Plant Physiology Flashcards

Plant Physiology

Objectives

  • Distinguish between shoots and roots and describe common modifications of each
  • Describe how meristematic tissue contributes to plant growth
  • Understand the parts of a leaf, leaf functions, and leaf modifications
  • Describe how transpiration moves water in plants
  • Understand common plant responses to stimuli

Lecture Organization

  • Plant body plan
  • Stems
  • Roots
  • Leaves
  • Plant behavior

Plant Body Plan

  • Plants have two distinct organ systems:
    • Shoot system: vegetative parts (leaves and the stems) and reproductive parts (flowers and fruits)
    • Root system: supports the plant and absorbs water and minerals

Plant Tissues

  • Plants have two basic tissue types:
    • Meristematic tissue: cells that constantly divide for plant growth.
    • Permanent tissue: cells that are no longer actively dividing

Meristematic Tissue

  • Meristematic tissue is the site of tissue growth
    • Apical meristems: tips of stems and roots; responsible for lengthening
    • Lateral meristems: growth in thickness or in a maturing plant
    • Intercalary meristems: monocots at the base of leaf blades

Permanent Tissues

  • Meristems give rise to distinct permanent tissues:
    • Dermal tissue: covers and protects the plant
    • Vascular tissue: transports water
    • Ground tissue: photosynthesis, provides a supporting matrix for the vascular tissue, and helps to store water and sugars

Vascular Tissue Arrangement

  • Vascular tissue arrangement differs in monocots/dicots
    • Arranged in vascular bundles running up and down the stem
    • Monocot stems: vascular bundles scattered throughout ground tissue
    • Dicot stems: vascular bundles arranged in a ring

Ground Tissue Types

  • There are three main types of ground tissue:
    • Parenchyma tissue
    • Collenchyma tissue
    • Sclerenchyma tissue

Parenchyma Cells

  • Parenchyma cells are the most common in plant tissue
    • Living cells found in stem, root, leaf interior, and fruit pulp
    • Form central pith and outer cortex in stems
    • Responsible for metabolic functions and wound repair
    • Store starch

Collenchyma Cells

  • Collenchyma cells are living support cells
    • Elongated cells with unevenly thickened walls
    • Support stem and leaves
    • Alive at maturity and usually found below the epidermis
    • Example: "strings" in celery stalks

Sclerenchyma Cells

  • Sclerenchyma cells are dead support cells
    • Provide support but many are dead at maturity
    • Have secondary cell walls thickened with lignin deposits
    • Fibers: long, slender cells
    • Sclereids: smaller-sized cells, give pears their gritty texture

Summary of Plant Body Plan

  • Shoot system: aboveground vegetative portions (stems and leaves) and reproductive parts (flowers and fruits)
  • Root system: supports the plant and is usually underground
  • Meristematic tissue: actively dividing cells that give rise to permanent tissue
  • Simple tissues: tissues with similar cell types like dermal and ground tissue
  • Complex tissues: made up of different cell types like vascular tissue

Stems

  • Stems are part of the shoot system
    • Range from millimeters to hundreds of meters in length; diameter also variable
    • Can be aboveground or underground (e.g., potato)
    • Can be herbaceous (soft) or woody
    • Provide support; hold leaves, flowers, and buds; store food
    • Connect roots to leaves, aiding in water and nutrient transport

Stem Characteristics

  • Stems are characterized by nodes and internodes
    • Nodes: points of attachment for leaves, aerial roots, and flowers
    • Internodes: stem regions between two nodes
    • Petiole: stalk extending from stem to leaf base
    • Axillary bud: between leaf base and stem; can give rise to branches or flowers

Stem Tissue Systems

  • Stem tissue consists of three systems:
    • Dermal
    • Vascular
    • Ground
  • Each system has characteristic cell types that perform specific tasks for plant growth and survival

Dermal Tissue: Epidermis

  • Dermal tissue consists primarily of epidermis
    • Single layer of cells covering and protecting the underlying tissue
    • Have transparent and non-photosynthetic cells
    • Bark: tough, waterproof outer layer of woody plants
    • Provides protection from damage

Dermal Tissue: Trichomes

  • Dermal tissue includes trichomes
    • Trichomes: hairlike structures on epidermal surface
    • Help to reduce transpiration, increase solar reflectance, and store compounds

Ground Tissue

  • Ground tissue is mostly parenchyma cells
    • Pith: ground tissue interior to vascular tissue
      • Soft, spongy parenchymal cells that store nutrients, provide support, and aid in nutrient transport
    • Cortex: layer between vascular tissue and epidermis
      • Stores carbohydrates, aids transport to roots, provides structural support

Stem Growth

  • Growth occurs as stems/roots lengthen/thicken
    • Primary growth: increase in shoot length; shoot apical meristem activity
    • Secondary growth: increase in thickness (girth); lateral meristem activity

Primary Growth

  • Primary growth increases length
    • Result of rapidly dividing cells in apical meristems and subsequent cell elongation
    • Enables continuous seeking of water (roots) or sunlight (shoots)

Secondary Growth

  • Secondary growth increases stem thickness
    • Result of lateral meristem activity
    • Include vascular cambium and cork cambium (in woody plants)

Periderm

  • Periderm replaces the epidermis as the plant matures
    • Lenticels: openings in periderm for gas exchange
      • Supplies oxygen to the living and metabolically active cells of the cortex, xylem, and phloem
      • Serve same function as stomata in leaves, but structurally different
      • Regions of porous tissue separated by large intercellular spaces

