Chapter 35.1 Plant Structure

Plant organs

Three vegetative organs: roots (absorb/anchor), stems (support/transport), leaves (photosynthesis)

Taproot system

Single large primary root + smaller lateral roots; common in eudicots; good for deep water access; e.g. carrots, dandelion

Fibrous root system

Many thin, similarly-sized roots; common in monocots; spreads horizontally; prevents soil erosion; e.g. grasses

Nodes

Points on a stem where leaves are attached

Internodes

Segments of stem between nodes

Axillary (lateral) buds

Buds in leaf axils that may develop into branches; suppressed by apical dominance

Terminal bud

Bud at the tip of the main shoot; contains the apical meristem

Leaf blade

Flattened photosynthetic portion of a leaf

Petiole

Stalk connecting the leaf blade to the stem

Dermal tissue system

Outermost protective covering; in primary growth = epidermis; in secondary growth = periderm (bark)

Epidermis

Single outer cell layer of primary plant body; produces cuticle; contains guard cells, trichomes, root hairs

Cuticle

Waxy layer on aerial epidermis; reduces water loss; secreted by epidermal cells

Ground tissue system

All tissue that is neither dermal nor vascular; includes parenchyma, collenchyma, sclerenchyma

Parenchyma

Most abundant plant cell type; thin flexible primary walls; alive at maturity; performs photosynthesis, storage, secretion, wound healing

Collenchyma

Ground tissue with unevenly thickened (non-lignified) primary walls; alive at maturity; provides flexible support in growing regions

Sclerenchyma

Ground tissue with thick, lignified secondary walls; DEAD at functional maturity; rigid structural support; types: fibers and sclereids

Fibers

Long sclerenchyma cells in bundles; structural support; examples include hemp, flax

Sclereids

Short, irregular sclerenchyma cells (stone cells); found in seed coats, nutshells, pear grit

Vascular tissue system

Xylem + phloem; runs continuously through plant body as vascular bundles

Xylem

Vascular tissue transporting water and minerals upward; contains tracheids and vessel elements; dead at maturity; lignified

Tracheids

Long, tapered xylem cells with pits; dead at maturity; present in all vascular plants

Vessel elements

Wider xylem cells with perforation plates (perforated end walls); dead at maturity; more efficient water flow; angiosperms

Phloem

Vascular tissue transporting sugars bidirectionally; contains sieve-tube elements and companion cells; alive

Sieve-tube elements

Phloem cells with sieve plates; alive but lack nucleus at maturity; transport sucrose

Companion cells

Phloem cells adjacent to sieve-tube elements; large nucleus, many mitochondria; assist loading and unloading

Meristems

Regions of actively dividing, undifferentiated cells; enable indeterminate growth throughout plant's life

Apical meristems

At root and shoot tips; drive primary growth (increase in length); produce epidermis, ground tissue, vascular tissue

Lateral meristems

Vascular cambium + cork cambium; drive secondary growth (increase in girth/diameter); in gymnosperms and eudicots

Vascular cambium

Lateral meristem producing secondary xylem (wood) inward and secondary phloem outward

Cork cambium

Lateral meristem producing periderm (bark) that replaces epidermis during secondary growth

Primary growth

Growth in length; driven by apical meristems; occurs in all vascular plants

Secondary growth

Growth in girth; driven by lateral meristems; mostly gymnosperms and eudicots; produces wood and bark