domingo, 17 de mayo de 2009

HOMEWORK

PLEASE ADD YOUR CHOICE OF FUNGI TO THE COMMENTS ON THE BLOG.

YOU WILL TURN ALL HOMEWORK TO ME IN CLASS. DO NOT EMAIL ME YOUR HOMEWORK, I NEED IT PRINTED.

THANKS

Z.
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domingo, 10 de mayo de 2009

FUNGI

Selected Themes in Biology II Prepa 6 A/B

THIS CHAPTER WILL NOT BE INCLUDED ON THE UPCOMING TEST

(ON YOUR UPCOMING EXAM ONLY: Plant Reproduction, Plant Responses and Medicinal Plants, from class notes and blogs, you already know this)

THIS HOMEWORK IS DUE ON THE FIRST DAY WHEN I SEE YOU NEXT TIME:

Selected Themes in Biology II

Homework # 7 (40 points)

Fungi

Define the following terms:

Fungi, heterotrophic, chitin, hyphae, mycelium, fruiting body, sporangium, sporangiophore, molds, Zygomycetes, zygospore, Ascomycota, sac fungi, spores, conidia, Basidiomycota, club fungi, imperfect fungi, Deuteromycota, decomposers, parasitic fungi, symbiotic relationships, lichens, poisonous fungi.

Draw and label the sexual and asexual reproduction cycles of the following types of fungi: Zygomycetes and Ascomycetes.

Draw and label the sexual reproduction cycles of Basidiomycetes.



FUNGI

Mini Project Assignment: (40 points)

Choose a Basidiomycetes (CLUB FUNGI) fungi and give a brief description of it including a photo.

The description should include physical description, habitat, whether or not it’s edible or poisonous, common and scientific name, name of family of fungi. *Please Include any interesting facts about the fungi.

I don’t want repeats of the fungi species, so what you are going to do is enter on the commentaries box your name, the scientific name and common name of the fungi of your choice. The person that writes the fungi first has a priority over it. If another person writes the same one has to go back and chose another one.

*Fit everything to one page, use single space and include photo. (Yes you can print this pic from the internet) NO COPY PASTE. NO PLAGIARISM.
Publicado por en 9 comentarios:

miércoles, 29 de abril de 2009

Medicinal Plants Project:

Here is the list of your assigned plants for the project:
This Project is still due May 6, 2009 (unless something else happens)

Grupo: 6A SEMESTR, PREPARATORIA Grado 3
Nombre Scientific Name Common Name
ALCARAZ DUEÑAS ALBA MONCERRAT Origanum vulgare Oregano
ALEMAN MAGRO HORACIO Salix alba Willow bark
CAMACHO GOMEZ ROMINA ALEXANDRA Chiranthodendron pentadactylon, Flor de manita
CHUMANCERO DELGADO ALICA Zingiber officinale Ginger
CORTES SOSA KAREN AURORA Calendula officinalis Calendula
GUTIERREZ VENEGAS LUIS Valeriana officinalis Valerian root
IBARGUENGOYTIA PEREZ CECILIA Glycine max Soy
LOPEZ REYNOSO FRANCISCO JAVIER Pithecollobium dulce Guamuchil
MARQUEZ MORGA ALEJANDRO Mentha × piperita Yerbabuena
MENDOZA RUIZ PAULINA MONSERRAT Rauvolfia serpentina Rauvolfia
OCHOA BANKER GABRIELA ANNA Camelia sinensis Green tea
PASOS ROMAÑA ANDRES Echinacea angustifolia Echinacea
RAMIREZ MARTINEZ JORGE ARMANDO Hypericum perforatum St. John's Wort
REYES JIMENEZ MONICA ALEGRIA Cinchona sp. Quinine
SALDAÑA LIZARRARAS MIGUEL ANGEL Taxus breviflolia Pacific yew, Taxol
VILLASEÑOR ULLOA KENYA Aloe vera Aloe vera
ZERMEÑO PEREZ ABRAHAM Mormodica cHaranthia Cundeamor, bitter melon

