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