Plant Cells and Function

Shoot system

Above ground parts for reproduction and photosynthesis.

Root system

Below ground parts for anchoring and nutrient absorption.

Primary cell wall

Outermost layer of plant cells.

Secondary cell wall

Tough inner layer providing structural support.

Middle lamella

Sticky layer between adjacent plant cells.

Plasmodesmata

Openings for communication between plant cells.

Parenchyma

Most abundant cell type, performs metabolic functions, can divide and differentiate into different cells.

Collenchyma

Somewhat metabolicaly active, has thicker walls for flexible support but lacks secondary wall.

Sclerenchyma

Provides structural support, dead at maturity (which allows cell walls to form a rigid skeleton), no metabolism, thick lignified secondary wall.

Sclerenchyma - Fibers

Long, slender sclerenchyma cells in bundles.

Sclerenchyma - Sclereids

Shorter sclerenchyma cells with irregular walls.

Dicots have…

Organized vascular bundles (monocot has scattered)

Xylem

Tissue conducting water and minerals upward.

Two types of water-conducting cells: tracheids and vessel elements.

Create tubes within vascular tissues (to move water), dead at maturity (leaving rigid cell structures), and have rigid lining secondary walls (to keep water flowing efficiently).

Phloem

Tissue transporting sugary sap downward.

Two types of cells: sieve-tube elements and companion cells.

Sieve-tube alive, lack organelles, have sieve plates to help regulate fluid movement.

Companion cells connected to sieve tube and are alive, they produce and transport protein and help sieve tube metabolism.

Dermal tissue

Protective outer layer of plant, includes stomata (pores for gas exchange + water release).

Plant Stem - Node

Area on stem where leaves attach.

Plant Stem - Internode

Stem region between two nodes.

Plant Stem - Petiole

Stalk connecting leaf to stem.

Plants modify stems for various reasons like…

Storage, reproduction, climbing, or protection.

Taproot system (root type)

Single thick root providing strong anchoring (excellent in windy enviornments)

Fibrous root system (root type)

Many fine roots, less anchoring power (more spread out but shallower)

Monocot veins

Parallel leaf vein pattern.

Dicot veins

Netlike leaf vein pattern.

Annuals

Plants completing life cycle in one year.

Biennials

Plants completing life cycle in two years.

Perennials

Plants living for many years.

Meristems

Specialized growth tissue in plants (made of parenchyma cells that are dividing)

Apical meristems

Located at tips of roots (root caps) and shoots, responsible for primary growth and elongation.

Lateral meristems

Responsible for secondary growth and increase in thickness/girth

Vascular cambium:

Produces: Secondary xylem (wood, toward the inside), secondary phloem (inner bark, toward the outside)

Cork cambium:

Forms cork, part of the outer bark

Provides protective outer layers as the plant expands

Root caps

Protective covering for root apical meristems.

Secondary growth

Thickening of stems and roots in woody plants.

Vascular cambium

Produces secondary xylem and phloem.

Cork cambium

Forms cork, part of outer bark.

Ovule -> Seed

After fertilization, the zygote becomes the embryo. Embryonic development produces a mature seed (endosperm, 1/2 cotyledons, a root, a shoot, and a tough seed coat).

The seed coat = eggshell

The endosperm = egg yolk (stored food)

The nutritive tissue that provides energy and nutrients to the developing embryo within the seed

The embryo = baby plant

Seed dormancy

Suspended growth period for seeds (allows for germination when favorable)

Eudicot seed

embryonic root emerges first and goes downward, shoots emerge from the soil with the apical meristem "hooked" downward to protect it.

Monocot seed

shoots are covered by a protective sheath and emerge straight from the soil.

Grafting

Combining features of two plants.

Asexual reproduction

Producing clones from parent plants.

Fragmentation (parts of parent develop), root sprouts, runners (stolon) (horizontal stems extend across ground and periodically produce new plants)