Flowering Plant Cells and Tissues

Cells and Tissues of Flowering Plants

• A cell is the basic unit of life in plants, similar to animals.
• A tissue consists of specialized cells performing a specific function.
• An organ comprises multiple tissues.

Meristem Cells

• Meristem cells are located in new and developing plant parts.
• They give rise to a differentiating daughter cell and a cell that persists as a meristem.

Plant Growth

• Primary growth is growth in length and occurs at apical meristems.
• Secondary growth is growth in width and occurs at lateral meristems.
• Plants can be herbaceous (non-woody) or woody.

Apical Meristem

• Apical meristems give rise to different plant tissues.
• Protoderm meristem forms the epidermal tissue, which protects the plant's outer covering.
• Ground meristem fills the interior of the plant with ground tissue.
• Procambium meristem forms the vascular tissue that transports water and nutrients while providing support.

Meristem Development

• Meristem cells are undifferentiated cells capable of dividing indefinitely, giving rise to many differentiated cells.
• Meristematic tissue enables flowering plants to continue growing throughout their lifetime.
• Apical meristems at stem and root tips increase tissue length.
• Apical meristems produce three types of meristem that create three specialized tissues: epidermal, ground, and vascular.

Epidermal Tissue

• It forms the outer protective covering of a plant.
• The epidermis contains closely packed epidermal cells.
• Epidermal cells exposed to air are covered with a waxy cuticle.
• Root epidermal cells have root hairs that increase the surface area for water absorption.
• Epidermal cells of stems, leaves, and reproductive organs have trichomes that protect from sun and moisture loss and discourage herbivory.
• The lower leaf surface contains stomata.
• In older woody plants, epidermis of the stem is replaced by periderm.
• The major component of periderm is cork.
• New cork is made by the cork cambium.

Ground Tissue

• It forms the bulk of a flowering plant.
• Parenchyma cells are the least specialized, most abundant, and are found in all organs of the plant.
• Parenchyma cells can divide and give rise to more specialized cells.
• Parenchyma cells contain chloroplasts and perform photosynthesis.
• Collenchyma cells have thicker primary walls.
• Collenchyma cells form bundles underneath the epidermis.
• Collenchyma cells provide flexible support for immature regions of the plant. Example: Strands in celery stalks
• Sclerenchyma cells have thick secondary walls impregnated with lignin and most are nonliving at maturity.
• The primary sclerenchyma cell function supports mature regions of the plant.
• Fibers are long, slender sclerenchyma cells grouped in bundles (hemp and rope).
• Sclereids are shorter, more varied sclerenchyma cells found in seed coats and nutshells.

Vascular Tissue

• It is composed of xylem and pholem.
• Xylem transports water and minerals from the roots to the leaves.
• Phloem transports sucrose and other organic compounds from the leaves to the roots.

Xylem

• Xylem contains tracheids and vessel elements that conduct water.
• Tracheids are long with tapered ends.
• Water moves across pits in the end and side walls of tracheids.
• Vascular rays, between trachied rows, conduct water across the plant width.
• Vessel elements are larger, with perforation plates in their end walls.
• Vessel elements form a continuous vessel for water and mineral transport.

Phloem

• Sieve-tube members function as conducting cells and contain cytoplasm but lack nuclei.
• Sieve plate is a cluster of pores in the wall of sieve-tube members.
• Each sieve-tube member has a companion cell.
• Plasmodesmata connect the sieve-tube member and companion cell.
• The companion cell contains a nucleus and is involved in transport function.

Organs of Flowering Plants

• Flowering plants (angiosperms) are diverse and share common structural features.
• Vegetative organs include all plant parts except reproductive structures and are concerned with growth and nutrition.
• A typical plant features three vegetative organs: roots, stems, and leaves.
• Most flowering plants possess a root system and a shoot system.
• The root system consists of the roots.
• The shoot system consists of the stem and leaves.
• Flowers, seeds, and fruits are structures involved in reproduction.

Stems

• The shoot system of a plant is composed of the stem, branches, and leaves.
• A stem is the main axis of a plant that elongates and produces leaves.
• Nodes are the areas where leaves attach to the stem.
• The internode is the region between nodes.
• At the stem end, a terminal bud contains an apical meristem and produces new leaves.
• A stem also has vascular tissue that transports water and minerals.

Leaves

• They are the major plant part that carries on photosynthesis.
• Foliage leaves are usually broad and thin.
• The blade is the wide portion of a foliage leaf.
• The petiole is the stalk attaching the blade to the stem.
• The leaf axil is the upper acute angle between the petiole and stem where the axillary bud is found..
• Tendrils are leaves that attach to objects.
• Bulbs are leaves that store food.

Monocots

• Monocots are single cotyledon plants.
• Cotyledons act as transfer tissue to endosperm.
• Nutrients are derived from the endosperm in monocots.
• Root vascular tissue is arranged in a ring in monocots.
• Monocots leaves have parallel venation.
• Flower parts are arranged in multiples of three in monocots.

Eudicots

• Eudicots are two cotyledon plants.
• Cotyledons supply nutrients to seedlings in eudicots.
• The root phloem is located between the xylem arms in edicots.
• The leaves have a netted venation in edicots.
• Flower parts are arranged in multiples of four or five in eudicots.

Terminal Bud

• The terminal bud contains the apical meristem, which produces leaves and other tissue during primary plant growth.

