Biology 🧬🦠

• 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
• Unicellular 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
• Anton Von Leeuwenhoek first saw and described a live cell
• Robert Brown later discovered the nucleus
• The invention of the microscope and its improvement leading to the electron microscope revealed all the structural details of the cell
• Cell theory

  • All living organisms are composed of cells and products of cells
  • All cells arise from pre-existing cells
• 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
• 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'
• Schwann also concluded, based on his studies on plant tissues, that the presence of cell wall is a unique character of the plant cells
• Rudolf Virchow first explained that cells divided and new cells are formed from pre-existing cells (Omnis cellula-e cellula)
• 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
• The cytoplasm is the main arena of cellular activities in both the plant and animal cells
• Besides the nucleus, the eukaryotic cells have other membrane bound distinct structures called organelles
• The prokaryotic cells lack such 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
• Mycoplasmas, the smallest cells, are only 0.3 µm in length while bacteria could be 3 to 5 µm
• The largest isolated single cell is the egg of an ostrich
• Among multicellular organisms, human red blood cells are about 7.0 µm in diameter
• Nerve cells are some of the longest cells
• The shape of the cell may vary with the function they perform
• The prokaryotic cells are represented by bacteria, blue-green algae, mycoplasma and PPLO (Pleuro Pneumonia Like Organisms)
• Prokaryotic cells are generally smaller and multiply more rapidly than the eukaryotic cells
• The four basic shapes of bacteria are bacillus (rod like), coccus (spherical), vibrio (comma shaped) and spirillum (spiral)
• All prokaryotes have a cell wall surrounding the cell membrane except in mycoplasma
• The genetic material is basically naked, not enveloped by a nuclear membrane in prokaryotes