BIO421 - PLANT TISSUES

What are the three basic parts of the body of an herb?

Leaves, stems, roots

What are the additional roles of modern stems beyond transport and support?

Produce leaves and hold them in sunlight, store sugar & nutrients during winter, serve as means of survival, serve as means of dispersal

How do orchids carry out photosynthesis?

Roots that contain chlorophyll; epiphytic roots are exposed to sunlight

What is the function of the residual shoot in shootless orchids?

Flowering and sexual reproduction

What is the function of cactus leaves?

Formation of buds that produce the defensive spines

What is an herb?

A plant that never becomes woody and is covered with bark; has primary tissues

What is known as the primary plant body?

Herbaceous body

What is known as the secondary plant body?

Woody body

What are the characteristics of a primary plant body?

Derived from shoot and apical meristems, composed of primary tissues (epidermis, cortex, pith), has herbaceous parts

What are the characteristics of a secondary plant body?

Derived from meristems other than apical meristems, only has primary tissues at root/shoot tips, composed of secondary tissues (wood and bark), has woody, bark-covered parts

Describe parenchyma cells.

Cells that have thin primary walls, are metabolically active, and remain alive after maturity

Describe collenchyma cells.

Cells with unevenly thickened primary walls, typically alive at maturity, providing plastic support

Describe sclerenchyma cells.

Cells with primary walls and secondary walls, dead at maturity, providing elastic support and some involved in water transport

Describe chlorenchyma cells.

Parenchyma cells involved in photosynthesis, have numerous chloroplasts, and thin walls allowing light and CO2 to pass through

Describe glandular cells.

Parenchyma cells that secrete nectar, fragrances, mucilage, resins, and oils; contain few chloroplasts but many dictyosomes and ER

Describe transfer cells.

Parenchyma cells that mediate short-distance transport of material via plasma membrane with numerous molecular pumps

How do some parenchyma cells function by dying at maturity?

Opening in stamens are formed by the death of parenchyma cells; large spaces are formed when the middle lamella decomposes

Describe the function of collenchyma cells in tissue support.

Exhibit plasticity, present as a layer just under epidermis or as bands next to vascular bundles, making tips stronger and more resistant while still able to elongate

How do collenchyma and parenchyma work together in stems?

Turgid parenchyma serves as air pressure that supports collenchyma acting as a container

Differentiate collenchyma and sclerenchyma.

Collenchyma is elastic and retains new shape after pressure dissipates, while sclerenchyma returns to original size

Why do plants develop sclerenchyma?

Some cells mature into sclerenchyma to maintain leaf shape and support after maturity; sclerenchyma retains its shape by supporting it with strength alone when plants no longer need to grow

What are the two types of sclerenchyma cells?

Conducting sclerenchyma and mechanical sclerenchyma

What are two types of mechanical sclerenchyma?

Sclereids and fibers

Describe sclereids.

More or less isodiametric; often dead at maturity, brittle, inflexible, form shells of walnuts, coconuts, or pits of cherries & peaches

Describe fibers.

Long; many are dead while others remain alive and are involved in storage; flexible, elastic, allow trunk & branches to sway without breaking

What is the function of living sclerenchyma cells?

Involved in storing starch or calcium oxalate

What are pits in sclerenchyma cells?

Areas where adjacent cells meet

Differentiate stem and shoot.

Stem is an axis; shoot is stem plus leaves

What are nodes?

Where leaves are attached

What are internodes?

The region between nodes

What is the leaf axil?

Stem area just above the point where a leaf attaches

What is the axillary bud?

A miniature shoot with a dormant apical meristem and several young leaves

Differentiate vegetative bud and flower bud.

Vegetative bud: axillary bud that grows into branch; Floral bud: axillary bud that grows into flower

What are bud scales?

Small, corky, waxy modified leaves that protect the delicate organs inside

What are terminal buds?

Located at the extreme tip of each stem

What is phyllotaxy?

The arrangement of leaves on the stem, important in leaf positioning so that they don't shade each other

Differentiate alternate, opposite, and whorled phyllotaxy.

Alternate: one leaf per node alternating; Opposite: two leaves per node; Whorled: two or more leaves per node

Differentiate distichous, decussate, and spiral phyllotaxy.

Distichous: leaves are arranged in two rows; Decussate: leaves are arranged in four rows; Spiral: each leaf is located slightly to the side of the ones immediately above & below it

What are tendrils?

Modified leaves or lateral branches capable of twining around small objects

What are stolons or runners?

Internodes are especially long and thin, extending greatly without using many nutrients; after finding suitable habitat, shorter internodes take over and may become independent plants

What are bulbs?

Short shoots that have thick, fleshy leaves (e.g., onion, daffodils, garlic)

What are corms?

Vertical, thick stems that have thin, papery leaves (e.g., crocus, gladiolus)

What are rhizomes?

Fleshy horizontal stems that allow a plant to spread underground

What are tubers?

Horizontal like rhizomes that only grow for a short period mainly for storing nutrients; its leaves are microscopic and its axillary buds are its eyes

What is a trunk?

Vertical main shoot

Describe the mechanism of axillary bud growth.

Not all axillary buds grow leaves; some remain dormant to act as reserves; only when the apical meristems disappear do axillary buds become active and replace it

Describe the epidermis.

