Overview
This lecture covers the structure, function, and classification of vascular plants, plant transport mechanisms, seed germination, and plant growth regulation.
Vascular Plant Structure
- Plants have two main organ systems: shoots and roots.
- Three tissue types: dermal (outer protection), ground (storage/support), vascular (transport).
- Major organs: leaf, stem, root.
- Angiosperms are flowering plants, split into monocots (one cotyledon) and dicots (two cotyledons).
- Cotyledons are the seed leaves, storing nutrients for the embryo.
- Vascular bundles (xylem + phloem): monocots (scattered bundles), dicots (bundles in a ring).
Root Systems & Function
- Taproot system: single thick main root with lateral roots.
- Fibrous system: many small, shallow roots.
- Root tip contains a root cap (protective), meristem (cell production), and root hairs (increase surface area).
- Roots anchor plants, absorb water/nutrients, transport materials, and may store carbohydrates.
- Root structure: epidermis (outer), cortex (storage/transport), endodermis (controls flow into vascular tissue), vascular tissue (xylem/phloem).
Stems & Leaves
- Herbaceous stems: non-woody; monocots (scattered bundles), dicots (bundles in a ring).
- Woody stems (dicots): grow thicker via vascular cambium; sapwood (young xylem), heartwood (old, rigid xylem).
- Special stems: tubers (storage), bulbs (modified stem/leaves), rhizomes (storage, new growth).
- Leaf identification: monocots (narrow, parallel veins), dicots (broad, branching veins).
- Leaf parts: cuticle (waxy layer), epidermis (protection), stomata (gas exchange), guard cells (control stomata), mesophyll (photosynthesis zone), xylem/phloem (transport).
Plant Transport
- Transport occurs via diffusion (including osmosis) and active transport.
- Diffusion moves substances from high to low concentration without energy.
- Osmosis is water diffusion across membranes.
- Active transport requires ATP to move substances against gradients.
Seed Germination
- Seeds enter dormancy (metabolism slows) before germination.
- Germination begins with water and heat absorption, breaking dormancy.
- Seed structure: embryo (epicotyl = leaf, hypocotyl = stem, radicle = root), endosperm (food), cotyledon (food), seed coat (protection), micropyle (water entry).
- Gibberellin hormone starts digestion of starch, increasing sugar and water uptake, leading to sprouting.
Plant Growth and Regulation
- Plant hormones (auxins, gibberellins, cytokinins, ethylene, abscisic acid) regulate growth and responses.
- Auxins: stimulate stem growth toward light.
- Gibberellins: promote cell division and elongation.
- Cytokinins: promote rapid cell division.
- Ethylene: triggers fruit ripening and aging.
- Abscisic acid: induces dormancy and closes stomata in dry conditions.
Plant Movement (Tropisms)
- Tropisms are directional growth responses to stimuli: phototropism (light), gravitropism (gravity), hydrotropism (water), thigmotropism (touch).
- Shoots show positive phototropism; roots show positive gravitropism.
- Other movements (e.g., turgor-driven, Venus flytrap) are non-directional and reversible.
Key Terms & Definitions
- Cotyledon — seed leaf storing nutrients for the embryo.
- Vascular bundle — strand of xylem and phloem in stems/roots.
- Xylem — vessel transporting water/minerals up from roots.
- Phloem — vessel transporting sugars from leaves to the plant.
- Meristem — region of plant where new cells are produced.
- Dormancy — period of slowed metabolism and suspended growth.
- Tropism — growth response toward or away from a stimulus.
Action Items / Next Steps
- Review root, stem, and leaf diagrams for monocots and dicots.
- Study the plant hormones and their effects.
- Prepare for questions on seed germination steps and plant transport methods.