Plant Structure and Development

At the cellular level:

  • chloroplasts- in photosynthetic cells

  • Tube shaped cells- transport resources

  • Cells w/ root hairs- increase surface area

At the tissue level:

  • Dermal tissue protect organs

  • Ground tissue- photosynthesis

  • Vascular tissue- support+transport

Plant structure+function:

Plant body= 2 major systems w/ organs that perform diff functions

Shoot system

  • Stems, alternate b/w nodes+ internodes

  • Nodes = cells differentiate→leaf growth

  • Internodes = areas of elongation b/w nodes

  • Apical (terminal) buds- main shoot, continues stem from top

    • Apical dominance= apical bud inhibits growth of axillary buds

      • resources devoted to elongation of this bud

      • removal of this bud signals axillary bud elongation

  • Axillary buds- form branches/lateral shoots

    • usually dormant in young shoots

  • Stem functions:

    • presentation of sex organs and dispersion of propagules

    • food storage

      • Ex: rhizomes = modified stems that store food, such as ginger+potatoes

    • Asexual Reproduction: ex- bulbs can split off

  • Leaves

    • Petiole = branch that grows from stem node

    • Blade = often flat part, main photosynthesis center for most plants

      • Monocot→veins typically parallel

      • Eudicot→veins netlike

      • Compound leaf- leaflet+petiole

      • Doubly compound leaf- leaflet

    • Flowers = whorls of modified leaves

    • Leaf functions+modifications:

      • Photosynthesis- sugar production

      • support- pea plant tendrils

      • protection- cactus

      • storage- succulents

      • reproduction- poinsettia red leaves attract pollinators

Angiosperms

  • Can be split into categories

    • Monocots

      • ~25% of angiosperms

      • orchids, palm, grasses (maize, rice, wheat)

    • Eudicots

      • ~75% of angiosperms

      • legumes, roses, apples, oaks, maples

    • Others (Plant Pals)

      • basal angiosperms and magnoliids (used to be grouped w/ eudicots)

Root system

  • Angiosperm eudicots+gymnosperms = taproot+ lateral roots

    • water/mineral absorption

    • physically anchor plant

    • some store carbs

  • Angiosperm monocots= fibrous root system

    • water/mineral absorption

    • physically anchor plant

    • pop out directly from stem

    • shallow soils/semi-arid system b/c water does not penetrate deep

    • can be useful for erosion control

  • Root hairs increase surface area→absorption

    • near root tios

    • projections from a single cell

    • constantly replaced

  • Modified roots

    • Storage- store carbohydrates + sugar consumed during flower production

    • Support

      • Prop roots: Mangroves, protect from floods, create their own ecosystems for fish, often relatively shallow root systems

      • Aerial roots: spread+disperse, epiphyte plants that grow on other plants, orchids, poison ivy hair rope, florida strangler fig

      • Pneumatophores: roots that facilitate gas exchange, some mangrove species, probably not cypress knees

Plant Tissue Systems

  1. Ground Tissue System: storage, photosynthesis, support

    1. pith (internal to vascular)

    2. cortex (external to vascular)

  2. Vascular Tissue System: conductive

    1. xylem (water+minerals, “root to shoot”)

    2. phloem (sugars+water to roots and new growth)

  3. Dermal Tissue System: protective

    1. epidermis (outer cell layer)

    2. cuticle (waxy outer layer)

Plasticity

  • Developmental plasticity- the same genotype can form diff phenotypes based on the environment

  • Plants can alter form w/ environmental conditions via indeterminate growth from meristems

  • more common in plants than animals’

Plant Cells

  • Plant cells mainly differ in the makeup of their cell walls

  1. Parenchyma

    • thin, flexible plant walls

    • “typical” plant cells w/ cellulose cell wall

    • Functions: photosynthesis, storing water+nutrients, gas exchange, may differentiate to replace separate organs or produce a new plant

  2. Collenchyma

    • thick primary cell walls made of pectin and cellulose

    • no lignin

    • no secondary walls

    • Functions: provide support w/o restraining growth

  3. Sclerenchyma

    • rigid secondary walls w/ lignin

    • cannot elongate

    • Function: mechanical support

    • often make up nonliving tissue

Meristems = generate new cells for growth and control development of plants

  • Primary growth in Apical Meristems = growth in length

    • herbaceous + woody plants

    • rapid cell division

    • can happen at roots or shoots

    • some cells stay in meristem while others move out as growth

  • Secondary growth in Lateral Meristems = growth in thickness

    • only woody plants

    • typically occurs more in warm+wet areas

    • tree rings = where secondary growth occurs

Plant Growth

  1. Annuals- <1 yr life cycle

    • ex: grains, legumes, some wildflowers

  2. Biennials- life cycle 2 yrs

    • flower in 2nd yr b/4 they die

    • ex: beets, carrots→harvested b/4 they flower

  3. Perennials- life cycle many yrs

    • ex: trees, shrubs, some grasses, some wildflowers→ some may flower once every many yrs