The outermost surface of an herbaceous stem; it is a single layer of parenchyma cells where all interchange of material occurs, shields delicate internal cells, and protects the plant from overheating

What is cutin?

A fatty substance that encrusts the outer tangential walls making the wall impermeable to water

What is a cuticle?

A protective layer on the epidermis

What is the function of cutin and wax?

Cutin and wax resist digestive enzymes and provide defense against pathogens.

What is the special chemical and its property in collenchyma?

Pectins - plasticity.

What is the special chemical and its property in sclerenchyma?

Lignin - strength & waterproofing.

What is the special chemical and its property in epidermis?

Cutin/waxes - waterproofing; indigestible.

What is the special chemical and its property in endodermis?

Suberin, lignin - waterproofing.

What is the special chemical and its property in cork (bark)?

Suberin - waterproofing.

How does the epidermis allow the entry of carbon dioxide?

Through stomata (guard cells + stomatal pore), which open during daytime permitting CO2 to enter.

What is the mechanism of guard cells?

Made of cellulose microfibrils, they absorb water and swell, becoming curved and pulling apart the inner walls.

What are trichomes?

Elongated epidermal cells, also called hairs.

What is the mechanism of trichomes?

They make it difficult for animals to access, shade underlying tissues, and create immobile air that sends water vapor back into the leaf.

What is the cortex?

Interior to the epidermis, made of chlorenchyma & collenchyma.

What is an aerenchyma?

Cortex parenchyma with large intercellular air spaces.

What are vascular tissues?

Tissues that make up a plant's vascular system.

Differentiate the two types of vascular tissue.

Xylem - conducts water and minerals; Phloem - distributes sugars and minerals.

What are the two types of conducting sclerenchyma cells in xylem?

Tracheids and vessel elements.

What are tracheids?

Long cells with tapered ends.

What are vessel elements?

Tend to be wider and shorter than tracheids, with perforations.

What is perforation?

Large hole at each end, where water passes through with little friction.

Describe annular thickenings.

Secondary wall deposition - set of rings on the interior face of the primary wall, in protoxylem.

Describe helical thickening.

Secondary wall deposition - in helices, interior to the primary wall in protoxylem.

Describe scalariform thickening.

Secondary wall deposition - ladder-like with coils connected, in metaxylem.

Describe reticulated thickening.

Secondary wall deposition - shaped like a net, in metaxylem.

Describe circulated bordered pit thickening.

Secondary wall deposition - shaped with holes, in metaxylem.

Differentiate the mechanisms of annular thickenings and those with pitted walls.

Annular thickenings are weak, allowing water movement; pitted walls are strong but slower for water movement.

How do tracheids obtain and transport water?

Tracheids obtain water from those below them, passing through pits.

What are the two types of conducting cells in phloem?

Sieve cells and sieve tube members.

How are tracheary elements different from sieve elements?

In sieve elements, parenchyma cells must remain alive to conduct.

What are sieve pores?

Areas of plasmodesmata that have enlarged as immature sieve pores begin to differentiate.

What are sieve areas?

Areas of sieve pores clustered together.

Describe a sieve cell.

It is elongated and spindle-shaped with sieve areas distributed all over its surface.

What changes occur during the differentiation of a young cell into a sieve tube member?

Nuclei degenerates, ribosomes and vacuoles break down, and plasmodesmata become sieve pores.

Describe sieve tube members.

Cells with large sieve areas and large sieve pores on the ends, stacked end to end.

What are sieve plates?

End-wall sieve areas with large sieve pores.

Name the accompanying cells that keep each sieve element alive.

Sieve cells: albuminous cells; Sieve tube members: companion cells.

What are vascular bundles?

Xylem and phloem occur together located interior to the cortex.

What is a pith?

Region of parenchyma similar to cortex, found at the center.

What do you mean by collateral?

Describes xylem & phloem strands running parallel to each other.

What is primary xylem?

Xylem of a vascular bundle, part of the primary plant body.

What is primary phloem?

Phloem of a vascular bundle, mixed with sieve elements and accompanying cells.

Differentiate plasmodesmata, pits, perforations, and sieve pores.

Plasmodesmata - tiny channels connecting protoplasm; Pits - water passage in tracheids; Perforations - water passage in vessel elements; Sieve pores - areas for substance passage in phloem.

What are shoot apical meristems?

Regions wherein stems grow longer by creating new cells at their tips.

What is the subapical meristem?

Region just below the apical meristem.

What occurs in the subapical meristem?

Visible differentiation begins; certain cells stop dividing and elongation starts.

What is protoxylem?

The first tracheids and vessel elements that constitute the first xylem to appear.

What is metaxylem?

Cells outside the protoxylem that have expanded, growing into the largest tracheary elements.

How does protoxylem grow despite being dead?

Its primary walls are glued by the middle lamella to the surrounding living cells.

What is protophloem?

Composed of matured exterior cells.

What is metaphloem?

Composed of cells closest to metaxylem.

When do metaxylem and metaphloem start to differentiate?

When all nodes and internodes have stopped elongating.

What is protoderm?

Epidermal cells in early stage of differentiation.

What are provascular tissues?

Young cells of xylem and phloem.