BIO 101 - General Biology (FUTIA) PDF

BIO 101 – GENERAL BIOLOGY(FUTIA) HISTORY AND PRESENT TRENDS IN CELL BIOLOGY First Cells Seen in Cork While the invention of the telescope made the Cosmos accessible to human observation, the microscope revealed the identities of microbes and shows what living forms were composed of. The cell was f...

BIO 101 – GENERAL BIOLOGY(FUTIA) HISTORY AND PRESENT TRENDS IN CELL BIOLOGY First Cells Seen in Cork While the invention of the telescope made the Cosmos accessible to human observation, the microscope revealed the identities of microbes and shows what living forms were composed of. The cell was first discovered and named by Robert Hooke in 1665. He remarked that it looked strangely similar to cellular or small rooms which monks inhabited, thus depriving the name. However, what Hooke actually saw was the dead cell walls of plant cells called the cork as it appeared under the microscope. Hooke’s description of these walls was published in Micrographia. The cell walls observed by Hooke gave no identification of the nucleus and other organelles found in most living cells. The first man to witness a live cell under a microscope was Anton van Leeuwenhoek, who in 1674 described the alga spirogyra. 1  BIO 101 – GENERAL BIOLOGY(FUTIA) Fig. 1 Electron Microscope of Cell (Source: Dennis Kunkel Microscopy, 2009) Formulation of the Cell Theory In 1838, Theodor Schwann and Matthias Schleiden were enjoying after-dinner coffee and talking about their studies on cells. It has been suggested that when Schwann heard Schleiden described plant cells with nuclei, he was struck by similarity of these plant cells to cells he had observed in animal tissues. The two scientists went immediately to Schwann’s lab to look at his slides. Schwann published his book on animal and plant cells Schwann (1839) the following, an account (a treatise) devoid of acknowledgements of anyone else’s contributions, including that of Schleiden (1838). He summarised his observations into three conclusions about cells:  The cell is the unit of structure, physiology, and organisation in living things.  The cell retains a dual existence as a distinct entity and a building block in the construction of organisms.  Cells form by free-cell formation, similar to the formation of crystals (spontaneous generation). We know today that the first two principles (tenets) are correct, but the third is clearly wrong. The correct interpretation of cell formation by division was finally promoted by others and formally enunciated in Rudolph Virchow’s powerful dictum, Omnis cellula e cellula…….. “All cells arise from pre-existing cells.” Modern Cell Theory Let us examine the following statements that represent the modern cell theory:  All known living things are made up of cells 2  BIO 101 – GENERAL BIOLOGY(FUTIA)  The cell is the structural functional unit of all living things  All cells arise from pre-existing cells by division. (Spontaneous Generation does not occur)  Cells contain hereditary information which is passed from cell to cell during cell division  All cells are basically the same in chemical composition  All energy flow (metabolism and biochemistry) of life occurs within cells. As with the rapid growth of molecular biology in the mid-20th century, cell biology research exploded in the 1950’s. it became possible to maintain, grow and manipulate cells outside of living organisms. The first continuous definition to be so cultured was in 1951 by George Otto Gey and coworkers, derived from cervical cancer cells taken from Henrietta Lacks, who died from the cancer in 1951. The cell line, which was eventually referred to as HeLa cells, have been the watershed in studying cell biology just as the structure of DNA was significant breakthrough of molecular biology. In an avalanche of progress in the study of cells, the coming decade included the characterisation of the minimal media requirements for cells and development of sterile cell culture techniques. You should also know that the study of cells was also aided by the prior advances in electron microscopy, and later advances such as development of transfection methods, discovery of small interfering RNA (siRNA), among others. A Timeline The following historical events are important in discussing cells and cell theory. 