Plant Kingdom Seedless Plants

PLANT KINGDOM SEEDLESS PLANTS I. Origin. Earth Chronology: 4.6 billion years ago: the earth formed. 4-3.8 billion years ago: life originated. 3.8 billion years ago: prokaryote anaerobes, heterotrophs. 3.5 billion years ago: oldest known fossils: microfossils and stromatolites; photosynthesis. 2.5 billion years ago: photosynthesis established, oxygen accumulated. 1.5 billion years ago: first eukaryotes. 700 million years ago soft-bodies multicellular life. 540 million years ago hard-bodied multicellular life. The colonization of land by plants probably occurred between 415 and 440 million years ago at the end of the Silurian. In a relatively short time of about 50 million years, plant diversified abundantly and colonized many land areas. Land plants probably are probably derived from a group of green algae called charophytes. Land plants share with the green algae the following traits: Chlorophyll a and b, xanthophylls (yellow carotenoids) and carotenes (orange carotenoids). Store carbohydrates in the form of starch. Cell wall made mostly of cellulose. Details of the formation of the cell plate. DNA and RNA sequences support their close relation to the charophytes. I. CHARACTERISTICS Multicellular eukaryotes that are photosynthetic autotrophs. Chloroplasts Chlorophyll a and b. Accessory pigments: carotenes and xanthophylls Cell wall made of cellulose, a glucose polymer. Store food in plastids in the form of starch. Alternation of generations. Formation of cell plate during cytokinesis. Evolutionary trend towards a larger sporophyte generation and a reduced gametophyte generation. Bryophytes, Seedless Vascular Plants, Gymnosperms, Angiosperms. II. ADAPTATIONS TO A TERRESTRIAL ENVIRONMENT. Waxy cuticle to protect against desiccation. Stomata for gas exchange and control of transpiration. Multicellular gametangia made of a layer of sterile cells to protect gametes: Antheridia produce sperms. Archegonia produce eggs. After fertilization, the egg develops into a multicellular embryo within the archegonium. Cell wall contains lignin, a polymer, to strengthen and support upright structures. Transport system or vascular tissue: Phloem for the transport of dissolved carbohydrates. Xylem for water and mineral transport. Land plants can be grouped into four groups (non-taxonomic): bryophytes, seedless plants, gymnosperms and flowering plants. III. ALTERNATION OF GENERATIONS. A life cycle characterized by a multicellular haploid gametophyte stage followed by a multicellular diploid sporophyte stage. Gametophyte (n) produces haploid gametes (n). Gametes fuse to form a diploid zygote, the new sporophyte (2n). Embryo of the sporophyte (2n) develops in the archegonium of the gametophyte (n). Sporophyte (2n) produces spores through meiosis. Spores (n) are the first stage of the gametophyte generation (n). BRYOPHYTES About 15,000 species worldwide divided into three Divisions: mosses, liverworts and hornworts. Their life cycle is similar but the three groups may not be closely related. I. CHARACTERISTICS Small plants found in moist environments, lack woody tissue and usually form mats spread over the ground. Gametophyte generation is dominant; sporophyte is parasitic on the gametophyte. Bryophytes have cuticle, stomata and multicellular gametangia that allow them to survive on land. Bryophytes need water to reproduce and most species lack vascular tissue (xylem and phloem). Water transport is mostly through capillary action, diffusion and cytoplasmic streaming. II. MOSSES Gametophyte is a "leafy" plant. Live in dense colonies forming mats on the ground, rocks, walls, tree trunks, etc. Lack true roots, stems and leaves. Rhizoids attach the gametophyte to the substrate. Some species have water and sugar conducting cells but they lack true xylem and phloem. The sperm must swim from the antheridium to the archegonium. III. LIVERWORTS AND HORNWORTS Liverwort gametophyte can be leafy or thalloid. Liverworts can reproduce asexually by gemmae, small bundles of cells produced in cup-like structure. Hornwort gametophytes are all thalloid. The sporophyte is horn-shaped and parasitic on the gametophyte. Hornworts have a single large chloroplast in their cells. IV. EVOLUTION. The evolutionary origin of the bryophytes is obscure. They do not seem to be in direct line with the vascular plants and might have evolved from a group o green algae. Alternatively, they may have evolved from early vascular plants by becoming simpler in their anatomy by losing their vascular tissue. FERNS AND FERN ALLIES. Also known as pteridophytes, they first appeared about 400 million years ago. I. CHARACTERISTICS Ferns and fern allies have vascular tissue made of xylem and phloem; they posses true roots, stems (rhizomes) and leaves (megaphylls). The sporophyte is the dominant generation. Gametophyte (prothallus) and sporophyte generations are photosynthetic and independent of one another. All species need water for reproduction; the sperm must swim from the antheridium to the archegonium. Branching is dichotomous. The Telome Theory attempts to explain the production of megaphylls in vascular plants: evolved from a branch system. In contrast, microphylls are considered to have evolved from small projections of the stem. They are scale-like projection with a single vein. II. FERNS About 14,000 extant species. Many species are extinct. Sporangia are often produced in clusters called sori (sing. sorus). Ferns are valuable ornamentals. Azolla, an aquatic fern, is an important fertilizer in the cultivation of rice. associated to Anabaena, a nitrogen fixing cyanobacteria. III. FERN ALLIES Whiskfern sporophytes consist of a rhizome with rhizoids, and upright branches; they lack true leaves and roots. Horsetails have true roots, stems and leaves. The stems are hollow. Their epidermal cells are impregnated with silica. Horsetails were the dominant plants about 300 million years. They were among the main contributors to the formation of coal, gas and petroleum (fossil fuels). The sporophytes of clubmosses consist of true roots, stems and leaves (microphylls). Some clubmosses (Selaginella) are heterosporous; Lycopodium is homosporous. Homospory: production of one kind of spores. Heterospory: production of two kinds of spores. Haploid megaspores develop into a female gametophyte. Haploid microspores develop into a male gametophyte. The sporangia of horsetails and clubmosses are arranged into an elongated conical structure called strobilus (pl. strobili). Seedless vascular plants arose about 420 million years ago in the mid-Silurian. Coal formed from the remains of horsetails, ferns and other seedless plants that lived during the Carboniferous, about 300 million years ago. The sporangia of horsetails and clubmosses are arranged into an elongated conical structure called strobilus (pl. strobili). Chapter 27 SEED PLANTS SEED SPORE Multicellular embryo Single cell Food supplied by tissue Food only in the cell Multicellular seed coat Covering not cellular Diploid sporophyte Haploid cell Product of fertilization Product of meiosis There are two groups of seed producing plants, gymnosperms and angiosperms. Produce seeds. Vascular tissue: xylem for water and mineral transport and phloem for dissolved sugars. Gametophyte is very reduced and totally dependent on the sporophyte. Heterosporous: microspores and megaspores. GYMNOSPERMS There are about 720 species found in all terrestrial habitats grouped into four divisions (phyla). They have great economic importance: lumber, paper, chemicals. I. CHARACTERISTICS OF GYMNOSPERMS Woody trees and shrubs. Xylem made of tracheids. Seeds are borne, exposed, in cones (megastrobilus). Pollinated by wind, seldom by insects. Single fertilization: sperm + egg embryo. Most are monoecious: male and female organs on the same individual. II. CONIPHEROPHYTA or conifers There are about 550 species of conifers. Many conifers produce resin, a complex mixture of organic compounds that protect the plant from insect and fungal attack. Resin is stored in resin ducts in the roots, stem, leaves and cones, Cone bearing gymnosperms, e. g. pines, firs, cypresses, etc. Leaves are needles or scale-like, rarely broad; venation is parallel and open. A male cone is called microstrobilus, and contains the microsporangia that produce microspores through meiosis that will develop into microgametophytes (pollen grains). The female cone is called the megastrobilus, which produce megasporangia in each of which a megaspore is produced through meiosis and will develop one megagametophyte. An egg will form within the megagametophyte. Pollination is by wind. Note: Study the life cycle of pine and learn the terminology. Pages 572 - 574. III. CYCADOPHYTA or cycads Important in the Triassic (248-213 m .y. a), which is called sometimes the Age of Cycads . Most species are extinct. There are about 140 living species in tropical and subtropical parts of the world. Cycads are palm or fern-like plants with compound leaves and simple seed cones. The are dioecious: plants are either male or female. They have a very large motile sperm within the pollen grain but do not need water for pollen transport. Pollination is by air and in some cases by ants. IV. GINKGOPHYTA or ginkgoes There is a single species of ginkgo alive today. It is native to China where it has been under cultivation for centuries. It has been found in the wild in only two locations. Ginkgoes are dioecious and have flagellated sperms. Pollination is by air and seeds are borne exposed rather than in cones. It is commonly planted in American cities because it is very resistant to pollution. V. GNETOPHYTA The gnetophytes consists of three genera and about 70 species. A group of rare plants that share some traits with angiosperms. Efficient water conducting cells in the xylem called vessel elements. Reproductive structures resemble flowers. ANGIOSPERMS There are about 235,000 species of flowering plants. This is the dominant group in terrestrial habitats. Our survival depends on them. food, medicine, lumber, etc. There are two groups of angiosperms: monocots and dicots. First appeared in the Cretaceous about 130 million years ago. I. CHARACTERISTICS Woody or herbaceous. Xylem