Stem Modifications

  • Stems are often modified
    • Stolons: stems running parallel to or just below ground surface
    • Runners: above-ground stolons producing clone plants at nodes (e.g., strawberries)
    • Tubers: modified stems storing starch (e.g., potatoes)
    • Bulbs: underground storage units with fleshy leaves (e.g., onions)

Aerial Modifications

  • Stems have aerial modifications
    • Tendrils: slender, twining strands for climbing support
    • Thorns: sharp outgrowths for plant protection

Summary of Stems

  • Stems bear leaves, flowers, and fruits.
  • Characterized by the presence of nodes and internodes
  • Composed of three tissue systems: dermal, vascular, and ground
  • Primary growth increases length; secondary growth increases thickness
  • Stems have numerous modifications depending on environmental conditions

Roots

  • Roots anchor, absorb, and store
    • Anchor plants to the soil, absorb water and minerals, and store products of photosynthesis
    • Most underground but some are adventitious (above ground)

Root Types

  • Roots include tap and fibrous types
    • Tap root: main root that grows down vertically with many smaller lateral roots; penetrates deep into the soil
      • Used by dicots
    • Fibrous root: located closer to the soil surface and forms a dense network of roots
      • Used by monocots

Root Tip Zones

  • Root tips are divided into three zones
    • Zone of cell division: closest to the root tip; actively dividing cells of root meristem
    • Zone of elongation: where newly formed cells increase in length, lengthening the root
    • Zone of maturation/differentiation: starts at the first root hair; where cells differentiate into special cell types

Root Tissues

  • Roots have vascular tissue
    • Epidermis surrounds areas of ground tissue and vascular tissue
      • Provides protection and helps in absorption
      • Root hairs: extensions of root epidermal cells
        • Aid absorption of water and minerals
      • Ground tissue includes cortex and pith

Root Modifications

  • Roots have modifications
    • Bulbous roots store starch (turnips)
    • Aerial and prop roots (mangrove trees) are aboveground roots that provide additional support to anchor the plant
    • Tap roots (carrots and beets) are modified for food storage
    • Epiphytic roots enable plants to grow on other plants

Summary of Roots

  • Roots anchor plants, absorb water/minerals, store food
  • Tap roots or fibrous structure
  • The root tip is protected by a root cap and has three growth zones: cell division, elongation, and maturation
  • Roots have modifications based on environment

Leaves

  • Leaves are where photosynthesis occurs
    • Usually green due to chlorophyll
    • Lamina: leaf blade
    • Petiole: attaches leaf to stem
    • Stipules: small, green appendages at base of petiole
    • Midrib: central vein branching into smaller veins
    • Margin: edge of the leaf

Leaf Venation

  • Leaf venation differs in monocots/dicots
    • Monocots: parallel venation
    • Dicots: reticulate venation (netlike pattern)
    • Ginkgo biloba: dichotomous venation (forking veins)

Leaf Epidermis

  • Leaf epidermis aids gas exchange
    • Epidermis: outermost layer on top and bottom of leaf
      • Helps in the regulation of gas exchange
      • Stomata: openings in epidermis for gas exchange
        • Surrounded by two guard cells to regulate opening and closing

Epidermis and Water Loss

  • Leaf epidermis protects against water loss
    • Usually one cell layer
    • Cuticle: waxy layer covering the leaf's surface
    • Trichomes: small hairs on some leaves
      • Deter herbivory and reduce transpiration by blocking air flow

Mesophyll

  • Mesophyll contains chloroplasts
    • Two arrangements of parenchyma cells:
      • Palisade parenchyma: column-shaped, tightly packed cells
      • Spongy parenchyma: loosely arranged cells of irregular shape
        • Allows gas exchange

Vascular Bundles

  • Leaves have vascular bundles
    • Xylem: transports water
    • Phloem: transports photosynthetic products

Leaf Adaptations

  • Plants have adaptations to their environment
    • Cacti spines are modified leaves to avoid water loss
    • Carnivorous plants have modified leaves to capture insects for nitrogen

Summary of Leaves

  • Leaves are primary photosynthetic organs
  • Consist of lamina, petiole, and various tissue layers (epidermis, mesophyll, vascular tissue)
  • Specialized leaf structures (needles, spines, etc.) exist for different environmental conditions

Plant Behavior: Water Movement

  • Water movement is driven by transpiration
    • Transpiration: loss of water through evaporation at the leaf surface
    • Cohesion: water sticks together
    • Adhesion: water sticks to the xylem

Plant Response to Light

  • Plants respond to light
    • Photomorphogenesis: growth and development of plants in response to light
    • Photoperiodism: ability to use light to track time
    • Phototropism: grow toward or away from light

Plant Response to Gravity

  • Gravitropism: roots grow into soil (positive) and shoots grow toward sunlight (negative)

Plant Hormones

  • Plants respond to hormones
    • Auxins: cell elongation
    • Cytokinins: promote cell division
    • Gibberellins: shoot elongation, seed germination, and fruit and flower maturation
    • Ethylene: fruit ripening
    • Abscisic acid: inhibits stem elongation; shuts things down during times of environmental stress

Plant Response to Wind and Touch

  • Plants respond to wind and touch
    • The movement of a plant due to directional pressure is called thigmotropism
    • A thigmonastic response is a touch response independent of the direction of stimulus
    • Thigmomorphogenesis is a slow developmental change in the shape of a plant subjected to continuous mechanical stress.

Summary of Plant Behavior

  • Transpiration causes water conduction through plants (regulated by opening/closing stomata)
  • Plants respond to light
  • Plant hormones are responsible for growth and development of the plant, fruit development and ripening, and dormancy in seeds and buds