Plant Structure and Function

Why We Care About Plants

  • Food: A major way we use plants. Even animals we eat consume plants.

  • Fuel: Wood for campfires/stoves; fossil fuels (oil, coal) originate from ancient plants.

  • Fibers: Materials like cotton, bamboo, hemp for clothing and construction.

  • Construction: Building houses, furniture.

  • Aesthetics: Used to beautify spaces.

  • Medicine: Pharmaceuticals (e.g., morphine from poppies) and traditional medicines.

Plant Evolution and Domestication

  • Domestication: Adapting wild plants/animals for human use, reflecting genetic changes.

  • Artificial Selection: Humans interfere with crop evolution.

  • Domestication is beneficial to the plant (increased reproductive success) and humans.

  • Plant evolution: Mosses → club mosses → ferns → gymnosperms (conifers, seeds) → angiosperms (flowering plants, flowers, fruits).

Monocots vs. Dicots (Eudicots)

  • Monocots: One cotyledon in the seed. E.g., grasses like wheat, barley, oats, rice.

  • Dicots (Eudicots): Two cotyledons in the seed. E.g., canola, legumes.

  • Monocot flowers: Parts in multiples of three (e.g., 6 petals).

  • Dicot flowers: Parts in multiples of four or five (e.g., 4 petals on canola).

  • Monocots: Parallel veins in leaves (e.g., maize).

  • Dicots: Reticulate (net-like) venation.

  • Monocots: Fibrous root system.

  • Dicots: Taproot system (e.g., carrot).

  • Stems: Monocots have scattered vascular bundles; dicots have organized rings.

Plant Structure

  • Organized into cells, tissues, and organs with specialized functions.

  • Shoot system (above ground): Photosynthesis in green leaves/stems.

  • Root system (below ground): Acquiring nutrients and water.

  • Growth occurs at meristems (shoot apical, root apical, cambiums).

  • Shoot/root apical meristems: Make plant grow longer.

  • Cambiums: Make plant grow wider.

  • Meristems contain undifferentiated cells with potential to become any cell type.

  • Primary meristems: Lengthen plant (shoot/root apical meristems).

  • Secondary meristems: Widen plant (cambiums).

  • Three tissue systems: Dermal (outermost), vascular (innermost, carries water/sugars), and ground tissue (between).

  • Three general cell types: Parenchyma (does work), collenchyma (supportive), and sclerenchyma (tough, protective).

Plant Organs: Roots

  • Regulate and provide water/nutrient uptake.

  • Anchor the plant.

  • Food storage (e.g., carrot).

  • Site of beneficial microbial interactions.

  • Dicots: Taproot system.

  • Monocots: Fibrous root system.

  • Root structure: Root cap, meristematic zone, elongation zone, maturation zone.

  • Maximize surface area with lateral roots and root hairs.

  • Vascular tissue is in the middle.

  • Phloem: Moves sugar.

  • Xylem: Moves water.

Stems

  • Support and height for leaves.

  • Site of new above-ground growth.

  • Transport water and sugars.

  • Sometimes a storage organ; sometimes performs photosynthesis.

  • Highway for xylem and phloem.

  • Arranged into phytomers (leaf, bud, internode, node).

  • Dicots/Monocots: Differ in stem structure.

  • Vascular cambium creates new vascular growth (xylem/phloem).

Leaves

  • Site of photosynthesis.

  • Flat, green to maximize light capture.

  • Blade (lamina): Surface of the leaf.

  • Petiole: Connects leaf to stem.

  • Midrib: Main rib in the middle.

  • Dicots: Reticulate venation.

  • Monocots: Unique leaf structure with a sheath that wraps around the stem.

  • Leaf Anatomy: Thin, horizontal, mesophyll cells with chloroplasts. Cuticle for water conservation; stomata for gas exchange.

  • Stomata: Pores that let in carbon dioxide and let out water and oxygen, made of two guard cells. The opening is called the stomatal pore.