elements have vessel elements and tracheids. Produce flowers. Pollinated by wind or animals. Double fertilization: egg + sperm embryo and 2 polar nuclei + sperm endosperm. Seeds enclosed in a fruit. MONOCOTS have floral parts in multiples of three and the seed contains one cotyledon. The endosperm provides the food for the embryo. Venation is usually parallel (there are exceptions). Their vascular bundles are scattered throughout the ground tissue. The root system is fibrous. DICOTS have floral parts in multiples of four or five, and their seeds contain two cotyledons. The cotyledons usually absorb the food from the endosperm first, and then provide the food for the embryo. Venation is netted. The vascular bundles in the stem cross-section are arranged in circles (rings). They usually have a taproot system for at leas part of their life. II. THE FLOWER The flower is a reproductive shoot or branch. It has four parts arranged in whorls or circles on a stalk or peduncle. The parts of the flower are the sepals (calyx), petals (corolla), stamens and carpels. Stamens consist of a filament and an anther. Carpels are also referred to as pistils. They consist of an ovary, a style and a stigma. Flowers may be borne singly or in clusters called inflorescence. Flower parts are considered modified leaves. Flowers may be ... Complete if has the four parts or incomplete if it lacks one of the parts. Perfect if it has both stamens and carpels or imperfect if it lacks one of them. See figure 27-10, page 579, for additional details of the floral structure. III. DOUBLE FERTILIZATION. It is characteristic of flowering plants. Double fertilization results in the formation of a diploid zygote and a triploid endosperm. The female gametophyte or embryo sac has an egg nucleus and two polar nuclei. One sperm fertilizes the egg nucleus and forms the zygote, 2n. Another sperm joins the two polar nuclei forming the triploid (3n) nutritive tissue called the endosperm. See figure 27-12, page 581, for details. Seeds develop from the ovule following fertilization. The ovary enlarges and forms the fruit. In some instances other tissues also enlarge and become part of the fruit. Fruits serve two purposes: protect the seed and aid in dispersal of the seeds. EVOLUTION OF SEED PLANTS Progymnosperms appeared about 375 million years ago in the Devonian. they reproduced by spores. had megaphylls. woody tissue of secondary xylem similar to modern gymnosperms. Their reproductive structures appear to be intermediate between those of spore producing plants and seed plants. conifers Progymnosperms seed ferns cycads and possibly ginkgoes Seed producing plants appeared in the Devonian, about 360 m. y. a. By the end of Jurassic, 180 million years ago, several lines of gymnosperms existed with features that resembled those of flowering plants. Different groups of seed plants apparently appeared independently several times. Angiosperms probably arose from ancient gymnosperms. They must have been dicots, which then gave rise to monocots. The oldest fossil record of angiosperms is pollen from the Cretaceous, about 130 m. y. a. The oldest flower fossil is 120 m.y.a. By late Cretaceous angiosperms had began to replace gymnosperms as the dominant group of land plants. Many angiosperm species apparently arose from changes in chromosome number. COMPARISON OF GYMNOSPERMS AND ANGIOSPERMS. GYMNOSPERMS ANGIOSPERMS GROWTH HABIT woody trees and shrubs woody or herbaceous XYLEM CELLS tracheids vessel elements and tracheids REPRODUCTIVE STRUCTURES usually cones flowers POLLEN TRANSFER wind animals, wind, water. FERTILIZATION egg + sperm = zygote double fertilization SEEDS exposed, borne on scales enclosed in the ovary (fruit) Chapter 28 KINGDOM ANIMALIA CHARACTERISTICS The following characteristics describe most animals: Diploid multicellular eukaryotes. Cells are specialized and organized into tissues, organs, etc. Heterotrophs that inhabit the sea, fresh water and land. Most are capable of locomotion at some stage of their lives. Most can respond adaptively to external stimuli and have well developed sense organs and nervous system. Most reproduce sexually, with large non-motile eggs and small flagellated sperms. The diploid zygote produced by fertilization divides by mitotic divisions, resulting in a ball of cells that usually hollows out to become a blastula. Sponges are an exception. About 35 phyla the majority of which are invertebrates. CLASSIFICATION Based on type of … Body cavity: acoelomate, pseudocoelomates, coelomates. Developmental pattern: protostomes, deuterostomes. Body symmetry: radial, bilateral. Types of sectioning a specimen: Sagittal section divides the body into right and left parts. Cross or transverse section divides the body into anterior and posterior parts. Frontal section divides the body into dorsal and ventral parts. Coelom or body cavity is fluid-filled space located between the outer body wall and the digestive tube. Germ layers: Endoderm forms the lining of the digestive tract. Mesoderm forms most body structures: muscles, bones, etc. Ectoderm gives rise to the outer covering of the body and the nervous system (if present). Diploblastic animals (cnidarians and ctenophores) have two germ layers. Triploblastic animals have three germ layers. Animals may be... Acoelomate: lack coelom or body cavity, e.g. cnidarians, ctenophores, flatworms.. Pseudocoelomate: coelom is partially lined with mesoderm, e.g. roundworms, rotifers.. Coelomate: coelom is completely lined with mesoderm. Animals can be classified as protostomes if the blastopore develops into the mouth and deuterostomes if it develops into the anus. Deuterostomes and protostomes have different pattern of cleavage: Radial cleavage is characteristic of deuterostomes; Spiral cleavage is followed by protostomes. Protostomes also have a determinate cleavage in which the fate of the embryonic cells is fixed very early in development. Deuterostomes have an indeterminate cleavage in which each cell keeps longer the capacity to develop into a full organism. Schizocoely method of coelom formation is characteristic of protostomes. Deuterostomes follow the enterocoely pattern of coelom formation. PHYLUM PORIFERA 1. Multicellular; body a loose aggregation of cells of mesenchymal origin. 2. Body with pores (ostia), canals, and chambers that serve for passage of water to the central cavity (spongocoel), and out of the open end, the osculum. 3. About 9,000 species have been identified; all are aquatic and mostly marine. 4. Symmetry radial or none. 5. Epidermis of flat pinacocytes; most interior surfaces lined with flagellated collar cells (choanocytes) that create water currents; a gelatinous protein matrix called mesohyl, which contains amebocytes, collencytes (secrete collagen), and skeletal elements (spicules). 6. Skeletal structure of calcareous (Class Calcarea) or siliceous crystalline spicules (Class Hexactinellida), or fibrillar collagen, a protein, and often combined with variously modified collagen (spongin) fibrils (Class Demospongiae). 7. No organs or true tissues; cells form a loose association but there is division of labor; digestion intracellular; excretion and respiration by diffusion. 8. Reactions to stimuli apparently local and independent; nervous system probably absent. 9. All adults sessile and attached to substratum. 10. Asexual reproduction by buds or gemmules and sexual reproduction by eggs and sperm; most are hermaphroditic; free-swimming ciliated larvae. PHYLUM CNIDARIA 1. Entirely aquatic; some in fresh water but mostly marine. About 10,000 species. 2. Radial symmetry or biradial (radial and bilateral) symmetry around a longitudinal axis with oral and aboral ends; no definite head. 3. Two basic body forms: polyp and medusa. 4. Exoskeleton or endoskeleton of chitinous, calcareous, or protein components in some. 5. Body with two layers, epidermis and gastrodermis; with mesoglea (diploblastic); mesoglea with cells and connective tissue in some (triploblastic). 6. Gastrovascular cavity or coelenteron (often branched or divided with septa) with a single opening that serves as both mouth and anus; extensible tentacles usually encircling the mouth or oral region. 7. Cnidocytes (stinging cells) located in the epidermis and gastrodermis contain special stinging organelles called nematocysts; nematocysts abundant on tentacles, where they may form batteries or rings. 8. Nerve net with symmetrical and asymmetrical synapses; some sensory organs; diffuse conduction. 9. Muscular system (epitheliomuscular type) of an outer layer of longitudinal fibers at base of epidermis and an inner one of circular fibers at base of gastrodermis; modifications of this plan in anthozoans, such as separate bundles of independent fibers in the mesoglea. 10. Reproduction by asexual budding (in polyps) or sexual reproduction by gametes in all medusae and some polyps; sexual forms monoecious or dioecious; planula larva. 11. No excretory or respiratory systems. 12. No coelomic cavity. Class Hydrozoa - Most hydrozoans are marine and colonial in form, and typically include both the medusa and polyp stage in their life cycle. Some, however, have no medusa stage, and some occur only as medusae and have no polyp stage. Examples: Hydra, Obelia. Class Scyphozoa - Class Scyphozoa (jellyfishes) includes most of the larger "jellyfishes". A few, such as Cyanea, may attain a bell diameter exceeding 2 m and tentacles 60 to 70 m long, but most range from 2 cm to 40 cm in diameter. Their polyp stage is absent or greatly reduced, and the medusae of this class have no velum. Examples: Aurelia, Cyanea. Class Anthozoa - Anthozoa means "flower animal," and anthozoans are indeed polyps with a flowery appearance. They do not have a medusa stage. Anthozoans are all marine and are found all over the world, in various sizes and habitats. Examples: Sea anemones, corals, sea fans. PHYLUM CTENOPHORA 1) ROWS OF COMB PLATES that give this animals their name: Cten = Greek for comb while phero = to bear. So Ctenophore means "bearer of combs". 2) COLLOBLASTS which are sticky prey capturing structures analogous in their function to the nematocysts of the Cnidarians, but actually not similar in their design. 