Plant Structure and Function Ch. 35

Morphology of a Flowering Plant Root system and shoot system are connected by vascular tissue that is continuous throughout plant

Monocots vs. Dicots

online/library/onlinebio/monocot_flower.gif /dicotflower1.jpg

Nucleus Plant Cell Chloroplast Cell Wall

Roots Functions –Anchor plant in the soil –Absorb water and minerals –Store food

Root Structure

Root Systems TaprootFibrous root

Red mangrove growing in seawater Adventitious prop roots support and securely anchor this shrub in the mud and loose sand of tidal waters. Close-up view of prop roots Numerous pores called lenticels which provide gas exchange and an additional source of oxygen for the submersed roots.

Cortex Epidermis Developing lateral root Vascular cylinder -xylem -phloem

Modified Roots Prop root Buttress roots. Aerial roots Storage roots.

Stems Functions –Support –Transport –Storage

Monocot arrangement

Dicot arrangement

Proximity of terminal bud inhibits growth of axillary buds (Apical dominance)

Modified Stems Stolons—allow asexual reproduction Bulbs—store food Tubers—store food Rhizomes—horizontal stem

Leaves Leaf structure –Shape –Size –Edges

Leaf Structure Mesophyll

Stomata

Modified Leaves Tendrils—allow plant to cling to support Spines—reduces water loss

Modified Leaves Storage—modified for water storage (succulents) Bracts—attracts pollinators

Modified Leaves Reproductive leaves— produce adventitious plantlets which fall off and take root

Tissue Systems --cube-shaped, thin and flexible cell walls --function in photosynthesizing and storing organic products and wound healing --elongated, thicker cell walls --cells grouped in strands or cylinders to support leaves and stems (parts that are still growing) --cells have rigid, thick walls with lignin --at maturity, consists of dead cells --supports and strengthens plant 1. Ground System Parenchyma Collenchyma Sclerenchyma

Tissue Systems 2. Vascular System Xylem -Conducts water and minerals from roots to plant -composed of dead cells that form water-pipe system Phloem -Conducts food throughout plant -composed of living cells arranged into tubules

Water-conducting Cells of Xylem

Sugar-conducting Cells of Phloem

Sheath of sclerenchyma phloem xylem parenchyma

Tissue Systems 3. Dermal Tissue System - Forms the outer covering of plants Epidermis-outer layer of cells covered by waxy cuticle Stomata-structures that regulate passage of gases into/out of plant

Meristems: Primary Growth Growing region where cells actively divide Apical meristems- grow in length at tips of stems and roots

Lateral meristems Add thickness to woody plants, a process called secondary growth Two lateral meristems –vascular cambium adds layers of vascular tissue called secondary xylem (wood) and secondary phloem –cork cambium replaces the epidermis with periderm, which is thicker and tougher

Primary Growth in Roots

Primary Growth in Shoots

Secondary growth occurs in stems and roots of woody plants but rarely in leaves Vascular cambium Produces secondary xylem and phloem Cork cambium Produces tough, thick covering for stems and roots Replaces epidermis

Anatomy of a Tree Trunk As a tree or woody shrub ages, the older layers of secondary xylem, the heartwood, no longer transport water and minerals The outer layers, known as sapwood, still transport materials through the xylem

Growth, morphogenesis, and differentiation produce the plant body The three developmental processes of growth, morphogenesis, and cellular differentiation act in concert to transform the fertilized egg into a plant

Growth: Cell Division and Cell Expansion By increasing cell number, cell division in meristems increases the potential for growth Cell expansion accounts for the actual increase in plant size

The Plane and Symmetry of Cell Division The plane (direction) and symmetry of cell division are immensely important in determining plant form If the planes of division are parallel to the plane of the first division, a single file of cells is produced

The Plane and Symmetry of Cell Division If the planes of division vary randomly, asymmetrical cell division occurs

The Plane and Symmetry of Cell Division The plane in which a cell divides is determined during late interphase Microtubules become concentrated into a ring called the preprophase band

Genetic Control of Flowering Flower formation involves a phase change from vegetative growth to reproductive growth It is triggered by a combination of environmental cues and internal signals Transition from vegetative growth to flowering is associated with the switching-on of floral meristem identity genes

Plant biologists have identified several organ identity genes that regulate the development of floral pattern

The ABC model of flower formation identifies how floral organ identity genes direct the formation of the four types of floral organs