Plant Structure, Reproduction, and Development

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Chapter 31

• Plant Structure, Reproduction, and Development

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• Plants are essential to human life.
• Our use of plants parallels the growth of
  civilization.
• Some plants, such as coastal redwoods, are among
  the largest and oldest organisms on earth.
• Coast redwoods are gymnosperms, a kind of plant
  that bears seeds on cones

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Man climbing a redwood tree.
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Most plants are angiosperms which will be the
focus of this discussion on plant structure.
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Angiosperms

• Angiosperms, or flowering plants, bear seeds in
  fruits.

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Two Main Groups of Angiosperms

• Monocots and Eudicots
• They differ in
• number of seed leaves (cotyledons)
• leaf venation
• arrangement of vascular system in stems
• number of flower parts
• root structure

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• Lily Monocot

• Rose Eudicot

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• Monocots
• one cotyledon
• parallel leaf venation
• scattered vascular bundles
• flower parts in 3s or multiples of 3
• fibrous roots

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• Eudicots
• two cotyledons
• branched leaf venation
• ring of vascular bundles
• flower parts in 4s or 5s (or multiples)
• taproot system

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Monocot or Eudicot?
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Typical Plant Body

• Three basic organs several types of tissues
  that perform a particular function.
• Roots
• Stems
• Leaves

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• Plants must draw resources from two different
  environments.
• They must draw water and minerals from the soil
  and CO2 and sunlight from aboveground.
• Neither roots nor shoots can survive without the
  other.

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• Plants absorb water and minerals from soil
  through roots.
• Plants absorb the suns energy and carbon dioxide
  from the air through shoots (stems and leaves).

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• Plant roots depend on shoots for carbohydrates
  produced via photosynthesis.
• Plant shoots depend on roots for water and
  minerals.

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Root System

• Anchors the plant in the soil.
• Absorbs and transports minerals.
• Stores food.

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• Monocots

• Dicots

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Root Hairs

• Found in both monocots and dicots.
• Increase surface area enormously.
• Cotyledons

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Shoot System

• Made up of stems, leaves, and adaptations for
  reproduction (flowers in angiosperms).
• Stems above ground and support the leaves and
  flowers.
• Nodes areas on the stems at which leaves are
  attached.

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Two Types of Buds

• Terminal Bud where a plant stem grows in
  length.
• Produces hormones (auxins) that inhibit the
  growth of the lateral buds (apical dominance).

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Apical Dominance

• Concentrates resources on height.
• Evolutionary adaptation that increases the
  plants exposure to height.
• Some axillary buds become flowers.

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Modified Roots, Stems, and Leaves
Modified stems used for reproducing asexually.
Used for food storage and asexual reproduction.
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Modified Leaves - Tendrils
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Purposes of Leaf Modifications

• Protection
• Cactus spine or rose thorns.
• Climbing
• Tendrils on pea plants or clematis.

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Three Tissue Systems Plant Body

• Dermal Tissue
• Ground Tissue
• Vascular Tissue

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Dermal Tissue

• Forms an outer protective covering.
• In many plants, it has a waxy covering to prevent
  water loss.
• Acts as a first defense against damage and
  disease.
• Usually a single layer of packed cells called the
  epidermis.

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Stomata

• Openings in the epidermis (pores) that enable gas
  exchange.
• Usually found on the underside of the leaf.
• Are opened and closed by guard cells.

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Vascular Tissue
Xylem and Phloem
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Vascular System

• Analogous to our circulatory system.
• Xylem dead cells that function to transport
  water from the roots to the aboveground plant.
• Phloem living cells that function to transport
  sugars from the aboveground plant to the roots.

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• Phloem

• Xylem

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Ground Tissue

• Lies between dermal and vascular tissue.
• Analogous to connective (muscle) tissue.
• Eudicot ground tissue divided into pith and
  cortex.
• Leaf ground tissue called mesophyll.

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Three Structures that Distinguish Plant Cells
from Animal Cells.
Chloroplast
Water-Filled Vacuole
Cell Wall
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Five Types of Plant Tissues

• Parenchyma cells
• Collenchyma cells
• Sclerenchyma cells
• Water-conducting cells (Xylem)
• Food-conducting cells (Phloem)

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Parenchyma Cells
Function in photosynthesis, metabolism, and food
and water storage.
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Collenchyma Cells
Have thick cells walls that give herbaceous
plants their structure.
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Sclerenchyma Cells

• Fibrous lignified cells.
• Gives pears their grittiness.
• Make up seed coats.