3) Radially symmetrical like the Cnidarians, but because of two long feeding tentacles that most Ctenophores have, they are only strictly symmetrical at two points so they are biradially symmetrical. 4) Ctenophores have real muscles, which are beneath the epidermis. These are used to contract the tentacles and in behaviors such as prey swallowing, pharyngeal contractions (swallowing) etc. 5) They are the largest organism that uses cilia to move. 6) Tentacles equipped with adhesive glue cells that trap plankton. ACOELOMATES PHYLUM PLATYHELMINTHES Three germ layers (triploblastic). 2.Bilateral symmetry; definite polarity of anterior and posterior ends. 3.Body flattened dorsoventrally in most; oral and genital apertures mostly on ventral surface. 4. Body with multiple reproductive units in one class (Cestoda). 5. Epidermis may be cellular or syncytial (ciliated in some). 6. Muscular system of mesodermal origin, in the form of a sheath of circular, longitudinal, and oblique layers beneath the epidermis or tegument. 7. No internal body space (acoelomate) other than digestive tube; spaces between organs filled with parenchyma. Digestive system incomplete (gastrovascular type), absent in Some; extensively branched. Nervous system consisting of a pair of anterior ganglia with longitudinal nerve cords connected by transverse nerves and located in the parenchyma in most forms 10. Simple sense organs, eyespots in some. 11. Excretory system of two lateral canals with branches bearing flame cells (protonephridia), lacking in some forms. 12. Respiratory, circulatory, and skeletal systems lacking. 13. Most forms monoecious; reproductive system complex, usually with well-developed gonads, ducts, and accessory organs; internal fertilization; life cycle simple in free-swimming forms and those with single hosts; complicated life cycle often involving several hosts in many internal parasites. Class Turbellaria - Turbellarians are mostly free-living worms than range in length from 5 mm or less to 50 cm. Usually covered with ciliated epidermis, they are typically creeping worms that combine muscular with ciliary movement to achieve locomotion. The mouth is on the ventral side. Example: Dugesia Class Trematoda - The trematodes are all parasitic flukes, and as adults they are almost all found as internal parasites of vertebrates. Examples: Clonorchis, Schistosoma Class Cestoda - The cestodes, or tapeworms, usually have long flat bodies made up of many reproductive units (proglottids) and have no digestive system. They also have a specialized structure called the scolex ("holdfast") which is the organ by which they attach to their host. It is usually provided with suckers and often with hooks or spiny tentacles. Examples: Taenia PHYLUM NEMERTEA Members of the phylum Nemertea are commonly called the ribbon worms. There are approximately 900 known species, most of that are benthic marine animals, although there are a few freshwater and terrestrial species and some deep water species. CHARACTERISTICS They are acoelomate, flattened dorso-ventrally and have circular, longitudinal, and dorsoventral muscles. One defining characteristic of the nemerteans is the presence of an eversible proboscis. Tube-within-a-tube body plan: outer body wall and inner digestive tract. Complete digestive system: mouth and anus. 4) Circulatory system with blood that travels through contractile vessels and may move in either direction. There is no heart and the pumping of blood is aided by the muscular contractions of the body associated with movement. PSEUDOCOELOMATES Pseudo = "false" ; coelom = body cavity The pseudocoelomate animals include the Rotifera, Gastrotrichia, Kinorhyncha, Loricifera, Priapulida, Nematoda, Nematomorpha, Acanthocephala, and Entoprocta. PHYLUM NEMATODA A group of worms widely distributed in the soil, fresh and salt-water environments; scavengers, carnivores and parasites. CHARACTERISTICS 1. Body bilaterally symmetrical, cylindrical in shape. 2. Body covered with a secreted, flexible, nonliving cuticle. 3. Fluid in pseudocoel forms a hydrostatic skeleton. 4. Complete digestive system. 5.Excretory system consists of specialized cells and/or canal system; flame cell protonephridia lacking. 6. Circulatory system lacking. 7. Sexual reproduction; sexes separate. Example: Ascaris PHYLUM ROTIFERA CHARACTERISTICS 1) Rotifera derive their name from their characteristic ciliated crown, or corona, which gives the impression of a rotating wheel when beating. 2) The body is usually divided into a head, trunk and foot. The head bears the corona, the trunk has a thickened cuticle with ridged plates and spines for defense and the foot often bears 1-4 projections called toes, which are used for attachment. Pseudocoelomate animals. Rotifers are "cell constant": each member of a species is composed of the same number of cells. Have a nervous system with a ganglion, nerves and an eye spot. Excretory system consists of protonephridia with flame cells. Chapter 29 COELOMATE PROTOSTOMES Coelom is the space completely surrounded by the mesoderm and lies between the digestive tube and the body wall. Advantages of the coelom: Provides space for many organs to function with freedom, e.g. heart, gonads. Allows the digestive cavity to move independently of body movements. Hydrostatic skeleton. Coelomic fluid transports oxygen, wastes, etc. to organs and tissues. Adaptations to life on land: Covering to prevent desiccation. Skeleton for support in a gaseous medium (air): exo and endoskeleton. Reproductive adaptations: internal fertilization, shells around the egg, uterine development. PHYLUM MOLLUSCA Mollusks form the second largest phylum in the animal kingdom with about 50,000 extant species, and about 35,000 fossil species. CHARACTERISTICS Bilateral symmetrical coelomate protostomes. Coelom reduced to a small cavity around some organs; hemocoel, part of the circulatory system is the main body cavity. Soft body usually covered with a shell. Body divided into three regions: head, foot and visceral mass. A thick epidermal layer of skin called the mantle covers the body; the mantle secretes the shell. Digestive system well developed; radula, a rasp-like organ with teeth; absent in bivalves. Open circulatory system except in many cephalopods; heart usually three-chambered, blood vessels, and sinuses present; respiratory pigments in blood. Gas exchange through gills, mantle, or body surface. Nervous system consists of a pair of ganglia, with nerve cords; ganglia forming a nerve ring in gastropods and cephalopods. 10. Sensory organs present (touch, smell, taste, equilibrium, and vision in some); eyes highly developed in cephalopods. 11. Sexes separate in most; fertilization external; many species pass through one or several larval stages. CLASS POLYPLACOPHORA or chitons. Animals with segmented shells made of 8 plates; head reduced; broad foot used in locomotion. CLASS GASTROPODA includes snails, slugs and nudibranchs. Marine, freshwater and terrestrial animals with body and shell coiled in some species (torsion); pulmonate mantle in terrestrial species; well developed head with tentacles and eyes; broad flat foot used in locomotion. CLASS BIVALVIA includes clams, oysters and mussels. Marine and freshwater animals with a two-part shell hinged dorsally; lack head and radula; suspension feeders. CLASS CEPHALOPODS, octopods and squids. Marine and predatory animals with the foot modified into tentacles, bearing suckers; tentacles surround the mouth of a large head; mouth with a horny beak and radula; eyes are very well developed; lack shell. Squids can learn to some degree. PHYLUM ANNELIDA There are about 15,000 species in the phylum. They may be marine, freshwater or terrestrial herbivores, carnivores, parasites, scavengers and suspension feeders. CHARACTERISTICS Bilateral symmetry; body tubular and segmented (metamerism). Coelom, body wall and many internal organs segmented by septa; well developed muscles form the body wall. Setae or parapodia present on each segment; absent on leeches. Complete digestive system, unsegmented. Gas exchange through skin or gills. Closed circulatory system; blood pigments transports oxygen. A pair of metanephridia in each segment. Nervous system made of simple brain made of two ganglia, double ventral nerve cord and sense organs (touch, eyes); pair of ganglia and nerves repeated in each segment. Reproduction sexual; hermaphroditic or separate sexes. CLASS POLYCHAETA. Polychaetes are characterized by having a well-developed head with eyes and antennae; paired appendages (parapodia) with setae on most segments; sexes separate. Mostly marine animals; about 10,000 species. CLASS OLIGOCHAETA. Terrestrial or freshwater worms characterized by having poorly developed head, few setae per segment, hermaphroditic, and have a clitellum. CLASS HIRUDINAE. Mostly freshwater blood-sucking parasites, some species adapted to humid terrestrial habitats; lack setae and parapodia; have a definite number of segments and an anterior and posterior sucker for attachment. PHYLUM ARTHROPODA The largest and most diverse phylum with over one million species found in all habitats. CHARACTERISTICS Bilateral symmetry. Body segmented into head, thorax and abdomen; in some head and thorax fuse into a cephalothorax. Coelom small and filled with fluid and internal organs. Jointed appendages that function in locomotion, feeding or copulatory organs. Exoskeleton secreted by the epidermis and made of protein, chitin, lipids and minerals; periodic molting to allow growth. Respiratory system varied: marine forms use gills; terrestrial species have a system of branching tubes called tracheae or plate-like structures called book lungs. Nervous system consists of a brain, double ventral nerve cord with many ganglia; sense organs well developed. Insects and crustaceans have compound eyes. Muscular system well developed; muscles for rapid motion. Circulatory system open with a dorsal tubular heart that pumps the hemolymph. Excretory system varied in the different subgroups. Malpighian tubules in insects. Reproduction sexual and sexes separate. SUBPHYLUM CHELICERATA First pair of appendages, the chelicerae, are used to manipulate food; cephalothorax and abdomen; lack mandibles and antennae. Classes Merostomata and Arachnida. SUBPHYLUM CRUSTACEA Mandibles present; two pairs of antennae; biramous appendages. Class Malacostraca. SUBPHYLUM UNIRAMIA Mandibles present; single pair of antennae; uniramous appendages. Classes Insecta, Chilopoda and Diplopoda. Arachnids comprise about 60, 000 species. They are characterized by having a cephalothorax, four pairs of legs, chelicerae, and no antennae; most are terrestrial carnivores. There are about 32,000 species of Crustaceans. They have a cephalothorax covered with a carapace, two pairs of biramous antennae, one pair of biramous legs per segment, and mandibles and maxillae. Antennal glands located on the head remove metabolic wastes. Statocysts help in maintaining balance. The Class Insecta is the most successful group of animals. There are about 750,000 described species. Their body is divided into head, thorax and abdomen, have three pairs of legs, one pair of uniramous antennae, have tracheal tubes for gas exchange, and undergo metamorphosis. Metamorphosis may be complete (egg, larva, pupa, adult) or incomplete (several nymphs that resemble the adult). Insecta are extremely successful due to their adaptations: exoskeleton, sense organs, segmentation, ability to fly, reproductive strategies, mechanisms of defense, etc. Centipedes belong to the class Chilopoda. There are about 3,000 species of centipedes. They have a head and segmented body, one pair of legs per segment, one pair of uniramous antennae, and mandibles and maxillae. 