Chapter 35Plant Structure,

Growth, and Development

Chapter 35Plant Structure,

Growth, and Development

Shannon Nugent

Austin Wetterau

Erin Strong

Anatomy of a PlantAnatomy of a Plant

• 3 Basic Organs:

• Roots, Stems, Leaves

• Absorb water from below and CO2 from above

• Root system and Shoot System

• Both depend on each other

• Roots starve without photosynthesis

• Shoot system depends on water and minerals absorbed

• 3 Basic Organs:

• Roots, Stems, Leaves

• Absorb water from below and CO2 from above

• Root system and Shoot System

• Both depend on each other

• Roots starve without photosynthesis

• Shoot system depends on water and minerals absorbed

RootsRoots

• Multicellular organ acting as an anchor, absorbs nutrients, and stores carbs

• Most gymnosperms or eudicots have a Taproot - main root

• Lateral roots - roots linked to main taproot

• Monocots - many small roots (fibrous root system)

• Multicellular organ acting as an anchor, absorbs nutrients, and stores carbs

• Most gymnosperms or eudicots have a Taproot - main root

• Lateral roots - roots linked to main taproot

• Monocots - many small roots (fibrous root system)

StemsStems

• Stem - an organ consisting of system of nodes where leaves attach with internodes

• Axillary bud - in angle of stem and leaf (branch)

• Apical bud - developing leaves

• Buds describe dormancy

• Possible Food storage and asexual reproduction

• Stem - an organ consisting of system of nodes where leaves attach with internodes

• Axillary bud - in angle of stem and leaf (branch)

• Apical bud - developing leaves

• Buds describe dormancy

• Possible Food storage and asexual reproduction

LeavesLeaves

• Main photosynthetic organ

• Monocots - parallel major veins

• Eudicots - branched network of veins

• Help taxonomists diversify many different plants

• Main photosynthetic organ

• Monocots - parallel major veins

• Eudicots - branched network of veins

• Help taxonomists diversify many different plants

35.235.2

• Intermediate growth - most plants grow continuously

• Plant life cycle: Annual, Biennial, Perennial

• Meristems make intermediate growth possible

• Initials - sources of new

• Derivatives - new cells from meristem

• Intermediate growth - most plants grow continuously

• Plant life cycle: Annual, Biennial, Perennial

• Meristems make intermediate growth possible

• Initials - sources of new

• Derivatives - new cells from meristem

35.3• Growth of Roots

– Primary growth produces the Primary plant body: parts of roots and shoot systems produced by apical meristems

– Tip of root is covered by the root cap: protects apical meristem  during primary growth

– zone of cell division includes apical meristem & 3 primary meristems (protoderm, procambrium, & ground)

35.3 cont.

• Growth occurs in 3 stages:

– zone of cell division (where new root cells are produced)-

– zone of elongation: root cells elongate

– -zone of differentiation: zone of maturation, become distinct cell types

• Primary growth produces epidermis, ground tissue, and vascular tissue

35.3 cont.

• Growth of Shoots

– vascular tissue runs through stem in strands called vascular bundles

– dicots = vascular bundles in ring, pith inside ring, cortex outside

– monocots = vascular bundles scattered through ground tissue

– Leaves develop from Leaf primordia: projections along side of apical meristem

35.3 cont.

• Tissue Organization

– Epidermis has stomata: tiny pores controlled by guard cells that allow gas exchange

– Ground tissue is located in the mesophyll

– Vascular tissue contains xylem and phloem

35.4• Secondary growth occurs in stems and

roots of woody plants

• Secondary Plant Body: tissues produced by vascular cambium and cork cambium-

– vascular cambium: cylinder of meristematic cells that forms secondary vascular tissue, increases vascular flow and support for shoots

– cork cambium: produces a tough, thick covering that protect the stem from water loss and invasion

• Primary and secondary growth occur simultaneously

35.4 cont.

• Vascular Cambium and Secondary Vascular Tissue

– As meristematic cells divide, they increase circumference of vascular cambium and add layers of secondary xylem (wood) to its interior and secondary phloem to exterior

– Some parts of vascular cambium are elongated & other parts are shortened and produce vascular rays: radial files of cells that connect the secondary xylem with secondary phloem

35.4 cont.• A year’s growth appears

as a distinct ring in tree trunks and roots

• Heartwood= old layers of secondary xylem that no longer transport water and minerals

• Sapwood= newest, outer layers of secondary xylem, transports xylem sap

35.4 cont.• Cork Cambium & Production of Periderm

– During secondary growth, epidermis is falls off and is replaced by two tissues produced by the first cork cambium

– Cork tissue functions as a barrier that protects stem/root from water loss, physical damage, and pathogens

– Periderm: consists of cork cambium plus the layers of cells it produces

– Lenticels: dot the periderm and enable living cells within a woody stem or root to exchange gases with outside air

– Bark: all tissues external to vascular cambium

– Components of bark = secondary phloem, most recent periderm, and old layers of periderm

35.5- Growth, Morphogenesis, and Differentiation Produce

the Plant Body

• Scientists believe that if they identify each gene’s function in a plant, they can discover a blue print of how plants develop

35.5 cont.• GROWTH

– When cell numbers increase, cell divisions in meristems increase the potential for growth

– Most increase in growth comes from cell expansion or elongation

35.5 cont.• Preprophase band

– Concentrated ring of microtubules. Disappears before metaphase, but predicts the future plan for cell division

• Water uptake accounts for 90% of plant cell expansion

• Vacuoles fill quickly from the water uptake & take up a lot of space in cells, letting the plant grow rapidly

35.5 cont.• Enzymes weaken the cross-links in

cell wall, letting it expand as water diffuses into the vacuole by osmosis

• Morphogenesis must occur for plant to develop properly– Cells must be organized into

multicellular arrangements of tissues and organs

35.5 cont.• Pattern formation- Development of

specific structures in specific locations

• Positional information is communicated by signals that continuously indicate to every cell its location in the developing structure– Ex. Hormones, proteins, mRNAs

provide positional info.

35.5 cont.• Critical step in morphogenesis

is proper establishment of axial polarity

• Morphogenesis is under the control of homeotic genes (master regulatory genes that over see major events in development)

35.5 cont.• Cellular differentiation depends on

the control of gene expression• Positional information is important to

all stages of development (growth, morphogenesis, and differentiation)

• Phase changes- When internal or environmental changes cause a plant to switch from developing one part to another