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Sclerenchyma

• Sclerenchyma cells
• Thick secondary cell wall containing lignin
• Lignin is a main component of wood
• Dead at maturity
• Rigid support
• Two types of sclerenchyma cells are fibers and
  sclereids
• Fiberslong and thin, arranged in bundles
• Sclereidsshorter than fibers, present in nut
  shells and pear tissue

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Water-Conducting Cells

• Tracheids and vessel elements that move water
  from the roots to the stomata in the leaves.
• Both have thick secondary cell walls
• Both are dead at maturity
• Chains of tracheids and vessel elements form
  tubes that make up the vascular tissue called
  xylem

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Xylem
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Food Conduction Cells

• Sieve tube members move nutrients both ways
  (roots to leaves and leaves to roots).
• No secondary cell wall
• Alive at maturity but lack most organelles
• Companion cells
• Contain organelles
• Control operations of sieve tube members
• Chains of sieve tube members, separated by porous
  sieve plates, form the vascular tissue called
  phloem

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Phloem
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Primary Growth Lengthen sRoots and Shoots

• Unlike animals, plant growth is indeterminate
• Growth occurs throughout a plants life
• Plants are categorized based on how long they
  live
• Annuals complete their life cycle in one year
• Biennials complete their life cycle in two years
• Perennials live for many years

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Primary Growth Lengthen sRoots and Shoots

• Plant growth occurs in specialized tissues called
  meristems
• Meristems are regions of active cell division
• Apical meristems are found at the tips of roots
  and shoots
• Primary growth occurs at apical meristems
• Primary growth allows roots to push downward
  through the soil and shoots to grow upward toward
  the sun

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Two Types of Growth

• Going Deeper

• Primary Getting Taller

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Primary Growth of a Root
Zone of Elongation Cells can lengthen by as much
as 10 times.
Zone of Maturation Cells differentiate into
dermal, vascular, and ground tissue.
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Primary Growth of a Shoot

• The apical meristems of shoot tips occur as buds
  at the stem tip and at the base of leaves
• Cells produced in the shoot apical meristem
  differentiate into dermal, vascular, and ground
  tissues
• Vascular tissue produced from the apical meristem
  is called primary vascular tissue (primary xylem
  primary phloem)

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Secondary GrowthIncreases Girth

• Secondary growth occurs at lateral meristems
• Lateral meristems are areas of active cell
  division that exist in two cylinders that extend
  along the length of roots and shoots.
• Vascular cambium is a lateral meristem that lies
  between primary xylem and phloem.
• Cork cambium is a lateral meristem that lies at
  the outer edge of the stem cortex.

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Secondary GrowthIncreases Girth
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Sexual Reproduction of Flowering Plants

• Flowers typically contain four types of highly
  modified leaves called floral organs
• Sepalsenclose and protect flower bud
• Petalsshowy attract pollinators
• Stamensmale reproductive structures
• Carpelsfemale reproductive structures
• Memory Hint Stamens - male

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Anther - produces pollen which develops into sperm
Stigma - site of pollination
Ovary - houses ovules, which contain developing
eggs
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Angiosperm Life Cycle Overview

• Fertilization occurs in the ovule the fertilized
  egg develops into an embryo encased in a seed.
• The ovary develops into a fruit, which protects
  the seed and aids in dispersal.
• The seed germinates under suitable conditions to
  produce a seedling, which grows into a mature
  plant.

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Life Cycle of a Angiosperm
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Development of Pollen and Ovules Culminates in
Fertilization

• Plant life cycles involve alternating diploid
  (2n) and haploid (n) generations.
• The diploid generation is called the sporophyte.
• Specialized diploid cells in anthers and ovules
  undergo meiosis to produce haploid spores
• The haploid spores undergo mitosis and produce
  the haploid generation
• The haploid generation is called the gametophyte.
• Gametophytes produce gametes via mitosis.

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Male Gametophyte

• The male gametophyte is a pollen grain.
• A cell in the anther undergoes meiosis to produce
  four haploid spores.
• Each spore divides via mitosis to produce two
  cells called the tube cell and generative cell.
• A tough wall forms around the cells to produce a
  pollen grain.
• Pollen grains are released from the anther.

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Female Gametophyte

• The female gametophyte is an embryo sac.
• A cell in the ovule undergoes meiosis to produce
  four haploid spores
• Three of the spores degenerate
• The surviving spore undergoes a series of mitotic
  divisions to produce the embryo sac.
• One cell within the embryo sac is an egg ready
  for fertilization.
• One central cell within the embryo sac has two
  nuclei and will produce endosperm.

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Development of pollen and ovules culminates in
fertilization.

• Pollination
• Transfer of pollen from anther to stigma.
• Pollen is carried by wind, water, and animals.
• Pollen grain germination
• Tube nucleus produces pollen tube, which grows
  down through the style to the ovary.
• Generative nucleus divides to produce two sperm.

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• Double fertilization
• One sperm fertilizes the egg to produce a zygote.
• One sperm fuses with the central cell nuclei to
  produce 3n endosperm.
• Endosperm (3n) nourishes the developing embryo.

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The Ovule Develops into a Seed

• The zygote divides many times via mitosis to
  produce the embryo.
• The embryo consists of tiny root and shoot apical
  meristems and one or two cotyledons.
• A tough seed coat develops.
• Seed dormancy
• Embryo growth and development are suspended
• Allows delay of germination until conditions are
  favorable

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Endosperm Food for the Embryo
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Pea Flower to Peas Seeds
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Seed Germination Completes the Life Cycle

• Germination breaks seed dormancy.
• Germination begins when water is taken up.
• Eudicot seedling shoots emerge from the soil with
  the apical meristem hooked downward to protect
  it.
• Monocot seedling shoots are covered by a
  protective sheath and emerge straight from the
  soil.