1595 - Jansen credited with 1st compound microscope 1655 - Hooke described ‘cells’ in cork 1674 - Leeuwenhoek discovered protozoa. He observed bacteria some nine years later 1833 - Brown described the cell nucleus in cells of the orchid 1838 - Schleiden and Schwann proposed cell theory 1840 - Albrecht von Roelliker realised that sperm cells and egg cells are also cell 1856 - N. Pringsheim observed how a sperm cell penetrate an egg cell 1858 - Rudolf Virchow (physician, pathologist and anthropologist) expounds his famous conclusion: omnis cellulae cellula, that is cells develop only from pre-existing 3  BIO 101 – GENERAL BIOLOGY(FUTIA) cells (cells come from pre-existing cells) 1857 - Kolliker described mitochondria 1879 - Flemming decribed chromosome behavior during mitosis 1883 - Germ cells are haploid, chromosome theory of heredity 1898 - Golgi described the Golgi apparatus 1938 - Behrens used differential centrifugation to separate nuclei from cytoplasm 1939 - Siemens produced the first commercial transmission electron microscope 1952 - Gey and coworkers established a continuous human cell line 1955 - Eagle systematically defined the nutritional needs of animal cells in culture 1957 - Meselson, Stahl and Vinograd developed density gradient centrifugation in cesium chloride solutions for separating nucleic acids 1965 - Ham introduced a defined serum-free medium. Cambridge Instruments produced the first commercial scanning electron microscope. 1976 - Sato And colleagues published different cell line that required different mixtures of hormones and growth factors in serumfree media. 1981 - Transgenic mice and fruit flies were produced. Mouse embryonic stem cell line was established. 1995 - Tsien identified mutant GFP with enhanced spectral properties 1998 - Mice were cloned from somatic cells 1999 - Hamilton and Baulcombe discovered siRNA as part of posttranscriptional gene silencing (PTGS) in plants. HISTORICAL VIEWPOINT OF CELL Histories of Cells Discoveries After the first observations of life under the microscope, it took two centuries of research before the 'cell theory’; the idea that all living things are composed of cells or their products were formulated. It proved even harder to accept that individual cells also make up nervous tissue. 4  BIO 101 – GENERAL BIOLOGY(FUTIA) The Jesuit priest Athanasius Kircher (1601−1680) showed, in 1658, that maggots and other living creatures developed in decaying tissues. In the same period, oval red-blood corpuscles were described by the Dutch naturalist Jan Swammerdam (1637−1680), who also discovered that a frog embryo consists of globular particles. Another new world of extraordinary variety,that of microorganisms, was revealed by the exciting investigations of another Dutchman, Antoni van Leeuwenhoek (1632−1723). The particles that he saw under his microscope were motile and, assuming that motility equates to life, he went on to conclude, in a letter of 9 October 1676 to the Royal Society, that these particles were indeed living organisms. In a long series of papers van Leeuwenhoek then described many specific forms of these microorganisms (which he called “animalcules”), including protozoa and other unicellular organisms. 5  BIO 101 – GENERAL BIOLOGY(FUTIA) Fig. 2 Leeuwenhoek Microscope (Source: Pelczar M.J. et al.,1986. Microbiology McGraw-Hill, International Editions) Under the microscope: drawings of the instruments used by Robert Hooke (left) and the cellular structure of cork according to Hooke (right) (reproduced from Micrographia, 1665). But the first description of the cell is generally attributed to Robert Hooke (1635−1702), an English physicist who was also a distinguished microscopist. In 1665 Hooke published Micrographia, the first important work devoted to microscopical observation, and showed what the microscope could mean for naturalists. He described the microscopic units that made up the structure of a slice of cork and coined the term "cells" or "pores" to refer to these units. Cella is a Latin word meaning 'a small room' and Latin-speaking people applied the word Cellulae to the six-sided cells of the honeycomb. By analogy, Hooke applied the term "cells" to the thickened walls of the dead cells of the cork. Although Hooke used the word differently to later cytologists (he thought of the cork cells as passages for fluids involved in plant growth), the modern term 'cell' comes directly from his book. Please note that the following scientists have contributed to the knowledge of the discoveries of cells. They are:  Hans and Zacharias Janssen (1595)  Dutch lens grinders, father and son  Produced first compound microscope of two lenses. Robert Hooke (1665)  English scientist  looked at a thin slice of cork (oak cork) through a