Kimberley Nguyen
35: Plant Structure, Growth, & Development
Overview: No Two Plants are Alike
 Plasticity is when plant form is controlled by environmental and genetic factors
35.1: The plant body has a hierarchy of organs, tissues, & cells
 Plants have organs, which are made up of tissues, which are made up of cells
 Roots: - help anchor a plant in soil, absorb minerals and water, store organic nutrients
- eudicots and gymnosperms have a taproot system and lateral roots branching off from it
- monocots have small roots, called a fibrous root system
- modified roots: prop roots, storage roots, “strangling” aerial roots, buttress roots, pneumatophores
 Stems: - a system of nodes (where leaves are attached) and internodes (segment between nodes)
- between a leaf and stem, is an axillary bud, which are unlikely form into a branch, while
terminal buds are at the tip of a branch and will develop since it gets all the nutrients  this
unbalanced spread of resources is called apical dominance
- modified stems: stolons, bulbs, tubers, rhizomes
 Leaves: - main photosynthetic organ, consisting of a flat blade and petiole
- angiosperms classified by leaf shape, spatial arrangement of leaves, and vein patterns
- modified leaves: tendrils, spines, storage leaves, bracts, reproductive leaves
 Dermal Tissue: outer protective covering and prevents water loss; epidermis and periderm
 Vascular Tissue System: transports materials in xylem and phloem
 Ground Tissue System: a filler tissue and for storage, photosynthesis and support; pith and cortex
 Common plant cell types: parenchyma, collenchyma, sclerenchyma, water-conducting cells in xylem, and
sugar-conducting cells in phloem
35.2 Meristems generate cells for new organs
 Animals undergo determinate growth, while plants undergo inderterminate growth
- Due to plant’s meristems which divide frequently to replace or provide additional cells
- Apical meristems: add cells to shoots and roots; process called primary growth
- Lateral meristams: vascular cambium which adds layers to vascular tissue and cork cambium
which replace epidermis and periderm cells; process called secondary growth
 Plants categorized on how long they live; annuals, biennials, and perennials
35.3 Primary growth lengthens roots & shoots
 primary growth: apical meristems produce the primary plant body
 roots: - root tip has a root cap to protect the apical meristem
- Root grows behind in the tip in 3 zones: cell division, elongation, maturation
- In young roots, the primary growth produces the epidermis, ground, and vascular tissues
Kimberley Nguyen
- Structure (exterior to centre): epidermis, cortex, endodermis, pericycle (where the lateral root
forms), vascular cylinder with xylem and phloem in centre (pith)
 In shoots: - divides at the tip of a terminal bud and is dome-shaped and creates internodes and leaves called
leaf primordia
- Stem structure (exterior to centre): epidermis, collenchyma cells, vascular tissue, ground tissue
- Leaf structure (top to bottom): upper epidermis with stomata, ground tissue with veins, lower
epidermis
35.4 Secondary growth adds girth to stems & roots in woody plants
 secondary growth: lateral meristems produce the secondary plant body in woody plants
 Primary and secondary growth occur simultaneously
 The vascular cambium is responsible for the thickening of a root or stem
- Made of fusiform initials and ray initials
- Over time, secondary xylem (wood) is mainly tracheids and fibre
- Each year, a boundary is created between early and late wood
 Trees have layers called heartwood and sapwood
 Epidermis replaced by periderm when it dies(2 cork cambium tissues: phelloderm and cork cells)
 Bark is made up of the secondary phloem, most recent periderm and older layers of periderm
35.5: Growth, morphogenesis, & differentiation produce the plant body
 There are 3 developmental processes: growth, morphogenesis and cellular differentiation.
 Growth: - the plane and symmetry of cell division determines plant form
 some undergo asymmetrical cell division
 the microtubule ring, preprophase band determines the plane of division
- water in vacuoles make cells expand rapidly and up due to cellulose microfibrils
- some cells expand in all directions since the microtubule arrangement is random
 Morphogenesis: - process of cells being organized into multicellular arrangements
- Pattern formation is determined by positional information
 Polarity as positional information
 Cellular Differentiation: - cells contain same genome, but are different in function and structure due to
gene expression
- Depends on positional information
 Phase changes:- juvenile phase to adult vegetative phase to adult reproductive phase
 Most significant change is the leaves of juvenile to adult
 Most significant change is flowering of vegetative to reproductive due to floral
meristem identity genes
 ABC model of flower formation depicts flower’s phenotype by showing which
genes are active