chapter 34

How is plant body organized

-Below ground the root system anchors the plant and takes in water and nutrients from the soil -aboveground the shoot system harvests light and carbon dioxide from the atmosphere to produce sugars

The shoot system anatomical features

-Stems are vertical aboveground structures consisting of nodes, where leavesare attached, and internodes, or segments between nodes -Axillary (orlateral)buds form at nodes just above the site of leaf attachment -An axillary bud may grow into a branch -The tip of each stem and branch contains an apical bud -Apical and axillary buds may develop into flowers

Dermal tissue systems

-made up of several different cell types and represent a complex tissue -Epidermal cells protect the surface of the plant •they secrete a waxy cuticle to reduce water loss and protect against pathogens -Stomata regulate gas exchange and water loss •a stoma is surrounded by two specialized guard cells which change shape to open and close the stoma

leaf size and shape

-may be compound -can also be needle like with a smaller surface are -adaptation of the needle minimizes transpiration -cactus spines that protect the stem are modified leaves -tubelike leaves of the pitcher plant trap insects

Ground tissue system

-most photosynthesis and carbohydrate storage takes place in ground tissue Made up of 3 distinct cells -Parenchyma -collenchyma -sclerenchyma-two types of cells •fiber cells are very long and are used in the production of hemp and paper •sclereids are tough coats of seeds and nuts

prickles

are comparable to hairs but can be quite coarse (for example Rose prickles), i.e. they are extensions of the cortex and epidermis.

Plant cells

•Although eukaryotic cells share many key features, plant cells have several features not found in animal cells -Plant cells are surrounded by a cellulose -rich primary cell wall -Some plant cells have a rigid secondary cell wall -Plant cells are connected by plasmodesmata •Plant cells may contain chloroplasts and a large vacuole that fills most of the cell's volume-Chloroplastsare the site of photosynthesis-Non-photosynthetic cells may have organelles that are similar to chloroplasts, but modified for storage of pigments, starch, oil, or proteins-Vacuolescontain an aqueous solution called cell sapand store waste, water, nutrients, pigments and toxins

what do cork cambia produce

•Cork cambium produces cork cellsto the exterior of the trunk -Secondary phloem, cork cambium, and cork cells make up the barkof a tree trunk -Gas exchange occurs through small openings called lenticels

Collenchyma cells function primarily in support

•Have primary cell walls that vary in thickness, even when mature they can continue to lengthen as they provide structural support to the growing regions of shoots •abundant in elongating stems and in petioles of leaves

Parenchyma cells

•Have relatively thin primary cell walls and are the most abundant and versatile plant cells -in leaves parenchyma tissue is the primary site of photosynthesis -in roots parenchyma cells mainly store starch •Many parenchyma cells are totipotent •Totipotency- parenchyma cells can continue to divide and develop into a mature plant -helps in the repair of wounds and in reproduction; new plants can grow from cuttings •When cut, parenchyma cells - divide to produce a mass of undifferentiated cells, a callus -roots can develop from the callus (bananas and seedless grapes)

The root system

•Many root systems have a taproot and lateral root •Key functions to root system -roots anchor the plant to soil -roots absorb ions and water from soil -roots conduct water and ions to shoot system -roots obtain energy from the sugar in the shoot system -roots store molecules produced in the shoot system •Diversity levels -morphology -phenotypic plasticity -modified roots •Herbaceuous plants roots are perennial even if interrupted by fire or drought -a new shoot system is produced each spring -phenotypic plasticity -root systems can vary even if the plants are the same type

modified leaves

•Onion bulbs store nutrients •The leaves of succulents store water •Tendrils enable vines to climb •The bright red leaves of poinsettias attract pollinators •The tubelikeleaves of the pitcher plant trap insects •Cactus spines protect the stem

Plant tissue systems

•Plant tissues are grouped into tissue systems, based on their structural features and location within the plant -Simple tissues consist of a single cell type; complex tissues contain several types of cells Tissue systems -Dermal tissue system -Ground tissue stem -Vascular tissue system

Importance of Surface Area and Volume Relationships

•Root and shoot systems both function in absorption -Roots absorb water and key nutrients -Shoots absorb light •Absorption takes place across a surface, but the cells that use the absorbed light and molecules occupy a volume -A plant is efficient in absorption if it has a large surface area relative to its volume

morphological diversity in shoot systems

•Shoot diversity can also be analyzed on three levels: 1.Morphological diversity among species 2.Phenotypic plasticity within individuals 3.Modified shoots with specialized functions •range in size from tiniest duckweed (5mm in diameter) to the giant sequoia (100ft in diameter and 300ft tall) •shape may vary allowing competition for light -short internodes give way to wide branching -narrow branching is a result of long internodes •The silverwood plants native to Hawaii demonstrate adaptive radiation and diversity among shoot systems •Lush environments as opposed to dry environments and natural selection -Lush environments and competition for light favors the taller shoot systems -Dry, windblown habitats favor short stems that require less water and are more anchored to the soil

structure of a tree trunk

•The older, innermost secondary xylem accumulates protective compounds such as resins and gums •Dark-colored, inner xylem is called heartwoodwhile light-colored, outer xylem is called sapwood •In areas with seasonality, the vascular cambium stops growing during the dry or cold season -This results in the formation of annual tree rings, with alternating early and late wood