compound microscope  observed tiny, hollow, room-like structures  called these structures 'cells' because they reminded him of the rooms that monks lived in 6  BIO 101 – GENERAL BIOLOGY(FUTIA)  only saw the outer walls (cell walls) because cork cells are not living. Anton van Leeuwenhoek (1674)  Dutch fabric merchant and amateur scientist  looked at blood, rainwater, scrapings from teeth through a simple microscope of one lens  observed living cells; called some 'animalcules'  some of the small 'animalcules' are now called bacteria. Matthias Schleiden (1838)  German botanist  viewed plant parts under a microscope  discovered that plant parts are made of cells. Theodor Schwann (1839)  German zoologist  viewed animal parts under a microscope  discovered that animal parts are made of cells Rudolph Virchow (1855)  German physician  stated that all living cells come only from other living cells. Bridge between Life and ‘Non-life? 7  BIO 101 – GENERAL BIOLOGY(FUTIA) The existence of an entire world of microscopic living things (microbes) was seen as a bridge between inanimate matter and living organisms that are visible to the naked eye. This seemed to support the old Aristotelian doctrine of 'spontaneous generation', according to which water or land bears the potential to generate, 'spontaneously', different kinds of organism. This theory, which implied continuity between living and non-living matter, natura non facit saltus, was disproved by the masterful experiments of the Italian naturalist Lazzaro Spallanzani (1729−1799). He and other researchers showed that an organism derives from another organism(s) and that a gap exists between inanimate matter and life. (But it was a century later before the idea of spontaneous generation was definitively refuted, by Louis Pasteur, 1822−1895) As a consequence, the search for the first elementary steps in the scala naturae was a motif in early-nineteenthcentury biological thought: what could be the minimal unit carrying the potential for life? Protoplasmic Constituents After Schleiden and Swann's formulation of cell theory, the basic constituents of the cell were considered to be a wall or a simple membrane and the nucleus. This simple membrane called “protoplasm” is a viscous substance. It soon became evident that the protoplasm was not a homogeneous fluid. Some biologists regarded its fine structure as fibrillary, whereas others described it as a reticular, alveolar or granular protoplasmic architecture. This discrepancy resulted partly from artefactual and illusory images due to fixation and staining procedures that caused a nonhomogeneous precipitation of colloidal complexes. Later, some staining of real cellular components led to the description of differentiated cellular elements, which were subsequently identified. The introduction of the oil- immersion lens in 1870, the development of the microtome technique and the use of new fixing methods and dyes greatly improved the identities of cellular components. Towards the end of the nineteenth century, the principal organelles that are now considered to be parts of the cell were identified. The term "ergastoplasm" (endoplasmic reticulum) was introduced in 1897; mitochondria were observed by several authors and named by Carl 8  BIO 101 – GENERAL BIOLOGY(FUTIA) Benda (1857−1933) in 1898. Camillo Golgi (1843−1926) discovered the intracellular apparatus, the golgi bodies in 1898. The protoplasm was not the only structure to have a heterogeneous appearance. Within the nucleus, the nucleolus and a stainable substance could be seen. Moreover, a number of structures (ribbons, bands and threads) appeared during cell division. As these structures could be heavily stained, they were called "chromatin" by Walther Flemming (1843−1905), who also introduced the term "mitosis" in 1882 and gave a superb description of its various processes. Flemming observed the longitudinal splitting of salamander chromosomes during metaphase and established that each half -chromosome moves to the opposite pole of the mitotic nucleus. This process was also observed in plants, providing further evidence of the deep unity of the living world. The Neuron Theory There was, however, a tissue that seemed to belie the cell theory, the nervous tissue. Because of its softness and fragility, it was difficult to handle and susceptible to deterioration. But it was its structural complexity that prevented a simple reduction to models derived from the cell theory. Nerve-cell bodies, nervous prolongations and nervous fibres