Chapter #35~ Plant Structure and Growth

Plants

• Nonvascular- no system of transport

• Vascular-system of transport (simple & complex)

• Gymnosperms – conifers…

Figure 35.1 A comparison of monocots and dicots

Angiosperm (flowering plants) structure

• Three basic organs: roots, stems, leaves– Roots (root system)

• fibrous: mat of thin roots

-- grass

• taproot: one large, vertical root -- carrot

• Stems (shoot system) – nodes: leave attachment – internodes: stem segments – axillary bud: dormant, vegetative

potential – terminal bud: apex of young shoot – apical dominance: inhibition of axillary

buds by terminal bud in young shoots

• Leaves (shoot system)– blade– petiole

Plant organ systems made of 3 tissue types

• 1. Dermal (epidermis): single layer of cells for protection

• cuticle

• 2. Vascular (material transport)– xylem: transports water and dissolved minerals

roots to shoots• 2 types of xylem cells: tracheids & vessel elements:

elongated cells dead at maturity

– phloem: transports food from leaves to roots and fruits

• sieve-tube members: (cells w/no nuclei or ribosomes) phloem tubes alive at maturity capped by sieve plates where 2 cells meet; companion cells (support cells for sieve cells)connected by plasmodesmata (thin tubes of cytoplasm)

Plant Tissue Cell Types• 3. Ground Tissues

– Parenchymaprimary walls thin and flexible; no secondary walls; large central vacuole; most metabolic functions of plant (chloroplasts)

• Collenchyma-- unevenly thick primary walls used for flexible plant support (no secondary walls ; no lignin- hardening agent)

• Sclerenchyma-- support element strengthened by secondary cell walls with lignin (may be dead; xylem cells); fibers (used to make hemp rope) and sclereids for support – (used to for nutshells)

Lily Parenchyma Cell (cross-section) (TEM x7,210). Note the large nucleus and nucleolus in the center of the cell, mitochondria and plastids in the cytoplasm.

Sclerenchyma cells. Some sclerenchyma cells occur in the fruits of Pear. These cells (sclerieds or stone cells)give pears their gritty texture

Collenchyma cells. Note the thick walls on the collenchyma cells occurring at the edges of the stem cross section

Plant Growth- life cycles

• Life Cycles

• annuals: 1 year (wildflowers; food crops)

• biennials: 2 years (beets; carrots)

• perennials: many years (trees; shrubs)

• Meristems

• apical: tips of roots and buds; primary growth

• lateral: cylinders of dividing cells along length of roots and stems; secondary growth (wood)

Primary growth – originates from apical meristem

• Roots

• root cap~ protection of meristem

• zone of cell division~ primary (apical) meristem

• zone of elongation~ cells elongate; pushes root tip

• zone of maturation~ differentiation of cells (formation of 3 tissue systems)

• Vid root growth

Primary Tissues of Roots• Outer lining of root is epidermis –cells give rise to root hairs that increase surface

area• Cortex~ moving in we get to the cortex – starch storing receptacle• endodermis – innermost layer of cortex – cylinder of cells

– walls between endodermis cells create casparian strip which blocks water from passing

• vascular cylinder – in from endodermis – composed of cells known as pericycle– Lateral roots~ arise from pericycle

Primary Tissues of Stems• a. from outside to inside: epidermis (covered with waxy cutin for

protection)→ cortex of stem contains parenchyma, collenchyma & schlerenchyma cells → (no endodermis because stem is not involved in water absorption) → vascular cylinder w/xylem & phloem

• b. vascular cambium – extends along entire length of plant – creates secondary xylem & phloem produced each year (tree rings)

• c. cork cambium – thick cover for stems & roots – it replaces epidermis when it dries up & falls off during secondary growth (protection)

Primary Tissues of Leaves• Epidermis/cuticle (waxy protection; prevent desiccation)

• Stomata (tiny pores for gas exchange and transpiration)/open & closed by guard cells

• Mesophyll: ground tissue between upper and lower epidermis (parenchyma with chloroplasts); palisade (most photosynthesis) and spongy (gas circulation)

Secondary Growth- increases girth of plant (woody tissue)

• F. Secondary Growth- increases girth of plant (woody tissue) - occurs at 2 lateral meristems