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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
Dicotsex: maples, oaks, elms, sunflowers, roses
Basic Plant TissuesParenchyma
- 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
StemsConsists 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 Layers1. 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 ringsb. 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
Reproduction1. 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