Grupo: 6B SEMESTR, PREPARATORIA Grado 3
Nombre
ALVAREZ TOSTADO MARTINEZ, RODOLFO E Mimosa tenuiflora tepezcohuite
CILVETI SALDIVAR, PIERRE Argemone mexicana Cardo
CLAVEL BENITEZ, ERIK EMMANUEL Ricinus communis higuerilla, ricino
FERNANDEZ VELASCO, CHRISTIAN JANEK Bougainvillea spectabilis bugambilia
HERRERA MAGAÑA, JESUS ALEJANDRO Heterotheca inuloides Arnica
IRASTORZA ICAZA, JUAN IGNACIO Artemisia absithium ajenjo, absinthe
JOYA GONZALEZ, MARIA ISABEL Opuntia spp. Nopal
MAYORAL RANGEL, ALAN Hintonia latiflora Cascara sagrada, copalquin,
OLARTE MENDOZA, VERONICA Tagetes lucida Pericon, marigold
PEÑA CAMPA, ARACELI HANNALI Datura stramonium Toloache
RODRIGUEZ GARCIA, MARLENE CECILIA Turnera difusa Damiana
WENZEL MELCHOR, CHARLENE JUANITA Digitalis purpurea Foxglove

IMPORTANT NOTE: Sometimes it may be that there are different species of the same genera, that are considered too, make sure you add those species in your explanation.

The guidelines have already been given in the assignment. Make sure you do them all to get full credit, if the plant is unavailable you may use a botanical illustration instead of the plant sample.

Have fun!!!

If you have any questions please send me an email to bioblog9@gmail.com

I will be checking this email everyday.

Z
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miércoles, 22 de abril de 2009

MEDICINAL PLANTS

All plants produce chemical compounds as part of their normal metabolic activities. These include primary metabolites, such as sugars and fats, found in all plants, and secondary metabolites found in a smaller range of plants, some useful ones found only in a particular genus or species. Pigments harvest light, protect the organism from radiation and display colors to attract pollinators. Many common weeds have medicinal properties.[40][41]

The functions of secondary metabolites are varied. For example, some secondary metabolites are toxins used to deter predation, and others are pheromones used to attract insects for pollination. Phytoalexins protect against bacterial and fungal attacks. Allelochemicals inhibit rival plants that are competing for soil and light.

Plants upregulate and downregulate their biochemical paths in response to the local mix of herbivores, pollinators and microorganisms.[42] The chemical profile of a single plant may vary over time as it reacts to changing conditions. It is the secondary metabolites and pigments that can have therapeutic actions in humans and which can be refined to produce drugs.

Plants synthesize a bewildering variety of phytochemicals but most are derivatives of a few biochemical motifs.

  • Alkaloids contain a ring with nitrogen. Many alkaloids have dramatic effects on the central nervous system. Caffeine is an alkaloid that provides a mild lift but the alkaloids in datura cause severe intoxication and even death.
  • Phenolics contain phenol rings. The anthocyanins that give grapes their purple color, the isoflavones, the phytoestrogens from soy and the tannins that give tea its astringency are phenolics.
  • Terpenoids are built up from terpene building blocks. Each terpene consists of two paired isoprenes. The names monoterpenes, sesquiterpenes, diterpenes and triterpenes are based on the number of isoprene units. The fragrance of rose and lavender is due to monoterpenes. The carotenoids produce the reds, yellows and oranges of pumpkin, corn and tomatoes.
  • Glycosides consist of a glucose moiety attached to an aglycone. The aglycone is a molecule that is bioactive in its free form but inert until the glycoside bond is broken by water or enzymes. This mechanism allows the plant to defer the availability of the molecule to an appropriate time, similar to a safety lock on a gun. An example is the cyanoglycosides in cherry pits that release toxins only when bitten by a herbivore.

The word drug itself comes from the Dutch word "druug" (via the French word Drogue), which means 'dried plant'. Some examples are inulin from the roots of dahlias, quinine from the cinchona, morphine and codeine from the poppy, and digoxin from the foxglove.

The active ingredient in willow bark, once prescribed by Hippocrates, is salicin, which is converted in the body into salicylic acid. The discovery of salicylic acid would eventually lead to the development of the acetylated form acetylsalicylic acid, also known as "aspirin", when it was isolated from a plant known as meadowsweet. The word aspirin comes from an abbreviation of meadowsweet's Latin genus Spiraea, with an additional "A" at the beginning to acknowledge acetylation, and "in" was added at the end for easier pronunciation.[43] "Aspirin" was originally a brand name, and is still a protected trademark in some countries. This medication was patented by Bayer AG.