7,500 species of millipedes form the class Diplopoda. They have a head and segmented body, two pairs of legs per segment, a pair of uniramous antennae, mandibles and maxillae. Chapter 30 DEUTEROSTOMES Echinoderms and chordates are... Deuterostomes. Radial embryonic cleavage pattern. Indeterminate cleavage: fate of cells is fixed later in development than in protostomes. Mesoderm develops from a pair of pouches that pocket out of the primitive gut: enterocoely. Cavity in mesodermal pockets becomes the coelom Biologists include hemichordates and chaetognaths as deuterostomes. The larva of echinoderms and hemichordates is very similar. Bilateral Ring of cilia around the mouth. Himichordates and chordates have Pharyngeal pouches. Dorsal nerve cord. Other phyla included sometimes among the deuterostomes are the lophophorids (Phoronida), bryozoans (Ectoprocta) and brachiopods (Brachiopoda). Chordates have about twice the number of genes found in invertebrates. A mutation the Cambrian (590-505 m.y.a.) could have resulted in a doubling of chromosome number. Further mutations on genes the play a role in embryonic development could have resulted in new body designs including the vertebrate head. ECHINODERMS CHARACTERISTICS Coelom well developed, filled with fluid that transports materials. Larva bilaterally symmetrical; adult with radial symmetry and usually pentamerous; complex metamorphosis. Head absent; mouth facing downward. Endoskeleton of made of CaCO3 plates and bearing spines; covered with a thin ciliated epidermis. Water vascular system consisting of canals filled with seawater through an opening called the madreporite; it is derived from the coelom. Free moving animals. Locomotion by tube feet connected to the water vascular system, or by moving the spines or arms. Gas exchange through a variety of structures, e.g. gills, respiratory trees. Excretory system absent; excretion by diffusion. Digestive system complete. 10. Circulatory system very reduced and function uncertain. It may or may not be homologous to the circulatory system of other phyla. 11. Simple nervous system; brain absent; nerve ring around the mouth with radiating nerves. 12. Reproduction sexual; sexes separate; external fertilization; a few species hermaphroditic. Echinoderms are carnivorous, bottom dwellers of the sea. They are found at all depths. About 7,000 extant and 13,000 extinct species make the phylum. Class Crinoidea - Body formed by a disc with a leathery skin containing calcareous plates; mouth turned upward. Five flexible arms branch form many more arms and lateral pinnules giving a feathery appearance; tube feet on the arms, coated with mucus to trap plankton. Suspension feeders. Class Asteroidea - Sea stars typically have five arms (though they may have more) which merge gradually with the central disc. Skin gills carry on gas exchange; tiny pincer-like pedicellariae keep the skin free of debris. On the aboral surface can be found the madreporite, a disc sealing the water vascular system and used to equalize the pressure. Class Ophiuroidea - Pentamerous (have five arms); arms slender and sharply set off from the central disc; lack pedicellariae; tube feet have no suckers, and not used in locomotion; tube feet may have a sensory function to detect food; ophiuroids use their entire arms for movement. The madreporite is located on the oral surface; anus is absent and undigested food is expelled from the mouth. E.g. Brittle stars Class Echinoidea - Echinoids lacks arms and have a compact body encased in a flat shell called test. Their pentaradial structure is evident in the arrangement of the ambulacral areas; tube feet and spines used in locomotion. Examples: Sea urchins, sand dollars Class Holothuroidea - Holothurians are elongated; their body is flexible and soft. They have become secondarily bilateral; their tube feet are well developed along only one ambulacral groove; endoskeleton is reduced to microscopic plates. Practice evisceration as a means of defense. Example: Sea cucumbers. Class Concentricycloidea - These are small (less than 1 cm in diameter) disk-shaped echinoderms have a concentric vascular rings. Just discovered in 1986, attached to and in crevices in wood. At >1000m off New Zealand and later at about 2000m in the Bahamas. Like echinoids and sea cucumbers but wit no arms. They have a big coelom, with a system with tube feet that have ampullae, and have a calcareous endoskeleton of ossicles. Tube feet in just one row in a circular arrangement along the periphery of the animal. One species has no gut...absorbs nutrients presumably. In the other species, there is a mouth and stomach and no anus. Where they fit is not yet clear. They live in submerged wood rich in bacteria. Recent cladistic studies have been made using nucleotide sequence in an attempt to understand the relationship among different echinoderm classes. In these cladistic studies "Xyloplax is consistently placed among asteroids. This result is stable over a wide range of analysis parameters and demonstrates that Xyloplax is a recent asteroid rather than a relict stem lineage of echinoderm. Hence, the rank of Class is an inappropriate representation of the evolutionary history of the concentricycloids." PHYLUM CHORDATA Chordates are coelomate animals with bilateral symmetry, segmented body, with a tube-within-a-tube body plan and three well-developed germ layers, an endoskeleton and closed circulatory system. About 47,000 species. Chordates share with other phyla the following characteristics: coelomates with bilateral symmetry, a tube-within-a-tube body plan, endoskeleton, and a close circulatory system with a ventral heart. DISTINGUISHING CHARACTERISTICS Notochord. Cartilaginous rod running underneath and supporting the nerve cord. Replaced by vertebrae in the adults of many groups. Dorsal nerve cord. Single, hollow, dorsal, above the notochord. Pharyngeal slits. Present in the embryo and adult of some species. Post-anal tail. Prominent in embryos of all groups but not in all adults. SYSTEMATICS PHYLUM CHORDATA Subphylum Urochordata Subphylum Cephalochordata Subphylum Vertebrata 1. UROCHORDATES Larval stage is chordate with gills, notochord and dorsal nerve cord. These structures are lost in the adult stage except for the gill slits, which are present in the adult. 2. CEPHALOCHORDATES. Share with the Vertebrata the following characteristics: Notochord, gill slits, dorsal nerve cord, metameric muscles, posterior direction of blood flow in the dorsal vessel and anterior blood flow in the ventral vessel, thyroid, homologous homeobox gene clusters. Larva similar to the Agnatha. - Notochord extends to the anterior end (cephalochordates!) and does not end at a brain. Adults are suspension feeders burrowing in the sea bottom. Example: Branchiostoma (=Amphioxus), lancelet 3. VERTEBRATES Vertebral column present; it replaces the notochord in most species. Pronounce cephalization: well developed brain. Cranium encloses and protects the brain. Two pairs of appendages. Muscles attached to the endoskeleton for movement. CLASS AGNATHA Jawless fish Long tubular body similar to an eel. Lack jaws. Cartilaginous skeleton. Notochord persist throughout life. Dorsal and ventral fins but lack paired fins. Heart with one atrium and one ventricle. Dorsal nerve cord with differentiated brain. Digestive systems without stomach. Sense organs of taste, smell and hearing. External fertilization. About 70 species found in both freshwater and marine environment e.g. lampreys and hagfishes. Their fossil record goes back to the Ordovician, 450-500 m.y.a. During the Silurian (440-408 m.y.a.) and Devonian (408-380 m.y.a.) fishes evolved jaws and paired fins. Acanthodians and placoderms were jawed and armored. CLASS CHONDRICHTYES Cartilaginous fishes Skin with placoid scales. Endoskeleton entirely cartilaginous. Notochord replaced by vertebrae. Two pairs of fins. Two-chambered heart. 