were observed in the first half of the nineteenth century. However, attempts at reconstructing a three-dimensional structure of the nervous system were frustrated by the impossibility of determining the exact relationships between cell bodies (somas), neuronal protoplasmic processes (dendrites) and nervous fibres. In 1865, Karl Deiters posthumously published work contains beautiful descriptions and drawings of nerve cells studied by using histological methods and microdissections made with thin needles under the microscope. These nerve cells were characterised by a soma, dendrites and a nerve prolongation (axon) which showed no branching. Kölliker, in the fifth edition of his important book on histology, published in 1867, proposed that sensory and motor cells of the right and left halves of the spinal cord were linked “by anastomoses” (direct fusion). 9  BIO 101 – GENERAL BIOLOGY(FUTIA) In 1872, the German histologist, Joseph Gerlach (1820−1896) expanded Kölliker's view and proposed that, in all of the central nervous system, nerve cells established anastomoses with each other through a network formed by the minute branching of their dendrites. According to this concept, the network or reticulum was an essential element of grey matter that provided a system for anatomical and functional communications, a protoplasmic continuum from which nerve fibres originated. The most important breakthrough in neurocytology and neuroanatomy came in 1873 when Golgi developed the 'black reaction', which he announced to a friend with these few words, "I am delighted that I have found a new reaction to demonstrate, even to the blind, the structure of the interstitial stroma of the cerebral cortex. I let the silver nitrate react with pieces of brain hardened in potassium dichromate. I have obtained magnificent results and hope to do even better in the future." This reaction provided, for the first time, a full view of a single nerve cell and its processes, which could be followed and analysed even when they were at a great distance from the cell body. The great advantage of this technique is that, for reasons that are still unknown, a precipitate of silver chromate randomly stains black only a few cells (usually from 1 to 5%), and completely spares the others, allowing individual elements to emerge from the nervous puzzle. Aided by the black reaction, Golgi discovered the branching of the axon and found that, contrary to Gerlach's theory, dendrites are not fused in a network. Golgi, however, failed to go beyond the 'reticularistic paradigm'. He believed that the branched axons stained by his black reaction formed a gigantic continuous network along which the nervous impulse propagated. In fact, he was misled by an illusory network created by the superimposition and the interlocking of axons of separate cells. Golgi's network theory was, however, a substantial step forward because it emphasised, for the first time, the function of branched axons in connecting nerve cells. According to Gerlach and Golgi, the nervous system represented an exception to cell theory, being formed not by independent cells but rather by a gigantic syncytium. The unique structure and functions of the nerve cell could well justify an infringement of the general rule. 10  BIO 101 – GENERAL BIOLOGY(FUTIA) Matters changed quickly in the second half of the 1880s. In October 1886, the Swiss embryologist Wilhelm His (1831−1904) put forward the idea that the nerve-cell body and its prolongations form an independent unit. In discussing how the axons terminate at the motor plate and how sensory fibres originate at peripheral receptors such as the Pacinian corpuscles, he suggested that a separation of cell units might be true of the central nervous system. The nervous tissue began to be considered, like any other tissue, as a sum of anatomically and functionally independent cells, which interact by contiguity rather than by continuity. Similar conclusions were reached, at the beginning of 1887, by another Swiss scientist, the psychiatrist August Forel (1848−1931), and, in 1891, Waldeyer introduced the term "neurons" to indicate independent nerve cells. Thereafter, cell theory as applied to the nervous system became known as the 'neuron theory'. Ironically, it was by using Golgi’s black reaction that the Spanish neuroanatomist Santiago Ramón y Cajal (1852−1934) became the main supporter of the neuron theory. His neuroanatomical investigations contributed to the foundations of the basic concepts of modern neuroscience. However, definitive proof of the neuron theory was obtained only after the introduction of the electron microscope, which allowed identification of synapses between neurons. 