1. Plant Structure and Function

2. Plant Structure and Growth
Angiosperm Structure
Three basic organs:
1. Roots (root system)
fibrous: mat of thin roots
taproot: one large, vertical root
2. Stems (shoot system)
nodes: leave attachment
internodes: stem segments
axillary bud: dormant, vegetative potential
terminal bud: apex of young shoot
apical dominance: inhibits axillary buds
3. Leaves (shoot system)
blade
petiole

3. Many plants have modified roots
(a) Prop roots
(b) Storage roots
(c) “Strangling” aerial roots
(d) Buttress roots
(e) Pneumatophores

4. Many Plants Have Modified Stems
Rhizomes. The edible base
of this ginger plant is an example
of a rhizome, a horizontal stem
that grows just below the surface
or emerges and grows along the
surface.
(d)
Tubers. Tubers, such as these
red potatoes, are enlarged
ends of rhizomes specialized
for storing food. The “eyes”
arranged in a spiral pattern
around a potato are clusters
of axillary buds that mark
the nodes.
(c)
Bulbs. Bulbs are vertical,
underground shoots consisting
mostly of the enlarged bases
of leaves that store food. You
can see the many layers of
modified leaves attached
to the short stem by slicing an
onion bulb lengthwise.
(b)
Stolons. Shown here on a
strawberry plant, stolons are horizontal stems that grow
along the surface. These “runners”
enable a plant to reproduce
asexually, as plantlets form at
nodes along each runner.
(a)
Storage leaves
Stem
Root
Node
Rhizome

5. (b)Spines. The spines of cacti, such as this prickly pear, are actually leaves, and photosynthesis is carried out mainly by the fleshy green stems.
(c) Storage leaves. Most succulents, such as this ice plant, have leaves modified for storing water.
(d) Bracts. Red parts of the poinsettia are often mistaken for petals but are actually modified leaves called bracts that surround a group of flowers Such brightly colored leaves attract pollinators.
(a) Tendrils. The tendrils by which this pea plant clings to a support are modified leaves. After it has “lassoed” a support, a tendril forms a coil that brings the plant closer to the support. Tendrils are typically modified leaves, but some tendrils are modified stems, as in grapevines.
Petiole
(a) Simple leaf. A simple leaf is a single, undivided blade. Some simple leaves are deeply lobed, as in an oak leaf.
(b) Compound leaf. In a compound leaf, the blade consists of multiple leaflets. Notice that a leaflet has no axillary bud at its base.
(c) Doubly compound leaf. In a doubly compound leaf, each leaflet is divided into smaller leaflets.
Axillary bud
Leaflet
(a)
(b)
(c)
(e)Reproductive leaves The leaves of some succulents produce adventitious plantlets, which fall off the leaf and take root in the soil.

6. Plant Tissues
1. Dermal (epidermis): single layer of cells for protection
cuticle
2. Vascular (material transport)
xylem: water and dissolved minerals roots to shoots
tracheids & vessel elements: xylem elongated cells dead at maturity
phloem: food from leaves to roots and fruits
sieve-tube members: phloem tubes alive at maturity capped by sieve plates; companion cells (nonconducting) connected by plasmodesmata
3. Ground (photosynthesis, storage, support): pith and cortex

7. Plant Cell Types
1. Parenchyma primary walls thin and flexible; no secondary walls; large central vacuole; most metabolic functions of plant (chloroplasts)
2. Collenchyma unevenly thick primary walls used for plant support (no secondary walls ; no lignin)
3. Sclerenchyma support element strengthened by secondary cell walls with lignin (may be dead; xylem cells); fibers and sclereids for support

8. Plant Growth Life Cycles annuals: 1 year (wildflowers; food crops)
biennials: 2 years (beets; carrots)
perennials: many years (trees; shrubs)
Meristems
apical: tips of roots and buds; primary growth
lateral: cylinders of dividing cells along length of roots and stems; secondary growth (wood)

9. Primary growth Roots root cap protection of meristem
zone of cell division primary (apical) meristem
zone of elongation cells elongate; pushes root tip
zone of maturation differentiation of cells (formation of 3 tissue systems)

10. Primary Tissues of Roots
Stele the vascular bundle where both xylem and phloem develop
Pith central core of stele in monocot; parenchyma cells
Cortex region of the root between the stele and epidermis (innermost layer: endodermis)
Lateral roots arise from pericycle (outermost layer of stele); just inside endodermis, cells that may become meristematic

11. Primary Tissues of Stems
Vascular bundles (xylem and phloem)
Surrounded by ground tissue (xylem faces pith and phloem faces cortex)
Mostly parenchyma; some collenchyma and sclerenchyma for support

12. Primary Tissues of Leaves
Epidermis/cuticle (protection; desiccation)
Stomata (tiny pores for gas exchange and transpiration)/guard cells
Mesophyll: ground tissue between upper and lower epidermis (parenchyma with chloroplasts); palisade (most photosynthesis) and spongy (gas circulation)

13. Secondary Growth Two lateral meristems
1. Vascular cambium produces secondary xylem (wood) and secondary phloem (diameter increase; annual growth rings)
2. Cork cambium produces thick covering that replaces the epidermis; produces cork cells; cork plus cork cambium make up the periderm; lenticels (split regions of periderm) allow for gas exchange; bark~ all tissues external to vascular cambium (phloem plus periderm)