botany

• Biology is the study of living organisms
• The detailed description of their form and appearance only brought out their diversity
• It is the cell theory that emphasised the unity underlying this diversity of forms, i.e., the cellular organisation of all life forms
• Cell theory also created a sense of mystery around living phenomena, i.e., physiological and behavioural processes
• The requirement of integrity of cellular organisation for living phenomena to be demonstrated or observed
• Physico-chemical approach to study and understand living organisms

  1. Analysis of living tissues for elements and compounds

  2. Describe the various processes in molecular terms

  3. Explain the abnormal processes that occur during any diseased condition
• Reductionist Biology


  The physico-chemical approach to study and understand living organisms
• In Chapter 9 of this unit, a brief description of biomolecules is provided
• All organisms are composed of cells
• Unicellular organisms


  Organisms composed of a single cell
• Multicellular organisms


  Organisms composed of many cells
• Both Unicellular and multicellular organisms are capable of independent existence and performing the essential functions of life
• Anything less than a complete structure of a cell does not ensure independent living
• Cell is the fundamental structural and functional unit of all living organisms
• Matthias Schleiden, a German botanist, examined a large number of plants and observed that all plants are composed of different kinds of cells which form the tissues of the plant


  1838
• Theodore Schwann, a British Zoologist, studied different types of animal cells and reported that cells had a thin outer layer which is today known as the 'plasma membrane'


  1839
• Schwann proposed the hypothesis that the bodies of animals and plants are composed of cells and products of cells
• Schleiden and Schwann together formulated the cell theory
• Rudolf Virchow (1855) first explained that cells divided and new cells are formed from pre-existing cells (Omnis cellula-e cellula)
• Cell theory


  • All living organisms are composed of cells and products of cells
  • All cells arise from pre-existing cells
• Cells that have membrane bound nuclei are called eukaryotic whereas cells that lack a membrane bound nucleus are prokaryotic
• In both prokaryotic and eukaryotic cells, a semi-fluid matrix called cytoplasm occupies the volume of the cell
• Besides the nucleus, the eukaryotic cells have other membrane bound distinct structures called organelles
• Prokaryotic cells lack membrane bound organelles
• Ribosomes are non-membrane bound organelles found in all cells - both eukaryotic as well as prokaryotic
• Animal cells contain another non-membrane bound organelle called centrosome which helps in cell division
• Cells differ greatly in size, shape and activities
• The prokaryotic cells are represented by bacteria, blue-green algae, mycoplasma and PPLO (Pleuro Pneumonia Like Organisms)
• Prokaryotes have something unique in the form of inclusions
• A specialised differentiated form of cell membrane called mesosome is the characteristic of prokaryotes
• Bacterial cells may be motile or non-motile
• If motile, they have thin filamentous extensions from their cell wall called flagella
• Besides flagella, Pili and Fimbriae are also surface structures of the bacteria but do not play a role in motility
• In prokaryotes, ribosomes are associated with the plasma membrane of the cell
• Inclusion bodies: Reserve material in prokaryotic cells are stored in the cytoplasm in the form of inclusion bodies
• The eukaryotes include all the protists, plants, animals and fungi
• In eukaryotic cells there is an extensive compartmentalisation of cytoplasm through the presence of membrane bound organelles
• Eukaryotic cells possess an organised nucleus with a nuclear envelope
• Eukaryotic cells have a variety of complex locomotory and cytoskeletal structures
• Their genetic material is organised into chromosomes