Plants: Leaves, Roots, Stems Chapter 13

Kingdom Plantae Botany: the scientific study of plant structures and processes Horticulture: the cultivation of plants, especially gardening and edible plants Arborist: a tree doctor

Properties of Plants Eukaryotic Multicellular Sexually Reproducing (pollination) Cells, vascular tissues, organs, systems Roots, stems, leaves Cell Walls (cellulose) Photosynthesis/Green (pigments, plastids) Producers (autotrophic)

THREE Types of Plants 1. Seeded, Vascular (Tissued) Plants Most plants Angiosperms (flowering plants/trees) Monocots and dicots Gymnosperms (non-flowering plants) conifers 2. Seedless, Vascular Plants Ferns 3. Seedless, Non-Vascular Plants Mosses Lichens, algae, fungi are NOT plants

Roots How water and nutrients come into the plant

Roots Keep plant anchored, not moving Absorb water, air, chemicals, and nutrients to stem

Root Systems Taproot Fibrous One larger root with many fibers Ex. Dandelions Carrots, Potatoes, Beets Generally equal sized fibers Ex. Grass

Root tips The tip of the root is the part that grows If it is cut off, the plant will not grow again The very tip is deadened cells which protect the root as it pokes downward Cells just behind the tip undergo mitosis and then elongate (the meristematic region/elongation regions) Root hairs are important because they penetrate between soil particles and get water that would normally be out of reach for the root

Stems How food and water are transported throughout the plant

Stems Organ of Transportation Carries water and nutrients from roots to leaves (where photosynthesis occurs) Support leaves at nodes. The #of nodes and distance between nodes in a given year tells how healthy the plant was that year. Diverse because of the thickness and strength of cells: tree trunks, ivy, lily vines, stalks (celery). Cactus stems actually conduct photosynthesis. Woody stems (trees) Herbaceous stems (green, flexible plants)

Herbaceous v. Woody Stems Woody stems (trees) Herbaceous stems (green, flexible)

Xylem & Phloem Xylem and Phloem are fibrous, vascular tissues that are bundled together inside the stem (vascular bundles) Xylem carries water up from the roots Phloem carries food down throughout the plant--sugar, nutrients Extra sugar can be stored as starch, lipids These are often stored in fruits, which grow and ripen as more sugar and water collect

Cross-Section of a Stem

Monocot Stem

Tree Trunks Tree trunks are interesting (woody) stems Xylem fibers form the wood of the trunk center Xylem is harder in leaf-bearing trees and softer in evergreen trees Phloem forms the layers inside of the bark Cork cells make up the outer bark; dead cells harden and prevent water from evaporating out Vascular Cambium produces phloem; Cork cambium produces cork Small openings, called lenticels, allow gas exchange

Woody Stem

Leaves Where photosynthesis and respiration occurs, to feed the plant and help it breathe

Veins Venation can be used to help identify leaves Pinnate Palmate Parallel Veins

Leaf Shape The type of leaf blade can also be used in plant identification Simple leaf Compound leaf The blade is different if the plant is a monocot or a dicot Monocots are single thin blade, parallel veins Dicots are branching veins with larger blades

Leaf Edges Leaf edges can also be used. Smooth Serrated

Leaf Arrangement 3 main types of leaf arrangement Alternate Opposite Whorled (windmill or pinwheel pattern)

Dermal tissues

Leaf Openings: Respiration Openings in the leaf permit water that has been drawn up through the stem, to exit the leaf through transpiration Stomata also permit gas exchange—CO2 in and O2 out; guard cells use energy to open and close the stomata The epidermis is waxy; it protects the leaf’s parts, and prevents the loss of too much water or air

Photosynthesis: Making Food Water + Light + CO2  Sugar + Oxygen Occurs because of chlorophyll in the chloroplasts In the upper layer of the leaf (the palisade layer), there are lots of cells with many chloroplasts; these float and angle towards the sun as it rises and sets In the lower layer of the leaf (the spongy mesophyll), there are more spaces for air exchange

Cross-Section of a Leaf

Growth

Water Circulation Growth depends on supply of water and oxygen (temperature and light) Roots absorb water from the soil, through osmosis Root pressure causes water to climb the stem through the xylem vein Capillarity also helps water to rise (adhesion of water molecules inside a thin diameter) as vapor exits the leaf Transpiration-Cohesion Theory currently says that water is pulled upwards as well. Transpiration occurs as leaves open and water evaporates into the atmosphere Cohesion between water molecules pulls the water column up toward the leaves

Cell vacuoles swell with water, exerting pressure on cell walls Cell walls made of cellulose packed inside the stem provide stiffness to the whole plant Watery cells on the inside of the stem are ground tissue Turgor Pressure

Nastic Movements Similar to “reflexes” Plant movements that can go back and forth Ex. Blooms opening and closing with the sun Venus fly traps Plants that close to the touch Occur as turgor pressure is lost or gained in certain cells

Flow of Food Photosynthesis generates the sugar needed for the plant to grow Must be translocated to new parts of the plant through the phloem vessels Does this through water circulation, osmosis, and pressure changes Can go upwards to be stored in fruit/flower Can go downwards to root tips, meristematic areas

Mineral Supply and Flow Plants absorb nitrogen, phosphorous, potassium, and other inorganic substances from the soil They use these in processes and substances they need These minerals are dissolved in water Absorption requires oxygen for active transport— minerals have to be pumped across the root membranes Fertilizer, manure/mulch, and crop rotation can replenish nutrients in the soil that have been used up by plants

Auxins Certain stimuli affect the amount of auxin or growth hormone Auxins increase the size and number of cells in certain spots. Overgrowth in an area makes the stem bend or curve. Auxin collects in root tips and buds; if these are cut off, the plant will stop growing. Cells will not elongate.

Tropisms Tropisms are different kinds of growth patterns that occur in response to auxins collecting in certain areas Positive phototropism: growth towards light Negative phototropism: growth away from light Gravitropism: growth towards the ground Thigmotropism: growth towards touch/stakes .

Synthetic Auxins Auxins are naturally found in plant cells, and vary from plant to plant. Synthetic auxins are used to help ripen fruits, or force bud/flower production. Some encourage more elongation. Some are used to inhibit budding or growth. Some induce dormancy. Some are used as selective weed/plant killers.