Plant Structure and Growth. Roots anchor the plant in the soil, absorb minerals and water, and store food Monocots have a fibrous root consisting.

Chapter 35Plant Structure and Growth

Roots anchor the plant in the soil, absorb minerals and water, and store food

Monocots have a fibrous root consisting of a mat of thin roots that spread out below the soil surface

Dicots have a taproot consisting of one large, vertical root that produces many smaller lateral roots◦ Often store food

Carrots, turnips, beats

The Root System

Increase the surface area of the root enormously

Extensions of individual epidermal cells on the root surface

Root Hairs

Roots that raise above ground from stems or leaves

Function as props that help support tall stems

Adventitious Roots

Shoots consist of stems and leaves Stems are alternating systems of nodes,

the points at which leaves are attached, and internodes, the stem segment between nodes

The angle formed by each leaf and the stem is an axillary bud that has the potential to form a vegetative branch◦ Most young plants’ are dormant and growth is

usually concentrated at the tip, called the terminal bud

The Shoot System

Phenomenon where axillary buds are put into a state of dormancy so that the terminal bud, or apical meristem receives all the nutrients

Increases the plant’s exposure to light Under certain circumstances, it may be

stopped and the axillary buds are allowed to grow◦ If top is eaten by an animal

Apical Dominance

Stolons: runners of strawberry plants, grow on the surface of the ground and enable a plant to colonize large areas asexually when the single parent plant fragments into many smaller offspring

Modified Shoots

Rhizomes: ginger plants, are horizontal stems similar to stolons except that they grow underground

Tubers: potatoes; swollen ends of rhizomes specialized for storing food

Bulbs: onions, vertical underground shoots consisting mostly of the swollen bases of leaves that store food

Main photosynthetic organs of most plants Generally consist of a flattened blade and a

stalk called the petiole which joins the leaf to the node of the stem

Leaves

The dermal tissue, or epidermis, is generally a single layer of tightly packed cells that cover and protect all young parts of the plant◦ Root hairs are extensions of this tissue◦ Secretes a waxy coating called the cuticle that

helps retain water The vascular tissue, in involved in the

transport of materials between roots and shoots◦ Xylem and Phloem

Plant Tissues

Tracheid and vessel elements are elongated cells that are dead at functional maturity, and found in xylem◦ Their secondary walls are interrupted by pits,

thinner regions where only primary walls are present

Sieve-tube members are alive at functional maturity, lack organelles◦ Nonconducting companion cells are connected

to the sieve tubes and serves that cell with nutrients and help load sugar into the tubes

Vascular Tissue

The tissue that is neither dermal nor vascular

In dicot stems, it is divided into pith, internal to the vascular tissue, and the cortex, external to the vascular tissue

Functions in photosynthesis, storage, and support

Ground Tissue

Parenchyma Collenchyma Sclerenchyma

Plant Cells

Thin and flexible walls with a large central vacuole

Transport sap in phloem Perform most of the metabolic functions,

synthesize and store various organic products Fleshy tissue of most fruit is composed of

parenchyma “Stem Cells” of the plants

◦ Least specialized, but can be turned into other cells Can grow an entire plant from one parenchyma cell

Parenchyma

Unevenly thicker cell walls Grouped in strands or cylinders and help

support young parts of the plant shoot◦ Strings of celery

Provide support without restraining growth◦ Do not have lignin in cell wall to make it strong

Collenchyma

Thick cell walls, cannot grow, function as support elements

Functionally mature cells are dead◦ Provide a skeleton that supports the plant

Vessel elements and tracheids are sclerenchyma cells

Fibers and sclerids function solely in support

Sclerenchyma

Primary growth: elongation of the plant, achieved by apical meristems

Secondary growth: progressive thickening of roots and shoots, achieved by lateral meristems◦ Cork cambium replaces the epidermis with a

secondary tissue, such as bark, that is thicker and tougher

◦ Vascular Cambium adds layers of vascular tissues Wood is the secondary xylem that accumulates over

the years

Growth