The leaf

•The vast majority of photosynthesis occurs in leaves -leaf relatively large surface area is available for absorbing photons and supporting photosynthesis •A simple leaf has two main structures an expanded blade and a stalk called a petiole •In a compound leaf the blade is divided into a series of leaflets -double compound are large and rarely damaged by wind or rain •Needlelike leaves reduce water loss by transpiration -adapted to very cold or hot climates

Trichomes perform an array of functions

•Trichomes are hairlike appendages that perform various functions -keep the plant cool and protect against damaging sunlight -minimize water loss -regulate gas exchange in the shoots -provide barbs or toxins to protect from herbivores

Thorns

•are modified branches or stems •may be simple or branched

Spines

•are modified leaves, stipules or parts of leaves such as extension of leaf veins

Leaf arrangement

•arrangement of leaves on a stem can vary -paired opposite each other on the stem -arranged in whorl -arranged to alternate on either side of the stem -found in a compact basal arrangement where internodes are extremely short-leading to the rosette growth form

Cambium

•differs from an apical meristem -forms a cylinder that runs the length of the root, trunk, or branch -cells divide to increase the width of the plant Two types of cambia in plants •vascular cambium- located between secondary xylem and secondary phloem •cork cambium- located near the outer perimeter of the root, trunk or branch

Epidermal cells

•epidermal cells of the dermal tissue secrete the cuticle a waxy layer that covers the shoot system protecting the leaves and reducing water loss •Epidermal cells consists of the following -cuticle, waxy substance that covers the surface, also protects against pathogens and viruses -stomata-regulate the exchange of gases -trichomes-protective structures

sclerenchyma

•function of sclerenchyma cells is to produce two cell walls, the primary and secondary cell wall •secondary cell wall consists of the substances lignin and cellulose

How does cambium initiate secondary growth

•in the stem of a woody eudicot a single layer of cells between xylem and phloem becomes meristematic and forms the vascular cambium •another ring of cells under the epidermis becomes meristematic and forms the cork cambium •each cambium produces secondary growth each year •secondary growth occurs in a similar fashion in roots

vasular tissue system

•made up of two tissues called xylem and phloem Xylem is made up of tracheas and vessel elements -tracheids are the water conjunction cells •pits are found on the sides and ends of the tracheids to assist in the conduction of the water -vessel elements also function in water movement Phloem structure -sieve tube elements and plants -companion cells

Primary growth extends plant body

•plants grow due to many types of meristems-undifferentiated cells that undergo mitosis. Two types of meristem -Apical-found at the root tip and develop the shoot and root -Primary meristems-three types •Protoderm-gives rise to dermal tissue system •Ground meristem-gives rise to the ground tissue system •Procambium- gives rise to the vascular tissue system

How is the primary root system organized

•root apical meristem is protected by a group of cells called the root cap -cells produced by meristem constantly replenish the cap, which regularly lose cells •root cap also senses gravity to determine the direction of growth and secretes a slimy lubricant (mucigel) to reduce friction as the apical meristem is pushed through soil Primary root is organized into three zones or division of cells -Zone of cellular division •apical meristem •ground meristem •procambium -Zone of cellular elongation -Zone of cellular maturation which contains root hairs

Modified roots

•root diversity and types of roots found among various types of plants •adventitious roots grow from different sources -ivy and anchor root system -corn and prop root-support -mangroves and their pneumatophores for gas exchange -carrot and the taproot

Secondary growth widens shoots and roots

•secondary growth increases the width of roots and shoots, increasing the amount of conducting tissue available and providing increased structural support •produces woos and occurs in species that have a cambium in addition to apical meristems

Modified stems

•stems vary according to the habitat -cactus tem is modified to store water and not support leaves -stolons grow horizontally producing adventitious roots and leaves -rhizomes grow horizontally also but function in asexual reproduction •rhizomes grow underground •tubers are a variation of the rhizome •thorns are also modified stems

Phenotypic plasticity in leaves

•sun leaves have a relatively small surface area which reduces water loss in areas of the body where light is abundant •shade leaves are relatively large and broad providing a high surface area that maximizes absorption of rare photos

What do vascular cambia produce

•vascular cambia in roots and stems produce the secondary xylem and secondary phloem -secondary xylem makes up word while secondary phloem makes up inner part of the trees bark -vascular cambium also produces sclerenchyma fibers and parenchyma cells formed in lateral rows of cells called rays •production of these tissues is highly asymmetrical with creation of more secondary xylem which is retained and accumulates as wood

Difference between sclerenchyma and collenchyma cells

Collenchyma cells- have expendable primary cell walls to support growth Sclerenchyma cells- are dead at maturity and function to support stems and other structures