9.1 Plant Structure and Growth

Fig. 29.1 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The basic morphology of plants reflects their evolutionary history as terrestrial organisms that must simultaneously inhabit and draw resources from two very different environments: Soil provides water and minerals Air is the main source of CO2 and light does not penetrate far into soil. Plants have evolved two systems: a subterranean root system and an aerial shoot system of stems and leaves.

Most angiosperms belong to either the monocots (65,000 species) or dicots (165,000 species) several other clades branched off before these.

9.1.2 Outline three differences between the structures of dicots and monocots

9.1.1 Draw and label plant diagrams to show the distribution of tissues in the stem

9.1.1 Draw and label plant diagrams to show the distribution of tissues in the leaf of a dicot

9.1.3 Dicotyledon Structure Dicotyledon – angiosperm that produces two leaves from the original seed Roots uptake H2O and minerals. Main root “tap root” has many offshoots Stem divides to produce petioles that support the leaves. Also contains vascular tissue in bundles.

Axillary buds on the stem provide tissues for lateral growth of branches and leaves Terminal bud contains structures for the growth and elongation of the main stem

Roots (dicot)- transverse section Absorb mineral ions and water from soil Anchor the plant Sometimes used in food storage Epidermis – outer surface that provides protection Cortex- outer region of root that conducts water from soil to vascular tissue Endodermis – tissue surrounding vascular tissue; acts as selective membrane

Xylem – vascular tissue that transports water Phloem – vascular tissue that transports organic molecules By branching and by root hairs, surface area of root is increased

Stem (dicot) – transverse section Connect leaves, roots and flowers and contain vascular tissue for transportation Epidermis may exchange some gas with enviro. but mainly for protection Vascular bundle – contains tissues that transport substances around the plant. Xylem portion also gives support, especially in woody plants

Cambium – cells that differentiate into xylem or phloem Cortex – primarily supportive tissue, some storage Pith – storage region; also provides support to the plant by turgor pressure Turgor pressure - when cells take up water and this exerts pressure against the cell membrane

Leaf (angiosperm) Cuticle – waxy upper layer that prevents loss of water from evaporation. Also helps deter herbivore and frost damage Upper epidermis – support and protection Palisade mesophyll – densely packed cells that contain many chloroplasts. Located in upper ½ of leaf where light is most intense

Spongy mesophyll – loosely packed cells Spongy mesophyll – loosely packed cells. Provides main gas exchange surface. Must be close to stomata. Stomata (stoma) – pores in underside of leaf that allow O2 to diffuse out and CO2 to diffuse in. Also water vapor will diffuse out (transpiration) Guard cells on either side of the stomata control opening and closing Lower epidermis – support and protection

Vascular bundles contain xylem and phloem tissue and spread out throughout leaf Xylem brings water to replace losses during transpiration Phloem transports the products of photosynthesis out of the leaf Broad, thin leaves help maximize the photosynthetic ability of the leaf

Roots There are two main types of roots: taproot systems (dicots) fibrous root systems (monocots)

9.1.4 Identify modifications of roots Prop Roots- thick roots that grow from the lower stem that brace the plant (e.g. corn) Storage roots -large roots that store carbohydrates and water (e.g. carrots and beets) Air roots- roots that extend above soil to aid uptake of oxygen, usually plants in wet places have them (e.g. mangroves) Buttress roots – large roots that develop near the bottom of the tree to provide stability

Storage Roots Buttress Roots Air Roots

9.1.4 Identify modifications of Stems Bulbs- vertical underground stems consisting of enlarged leaf bases that store food (e.g. onions) Tubers –Horizontally growing stems below ground that are modified as carbohydrate storage structures (e.g. potatoes) Rhizomes- horizontal stems that grow just below the surface to allow plant spreading (e.g. ginger plant) Stolons – horizontal stems that grow above ground and allow a plant to reproduce asexually (e.g. strawberries)

Bulb Tubers

9.1.4 Identify modifications of Leaves Tendrils- structures that coil around objects to aid in support and climbing (e.g. pea plants) Reproductive leaves –produce tiny plants along the leaf margins that fall to the ground and take root (e.g. kalanchoe plants) Bracts or floral leaves- colored leaves that surround flowers and attract insects for pollination (e.g. poinsettia) Spines – reduce water loss, may be associated with modified stems that carry out photosynthesis (e.g. cacti)

Tendrils Reproductive Leaves                          Floral Leaves Spines

9.1.5 State that dicots have apical and lateral meristems Plants grow throughout their lifetime This is called indeterminite growth (animals exhibit determinite growth) Meristematic tissue serves to create new growth, it is a lot like a stem cell in animals, as it is able to develop into any type of plant tissue Dicots have two types of meristem Apical Lateral

9.1.6 Compare growth due to apical and lateral meristems in dicots Apical meristems Also called primary meristems Occurs at the tips of roots and and stems Allows roots to extend into soil and stems to grow taller Results in non-woody stems and roots Lateral meristems Also called secondary meristems Woody plants have active lateral meristems Allow growth in the thickness of a plant Results in woody stems and roots

Apical Meristems

Two types of Lateral Meristem Cork cambium Occurs within the bark of a plant Produces the cork cells of the outer bark Vascular cambium Produces secondary vascular tissue (xylem and phloem) Lies between the secondary phloem (on the outside) and the secondary xylem (on the inside) Secondary xylem is a major component of wood

9.1.6 Compare growth due to apical and lateral meristems in dicots

Tropism A tropism is a growth or movement response to directional external stimulus May be positive (toward) or negative (away) Common stimuli include chemicals, gravity, touch, and light. video

9.1.7 Explain the Role of Auxin in Phototropism If an area is crowded with plants, or light is scarce, a plant would be benefitted most by growing or moving toward the light Auxins are plant hormones that cause positive phototropism of plant shoots and seedlings Auxins are found in seed embryos, meristems of apical buds, and young leaves