Lecture 1 - Introduction to Plant Diversity (PEBO 102) PDF

PEBO 102: PLANT DIVERSITY (MORPHOLOGY & FUNCTION) LECTURE 1 INTRODUCTION TO DIVERSITY General Outline of the Lectures on Diversity Studies The diversity in Plant life can be understood from the following points: I. Diversity on The Basis of Classification (Representatives) II. Diversity on The...

PEBO 102: PLANT DIVERSITY (MORPHOLOGY & FUNCTION) LECTURE 1 INTRODUCTION TO DIVERSITY General Outline of the Lectures on Diversity Studies The diversity in Plant life can be understood from the following points: I. Diversity on The Basis of Classification (Representatives) II. Diversity on The Basis of Habitat III. Diversity on The Basis of Habit or Life form/ Morphology IV. Diversity on The Basis of Size V. Diversity on The Basis of Life-Cycle or Life-Span VI. Diversity on The Basis of Nutrition VII. Diversity on the Basis of Economic Importance or Usefulness Week 1: Introduction to Course Outline & Background to Plant Diversity Studies Introduction Introduction cont’d This course, PEBO 102 will focus on the study of diversity in plant forms (mosses, ferns, cone bearing/conifers & flowering plants) and other allied species (fungi and algae). Introduction cont’d Brief Background Traditionally, the term plants was used for a wide variety of organisms including the algae and fungi, but now modern botanists confine the term to mosses, ferns, cone-bearing plants/conifers and flowering plants, as well as the various relatives of each of these groups. Most modern textbooks, therefore, group members of the Plant Kingdom into three main categories: Non-vascular plants, i.e. mosses and their relatives (Byrophytes) Seedless vascular plants, i.e. ferns and their relatives (Pteridophytes) Seed plants, i.e. cone-bearing plants (Gymnosperms) and flowering plants (Angiosperms) CLASSIFICATION OF LIVING THINGS There are at least 5 million different kinds of organisms in the biosphere and this great diversity necessitated the classification of living things into groups with similar characteristics. Taxonomy is the scientific discipline that deals with the classification of living things. The practice of referring to organisms by Latin names began in the middle ages (i.e. between the 5th and 15th centuries) when Latin was the language of scholarship (learning).  Initially, organisms were grouped into genera (singular: genus) and were then identified by descriptive Latin phrase names, known as polynomials. For example, catnip (also known as catmint, catswort or “marijuana for cats”) was referred to as Nepeta floribus interrupte spicatus pedunculatus (meaning “Nepeta with flowers in an interrupted pedunculate spike”). By the end of the 17th century, the first word in such a polynomial was widely accepted to designate the name of the group, or genus, to which an organism belonged. Thus, phrases describing the different kinds of roses began with the genus name Rosa; all oak trees were identified with polynomials beginning with the word Quercus, and those referring to willows began with the word Salix.  Simpler system of classification of living things was introduced by the 18th century Swedish professor and naturalist, Carolus Linnaeus, whose two-volume publication (Species Plantarum) in 1753 contained brief analytical descriptions of every known species of plant at that time. Although in the Species Plantarum Linnaeus used polynomial designations and regarded them as the “proper” names for the species, he also added an important innovation to the system. In the margin of his publication, next to the proper names, he entered a single word which, together with the generic name, formed a convenient “shorthand” designation for the species. For example, taking into consideration a more familiar characteristic of the catnip plant, Linnaeus entered “cataria” (meaning “cat-associated”) in the margin next to its proper name; thus renaming it Nepeta cataria. The convenience of this binomial system of classification made it very popular and explains why it has remained in use till date.  In general, the scientific name of every species is a binomial consisting of two words – the generic name and the specific epithet. Thus the sweet pea (an annual leguminous climber native to the eastern Mediterranean) is scientifically known as Lathyrus odoratus. Lathyrus is the Greek word for pea and odoratus is a latin word meaning fragrant or perfumed. Note that usually an effort is made to ensure that the specific epithet (or species name) is descriptive.  