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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