Few herbal remedies have conclusively demonstrated any positive effect on humans, mainly because of inadequate testing.[74] Many of the studies cited refer to animal model investigations or in-vitro assays and therefore cannot provide more than weak supportive evidence.

  • Aloe vera has traditionally been used for the healing of burns and wounds.[75] A systematic review (from 1999) states that the efficacy of aloe vera in promoting wound healing is unclear, while a later review (from 2007) concludes that the cumulative evidence supports the use of aloe vera for the healing of first to second degree burns.[76][77]
  • Agaricus blazei mushrooms may prevent some types of cancer.[78]
  • Artichoke (Cynara cardunculus) may reduce production cholesterol levels according to in vitro studies [79] and a small clinical study.[80]
  • Blackberry (Rubus fruticosus) leaf has drawn the attention of the cosmetology community because it interferes with the metalloproteinases that contribute to skin wrinkling.[81]
  • Black raspberry (Rubus occidentalis) may have a role in preventing oral cancer.[82][83][84]
  • Butterbur (Petasites hybridus)
  • Calendula (Calendula officinalis) has been used traditionally for abdominal cramps and constipation.[85] In animal research an aqueous-ethanol extract of Calendula officinalis flowers was shown to have both spasmolytic and spasmogenic effects, thus providing a scientific rationale for this traditional use.[86] There is "limited evidence" that calendula cream or ointment is effective in treating radiation dermatitis.[87][88]
  • Cranberry (Vaccinium oxycoccos) may be effective in treating urinary tract infections in women with recurrent symptoms.[89]
  • Echinacea (Echinacea angustifolia, Echinacea pallida, Echinacea purpurea) extracts may limit the length and severity of rhinovirus colds; however, the appropriate dosage levels, which might be higher than is available over-the-counter, require further research.[90][91]
  • Elderberry (Sambucus nigra) may speed the recovery from type A and B influenza.[92] However it is possibly risky in the case of avian influenza because the immunostimulatory effects may aggravate the cytokine cascade.[93]
  • Feverfew (Chrysanthemum parthenium) is sometimes used to treat migraine headaches.[94]Although many reviews of Feverfew studies show no or unclear efficacy, a more recent RTC showed favorable results[95][96][97]Feverfew is not recommended for pregnant women as it may be dangerous to the fetus.[98][99]
  • Gawo (Faidherbia albida), a traditional herbal medicine in West Africa, has shown promise in animal tests [100]
  • Garlic (Allium sativum) may lower total cholesterol levels[101]
  • German Chamomile (Matricaria chamomilla) has demonstrated antispasmodic, anxiolytic, antiinflammatory and some antimutagenic and cholesterol-lowering effects in animal research.[102] In vitro chamomile has demonstrated moderate antimicrobial and antioxidant properties and significant antiplatelet activity, as well as preliminary results against cancer.[103][104] Essential oil of chamomile was shown to be a promising antiviral agent against herpes simplex virus type 2 (HSV-2) in vitro. [105]
  • Ginger (Zingiber officinale), administered in 250 mg capsules for four days, effectively decreased nausea and vomiting of pregancy in a human clinical trial.[106][107]
  • Green tea (Camelia sinensis) components may inhibit growth of breast cancer cells[108] and may heal scars faster.[109]
  • Purified extracts of the seeds of Hibiscus sabdariffa may have some antihypertensive, antifungal and antibacterial effect. Toxicity tested low except for an isolated case of damage to the testes of a rat after prolonged and excessive consumption.[110]
  • Honey may reduce cholesterol.[111] May be useful in wound healing.[112]
  • Lemon grass (Cymbopogon citratus), administered daily as an aqueous extract of the fresh leaf, has lowered total cholesterol and fasting plasma glucose levels in rats, as well as increasing HDL cholesterol levels. Lemon grass administration had no effect on triglyceride levels. [113]
  • Magnolia