Annual vs Perennial Plants

• Annual plants live for only one growing season, produce enough vegetative structures to support flower and seeds, and die after seed dispersal.
• Perennial plants live for three or more seasons, and spend energy making vegetative structures to survive for years.
• Flower-inducing genes LEAFY and Apetala 1 are the difference between annuals and perennials.
• When Apetala 1 gene turns on (with the help of the LEAFY gene), the apical meristem stops vegetative growth and switches to flower production.
• Blocking flower-inducing genes in annuals induces perennial growth.

Eudicot Root

• Contains a root cap containing the root apical meristem.
• The zone of cell division contains primary meristems.
• The zone of elongation contains cells lengthening and becoming specialized.
• The zone of maturation contains fully differentiated cells.

Tissues of a Eudicot Root

• Epidermis is the outer layer.
• The Cortex is composed of parenchyma cells and allows water and minerals to move.
• The Endodermis forms the boundary between the cortex and inner vascular cylinder.
• The Casparian strip is in the cell wall.
• Vascular tissue contains xylem and phloem.
• The Pericycle is mitotically active and is the starting point for development of branch or lateral roots.

Other Root Types

• Monocot root ground tissue's pith is surrounded by the perivascular ring, and has the dame growth zones as eudicot roots
• Primary root (taproot) is fleshy, is a long single root that that grows striaght down and stores food eg. carrots, beets, turnips
• Fibrous root system is slender roots and lateral branches, anchors the plant to soil, and is found in monocots
• Adventitious roots develops from organs of the shoot system instead of the root system
• Prop roots are adventitious
• Epiphytes which lives in or on trees, have aerial roots

Root Specializations

• Roots may have specialization for storage, prop roots for support, pneumatophores for oxygen acquisition, or be multifunctioning.

Root Symbiotic Relationships

• Mycorrhizae are mutualistic associations between roots and fungi.
• The fungus provides water and minerals (through extended filaments), and the plant provides sugars.
• Root nodules contain nitrogen-fixing bacteria.
• Plants cannot extract nitrogen from the air, but bacteria in nodules can take up and reduce atmospheric nitrogen.
• Plants get nitrogen from bacteria, which receive carbohydrates from the plant.

Anatomy of a Woody Twig

• A terminal bud contains the shoot tip, protected by bud scales.
• Each spring, bud scales drop, leaving a scar.
• Each scar represents one year of growth.
• A shoot apical meristem produces new cells that elongate and increase stem length.
• A terminal bud protects the shoot apical meristem and is envelops by leaf primordia. Specialized primary meristems include the protoderm (gives rise to the epidermis), the ground meristem (gives rise to pith and cortex), and the procambium (produces primary xylem and phloem).
• Mature vascular bundles contain vascular cambium.

Herbaceous Stems

• Mature nonwoody stems only exhibit primary growth.
• The outermost tissue is covered with a waxy cuticle.
• Stems have distinctive vascular bundles.
• Herbaceous edicots' have vascular bundles arranged in a distinct ring.
• Monocots have vascular bundles scattered throughout their stems.

Woody stems

• Woody plants have both primary and secondary tissues.
• Primary tissues form each year from primary meristems.
• Secondary tissues develop during first and subsequent years from lateral meristems.
• Primary growth increases plant length.
• Secondary Growth increases the girth.
• Woody stems have 3 regions: bark, wood, pith

Woody Stem’s Bark

• Bark of a tree contains cork, cork cambium, cortex, and phloem. Bark can be removed, however, it is harmful since organic nutrient transport would be ceased.
• Girdling, (removing bark from around the tree) leads to the death of the tree.
• Cork cells are impregnated with suberin, which impedes gas exchange except at lenticels.

Woody Stems Wood

• Wood is secondary xylem that builds up year after year.
• Vascular cambium is dormant during winter.
• "Annual ring” is spring (more open cells for good water flow) and summer wood
• Summer wood (when growth slows) has less vessels
• Heartwood’s ( the older annual rings in center of the tree) functions are water and waste transport.

Stem examples of Diversity

• Stolonsare horizontal, above ground, stems which make new clone plants where they touch the ground.
• Rhizomes are underground horizontal stems and contribute to asexual reproduction.
• Tubers and Corms (enlarged underground stems) store nutrients for next season.
• Sugar cane produces table sugar
• Cinnamon and quinine are produced from bark.
• Wood is used to produce paper and building materials.

Leaves

• Leaves: Carry outphotosynthesis which requires water, carbon dioxide and sun.
• Foliage Leaves, broad & thin
• Blade: Wide portion of foliage leaf
• Petiole: Stalk attaching blade to stem
• *Leaf axil: Upper cute angle between petiole and stem where axillary bud found
• Tendrils: Leaves that attach to objects ( modified tendrils)

Leaf parts

• Epidermis (upper and lower)
• Waxy cuticle
• Trichomes: Lower epidermis has stomata.

Mesophyll Layer

• Eudicot leaves: Palisade mesophyll (elongated cells) is spongy mesophyll containing irregular cells bounded by air spaces.
• Contains many chloroplasts.

Leaf Diversity

• Leaf arrange may be alternate opposite or whorled on the stem.
• Plants adapted to conditions : Dry, moist, cold
• Blade (broad portion of the leaf) may be simple or compound.
• Plants adapted for conditions through:
• Shade leaves ( capture more light in dark)
• Spines
• Climbing leaves (modified tendrils)
• Reduced leaves

Insectivorous plants

• Some plants are specialized for catching insects for survival.
• Sundew
• Venus flytrap