specific epithet is meaningless when written alone. For example, odoratus could refer to any of the several different species of organisms that happen to have this word as part of their name. Incidentally, Sternotherus odoratus is a small turtle that is native to southeastern Canada and much of the eastern United States. It is also known as the common musk turtle or stinkpot due to its ability to release a foul musky odour from scent glands on the edge of its shell, possibly to deter predation.  Since a specific epithet could refer to a plant or animal species, as shown in the above examples, it is important that a specific epithet is always preceded by the name or initial letter of the genus in question; e.g. Lathyrus odoratus or L. odoratus. Scientific names are always printed in italics or are underlined when written or typed. It is not uncommon, particularly among cultivated plants, to have new races develop within a species. Thus species can be further divided into subspecies or varieties. The scientific names of subspecies or varieties may consist of three parts. For example, Lathyrus odorata var. nanellus is a trinomial referring to the dwarf sweet pea. THE MAJOR GROUPS OF LIVING THINGS A classification that depicts genetic relationships is said to be a natural or phylogenetic classification. Differences in photosynthetic pigments, manner of leaf development, structure of the conducting or vascular tissues, and modes of reproduction are some of the important features that are considered in separating plants into divisions.  Early taxonomists classified living things as either plant or animal. By definition, animals could move, eat breathe and had bodies that were definitely limited in size. Plants, on the other hand, could not move, eat or breathe, and were presumed to manufacture their own food and seemed to grow indefinitely. Thus, initially, fungi and bacteria were grouped with the plants and protozoa (e.g. Amoeba) were grouped with the animals.  However, taxonomists began to have challenges with organisms such as Chlamydomonas, which moves and manufactures its own food. Clearly, such an organism could not be classified as either plant or animal, and by the 1930s, it was evident that the traditional classification of living things into two distinct kingdoms needed to be revised. With the accumulation of new information, it has become evident that the most fundamental distinction in living organisms is that between the prokaryotes and the eukaryotes.  PROKARYOTES do not have true nuclei, i.e. their nuclei are not bound by a membrane. prokaryotic organisms lack membrane-bound cellular organelles Their genetic material is contained in a single circular molecule of DNA that is not associated with proteins. Although genetic recombination is known to occur in prokaryotes, it is achieved through division mechanisms other than sexual reproduction.  Reproduction is predominantly by cell division, and the mode of nutrition is mainly by absorption, although some are photosynthetic or chemosynthetic (Chemosynthesis is an alternate way to generate energy and make sugars to photosynthesis. Instead of using light as the energy source, chemosynthetic organisms use some chemical as the energy source. Typical chemicals for this are hydrogen sulfide, hydrogen or ammonia). They exhibit solitary unicellular or colonial unicellular organization, and are either motile by simple flagella or by gliding, or are non-motile. The cell walls of most prokaryotes contain muramic acid, and this and other biochemical peculiarities distinguish them from all other organisms. Prokaryotes are, therefore, recognized as a separate kingdom – the Kingdom Monera, which comprises all bacteria including cyanobacteria (the blue-green algae).  EUKARYOTES, on the other hand, have a definite nucleus bounded by a double membrane. Within the nuclear envelope are complex chromosomes in which the DNA is associated proteins. All eukaryotic organisms possess complex cellular organelles such as mitochondria, and most, especially plants, have vacuoles that are bounded by a single membrane or tonoplast.  Many eukaryotes also exhibit two important features that are absent in prokaryotes – integrated multicellularity and sexual reproduction. Although the cells of prokaryotes may remain together in filamentous or even three-dimensional masses following cell division, there is no overall integration of the entire mass due to the absence of protoplasmic connections between the individual cells. In plant eukaryotes, however, the protoplasts of contiguous cells are connected by plasmodesmata, whereas in animals the protoplasts are in more direct contact due to the absence of cell walls.  UNICELLULAR MULTICELLULAR Concept of Uni & Multicellularity Plants are generally multi- cellular photosynthetic organisms that are found essentially in water (aquatic) and on land (terrestrial). However, few are single-celled or unicellular.