  • Milk thistle extracts have been recognized for many centuries as "liver tonics.".[114] Research suggests that milk thistle extracts both prevent and repair damage to the liver from toxic chemicals and medications.[115]
  • Nigella sativa (Black cumin) has demonstrated analgesic properties in mice. The mechanism for this effect, however, is unclear. In vitro studies support antibacterial, antifungal, anticancer, anti-inflammatory and immune modulating effects.[116][117][118][119][120][121][122][123][124][125][126][127] However few randomized double blind studies have been published.
  • Ocimum gratissimum[128][129] and tea tree oil can be used to treat acne.
  • Oregano may be effective against multi-drug resistant bacteria.[130]
  • Pawpaw can be used as insecticide (killing lice, worms).[131],[132]
  • Peppermint oil may have benefits for individuals with irritable bowel syndrome.[133][134]
  • Phytolacca or Pokeweed is used as a homeopathic remedy to treat many ailments. It can be applied topically or taken internally. Topical treatments have been used for acne and other ailments. It is used to treatment tonsilitis, swollen glands and weight loss.[citation needed]
  • Pomegranate contains the highest percentage of ellagitannins of any commonly consumed juice. Punicalagin, an ellagitannin unique to pomegranate, is the highest molecular weight polyphenol known.[135] Ellagitannins are metabolized into urolithins by gut flora, and have been shown to inhibit cancer cell growth in mice.[136][137]
  • Rauvolfia Serpentina, high risk of toxicity if improperly used[citation needed], used extensively in India for sleeplessness, anxiety, and high blood pressure.[138]
  • Rooibos (Aspalathus linearis) contains a number of phenolic compounds, including flavanols, flavones, flavanones, flavonols, and dihydrochalcones.[139] Rooibos has traditionally been used for skin ailments, allergies, asthma and colic in infants.[140] In an animal study with diabetic mice, aspalathin, a rooibos constituent improved glucose homeostasis by stimulating insulin secretion in pancreatic beta cells and glucose uptake in muscle tissue.[141]
  • Rose hips – Small scale studies indicate that hips from Rosa Canina may provide benefits in the treatment of osteoarthritis.[142][143][144]Rose hips show anti COX activity.[145]
  • Salvia lavandulaefolia may improve memory[146]
  • Saw Palmetto can be used for BPH. Supported in some studies,[147] failed to confirm in otherrs.[148]
  • Shiitake mushrooms (Lentinus edodes) are edible mushrooms that have been reported to have health benefits, including cancer-preventing properties.[149] In laboratory research a shiitake extract has inhibited the growth of tumor cells through induction of apoptosis.[150] Both a water extract and fresh juice of shiitake have demonstrated antimicrobial activity against pathogenic bacteria and fungi in vitro.[151][152]
  • Soy and other plants that contain phytoestrogens (plant molecules with estrogen activity) (black cohosh probably has serotonin activity) have some benefits for treatment of symptoms resulting from menopause.[153]
  • St. John's wort, has yielded positive results, proving more effective than a placebo for the treatment of mild to moderate depression in some clinical trials[154] A subsequent, large, controlled trial, however, found St. John's wort to be no better than a placebo in treating depression[155] However, more recent trials have shown positive results[156][157][158] or positive trends that failed significance.[159] A 2004 meta-analysis concluded that the positive results can be explained by publication bias[160] but later analyses have been more favorable.[161][162]The Cochrane Database cautions that the data on St. John's wort for depression are conflicting and ambiguous.[163]
  • Stinging nettle In some clinical studies effective for enign prostatic hyperplasia[164] and the pain associated with osteoarthritis.[165] In-vitro tests show antiinflammatory action.[166] In a rodent model, stinging nettle reduced LDL cholesterol and total cholesterol. [167] In another rodent study it reduced platelet aggregation.[168]
  • Valerian root can be used to treat insomnia. Clinical studies show mixed results and researchers note that many trials are of poor quality.[169][170][171]
  • Vanilla