5 to 7 pairs of gills with separate and exposed gill slits. No swim bladder or lung. Internal fertilization and separate sexes. Oviparous, ovoviviparous; viviparous. CLASS OSTEICHTHYES Bony fishes Skin usually with overlapping dermal scales, some fish without scales. Skeleton with many vertebrae replace the notochord. Median and paired fins supported by fin rays of cartilage or bone. Jawed mouth terminal; most have many teeth. Gills supported by bony gill arches and covered by a common bony flap, the operculum. Two-chambered heart. Swim bladder usually present. Sexes separate and fertilization is usually external. Development oviparous. Bony skeleton provides excellent support and stores calcium. Descendants of the bony fishes moved onto land during the Devonian (408-380 m.y.a.). Lobed-finned fishes are very similar to those that moved onto land. There are three extant species of lung fishes and one coelacanth. CLASS AMPHIBIA Aquatic larva undergoes metamorphosis into a terrestrial adult in many species. Skin smooth and moist with many glands, some of which may be poison glands; no scales; involved in gas exchange. Respiration by lungs, skin and gills, either separately or in combination; external gills in the larval form and may persist throughout life in some. Three-chambered heart: two atria and one ventricle. Systemic and pulmonary circulation. Ectothermal. Separate sexes; fertilization usually external in frogs and toads and mostly internal in salamanders and caecilians. Most species return to water to reproduce. Order Apoda - caecilians. Order Urodela - salamanders and newts. Order Anura - frogs and toads. CLASS REPTILIA Snakes, turtles, crocodiles, lizards Body covered with horny scales. Paired limbs, usually with five toes, adapted for many forms of locomotion (climbing, running or paddling); limbs vestigial or absent in snakes and some lizards. Mouth with undifferentiated teeth. Lungs used in respiration, no gills. Three-chambered heart in most (crocodiles have four-chambered heart); ventricle partly divided. Ecothermic, behavior used in thermoregulation. Internal fertilization and separate sexes; adapted to reproduction on land. Eggs covered with shells; extraembryonic membranes (amnion, chorion, yolk sac, and allantois) present; oviparous. Terrestrial vertebrates (reptile, birds and mammals) are called amniotes because their embryos are enclosed in the amnion. Reptiles dominated the earth during the Mesozoic (250-65 m.y.a.). Mass extinction of animals, including dinosaurs, occurred at the end of the Cretaceous (65 m.y.a.). CLASS AVES Birds Feathers and leg scales. Skeleton fully ossified, with air cavities; horny beak with no teeth; single bone in middle ear. Excrete solid waste in the form of uric acid. Digestive track with a crop for storage, gizzard for grinding and proventriculus that secretes gastric juices. Nervous system and senses of vision and hearing well developed. Four-chambered heart. Endothermic. Respiration by slightly expansible lungs with thin air sacs. Lack diaphragm. Sexes separate. Fertilization internal; eggs with much yolk and calcareous shells. Vocal calls and complex songs. Complex behavior, e.g. courtship, migration. Early birds had reptilian characteristics and probably evolved from reptiles. There are about 9,000 species of modern birds divided into 27 orders. Some zoologists think that the class Aves should be a subclass of the Reptilia. CLASS MAMMALIA Body covered with hair. Skin with sweat, scent, sebaceous and mammary glands. Mouth with differentiated teeth. Four limbs in most, adapted for many forms of locomotion. Four-chambered heart. Respiration system with lungs and larynx. Muscular diaphragm present. Highly developed nervous system and brain. Three ear ossicles. Endothermic. Internal fertilization; mostly viviparous; fetal membranes (amnion, chorion, allantois). Females nourish the young with milk from mammary glands. Prototheria: egg-laying mammals (monotremes); eggs may be carried in a pouch on the abdomen or kept in a nest. Metatheria: part of their development occurs in the mother's uterus and part in an external maternal pouch (marsupials). Eutheria: entire development in utero (placental mammals); the placenta is an organ of exchange that develops between the embryo and the mother. Chapter 31 PLANT STRUCTURE, GROWTH AND DIFFERENTIATION There are about 262,000 species of plants. About 235,000 species or 90%, are angiosperms. Angiosperms can be either herbaceous or woody. Herbaceous plants can be annuals, biennials and perennials. Woody plants are perennials. THE PLANT BODY The plant body consists of a root system and a shoot system. The shoot system consists of a stem that bears leaves, flowers, fruits and sometimes adventitious roots. Plants are made of cells organized into tissues and organs. Roots, stems, flowers and fruits are organs. There are three tissue systems that extend throughout the entire body of the plant. Each tissue system contains two or more tissues, which can be simple or complex depending on the kinds of cells that form the tissue. A growing plant cell secretes a primary cell wall that stretches as the cell increases in size. The secondary cell wall is deposited after the cell stops growing. CELL TYPES Parenchyma cells Living cells at maturity. Have thin primary walls. Function in storage, secretion and photosynthesis. Found throughout the body of the plant. Collenchyma cells Living cells at maturity. Have unevenly thickened primary cell walls. Function in support in flexible parts of the plant. Found in petioles, leaf veins and other parts of the plant that must be flexible. Sclerenchyma cells Have both primary and thickened secondary cell walls. Cells are often dead at maturity. Secondary wall with pits. Provide structural support. There are two types of sclerenchyma cells: sclereids and fibers. Sclereids may be living or dead at maturity. Short, cubical cells. Sclereid rich tissue may be hard and inflexible. Form part of the shell and pits of fruits, e.g. coconuts, walnuts, cherries, etc. Fibers are often dead at maturity. Long, tapered cells often in clumps. Have few pits in their secondary wall. Provide strength and elasticity. Found throughout the plant body, common in stems and some leaves. Tracheids Dead at maturity. Long and tapered cells. Have secondary walls except at pits. Pits on lateral and end walls. Conduction of water and minerals. Vessel elements Dead at maturity. Long and cylindrical cells joined end to end. Secondary cell wall except at pits. End walls have perforations. Conduction of water and minerals. Sieve tube members Living cells at maturity. Lack nucleus and other organelles at maturity. Elongated cells, cylindrical, joined end to end. Secondary cell wall present. End walls are sieve plates with holes. Cytoplasm extends from one cell to the next through the holes of the sieve plate. Conduct the products of photosynthesis. Companion cells Living cells at maturity. Associated to a sieve tube member by means of plasmodesmata. Assists in moving sugars in and out of sieve tube members. The nucleus is thought to direct the activity of both cells. TISSUES 1. GROUND TISSUE SYSTEM Composed of three simple tissues. Parenchyma tissue parenchyma cells Collenchyma tissue Collenchyma cells Sclerenchyma tissue sclereids, fibers 2. VASCULAR TISSUE SYSTEM Composed of two complex tissues. Xylem Tracheids Vessel elements Parenchyma cells Fibers Phloem Sieve tube members Companion cells Parenchyma cells Fibers 3. DERMAL TISSUE SYSTEM Composed of two complex tissues. Epidermis Parenchyma cells Guard cells Trichomes Periderm Cork cells Cork cambium cells Cork parenchyma Ground tissue performs many functions: Photosynthesis, storage, secretion, flexible and rigid structural support Parenchyma cells have thin primary walls; polyhedral cells; function in photosynthesis, storage and secretion; remain alive at maturity. Collenchyma cells have an unevenly thickened primary wall; provide flexible structural support in soft non-woody organs; cells elongated; remain alive at maturity. Sclerenchyma cells have primary and thick secondary walls; provide rigid support to organs; cells usually die at maturity; fibers are long and tapered; sclereids are short and cubical. Vascular tissue system conducts materials throughout the plant body and provides support. Xylem conducts water and minerals from the roots to all parts of the plant; tracheids and vessel elements are the conducting cells and are dead at maturity; both have wall pits for lateral transport. Phloem transports sugars in solution to all plant parts; sieve tube members are the conducting cells; companion cells regulate the metabolism of the sieve tube members; both remain alive at maturity; sieve tube members lack nucleus and other organelles. Dermal tissue system is the outer protective covering of herbaceous plants and the young tender parts of woody plants. Epidermis usually consists of a single layer of parenchyma cells with guard cells and trichomes; secretes the waxy cuticle; gas exchange occurs through the stomata. It is made of parenchyma type cells. Periderm forms the outer bark of woody plants; cork cells are dead at maturity and filled with suberin, a water proof substance; cork parenchyma functions as a storage tissue. GROWTH Growth in plants is localized in regions called meristems. It involves cell division, cell elongation and cell differentiation. Primary growth causes the roots and stems to elongate. It occurs in all plants. The apical meristem at the tip of roots and stems is responsible. Secondary growth is an increase in stem and root girth. It occurs in woody plants only. It is due to the activity of the lateral meristems: vascular cambium and cork cambium. Vascular cambium forms a cylinder along the length of roots and stems, between the xylem and phloem; it produces more xylem and phloem. Cork cambium is located in the outer bark. Chapter 32 LEAF STRUCTURE AND FUNCTION LEAF FORM Leaves are organs and vary greatly in external form. They may range in length from about 20 m (65 ft) to about 0.15 cm (0.06 in). Their principal parts are blade, petiole and stipules (may be absent). Leaves can be simple or compound. Their arrangement along the stem can be alternate, opposite or whorled. Their venation may be netted or parallel. Veins can be arranged pinnately or palmately LEAF TISSUES 1. Epidermis There are upper and lower epidermises that form the surface of the leaf. Made of living parenchyma cells. Lack chloroplasts. Covered with a waxy layer, the cuticle. Have small openings for gas exchange called stomata (sing. stoma). Guard cells flank each stoma. Trichomes or hairs may be present. 2. Mesophyll The photosynthetic tissue found in between the two epidermises is called mesophyll. It consist of... Made of living parenchyma cells. Abundant chloroplasts. Usually loosely arranged with many air spaces. Often arrange in two regions: palisade and spongy mesophyll. 