Topic 14'1 The Structure

1
Topic 14.1The Structure Growth of Flowering
Plants

• Biology 1001
• November 9, 2005

2
II. Plant Growth and Organization of Primary
PLANT Tissues

• An Overview of Plant Growth
• Plants exhibit indeterminate growth
• Growth continues throughout the plants life
• Most plants grow continuously
• A typical plant consists of embryonic,
  developing, and mature organs
• Leaf growth is determinate
• When do plants die?
• Annuals (eg. Wildflowers and grains) complete a
  life cycle in a year
• Biennials (eg. Beets and carrots) live two
  years, usually with an intervening cold period
• Perennials (eg. Trees, shrubs and some grasses)
  live many years

3
An Overview of Plant Growth

• Primary and Secondary Growth
• Primary growth produces the primary plant body
  the whole herbaceous plant, or the youngest parts
  of a woody plant
• Involves the apical meristems located at the tips
  of roots and in the buds of shoots and lengthens
  the roots and shoots
• Secondary growth produces the secondary plant
  body the woody parts of the stems and roots
  of a woody plant (leaves do not generally
  experience secondary growth)
• Involves the lateral meristems, the vascular
  cambium and the cork cambium, and adds girth to
  the plant
• Primary secondary growth occur at the same time
  in different parts of the plant

Figure 35.10!!
4
Primary Growth of Roots

• Growth of the root occurs just behind the root
  cap, where new cells are produced in the apical
  meristem
• The root cap protects the root as it pushes
  through the soil it also secretes a lubricating
  polysaccharide slime
• Growth occurs in three zones of cells at
  successive stages of primary growth
• The zone of cell division includes the apical
  meristem and its derivatives
• In the zone of elongation root cells elongate up
  to 10X their length
• In the zone of maturation cells complete their
  differentiation and become functionally mature

Figure 35.12!!
5
Organization of Primary Tissues in Young Roots

• Primary growth produces the epidermis, ground
  tissue vascular tissue of the young root
• The vascular tissue (xylem phloem),
  collectively called the stele, consists of a
  lobed core of xylem with phloem between the lobes
  in dicots
• In monocots the stele has a central core of
  parenchyma cells and alternating rings of xylem
  and phloem
• The ground tissue is called cortex
• The innermost layer of the cortex is the
  endodermis
• The outermost layer of the stele is the
  pericycle, from which lateral roots arise

Figure 35.13!!
6
Primary Growth of Shoots

• A shoot apical meristem is a dome-shaped mass of
  dividing cells at the tip of the terminal bud
• Leaves arise as leaf primordia from the sides of
  the apical meristem
• Axillary buds develop from clumps of meristematic
  cells left by the apical meristem at the bases of
  the leaf primordia
• Growth and differentiation occur as cells divide
  elongate at older internodes below the shoot
  apex

Figure 35.15!!
7
Tissue Organization of Stems and Leaves

• Stems
• The epidermis covers the stem as part of the
  dermal tissue system
• The vascular tissue runs the length of the stem
  in vascular bundles, arranged in a ring in a
  dicot with xylem facing inward, phloem outward
• The ground tissue is arranged as pith cortex
  (internal and external to the vascular tissue) in
  the dicot, and consists of mostly parenchyma
  cells, with some collenchyma and/or sclerenchyma
• Leaves
• The epidermis is interrupted by stomata for CO2
  and H2O exchange stomata are pores flanked by
  two guard cells, which regulate the opening and
  closing of each stoma
• Ground tissue in the leaf is called mesophyll
  (palisade spongy) and consists of
  photosynthetic parenchyma cells
• Veins are the leafs vascular bundles they are
  connected to the stem by leaf traces, and each is
  enclosed by a bundle sheath. They network
  throughout the leaf to bring the xylem phloem
  into contact with all the ground tissue

8
Primary Tissue Organization of Stems
Figure 35.16a!!
9
Tissue Organization of Leaves

• Figure 35.17!!