Chapter 35: Plant Structure, Growth, and Development (mostly angiosperms: monocots and eudicots)

Key Concepts (5)

(1) The plant body has a hierarchy of organs, tissues, and cells.
- Cells -->Tissue-->Organ-->Organ system-->Organism

(a) Three basic plant organs: Roots, Stems, and Leaves!
- Draw resources below and above ground
- Below: Water & Minerals
- Above: CO2 & light
- The three basic organs help with drawing these resources
- Organs are organized into Organs systems: 1) root system (roots) and 2) shoot system (stems and leaves)
- Both systems very important for survival
- Root system: 1) nonphotosynthetic (therefore w/o shoot system, would starve without organic materials from shoot system)
- Shoot system: 1) Depends on water & minerals that roots absorb from soil.
- Reproductive shoots: flowers (w/ leaves for sexual reproduction)
(1a) Roots!
- Roots: organ that anchors the vascular plant (in soil), absorbs minerals and water, and stores organic material.
- Taproot system (Angiosperm Eudicots / Gymnosperms): penetrates into ground & consists w/ one taproot (main vertical root) that develops from embryonic root)
- Taproot (from taproot system): have lateral roots growing from it.
- Angiosperm Eudicots: taproot stores organic nutrients that plants use up during flowering and fruit production (therefore, root crops like carrots are harvested before they flower)
- Fibrous root system (Seedless vascular plants / Monocots): Embryonic root dies and has no main root (grasses)…instead, they have many small roots that grow from stem. The small roots then form their own lateral roots. It is shallower than an actual taproot system, but make excellent ground cover preventing erosion. Monocots (bamboo/ palm) are anchored by rhizomes (horizontal underground stems).
- Adventitious: Roots growing from stem, so grass in adventitious.

So…basically, the root system helps anchor a plant…however! The absorption of water and minerals occur near the root TIPS with a buncha root hairs (which increase surface area). A root hair is like an extension of a root epidermal cell kinda like a protective cell on a plant surface.
BEWARE!! DO NOT CONFUSE ROOT HAIRS FROM LATERAL ROOTS (multicellular organs)!!

- Absorption is enhanced by symbiotic relationships btwn plant roots and fungi and bacteria.
- A lot of plants have modified roots. Some of these modified roots came from roots, adventitious, and leaves (rare). The modified roots give MORE support and anchorage, while the other modified roots store water and minerals…or absorb oxygen or water from air (yes, roots can be above the ground like the strangling aerial root).

(2a) Stems!
- Stem: organ w/ a lot of nodes (point at which leaves are attached) and internodes (stem segments btwn nodes).
- Axillary bud (it can form a lateral shoot aka branch): located btwn stem and leaf. In a young shoot, most do not grow (dormant).
- Instead, elongation concentrated near the shoot apex, which has a TERMINAL BUD gives rise to leaves and nodes and internodes b/c it concentrates all resources to elongate at terminal bud.
- Apical dominance: Terminal bud kinda inhibits growth of axillary bud. It might have happened b/c there’s more light at the top for plant to use.
- However, if there is no light at the top, but at the side, then the axillary bud starts to grow. Axillary bud gives rise to lateral shoot (branch) with its own terminal bud, leaves and axillary buds!
- If the terminal bud is removed in any way, the axillary bud stimulates growth. This results in “bushier” plants.
- Modified stems like rhizomes and bulbs are mistaken for roots…when they are actually…well…modified stems!

(3a) Leaves!
- Leaf: MAIN photosynthetic organ of most vascular plants (although green stems also perform photosynthesis)
- Consist of blade and petiole (stalk that joins leaf to node of stem)
- Grasses and other monocots (palms) lack petioles
- Instead, base of the leaf forms sheath that covers the stem
- Monocots vs eudicots:
~arrangement of veins (vascular tissue of leaves)
- monocots have parallel major veins across length of leaf blade
- eudicots have multibranched network of major veins
- Classification of angiosperms: taxonomists rely on floral morphology (leaf shape, spatial arrangement of leaves, pattern of leaf’s veins)
- Doubly compound vs compound vs simple leaves
- Large leaves can hold off strong wind/ confine pathogens to one leaflet
- Most leaves for photosynthesis, but some have leaves for other fcns like support, protection, storage, and reproduction.
- Modified leaves: 1) Tendrils (can be modified stems/ coils up for more support) 2) Spines (cactus prickly spines are leaves) 3) Storage leaves (Succulants that store a LOT of water) 4) Bracts (ex. red Poinsetta leaves attracts pollinators) 5) Reproductive leaves (Succulant that produce adventitious plantlets that fall of the leaf and grow in soil.