3. Venation Veins and diffusion cooperate in the movement of materials in veins. Veins or vascular bundles extend through the mesophyll. Each vein contains xylem and phloem tissue. Xylem is usually restricted to the upper side of the vein, and phloem to the lower side of the vein. A non-vascular parenchymatous layer of cells called the bundle sheath surrounds veins. The bundle sheath extensions are support columns of cells that extend from the vein to the upper and lower epidermis. May be composed of parenchyma, collenchyma or sclerenchyma cells. Monocot leaves usually have parallel venation and it is not differentiated into palisade and spongy mesophyll; the guard cells are shaped like dumbbells Dicot leaves have netted venation, mesophyll differentiated into two regions, and the guard cells are bean-shaped. Subsidiary cells are epidermal cells associated with the stomata and are involved in the opening and closing of the stomata. Gymnosperms normally have parallel or free venation (not netted). FUNCTION Photosynthesis is the primary function of leaves. A single red maple leaf fixes about 454 kg (1,000 pounds) of CO2 into carbohydrates in one summer. Transparent epidermal cells allow sunlight penetrate to the palisade mesophyll, where most of the photosynthetic activity takes place. Open stomata allow CO2 to enter the air spaces and O2 to escape into the atmosphere. Loose arrangement of the spongy mesophyll allows gas exchange to occur readily within the leaf. Veins and veinlets bring the water needed for photosynthesis and carry away photosynthates. Support tissue allows the leaf to remain expanded facing the sun. The anatomy of the leaf reflects the environment in which the plant lives, e.g. hydrophytes have large air spaces for floatation. Conifers have adaptations that allow the leaves to survive cold and drought: Needle shape with little exposed surface. Thick waxy cuticle. Sunken stomata. STOMATAL OPENING AND CLOSING. Stomata are open or closed according to the physiological needs of the plant. Photosynthesis: gas exchange. Transpiration: loss of water. In mesophytes, the stomata are usually open during the day and closed at night. CAM plants do the reverse. Light and dehydration also affect the opening or closing of the stomata. A low concentration of CO2 in the leaf induces stomata to open even in the dark. The opening and closing of stomata are controlled by changes in the shape of the guard cells that surround the pore. Potassium ion mechanism. Light triggers an influx of K+ into the guard cells. It occurs through active transport; ATP required. Osmotic pressure decreases and water moves into the guard cells. The increase turgidity of the cells causes a change in shape and the stoma opens. Opening of the stomata is most pronounced in blue light, and to a lesser extent in red light. Light proton pump moves H+ K+ actively transported water diffuses into out of the guard cell through specific K channels the guard cells guard cells change shape and open the stoma. The stoma may close by a reversal of the process when light decreases. Loss of turgidity closes the stoma. TRANSPIRATION The loss of absorbed water is 99%. Only about 1% to 3% of the lost water passes through the cuticle. Most is lost through the stomata. Environmental factors increase the rate of transpiration, e.g. wind, relative humidity, temperature. Transpiration is both beneficial and harmful to the plant. GUTTATION When transpiration is negligible and soil moisture is high, plants release liquid water through the end of veinlets near the leaf margin. LEAF ABSCISSION Metabolism slows down during the wintertime and there is little need for leaves. Water absorption from roots slows down or stops altogether during winter. Leaves will continue to lose water that could not be replaced. Involves physiological changes initiated by plant hormones. Sugars, amino acids and minerals are removed from the leaves. Chlorophyll breaks down. The abscission zone is located at the base of the petiole. Made of thin walled parenchyma cells. Lacks fibers and is anatomically weak. Cork cells developed on the stem side of the abscission zone. Enzymes dissolve the middle lamella of parenchyma cells. Protective layer of cork seals off the wound and forms the scar. LEAF FUNCTIONS Photosynthesis is principal function of leaves. Spines are leaves adapted to provide protection. Succulent leaves are photosynthetic and store water. Some tendrils are leaves modified for grasping. Bud scales are leaves modified to protect the apical meristem. Sepals are modified leaves that protect developing flowers. Bulbs are made of leaves modified to store food underground. Some leaves are modified to trap insects. Chapter 33 STEM AND PLANT TRANSPORT FUNCTIONS Support of the photosynthetic, reproductive and storage parts. Conduction of water and metabolites. Production of new stem tissues. EXTERNAL MORPHOLOGY Terminal and lateral buds. Covered with bud scales while dormant. Contain meristem and produce primary tissues. Lateral buds are associated with leaf axils. Bud scale scars. Nodes and internodes. Nodes are the regions of leaf attachment. Internodes are the space between two nodes. Leaf scars and bundle scars. Lenticels. Loosely arranged cells that allow gas exchange. Broken epidermis. HERBACEOUS STEMS Herbaceous stems have epidermis, cortex, pith (both also known as ground tissue), and vascular tissue. a) Herbaceous dicots have the vascular bundles arranged in a circle in cross section, and have a distinct cortex and pith. b) Herbaceous monocots have vascular bundles scattered throughout the ground tissue; there are no distinct cortex and pith regions. WOODY STEMS Woody dicot plants undergo secondary growth, an annual increase in width of stems and roots. It is the result of the activity of the vascular cambium and cork cambium. Secondary growth in monocots is very rare. Woody monocots increase their diameter by the enlargement of the primary tissue behind the apical meristem, e.g. palms. Vascular cambium is located between the xylem and the phloem. Secondary xylem (wood) is produced to the inside Secondary phloem (inner bark) to the outside. Cork cambium is located near the surface of the stem. Cork parenchyma is produced toward the inside. Cork cells, periderm, are produced toward the outside. Rays are chains of parenchyma cells that radiate out of the center of the stem and transport materials laterally between the secondary xylem and secondary phloem TRANSPORT IN PLANTS Water potential is a measure of the free energy of water. Water potential is a measure of the cell's ability to absorb water by osmosis. It also measures the water's tendency to evaporate from the cell. The free energy of pure water is 0 megapascals ( 1 MPa = 10 atmospheres or 14.5 pounds/inch2). When solutes dissolve in water, the free energy of water decreases and the water potential becomes a negative number. Water moves from the region of high water potential (very negative) to the region of lower water potential (less negative). Roots have many solutes dissolved in their cells, which lowers their water potential in relation to the soil in which they grow. Water moves in from the soil into the roots by osmosis. When soil is very dry, its water potential is very low. Unless the soil is extremely dry, roots have a lower water potential (very negative) than the soil and water tends to move by osmosis from the soil into the roots. Tension-cohesion theory Also known as the Transpiration-Cohesion Theory. There is a gradient in water potential from the atmosphere down to the soil. The atmosphere has very negative water potential. Leaves have higher water potential than the atmosphere and lose water to it. Stems have higher water potential than the leaves; the roots higher than the stem; and the soil higher than the roots. The gradient creates a pull of the column of water in the xylem due to the hydrogen bonds that exist between the water molecules (cohesion). Adhesion of the water molecules to the xylem walls maintains an unbroken column of water. Root pressure pushes water from the root up the stem. Not strong enough to push the up tall plants. It is very low or non-existent during the summer months. Movement of water is greatest in the summer months when root pressure is the lowest. Guttation is the result of root pressure. TRANSLOCATION OF SUGAR Sucrose is the main sugar translocated in the phloem. Sugars moves from the source where it is being produced, to the sink, where the sugars are being utilized or stored. Pressure flow theory. This theory postulates that sugar moves in the phloem by means of a pressure gradient that exists between the source, where sugar is loaded into the sieve tube members, and the sink, where sugar is removed from the phloem. Sucrose and other carbohydrates is actively loaded into the sieve tubes at the source. It requires ATP. ATP supplies energy to pump protons out of the sieve tube members. Creates proton gradient. The gradient drives the uptake of sucrose through channels by the cotransport of protons back into the sieve tube members. As a result water moves into the sieve tubes by osmosis increasing the hydrostatic pressure in the sieve tubes. Sugar is actively or passively unloaded from the sieve tube into tissues at the sink. As a result water leaves the sieve tubes at the sink decreasing the hydrostatic pressure inside the sieve tubes. A gradient is created between the source and sinks which drives the flow within the sieve tubes. Other substances transported in the phloem are hormones, ATP, amino acids, inorganic ions, viruses and complex organic molecules like sugar-alcohol compounds. Chapter 34 ROOTS AND MINERAL NUTRITION FUNCTIONS Anchorage of the plant. Absorption of water and minerals. Conduction of water, mineral and other materials. Storage of food and other nutrients. In certain species, roots are modified to perform other functions. ROOT SYSTEMS Taproot system. One main root from which lateral secondary roots branch out. Many trees lose their taproot at maturity. Their root system consists of large, shallow secondary roots. 