cells is high, the stoma open.
Plants regulate the opening and closing of their stomata to balance water loss with rates of photosynthesis. A stoma opens or closes in response to the changes in pressure within the guard cells that surround the opening. When the guard cells are swollen with water the stoma is open.
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28. When water pressure within guard cells decreases, the stoma closes.
Leaf Functions
When water pressure within guard cells decreases, the stoma closes.
Plants regulate the opening and closing of their stomata to balance water loss with rates of photosynthesis. A stoma opens or closes in response to the changes in pressure within the guard cells that surround the opening.
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29. Leaf Functions
Plants regulate the opening and closing of their stomata to balance water loss with rates of photosynthesis.
Stomata are open in daytime, when photosynthesis is active, and closed at night, to prevent water loss.
In hot, dry conditions stomata may close even in bright sunlight, to conserve water.
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