Metabolism is the set of chemical reactions that occur in living organisms in order to maintain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories. Catabolism breaks down organic matter, for example to harvest energy in cellular respiration. Anabolism, on the other hand, uses energy to construct components of cells such as proteins and nucleic acids.

SECONDARY METABOLISM

Secondary metabolites are organic compounds that are not directly involved in the normal growth, development or reproduction of organisms. Unlike primary metabolites, absence of secondary metabolities results not in immediate death, but in long-term impairment of the organism's survivability/fecundity or aesthetics, or perhaps in no significant change at all. Secondary metabolites are often restricted to a narrow set of species within a phylogenetic group

Function

The function or importance of these compounds to the organism is usually of an ecological nature as they are used as defenses against predators, parasites and diseases, for interspecies competition, and to facilitate the reproductive processes (coloring agents, attractive smells, etc). Since these compounds are usually restricted to a much more limited group of organisms, they have long been of prime importance in taxonomic research.

Secondary metabolites may be likely candidates for drug or other technological development directly, or as an inspiration for unnatural products. This will concern secondary metabolites in plants, bacteria, fungi and many marine organisms (sponges, tunicates, corals, snails). In some cases, higher organisms will host a microorganism which is the actual producer of the product in question, as part of a symbiotic relationship.

Categories of Secondary metabolites:

Most of the secondary metabolites of interest to humankind fit into categories which classify secondary metabolites based on their biosynthetic origin. Since secondary metabolites are often created by modified primary metabolite synthases, or "borrow" substrates of primary metabolite origin, these categories should not be interpreted as saying that all molecules in the category are secondary metabolites (for example the steroid category), but rather that there are secondary metabolites in these categories.

Small Molecules

Big "small molecules", produced by large, modular, "molecular factories"



Alkaloids are naturally occurring chemical compounds containing basic nitrogen atoms.[1] The name derives from the word alkaline and was used to describe any nitrogen-containing base. Alkaloids are produced by a large variety of organisms, including bacteria, fungi, plants, and animals and are part of the group of natural products (also called secondary metabolites). Many alkaloids can be purified from crude extracts by acid-base extraction. Many alkaloids are toxic to other organisms. They often have pharmacological effects and are used as medications and recreational drugs. Examples are the local anesthetic and stimulant cocaine, the stimulant caffeine, nicotine, the analgesic morphine, or the antimalarial drug quinine. Some alkaloids have a bitter taste.



YOU ARE TO GO TO THE FOLLOWING SITE http://www.genome.jp/kegg/plant/
AND CHECK OUT THE SECONDARY METABOLIC PATHWAYS OF PLANTS.

Ethnobotany (from "ethnology" - study of culture[1] and "botany" - study of plants) is the scientific study of the relationships that exist between people and plants.

Ethnobotanists aim to reliably document, describe and explain complex relationships between cultures and (uses of) plants: focusing, primarily, on how plants are used, managed and perceived across human societies (eg. as foods; as medicines; in divination; in cosmetics; in dyeing; as textiles; in construction; as tools; as currency; as clothing; in literature; in rituals; and in social life.)[2]


Source Wikipedia.org
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martes, 17 de febrero de 2009

The Plant Kingdom

Text taken from this website

http://4e.plantphys.net/article.php?ch=1&id=399


The Plant Kingdom

Since the time of Aristotle (384–322 B.C.E.), biologists have sought to classify organisms. At first the purpose was ease of identification ("artificial" classification schemes). Carolus Linnaeus (1707–1778), arguably the greatest of the pre-modern Naturalists, sought to classify plants and other organisms according to affinity groups that reflected the mind of the Creator. Later, after Darwin, the goal of classification was to show evolutionary relationships ("natural" classification schemes). For the past 150 years, biologists have emphasized natural systems of classification and have attempted to define morphological criteria that reveal evolutionary relationships.

We now know that morphology, the form and structure of organisms, is the end product of the actions of genes. Virtually all of the information needed to form a complete organism is encoded in its DNA sequences, both nuclear and cytoplasmic (mitochondria and chloroplasts). DNA sequence analysis has thus provided evolutionary biologists with a powerful new tool for arriving at a truly natural classification system

On the basis of phylogenetic analyses of highly conserved DNA sequences, living organisms have been divided into three major domains: Bacteria, Archaea, and Eucarya (Woese et al. 1990) (Web Figure 1.1.A).

1
Web Figure 1.1.A Natural classification scheme and phylogeny of living organisms, including endosymbiotic events.
  1. The common ancestor of all the organisms first gave rise to the Bacteria and the common ancestor of the Archaea and the Eucarya.
  2. The Archaea branch off from the Eucarya lineage.
  3. The Eucarya common ancestor acquires mitochondrial endosymbiont (an alpha-proteobacterium-like cell).
  4. A heterogeneous group of eukaryotes called protists branch off the lineage leading to plants, fungi, and animals.
  5. The common ancestor of fungi and animals form a branch, followed by a divergence into the fungal and animal lineages.
  6. The common ancestor of plants, green algae, red algae, and glaucophytes acquires chloroplast endosymbiont (a cyanobacterium).
  7. The three lineages of glaucophytes, red algae, and green algae diverge.
  8. Various lineages of protists acquire chloroplasts via green or red algal endosymbionts.
  9. The earliest branch of green algae (Green Algae I) diverge.
  10. The later branch of green algae (Green Algae II, Characeae, Coleochaetales) diverge.
  11. The remaining lineage leads to plants.
(Phylogenetic tree courtesy of Dr. J. Peter Gogarten, Dept. of Molecular and Cell Biology, University of Connecticut) (Click image to enlarge.)

