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Chapter 5: Tissues and the Primary Growth of Stems (Internal Organization…
Chapter 5: Tissues and the Primary Growth of Stems
Basic Types of Cells and Tissues
Collenchyma
Because cell walls are thick, they require more glucose for their production
Usually produced only in shoot tips and young petioles
Must be present in elongating shoots tips. Ex) Vining plants such as grapes
Provides additional support in many types of plants
Cells have primary wall that remains thin in some areas but thickened in other areas
Sclerenchyma
Winds, animals, or snow can be harmful
Supports the plant by its strength and structure alone
Develop from parenchyma cells in mature organs
Does not participate in photosynthesis
Has both a primary wall and a thick secondary wall that is almost always lignified
Mechanical
Fibers
Sclereids
All have elastic secondary walls
Conducting
Tracheids
Vessel element
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Parenchyma
Tissue is composed of parenchyma cells
Most common type of cell and tissue, constituting all soft parts of a plant
Cells only have primary walls that remain thin
Ex) Soft leaves, petals, fruits, and seeds
Chlorenchyma are parenchyma cells involved in photosynthesis
Transfer cells are parenchyma cells that mediate short-distance transport of material
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External Organization of Stems
Leaves and Nodes
Internodes - regions between nodes
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Wide (asparagus)
Intermediate
Narrow (alfalfa sprouts)
Leaf axils - stem area just above the point where the leaf attaches
Where leaves are attached
Axillary bud - a miniature shoot with a dormant apical meristem and several young leaves
Phyllotaxy - important in positioning leaves so that they do not shade each other
Bud scales protects organs inside
Terminal bud - extreme tip of each stem
Other External Parts of the Stems
Corms
Vertical, thick stems that have thin, papery leaves (crocus and gladious).
Rhizomes
Are fleshy horizontal stems that allow a plant to spread underground (bamboo, irises, and canna lilies)
Bulbs
Are short shoots that have thick, fleshy leaves (onions, daffodils, garlic).
Tubers
Horizontal like rhizomes, but they grow for only a short period and are mainly a means of storing nutrients (potatoes).
Stolons
Are horizontally oriented stems that grow along the soil surface. Their function is vegetative production.
Internal Organization of Stems
Epidermis
Single layer of parenchyma
Barrier against invasion by bacteria and fungi and small insects
The outermost surface of an herbaceous stem
Cutin - fatty substance that makes up the wall impermeable to water.
Guard cells and a stomatal pore together constitute a stoma
Some epidermal cells elongate outward and become trichomes, also called hairs
Cortex
Superficial portion of the plant
The tissue located between the vascular bundles and epidermis
Cortical cells may contain stored carbohydrates or other substances such as resins, latex, essential oils, and tannins.
Interior to the epidermis
Vascular Tissues
2 Types of Vascular Tissue
Xylem
Has 2 types of conducting cells
First Type: Tracheids
Second Type: Vessel Elements
Both Types are sclerechyma
Composed of annular thickenings, helical thickenings, scalariform thickenings, and reticulate thickenings
Transports water from roots to shoots and leaves, but it also transports some nutrients
Has a primary and secondary cell wall
Phloem
Has 2 types of conducting cells
First Type: Sieve tube members
Second Type: Sieve cells
They are associated with albuminous and companion cells
They are parenchyma cells
Only have primary walls and must remain alive in order to conduct
Can develop into sieve pores
Proteins and mRNAs are transported
Walls between conducting cells and controlling cells have many complexes
Phloem is the vascular tissue responsible for the transport of sugars from source tissues (ex. photosynthetic leaf cells) to sink tissues (ex. non-photosynthetic root cells or developing flowers).
