Topic 7: Plant Organization Cells and Tissues

Growth

An increase in the size of a tissue, which occurs through either…

• cell division (increasing the number of cells)

• cell elongation (increasing the size of individual cells)

Determination

The stage when a cell becomes committed to a specific fate or tissue identity

Differentiation

The actual process where a cell expresses the specific characteristics associated with its determined fate or tissue identity

Shoot Apical Meristem (SAM)

A primary site of cell division located at the tip of the shoot apex, it is the orgin of all new cells for primary shoot growth

Root Apical Meristem (RAM)

A primary site of cell division at the tip of the root apex; it serves as the origin for all cells involved in primary root growth

Radicle

The embryonic root, tipped by the RAM, which is typically the first structure to emerge from the seed coat to access water

Hypocotyl

The embryonic shoot located below the cotyledons ("____" meaning below)

In eudicots, it often emerges as a bent apical hook to protect the SAM as it pushes through the soil

Epicotyl

The embryonic shoot located above the cotyledons ("____" meaning above), which is tipped by the SAM

Coleoptile

A protective sheath that covers and protects the emerging shoot (epicotyl) specifically in monocot (grass) seedlings

Node

The specific site on a stem where structures like leaves or buds extend

Internode

The segment of the stem located between two nodes

Blade

The wide, expanded portion of a leaf

Petiole

The stem-like structure that supports and attaches the leaf blade to the stem

Axil

the upper angle formed between the stem and a leaf, branch, or petiole

axillary bud

• an embryonic shoot located in the axil—the angle between the upper side of a leaf petiole and the stem

• develop into lateral branches, new leaves, or flowers,

Dermal Tissue

The outermost layer that covers and protects the plant

Vascular Tissue

The system responsible for transporting water, minerals, and sugars throughout the plant

Ground Tissue

All tissues that are not dermal or vascular; these can serve as sites for photosynthesis, support, or storage

Parenchyma

• GROUND TISSUE

• Cells that are alive at maturity with simple cell walls

• They perform diverse functions, including photosynthesis, starch storage, and water movement, and can differentiate into other types to heal wounds

• potato is made up of this

Collenchyma

• GROUND TISSUE

• Living cells with thick cell walls (especially at the corners) that provide structural support to the plant

• like cellery stick “stings”

Sclerenchyma

• GROUND TISSUE

• Cells with very thick walls reinforced with lignin; they function primarily in support and protection and are often dead when functional

Sclereids

• part of the schlerenchyma

• Small, thick-walled sclerenchyma cells found in nut shells, seed coats, and the grit of pears

Fibers

• part of the schlerenchyma

• Long, slender sclerenchyma cells found in bunches that provide structural support, such as those used to make hemp rope

Epidermis

• DERMAL TISSUE

• The outermost layer of tightly packed cells on all plant organs

Pavement Cells

• DERMAL TISSUE

• The standard, tightly packed cells that make up the bulk of the epidermis.

Guard Cells

• DERMAL TISSUE

• Specialized epidermal cells that form stomata to regulate gas exchange, such as allowing carbon dioxide into leaves

Trichomes

• DERMAL TISSUE

• Hairlike outgrowths on stems, leaves, or flowers that can defend the plant, regulate temperature, or reduce evaporation

Root Hairs

• DERMAL TISSUE

• Outgrowths of the root epidermis that significantly increase surface area for the absorption of water and minerals

Xylem

• VASCULAR TISSUE

• Tissue that conducts water and minerals upward from roots

Tracheids

• part of the XYLEM

• Narrow, dead cells with lignified walls; water moves between them laterally through pits

Vessel Elements

• part of the XYLEM

• Wider, dead cells that connect end-to-end to form long vessels for free water movement through perforated end walls

Phloem

• VASCULAR TISSUE

• Tissue consisting of living cells that transports sugars and organic nutrients throughout the plant

Sieve-tube Elements

• part of the PHLOEM

• Cells connected end-to-end to form tubes; they lack a nucleus at maturity and have porous end walls called sieve plates

Companion Cells

• part of the PHLOEM

• Non-conducting cells connected to sieve-tube elements by plasmodesmata; they provide the nutrients and molecules necessary to keep the sieve-tube elements alive