The Eucarya include the eukaryotes, organisms whose cells contain a true nucleus. The Bacteria, or eubacteria, which include the cyanobacteria, lack a true nucleus and are therefore prokaryotic. The Archaea, or archaebacteria, are also prokaryotic, but they differ from the Bacteria: Besides their morphological and biochemical differences, they are often adapted to extreme environments, such as sulfur hot springs or saline ponds. Phylogenetic studies have indicated that the Archaea and Eucarya split after the Bacteria separated from the common ancestor. Thus Archaea and Eucarya represent sister groups. This closer relation between Archaea and Eucarya is reflected in their similar promoter structures and RNA polymerases, the presence of histones, and many other characteristics.

Fungi were formerly classified as algal-like plants that had lost their chloroplasts. However, as the phylogenetic tree in Web Figure 1.1.A shows, fungi and animals branched off from the Eucarya lineage before the appearance of choloroplasts. They are thus more closely related to animals than to plants. Fungi are heterotrophic; that is, they depend on other organisms for their food, and they satisfy their nutritional needs by absorbing inorganic ions and organic molecules from the external environment. Most fungal species are filamentous and possess cell walls made of chitin, the same substance that is found in insect exoskeletons.

A recent phylogenetic tree of the plant kingdom is shown in Web Figure 1.1.B.

1
Web Figure 1.1.B Phylogenetic Tree of the plant kingdom, with approximate time scale on the horizontal axis. Modified from: Palmer, J.D. et al. 2004. The plant tree of life: an overview and some points of view. Am. J. Bot. 91, 1437–1445.

(Courtesy of Dr. Jeffrey D. Palmer, Department of Biology, Indiana University, Bloomington) (Click image to enlarge.)

Bryophytes are small (rarely more than 4 cm in height), very simple land plants, and the least abundant in terms of number of species and overall population. Bryophytes do not appear to be in the direct line of evolution leading to the vascular plants; rather, they seem to constitute a separate minor branch. Bryophytes include mosses, liverworts, and hornworts. These small plants have life cycles that depend on water during the sexual phase. Water facilitates fertilization, the fusion of gametes to produce a diploid zygote, a feature also seen in the algal precursors of these plants. Bryophytes are like algae in other respects as well: They have neither true roots nor true leaves, they lack a vascular system, and they produce no hard tissues for structural support. The absence of these structures that are important for growth on land greatly restricts the potential size of bryophytes, which, unlike algae, are terrestrial rather than aquatic.

The ferns represent the largest group of spore-bearing vascular plants. In contrast to the bryophytes, ferns have true roots, leaves, and vascular tissues, and they produce hard tissues for support. These architectural features enable ferns to grow to the size of small trees. Although ferns are better adapted to the drying conditions of terrestrial life than bryophytes are, they still depend on water as a medium for the movement of sperm to the egg. This dependence on water during a critical stage of their life cycle restricts the ecological range of ferns to relatively moist habitats.

The most successful terrestrial plants are the seed plants. Seed plants have been able to adapt to an extraordinary range of habitats. The embryo, protected and nourished inside the seed, is able to survive in a dormant state during unfavorable growing conditions such as drought. Seed dispersal also facilitates the dissemination of the embryos away from the parent plant.

Another important feature of seed plants is their mode of fertilization. Fertilization in seed plants is brought about by wind- or insect-mediated transfer of pollen, the gamete-producing structure of the male, to the sexual structure of the female, the pistil. Pollination is independent of external water, a distinct advantage in terrestrial environments. Many seed plants produce massive amounts of woody tissues, which enable them to grow to extraordinary heights. These features of seed plants have contributed to their success and account for their wide range.

There are two categories of seed plants: gymnosperms (from the Greek for "naked seed") and angiosperms (based on the Greek for "vessel seed," or seeds contained in a vessel). Gymnosperms are the less advanced type; about 700 species of gymnosperms are known. The largest group of gymnosperms is the conifers ("cone-bearers"), which include such commercially important forest trees as pine, fir, spruce, and redwood.

