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