Plant Structure and Function
Plants
• Nonvascular (non-tracheophyte)
- earliest plants, related to algae
- no special vascular tissues devoted to transport
- grow close to ground, near water
- use spores rather than seeds to reproduce
mosses
liverworts
hornworts
• Vascular (Tracheophytes )
- have true leaves, stems, roots
- vascular tissues: create “tubes” through plants
Xylem
- carries water and dissolved minerals upward from the roots
through the stem and leaves
- provides structural support
Phloem
- distributes products of photosynthesis,
amino acids and carbohydrates (food)
from leaves to the rest of the plant.
- carries materials up and down plant
Types of Tracheophytes
Ferns
- diploid sporophyte produces haploid spores
- no true seeds
Types of Tracheophytes
Seeded Plants
Gymnosperms
- use seeds for reproduction inside cones “hidden seeds”
- some cones are female, some are male
- female cones produce spores that, after fertilization, become
eggs enclosed in seeds that fall to the ground
- male cones produce pollen, which is taken by the wind and
fertilizes female eggs
ex: Coniferous trees- pines and firs
Types of Tracheophytes, cont.
Angiosperms
- flowering plants
- most highly evolved plants
- true roots, stems, leaves, well developed vascular
systems
- reproductive structures in flowers
- most dominant in present times
Two types (based on embryos)
1. monocots (single cotyledon- seed coat)
2. dicots (double cotyledons- seed coats)
Monocots
ex: grasses, grains
Dicots
ex: maples, oaks, elms, sunflowers, roses
Basic Plant Tissues
Parenchyma
- least specialized
- thin walled, loosely packed, large
vacuole
- contain chloroplasts
- storage centers for nutrients, H2O
- gives support and shape to plant
Collenchyma
- thickened cells walls where they meet
- supports young plants
- present in non-woody older plants and
leaves
Sclerenchyma
- thick rigid secondary walls with lignin
- strengthens and supports mature
plants
Other Plant Tissues
Vascular
- phloem
- xylem
Chlorenchyma (mesophyll)
- photosynthetic
- leaves
Dermal (epidermis)
- protects exterior of plant’s body
- forms root hairs
Meristem (cambium)
- embryonic, undifferentiated, constantly dividing
- found in roots and shoots
Structures of the Plant
Plant Structures
Shoot System
Shoot = stem, branches, leaves,
flowers and fruit
Two kinds of shoots
• vegetative shoots- stems and leaves
• floral shoots- bear flowers
Stems
Consists of:
* nodes- where the leaves are attached
* internodes- stem segments between
nodes
- can be herbaceous (non-woody) or woody
- used for support and conduction
-two kinds of buds
1. Axillary buds- found in the angle
between the leaf and the stem
2. Terminal buds- found at the end of
the stem
(where most growth occurs)
Tissue Arrangement in Stems
Monocot Stem
Dicot Stem
Leaves
•primary photosynthetic
organs of a plant
•consist of two parts - the
blade and the petiole
•The veins of a leaf are the
vascular bundles,
collections of xylem and
phloem
Leaves
Layers
Epidermis
two exterior surfaces
-epidermal cells secrete a waxy,
cuticle to protect against water
loss and fungal or bacterial attack
-gases can diffuse though
stomata (small openings on the
underside of the leaf)
- transpiration
-guard cells swell or relax to close
or open stomata and limit gas and
water exchange
Layers
Mesophyll: layer in between
epidermis
- rich in chloroplasts
Two Layers
1. palisade layer
- chloroplasts in columns just
below the epidermal cells to
capture light
2. spongy layer
- cells are less ordered and
more diffuse, leaving large
intracellular spaces that
facilitate the exchange of
carbon dioxide and oxygen.
Roots
-draw water and minerals from the
soil and pass them upward through
xylem and phloem to the stem and
leaves
-responsible for storing the plant’s
organic nutrients passed downward
from the leaves through the phloem
-system of root hairs radiate from
roots, increase the absorptive
surface area
-anchor plant in the soil.
-Meristem: area of growth in roots
and stems
(rapidly mitotic divisions in cells)
Growth in Vascular Plants
• Primary growth
- growth of vertical length
- occurs in the apical meristem (tip of both root and shoot)
•Secondary growth
- growth of increase in diameter
- occurs in lateral meristem
- two kinds of tissue involved
in secondary growth
1. vascular cambium
produces:
a. secondary xylem
(wood of tree trunk)
- annual rings
b. secondary phloem
- secondary growth tissue
- conducts food through plant
2. cork cambium
produces tough, thick covering of
stem and root
Monocot vs Dicot
Root Cross Sections
Dicot Root
Vascular Bundles
Plant Behavior: Tropisms
• Phototropism:
- tendency of a plant to move toward light.
- results from the rapid elongation of cells on the dark side of
the plant
- causes the plant to bend in the opposite direction
• Gravitropism:
- tendency to grow toward or against gravity.
- positive: downward growth toward Earth
- negative: upward growth toward sky
- controlled by auxin
Reproduction
1.
Asexual (vegetative propagation)
- produce genetically identical offshoots (clones) of themselves
- develop into independent plants
tubers
bulbs
runners
grafting
2.
•
Sexual
alternation of generations
- fluctuation between these diploid and haploid stages
- nonvascular plants: dominant generation is haploid
gametophyte constitutes the main plant
- tracheophytes: dominant generation is diploid
sporophyte constitutes the main plant
produce male and female haploid spores:
microspores (male) and megaspores (female)
fertilization occurs when a male and female
gamete join to form a zygote
resulting embryo, encased in a seed coating, will
eventually become a new sporophyte.
Reproduction in Flowering Plants
Fertilization
•pollen grain contacts the stigma
•it sends a pollen tube down into the ovary
at the pistil’s base
• as the pollen tube penetrates the ovule, it
releases two sperm cells
•One fuses with egg to create a diploid zygote
•other joins with the fusion nucleus to form
a triploid nucleus.
•triploid nucleus turns into an endosperm,
(nourishes the developing embryo)
•ovule becomes a seed, encasing the
embryo and endosperm in a seed coat
•in angiosperms, the ovary containing the
ovules develops into a fruit after fertilization