11  BIO 101 – GENERAL BIOLOGY(FUTIA) THE CELL THEORY People and Things that have made History Anaximander A member of the Greeks in the sixth century B.C. who resided on the Ionian Islands. He is credited with coming up with the primary thoughts of evolution. His perspective was that creatures from the sea were forced to come ashore, thereby evolving into land creatures. Plato Plato did not directly aid in the progress of biological thinking. His view was not experimental, but more philosophical. Many of his students went on to influence the progression of biological studies in the field of classification. The Atomists The most noted of this group of Greek philosophers was Democritus (460 - 370 B.C.). He followed Anaximander's view of evolution. Democritus is credited as being the father of atomic theory which connects directly to biology. One important theory of his was simply that if you have nothing, nothing may be created out of it. Aristotle Aristotle (384 - 322 B.C.) was known for his experimental approach and numerous dissections. He was drawn to animal classification in order to discover aspects of connection between the soul and the human body. Some of his animal classifications still stand today. One of his famous thoughts is a foreshadowing of Mendelian genetic concepts:  “It is evident that there must be something or other really existing, corresponding to what we call by the name of Nature. For a given germ does not give rise to any random living being, nor spring from any chance one, but each germ springs from a definite parent and gives rise to a predictable progeny. And thus it is the germ that is the ruling 12  BIO 101 – GENERAL BIOLOGY(FUTIA) influence and fabricator of the offspring.” The Microscope This instrument opened up new doors in the field of biology, by allowing scientists to gaze into a new world: the cellular world. Galileo is credited with the invention of the microscope. Two of the main pioneers in microscope usage were Athanasius Kircher and Antonie von Leeuwenhoek. Robert Hooke This English naturalist (1635 - 1703) coined the term ”cell“ after viewing slices of cork through a microscope. The term came from the Latin word cella which means ”storeroom“ or ”small container“. He documented his work in the Micrographia, written in 1665. Jean-Baptiste De Lamarck The majority of this Frenchman's work (1744 - 1829) dealt with animal classification and evolution. He is credited with taking steps towards the creation of the cell theory with this saying:  “Every step which Nature takes when making her direct creations consists in organising into cellular tissue the minute masses of viscous or mucous substances that she finds at her disposal under favorable circumstances.” The Cell: An Individual Unit of Life In 1824, Rene Dutrochet discovered that” the cell is the fundamental element in the structure of living bodies, forming both animals and plants through juxtaposition.” In Berlin, Johannes Muller created connections between biology and medicine, prompting the connective thinking of his students, such as those of Theodore Schwann. Schwann created the term ”cell theory“ and declared that plants consisted of cells. This declaration 13  BIO 101 – GENERAL BIOLOGY(FUTIA) was made after that of Matthias Schlieden's (1804 - 1881) that animals are composed of cells. Biogenesis German pathologist Rudolf Virchow (1821 - 1902) altered the thought of cellular biology with his statement that” every cell comes from a cell“. Not even twenty years after this statement, processes of cell reproduction were being described. Virchow had completed the thought behind the basic cell theory. The Cell Theory Hints at the idea that the cell is the basic component of living organisms emerged well before 1838−1839, which was when the cell theory was officially formulated. Cells were not seen as undifferentiated structures. Some cellular components, such as the nucleus, had been visualised, and the occurrence of these structures in cells of different tissues and organisms hinted at the possibility that cells of similar organisation might underlie all living matter. The abbot Felice Fontana (1730−1805) glimpsed the nucleus in epithelial cells in 1781, but this structure had probably been observed in animal and plant cells in the first decades of the eighteenth century. The Scottish botanist Robert Brown (1773−1858) was the first to recognise the nucleus (a term that he introduced) as an essential constituent of living cells (1831). In the leaves of orchids, Brown observed "a single circular areola, generally somewhat more opaque than the membrane of the cell. This areola, or nucleus of the cell as perhaps it might be termed, is not confined to the epidermis, being also found not only in the pubescence of the surface, but in many cases in the parenchyma or internal cells of the tissue". Brown recognised the general occurrence of the nucleus in these cells and apparently thought of the organisation of the plant in terms of cellular constituents. Meanwhile, technical improvements in microscopy were being made. The principal drawback of microscopes since van Leeuwenhoek's time was what we now call 'chromatic aberration', which diminishes the resolution power of the instrument at high magnifications. Only in the 1830s were achromatic microscopes introduced, allowing more precise histological observations. Improvements were also made in tissue- 14  BIO 101 – GENERAL BIOLOGY(FUTIA) preservation and - treating techniques. In 1838, the botanist Matthias Jakob Schleiden (1804−1881) suggested that every structural element of plants is composed of cells or their products. The following year, a similar conclusion was elaborated for animals by the zoologist Theodor Schwann (1810−1882). He stated that "the elementary parts of all tissues are formed of cells" and that "there is one universal principle of development for the elementary parts of organisms and this principle is in the formation of cells." The conclusions of Schleiden and Schwann are considered to represent the official formulation of 'cell theory' and their names are almost as closely linked to cell theory as are those of Watson and Crick with the structure of DNA. According to Schleiden, however, the first phase of the generation of cells was the formation of a nucleus of "crystallization" within the intracellular substance (which he called the "cytoblast"), with subsequent progressive enlargement of such condensed material to become a new cell. This theory of 'free cell formation' was reminiscent of the old 'spontaneous generation' doctrine (although as an intracellular variant), but was refuted in the 1850s by Robert Remak (1815−1865), Rudolf Virchow (1821−1902) and Albert Kölliker (1817−1905) who showed that cells are formed through scission of pre- existing cells. Virchow's aphorism omnis cellula e cellula (every cell from a pre-existing cell) thus became the basis of the theory of tissue formation, even if the mechanisms of nuclear division were not understood at the time. Cell theory stimulated a reductionist approach to biological problems and became the most general structural paradigm in biology. It emphasised the concept of the unity of life and brought about the concept of organisms as "republics of living elementary units". As well as being the fundamental unit of life, the cell was also seen as the basic element of pathological processes. Diseases came to be considered (irrespective of the causative agent) as an alteration of cells in the organism. Virchow's Cellularpathologie was the most important pathogenic concept until, in this century, the theory of molecular pathology was developed. CELL 15  BIO 101 – GENERAL BIOLOGY(FUTIA) A cell is the basic structural and functional unit of a living organism. According to cell theory postulates, a cell is the basic building block of life, which makes anything alive and is self-sufficient to carry out all the fundamental functions of an organism. 16  BIO 101 – GENERAL BIOLOGY(FUTIA) What are Cell Organelles? The cellular components are called cell organelles. These cell organelles include both membrane and non-membrane bound organelles, present within the cells and are distinct in their structures and functions. They coordinate and function efficiently for the normal functioning of the cell. A few of them function by providing shape and support, whereas some are involved in the locomotion and reproduction of a cell. There are various organelles present within the cell and are classified into three categories based on the presence or absence of membrane. Organelles without membrane: 17  BIO 101 – GENERAL BIOLOGY(FUTIA) The Cell wall, Ribosomes, and Cytoskeleton are non-membrane-bound cell organelles. They are present both in the prokaryotic cell and the eukaryotic cell. Single membrane-bound organelles: Vacuole, Lysosome, Golgi Apparatus, Endoplasmic Reticulum are single