2. Fibrous root system. Several to many roots of the same size. They arise directly from the stem and are called adventitious roots. ROOT STRUCTURE Root structure is different from that of the stem. It differs in. Root cap, a protective layer that covers the apical meristem and orients the root to grow downward. Root cap responds to gravity (gravitropism). Root hairs, short-lived extensions of the epidermal layer, to increase absorption. Roots have a pericycle and endodermis present. Roots lack nodes and internodes. ARRANGEMENT OF VASCULAR TISSUE. Epidermis protects the internal tissues and absorbs water and dissolved minerals. Cortex, ground tissue made of parenchyma cells that store starch. Endodermis, the innermost layer of the cortex, controls mineral uptake into the xylem. Cells have a Casparian strip around the radial and transverse walls, that is impermeable to water and minerals. The Casparian strip is made of suberin. Apoplast travels through the porous walls between cells; symplast travels from cell to cell through their cell cytoplasm. Minerals most pass through carrier proteins in the plasma membrane of the endodermal walls. It requires ATP. 5. The stele forms a central cylinder. It is made of the pericycle, xylem, phloem, and in some cases pith. Pericycle is the place where lateral roots originate. Xylem normally has several extensions or "arms". Phloem is located in groups between the arms. Vascular cambium gives rise to secondary tissue in woody dicots and gymnosperms. It is located between the xylem and the phloem. Pith is absent in dicot roots and present in monocot roots. The stele is surrounded by the endodermis. Woody dicots and gymnosperms exhibit considerable growth in root girth. Vascular cambium and cork cambium are active. Annual rings present in temperate climate. 6. Roots of many angiosperms have a second compact layer with Casparian strip called exodermis. It develops from the outermost layer(s) of the cortex It forms a layer below the epidermis. It is presumed that it prevents the excessive loss of water to the soil and protects against attack by microorganisms. 7. A periderm of secondary origin, composed of cork, cork cambium and cork parenchyma develops after the first year. It originates from the pericycle. The primary phloem, cortex and epidermis are destroyed and shed with the increase in girth. SPECIALIZED FUNCTIONS OF ROOTS Prop roots develop from branches and stems for extra support, e.g. corn, figs. Pneumatophores help in getting oxygen to submerged roots, e.g. cypress, mangrove. Contractile roots pull the corm or bulb deeper into the soil, e.g. daffodils. Fleshy roots are specialized for storage, e.g. sweet potatoes, beets. Epiphytes have roots adapted to a variety of functions: photosynthesis, moisture absorption and support, e.g. orchids Parasitic plants have roots called haustoria (haustorium) adapted to penetrating the tissues of the host plant, e.g. mistletoe. ROOT ASSOCIATIONS Root grafts are common among trees that grow closely together. Mycorrhizae are mutualistic associations between roots and fungi. Root nodules house nitrogen-fixing bacteria. SOIL Soil is made of inorganic materials, organic matter, soil air, soil water and soil organisms. Most soils are formed from rock (parent material) that is gradually broken down into smaller and smaller particles by chemical, physical and biological processes called weathering. The texture of the soil is determined by the percentages (by weight) of the different size inorganic particles. Particles larger than 2mm in diameter are called gravel and stone and are not considered soil particles. Inorganic materials come from the weathered parent rock. Chemical and mechanical weathering. Sand (0.02 - 2.0 mm), silt (0.002 - 0.02 mm) and clay (< 0.002 mm). Clay particles have the greatest surface area and determine the fertility of the soil. Each clay particle has a negative charge on its outer surface. Cations bind to the surface of the clay particles. Roots secrete protons, H+, which are exchanged for the cations bound to the clay particles. Lowering of the pH increases the solubility of many cations. Plant roots absorb the resulting free ions. This process is called cation exchange. Many anions are very soluble and remain in solution in the ground water. Loam contains ideally 40% sand, 40% silt and 20% clay. Maximum capacity for holding cations and water, and being well aerated. Loam is the best soil for agriculture. Organic matter consists of waste and the remains of organisms in different stages of decomposition. Humus is the partially decayed organic portion of the soil. Humus holds water and minerals. Bacteria and fungi are the principal decomposers in the soil. Organic matter adds nutrient to the soil and increases its water holding capacity. Soil organisms form a complex ecosystem. Bacteria, fungi, algae, worms, insects, plant roots, mammals. Organisms perform different functions: decomposition, aeration, and addition of nutrients. Soil air has the same gases as atmospheric air but usually indifferent proportions. About 30% to 60% of the soil volume is composed of pores or air spaces. CO2 forms carbonic acid when mixed with water. N2 is used by nitrogen fixing bacteria. O2 is needed by most organisms and plant roots. Soil water originates as precipitation, which drains downward, or as ground water, which rises from the water table. Percolating water removes dissolved minerals and carry them downward out of the reach of roots - a process called leaching. Some anions are very soluble and easily removed by leaching. Soils could be acidic or alkaline. Acidic soils have less ability to hold mineral nutrients (cations). Cation exchange and decomposition decrease the pH of the soil. Optimum pH for most plants is 6 to 7. NUTRIENTS About 60 naturally occurring elements have been found in plant tissues. Not all these 60 elements are considered essential for plant growth. Plants require 16 essential elements for normal growth. Macronutrients are required in large quantities: Carbon, oxygen, nitrogen, hydrogen, potassium, phosphorus, sulfur, magnesium and calcium. Micronutrients are needed in trace quantities: Iron, boron, manganese, copper, zinc, molybdenum and chlorine. Magnesium is needed for chlorophyll. Potassium is an activator for over 40 enzymes, important in stomatal function and contributes to osmosis causing the turgidity of the cell, and ionic balance. Iron is a component of electron transport systems. Calcium is an enzyme activator, involved in membrane permeability and in cell walls. Iron, manganese, copper, zinc, and molybdenum are enzyme activators. HUMAN IMPACT In natural ecosystems, essential nutrients are returned to the soil when plant parts die and decompose. Crops, which contain minerals, are removed from the nutrient cycle when they are harvested. The essential elements in the shortest supply are called limiting factors. Nitrogen, phosphorous and potassium are often the most easily depleted (limiting factors). Human mismanagement can create mineral depletion, erosion and salinization. Mineral depletion can be counteracted by the application of fertilizers, both organic and inorganic. Exposed soil is subject to erosion by wind and water. About 4 billion metric tons of topsoil is lost from U.S. cropland every year. Salinization occurs when the soil is improperly irrigated. Evaporation leaves salts behind that accumulate over the years. Chapter 35 REPRODUCTION IN FLOWERING PLANTS. In flowering plants the diploid sporophyte generation is larger and nutritionally independent. The haploid gametophyte generation, which is located in the flower, is microscopic in size and nutritionally dependent of the sporophyte. The gametophyte gives rise to gametes by mitosis. Fertilization produces the diploid sporophyte, which produces spores by meiosis. One haploid spore gives rise to the haploid gametophyte. FLOWER The flower is a modified branch apex, and is involved in sexual reproduction. Reproductive and accessory organs are normally arranged in whorls or circles of structures: Sepals, petals stamens, and carpels. The whorls of organs sit on an enlarged branch end called the receptacle. The sepals form the calyx and protect the flower bud. The petals form the corolla and attract animals to assist in pollination. Petals may or may not be present. The stamens are the male reproductive organs. They consist of a filament and an anther. Pollen grains form in the anthers. Each pollen grain contains two cells; one produces two sperm nuclei, and the other produces a pollen tube to transfer the sperm nuclei to the ovule. A pollen grain represents a male gametophyte. The carpels are the female reproductive structures. A flower may have one or several carpels. Carpels may be separate or fused. Carpel usually has a style and stigma. Ovary is another name for the lower portion of the carpel. An ovary may be formed by various fused carpels. Pistil is another name for the female reproductive structure. A pistil may be formed by a single carpel or by several fused carpels. The ovary contains one or several ovules. The ovule produces contains the embryo sac. The embryo sac produces two polar nuclei and one egg. The egg and the polar nuclei are involved in the process of double fertilization. POLLINATION Pollination is the transfer of pollen from the anther to the stigma. Plants can self-pollinate or cross-pollinate. Flowering plants and their animal pollinators have evolved together. Pollinators use nectar and pollen as sources of energy and protein. It is estimated that insects pollinate about 70% of flowering plants. About 30% of our food come from crops pollinated by bees. Plants pollinated by wind often have reduced or absent petals, produce large amounts of pollen and do not have scent. Insect-pollinated flowers often have yellow or blue petals and have scent. Bird-pollinated flowers are often yellow, red or orange, and do not have scent. Bat-pollinated flowers are creamy white and have strong scent. Fly-pollinated flowers often smell like decaying flesh. FERTILIZATION Fertilization is the fusion of gametes. Double fertilization is a unique phenomenon that occurs in angiosperms only. Egg and one sperm form the zygote. The two polar nuclei and the second sperm form the endosperm. Embryonic development follows a pattern: Proembryo globular embryo heart-shaped embryo torpedo stage mature