STRUCTURE AND ORGANIZATION OF PLANTS

Chapter 25

Plant Organs

Roots- at least equivalent to shoot system Absorbs nutrients with root hairs Produce growth hormones Coordinate shoot and root size

Stem- Main axis of plants Node is where leaves attach, internode is between leaves Support plant, transport products, may act as water

reservoir Leaves- vary greatly and can be specialized

Carry on photosynthesis Blade- wide portion of leaf Petiole- attaches blade to stem Axillary bud- site of branch or flower origin

Plant Tissues

Plants may grow their entire life because they have meristematic tissue.

Apical meristems are located at or near tips of stems and roots where length is increased.

Meristems are responsible for primary growth.

Plant Tissues

Three specialized tissues Epidermal- forms outer protective

covering Ground- fills interior of plant Vascular- transports water and nutrients

and provides support

Epidermal Tissue

Herbaceous and young woody plants are entirely covered by epidermis

Cuticles are waxy coverings on epidermis to prevent water loss and disease resistance

Root hairs are a specialized epidermal tissue that are long and slender to increase surface area for absorption

Trichomes are hairs found on stems, leaves, and reproductive organs. They protect the plant from too much sun and conserve moisture

Epidermal Tissue

Guard cells are on the lower epidermis of eudicots and both surfaces of monocots. They surround stomata and control their opening/closing

Periderm- composed of boxlike cork cells that replaces epidermis of the stem on older woody plants. They are waterproof and chemically inert. Non-living and resistant to attack by pathogens

Lenticles- cracks and ridges on stem surface from cork overproduction that allows for gas exchange.

Ground Tissue

Three types of cells Parenchyma-

Most abundant and least specialized May carry on photosynthesis or store products May divide and give rise to specialized cells

Collenchyma Similar to parenchyma but have thicker primary walls Give flexible support to immature regions of plant bodies.

Sclerenchyma Thick secondary walls imbedded with lignin Lignin makes plants tough/hard Most are non-living Support mature regions of the plant

Vascular Tissue

Xylem Transport water and minerals from the roots to

the leaves Composed of 2 hollow, non-living conducting

cells tracheids – elongated with tapered ends. Water

moves along end walls and side walls where there are pits

vessel elements- larger, may have perforation plates and form a continuous vessel for water and mineral transport

Parenchyma cells provide storage and fibers give support

Vascular Tissue

Phloem Sieve-tube members- contain no nuclei,

pore clusters at end wall Companion cell has nucleus and is

connected to sieve-tube member by plasmodesmata Nucleus controls function of both cells

Vascular tissue

Roots Stem Leaves

Vascular cylinder Vascular bundles Leaf veins

Root Organization- Eudicots Apical meristem is protected by the

root cap Primary meristem is in the zone of

cell division and provides cells to the zone of elongation. The cells lengthen and become specialized. The zone of maturation contains fully differentiated cells. ZofM is also were root hairs are borne.

Eudicot Root Tissue

Epidermis- single layer of outer cells Thin walled and rectangular. In the Zone of Maturation, many have root

hairs Cortex

Large, thin walled parenchyma cells Irregularly spaced and loosely packed Water and minerals move throughout

without entering cells Functions in food storage

Eudicot- Root Tissue

Endodermis Single layer of rectangular cells Fit snugly together and bordered on all 4 sides by

Casparian strip Prevents the passage of water and minerals to

adjacent cells Entrance of material is only through cortex side of

cell

Vascular Tissue Pericycle- first layer of cells within vascular

cylinder and can start development of roots. Xylem is star-shaped and phloem is found

between arms of xylem

Monocot Root Organization

Do not have secondary growth Ground tissue of root’s pith is

centrally located with a ring of vascular tissue composed of alternating xylem and phloem bundles.

Have same tissue layers as eudicots

Root Diversity

Primary roots- dominant root that grows straight down; fleshy and stores food Taproots we consume are carrots, beets,

turnips, radishes, and sweet potatoes Fibrous root system- Slender with

lateral branches; Forms from the lower nodes of the stem when the first primary root dies.

Root Specializations

Adventitious roots- develop from shoot system (corn)

Pneumatophores- project above water and acquire oxygen- black mangroves

Mycorrhizae Root Nodules- provide housing for

nitrogen fixing bacteria- peas, beans, legumes

Stem Organization

Terminal bud- contains shoot tip protected by bud scales

Leaf and bundle scars mark location of dropped leaves (bud scale scars tell plant age)

Apical meristem- produces new cells at shoot tip

Shoot apical meristem- protected within terminal bud where leaves develop

Vascular cambium- contain mature vascular bundles

Herbaceous Stems

Mature, nonwoody Epidermis is covered by cuticle Eudicot- Vascular bundles within ring

that separates cortex from central pith

Monocot- scattered vascular bundles

Woody Stems

Primary tissue- formed each year from primary meristems behind shot apical meristem

Secondary tissue- develop during first year and subsequent years of growth from lateral meristems

Stem Diversity

Stolon- aboveground horizontal stems that produce new plants wherever it touches the ground. Example-strawberries

Rhizome- underground horizontal stems- may be long and thin (sod) or thick and fleshy (irises)

Tuber- enlarged portion of rhizome that functions in food storage (potato)

Corm- bulbous underground stems. Lie dormant during winter and produce new plants in spring (onion)

Leaf Organization

Cuticle Upper epidermis- contains stomata

(M) Meosphyll

Palisade= elongated cells Spongy= irregular cells surrounded by

air spaces Lower epidermis- contains stomata

(E&M) Cuticle

Leaf Diversity

Leaves are adapted to a variety of environmental conditions. Simple Compound Pinnate Palmate Alternate Opposite Whorled