Two types of cones are present: male cones, which produce pollen, and female cones, which bear ovules. The ovules are located on the surfaces of specialized structures called cone scales. After wind-mediated pollination, the sperm reaches the egg via a pollen tube, and the fertilized egg develops into an embryo. Upon maturation, the cone scales, which are appressed during early development, separate from each other, allowing the naked seeds to fall to the ground.

Angiosperms, the more advanced type of seed plant, first became abundant during the Cretaceous period, about 100 million years ago. Today, they dominate the landscape, easily outcompeting their cousins, the gymnosperms. About 250,000 species are known, but many more remain to be characterized. A typical angiosperm life cycle, that of Zea mays (corn), is shown in Web Figure 1.1.C. The major innovation of the angiosperms is the flower; hence they are referred to as flowering plants. There are other anatomical differences between angiosperms and gymnosperms, but none so crucial and far-reaching as the mode of reproduction.

1
Web Figure 1.1.C Life cycle of corn (Zea mays), a monocot. The vegetative plant represents the diploid sporophyte generation. Meiosis occurs in the male and female flowers, represented by the tassels and ears, respectively. The haploid microspores (male spores) develop into pollen grains, and the single surviving haploid megaspore (female spore) divides mitotically to form the embryo sac (megagametophyte). The egg forms in the embryo sac. Pollination leads to the formation of a pollen tube containing two sperm cells (the microgametophyte). Finally, double fertilization results in the formation of the diploid zygote, the first stage of the new sporophyte generation, and the triploid endosperm cell. (Click image to enlarge.)

Flower Structure and the Angiosperm Life Cycle

The flower consists of several leaflike structures attached to a specialized region of the stem called the receptacle (Web Figure 1.2.A). Sepals and petals are the most leaflike. Petals have the primary function of attracting insects to serve as pollinators, accounting for their often showy and brightly colored appearance. The stamen is the male sexual structure, and the pistil is the female sexual structure. The pistil is composed of one or more united carpels; the pistil, or in some flowers a whorl of pistils, is sometimes referred to as the gynoecium. The stamen consists of a narrow stalk called the filament and a chambered structure called the anther. The anther contains tissue that gives rise to pollen grains. The pistil consists of the stigma (the tip where pollen lands during pollination), the style (an elongated structure), and the ovary. The ovary, the hollow basal portion of the pistil, completely encloses one or more ovules. Each ovule, in turn, contains an embryo sac, the structure that gives rise to the female gamete, the egg.

2
Web Figure 1.2.A Schematic representation of an idealized flower of the angiosperms. (Click image to enlarge.)

After landing on the stigma, the pollen grain germinates to form a long pollen tube, which penetrates the tissues of the style and ultimately enters the cavity of the ovary, which houses the ovule. Within the ovary, the pollen tube enters the ovule and deposits two haploid sperm cells in the embryo sac (see Web Figure 1.2.B). One sperm cell fuses with the egg to produce the zygote; the other typically fuses with the two polar nuclei to produce a specialized storage tissue termed the endosperm, which provides nutrients to the growing embryo. Endosperm tissue also provides the bulk of the worldrquote s food supply in the form of cereal grains. As in conifers, in angiosperms the outer tissues of the ovule harden into a protective seed coat. Angiosperm seeds have a second layer of protective tissues, the fruit. The fruit consists of the ovary wall and, in some cases, receptacle tissue.



Angiosperms are divided into two major groups, dicotyledons (dicots) and monocotyledons (monocots). This distinction is based primarily on the number of cotyledons, or seed leaves. In addition, the two groups differ with respect to other anatomical features, such as the arrangement of their vascular tissues, and their floral structure.

As the dominant plant group on Earth, and because of their great economic and agricultural importance, angiosperms have been studied much more intensively than other types of plants, and they are discussed extensively in this book. Plant physiologists have focused on a relatively small number of species that represent convenient experimental systems for the study of specific phenomena. Therefore, while we focus on these famous few, it is important to keep in mind the tremendous diversity of form and function that exists within the angiosperms, and the even greater diversity of form and function that is found within the plant kingdom as a whole.


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Selected Themes in Biology II

This is the Blog for the class Selected Themes in Biology II.

This Class has no text book so this is going to be your text book from now on, due to complaints from the administration because they did not want to copy entire chapters of books for you based on copyright infringement violations.

Any complaints about unavailability of computer or access to internet should be taken to administration.

You are required to check this blog daily for your reading assignments.

You may also write commentaries on the entries.
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