embryo. A mature embryo consists of a radicle, hypocotyl, one or two cotyledons and the plumule. The mature seed contains the embryo and the nutritive tissue (endosperm or cotyledons). Seeds are enclosed in fruits. Fruits are ripened ovaries. FRUIT CLASSIFICATION Simple fruits develop from a single pistil. One or several carpels involved. May be fleshy (e.g. berries) or dry (e.g. grains). Aggregate fruits develop from a single flower with many separate ovaries (e.g. blackberries, gumballs). Multiple fruits develop from a many flowers growing closely together on a common axis (e.g. pineapple). Accessory fruits develop from tissues other than the ovary (e.g. strawberry, apples, and pears). Seeds and fruits are adapted to various means of dispersal, including wind, water, animals and explosive dehiscence. ASEXUAL REPRODUCTION Offspring are formed without the fusion of gametes. Offspring are genetically similar to the parent plant. Stems, leaves and roots may be adapted to asexual reproduction. Apomixis is the formation of seeds without fertilization. Modified stems may give rise to independent plants in time: Rhizomes are underground horizontal stems that may or may not be fleshy. They produce new plants by fragmentation of the old rhizome. Tubers are fleshy underground stems enlarge for food storage. Tubers produce independent plants once the parent plant dies. Bulbs are modified underground buds attached to short stems with storage leaves. It frequently forms axillary buds that separate and grow into independent plants. Corms are short, erect underground stems that store food in their tissues and are covered with papery leaves. Small axillary buds give rise to new corms. Stolons or runners are horizontal, aboveground stems. They produce buds that give rise to small plants that root and become independent. Modified leaves can produce plantlets that break off and give rise to new plants. Chapter 36 GROWTH RESPONSES AND REGULATION The ultimate control of plant growth and development is genetic. Location of a cell in the plant body and environment influence gene expression in plants. Chemical signals from adjacent cells may help the cell perceive its location in the plant body. Environmental cues like changes in light and temperature influence gene expression. Plant hormones are chemicals that are produce in one part of the plant and transported to another part where they cause a physiological response. SEED GERMINATION A mature seed is one with a fully developed embryo. Mature seeds are often dormant and may not germinate even if conditions are ideal. Seed germination is influenced by external and internal factors. External environmental factors: oxygen, light, water and temperature. Imbibition of water by the seed. Oxygen for cell respiration from food in the endosperm. Optimal temperature for most plants is 25o to 30oC (77o-86o F). Some plants require exposure to freezing temperatures. Some require light and some do not. Internal factors are the maturity of the embryo and the presence or absence of chemical inhibitors. Germination pattern is different in monocots and dicots. Dicots produce a "hook" that pushes out of the ground. Monocots grow produce a plant that grows straight out of the ground and is protected by the coleoptile. Stems and roots have the ability to grow throughout the lifetime of the plant: indeterminate growth. Leaves and flowers stop growing at some point: determinate growth. PHOTOPERIODISM Photoperiod is the length of daylight in a 24-hour day. Short-day plants (long-night plants) flower when the night length is equal to or greater than some critical period. Plant detects the shortening of the day or lengthening of the night. Minimum critical night length varies with the species. Fall flowers like poinsettias, chrysanthemums. Long-day plants (short-night plants) flower when the night length is equal to or less than some critical period. Plant detects the lengthening of the day and shortening of the night. Maximum critical night length varies with the species. Spring flowers. Day-neutral plants do not respond to photoperiod. Many originated in the tropics where there is little difference in day length throughout the year. Tomato, beans, corn, cucumber, etc. The photoreceptor for photoperiodism is a group of five blue-green pigments Each coded by different gene. Collectively called phytochrome. Found in the cells of all vascular plants. Phytochrome detects the varying periods of day length. Blue-green pigment that absorbs light. Open tetrapyrrole attached to a protein. Phytochrome occurs in two forms: one form, Pr, absorbs red light at 660 nm and the other form, Pfr, absorbs far-red light at 730 nm. The shape of the molecule changes when light is absorbed. During the day the amount of Pfr increases due to red light. At night Pfr, which is less stable, reverts slowly to Pr. Pfr inhibits flowering in short-day plants (read long-night plants). These plants need long days and short nights in order to flower. Long period of darkness allows all of the Pfr to revert to Pr and the inhibition disappears: the plant blooms. In long-day plants (read short-night plants) Pfr induces flowering. Long days produce large amount of Pfr During the short night only part of the Pfr changes to Pf . The plant has sufficient Pfr left to flower. Experiments show that an internal clock is also at play here. VERNALIZATION Low temperature is needed by some plants in order to bloom. It usually requires temperature between 0oC and 10oC. The part of the plant needed to be exposed to low temperature varies: seed or apical meristem. Other plants bloom early if exposed to low temperature, if not exposed then they bloom later. Hormone level interacts with external factors and modifies their effect. CIRCADIAN RHYTHMS These internal timers or biological clocks of organisms. They are alternating patterns of activity that occur at regular intervals. Approximate 24-hour period (20-30 hour periods). Independent of temperature and light cycles. Reset by the sun every day. Opening and closing of stomata, sleep movements, opening of flowers. NASTIC MOVEMENTS Changes in turgor cause plant part to move. The movements are temporary and reversible. The direction of the movement is predetermined and independent of the direction of the stimulus. In the case of Mimosa, an electrical impulse created by the stimulus induces a chemical signal that increases the membrane permeability to certain ions thus changing the turgor of the cells. e. g. sleep movement, solar tracking, sensitive leaves. TROPISMS Tropism is growth response to an external stimulus from a specific direction. Changes are permanent and irreversible. Phototropism is a response to the direction of light. A flavoprotein acts a photoreceptor of blue light (500 nm). Gravitropism (syn. geotropism) is a response to gravity. Statoliths made of starch accumulate at the bottom of cells in the root cap in response to gravity. The side of the cell opposite to the statoliths elongates. Gravitropism may be positive (toward) or negative (away from). Thigmotropism is a response to contact with a solid object. Water, temperature, oxygen and chemicals may also cause tropism in plants. Heliotropism is the ability to follow the sun's movement across the sky. It is triggered by blue light. Many heliotropic leaves have pulvini at the base of the petiole. THIGMOMORPHOGENESIS Mechanical stress due to the action of wind, rain, etc. in exposed places causes plants to grow shorter and stockier. HORMONES Plant hormones are chemical messengers. Produced in one part of the plant. Transported to another part of the plant. Causes a physiological response: regulate growth and development. Each hormone type causes several responses. The responses of different hormones overlap. There are five classes of plant hormones. AUXIN It is produce in the apical meristem of shoots, in young leaves and in seeds. It is transported downward in parenchyma cells. It causes cell elongation, inhibits lateral bud development, stimulates fruit development and inhibits abscission. GIBBERILLIN It is produced in young leaves, roots, shoot apical meristem and in the seed embryo. Method of transport in the plant is unknown. It promotes seed germination, cell division and elongation, fruit development, flowering in some plants and breaks seed dormancy. CYTOKININS They are produced in the roots. Travel upward in the xylem. Promote cell division and differentiation in which unspecialized cells become specialized, stimulates lateral bud development, inhibits abscission and delays senescence. Zeatin was the first isolated naturally occurring cytokinin. ETHYLENE It is a gaseous hormone produced in stem nodes, aging tissues and ripening fruits. It probably diffuses out of the tissue that produces it. It promotes ripening of the fruits and abscission, inhibits cell elongation, stimulates germination of seeds and it is involved in responses to wounds and infections by microorganisms. ABSCISIC ACID It is produced in older leaves, the root cap and stems. Stressed plants produce abscisic acid It travels in the vascular tissue. It inhibits seed germination and promotes winter and seed dormancy, formation of bud scales. It causes the closing of stomata in plants under water stress Grafting experiments suggest the existence of a substance (florigen) that causes flowering in plants, and others that inhibit flowering. Neither has been isolated yet. OTHER CHEMICALS INVOLVED IN PLANT GROWTH AND DEVELOPMENT. Polyamines are organic molecules with two or more amine groups (- NH2). They may be involved in gene expression and increase the transcription of DNA and translation of mRNA. They exist in high concentration in plant tissues and are not transported extensively through the plant. Systemin, a plant polypeptide, stimulates plant defenses that produce chemicals that disrupt insect digestion. Present in very small quantities. Oligosaccharins are cell-wall fragments consisting of short, branched chains of sugar residues. Present in quantities lower than hormones. Bind to membrane receptors and affect gene expression and have many effects on plants. Salicylic acid help to defend the plant against insect attack and promotes wound healing.