Plant Structure and Function

Types of Plant Cells Parenchyma Thin flexible cell walls. 2 main functions – storage and food production. Large vacuole stores water, starch and oils. Can contain many chloroplasts.

Types of Plant Cells Collenchyma Typically long cells. Unevenly thickened cell walls. Thin parts can stretch and grow. Provide support for surrounding tissue. ie. – tough strands in celery.

Types of Plant Cells Sclerenchyma Thick and rigid. Used for support Two types: fibers and stone cells. Fibers – long thin strands, support, strength, vascular tissue. Stone cells – circular cells Gritty texture of pears Fruit pits

Plant Tissues Dermal or Epidermis Flattened parenchyma cells cover and protect plant like skin Produce a waxy cuticle – prevents water loss.

Plant Tissues Dermal or Epidermis Contain stomata: openings that control gas exchange. Guard cells control opening and closing.

Plant Tissues Dermal or Epidermis Root hairs: extensions of cell that help absorb water and minerals.

Plant Tissues Dermal or Epidermis Trichomes: hair like – give fuzzy texture Reduce evaporation. Some protect by secreting toxic substances.

Plant Tissues Vascular Tissues Transport food minerals and water through the plant. Two types: Xylem – Moves water and minerals from roots to rest of plant. Phloem – Transport sugars and organic compounds from leaves to rest of plant.

Plant Tissues Xylem Two types Tracheids: In conifers. Tubular, tapered ends, dead at maturity. Cell walls have pits for water flow across cells. Vessel elements: In Anthopytes. Wider and shorter. Openings in end walls for water flow through cells.

Plant Tissues Xylem

Plant Tissue Phloem Transport sugars and organic compounds. Living, tubular cells. Phloem cells are called sieve tube members. Have cytoplasm but no nucleus or ribosomes. Companion cells – next to each sieve tube member. Help manage transport.

Plant Tissues Ground Tissue All other tissues Mostly parenchyma Functions: photosynthesis, storage, support. In stems and roots: have large vacuoles to store starch and water.

Plant Tissues Meristematic Tissues Region of actively dividing cells. Small, round, with large nuclei. Apical meristems: At tips of roots and stems. Increase length. Lateral meristems: Cylinders of dividing cells in roots and stems. Increase diameter. Vascular cambium: produce xylem and phloem. Cork cambium: produces tough covering for root and stems.

Meristems

Roots Anchor, absorb water and minerals from soil. Some used for food storage (carrots) Two types Taproots: central fleshy with small branch roots. (carrots, beets) Fibrous roots: numerous branches from central point.

Root Variations Adventitious roots: Aerial roots: Prop roots above ground to support tall plants. Aerial roots: Cling to objects to provide support.

Root Structure Epidermis: outer layer. Root hair: extension of single epidermal cell. Absorbs water, oxygen and minerals.

Root Structure Cortex: next layer. Transports water and ions into vascular core. Made of parenchyma cells sometimes used for storage

Root Structure Endodermis: forms waterproof seal around vascular tissue. All water and minerals must pass through endodermis cells.

Root Structure Pericycle: just within endodermis. Gives rise to lateral roots (offshoots of older roots).

Root Structure Xylem and phloem: center of root. Transport of water, minerals and organic materials through plant.

Dicot vs. Monocot Root

Dicot vs. Monocot Root

Root Growth Apical meristem Vascular cambium Root cap Lengthens root Increase diameter Found between xylem and phloem Root cap Layer of cells at root tip. Protection

Stems Transport, support and storage. Some are Underground Corm: short, thick, surrounded by leaf scales. (gladiolus) Tuber: swollen underground stem with buds that sprout new plants. (potato) Rhizomes: (iris)

Stem: Internal Structure Vascular tissue arranged in bundles. Dicot Monocot

Woody Stems Secondary Growth: thickness from vascular cambium. Xylem: wood – causes growth rings. Bark: old phloem and cork cambium.

Stems – Material Transport Xylem: transports water from roots to leaves. Phloem: transports sugars, minerals, and hormones. Source: photosynthetic tissue – mostly leaves. Sink: storage area (cortex of roots) Translocation: movement from source to sink.

Leaf Variation Simple: blade no divided Compound: divided into leaflets Alternate: only one leaf from a single point on stem Opposite: leaves in pairs along stem Whorled: three or more leaves occurring at same place on stem

Leaf Structure Vascular tissue in veins. Epidermis: outer layer of cells. Two layers of Mesophyll. Palisade mesophyll: Most photosynthesis. Spongy mesophyll: Loosely packed with irregular shaped cells. Air spaces for gas exchange: O2, CO2, H2O. Gases move in and out of stomata.

Transpiration Loss of water vapor through the stomata.

Leaf Venation Patterns Parallel – monocots Netlike – dicots

Leaf Modifications Cactus spines: leaves that reduce water loss and protect plant. Bulb: short stem covered by large fleshy leaves, modified for food storage. Pitcher plant: modified to trap insects. Aloe vera: adapted to store water.

Hormones Tropisms Nastic Responses Plant Responses Hormones Tropisms Nastic Responses

Plant Hormones Chemicals produced in one part of an organism and transported to another to cause a change in growth or development.

Auxins: Hormone Promote cell elongation. (IAA) Indoleacetic acid. Produced in apical meristem. Increases cell division and promotes cell elongation. Weakens connections between cellulose fibers in the cell wall allowing cells to stretch.

Auxin Auxins produced in apical meristem inhibits growth of side branches. Remove stem tip – branches form

Gibberellins: Hormone Growth hormone. Stimulates cell elongation. Also increases rate of seed germination and bud development.

Cytokinins: Hormone Stimulate cell division or cytokinesis. Stimulate production of proteins needed for mitosis. Produced in meristem of roots and travel up xylem to rest of plant.

Ethylene: Hormone A gas that speeds ripening of fruits.

Tropism Response to an external stimulus from a particular direction. Positive tropism: plant grows toward stimulus. Negative tropism: plant grows away from stimulus.

Types of Tropism Phototropism: growth toward light. More auxin on side of stem away from light. Cell elongation on one side – dark side. Gravitropism: direction of plant growth in response to gravity. Stems up and roots down. Thigmotropism: response to touch. Tendrils of vine coil around objects.

Nastic Responses Response movement that is not dependent on direction of stimulus. Mimosa Venus Flytrap