membrane-bound organelles present only in a eukaryotic cell. Double membrane-bound organelles: Nucleus, mitochondria and chloroplast are double membrane-bound organelles present only in a eukaryotic cell. Assignment: Differentiate between the Prokaryotic and Eukaryotic cells and list their examples List of Cell Organelles and their Functions Plasma Membrane The plasma membrane is also termed as a Cell Membrane or Cytoplasmic Membrane. It is a selectively permeable membrane of the cells, which is composed of a lipid bilayer and proteins. The plasma membrane is present both in plant and animal cells. It functions as the selectively permeable membrane, by permitting the entry of selective materials in and out of the cell according to the requirement. In an animal cell, the cell membrane functions by providing shape and protects the inner contents of the cell. Based on the structure of the plasma membrane, it is regarded as the fluid mosaic model. According to the fluid mosaic model, the plasma membranes are subcellular structures, made of a lipid bilayer in which the protein molecules are embedded. Cytoplasm 18  BIO 101 – GENERAL BIOLOGY(FUTIA) The cytoplasm is present both in plant and animal cells. They are jelly-like substances, found between the cell membrane and nucleus. They are mainly composed of water, organic and inorganic compounds. The cytoplasm is one of the essential components of the cell, where all the cell organelles are embedded. These cell organelles contain enzymes, mainly responsible for controlling all metabolic activity taking place within the cell and are the site for most of the chemical reactions within a cell. Nucleus The nucleus is a double-membraned organelle found in all eukaryotic cells. It is the largest organelle, which functions as the control centre of the cellular activities and is the storehouse of the cell’s DNA. By structure, the nucleus is dark, round, surrounded by a nuclear membrane. It is a porous membrane (like cell membrane) and forms a wall between cytoplasm and nucleus. Within the nucleus, there are tiny spherical bodies called nucleolus. It also carries an essential structure called chromosomes. Chromosomes are thin and thread-like structures which carry another important structure called a gene. Genes are a hereditary unit in organisms i.e., it helps in the inheritance of traits from one generation (parents) to another (offspring). Hence, the nucleus controls the characters and functions of cells in our body. The primary function of the nucleus is to monitor cellular activities including metabolism and growth by making use of DNA’s genetic information. Nucleoli in the nucleus are responsible for the synthesis of protein and RNA. Endoplasmic Reticulum The Endoplasmic Reticulum is a network of membranous canals filled with fluid. 19  BIO 101 – GENERAL BIOLOGY(FUTIA) They are the transport system of the cell, involved in transporting materials throughout the cell.  There are two different types of Endoplasmic Reticulum: Rough Endoplasmic Reticulum – They are composed of cisternae, tubules, and vesicles, which are found throughout the cell and are involved in protein manufacture. Smooth Endoplasmic Reticulum – They are the storage organelle, associated with the production of lipids, steroids, and also responsible for detoxifying the cell. Mitochondria Mitochondria are called the powerhouses of the cell as they produce energy-rich molecules for the cell. The mitochondrial genome is inherited maternally in several organisms. It is a double membrane-bound, sausage-shaped organelle, found in almost all eukaryotic cells. The double membranes divide its lumen into two distinct aqueous compartments. The inner compartment is called a ‘matrix’ which is folded into cristae whereas the outer membrane forms a continuous boundary with the cytoplasm. They usually vary in their size and are found either round or oval in shape. Mitochondria are the sites of aerobic respiration in the cell, produces energy in the form of ATP and helps in the transformation of the molecules. For instance, glucose is converted into adenosine triphosphate – ATP. Mitochondria have their own circular DNA, RNA molecules, ribosomes (the 70s), and a few other molecules that help in protein synthesis. Plastids Plastids are large, membrane-bound organelles which contain pigments. Based on the type of pigments, plastids are of three types: 1. Chloroplast 20  BIO 101 – GENERAL BIOLOGY(FUTIA) Chloroplasts – Chloroplasts are double membrane-bound organelles, which usually vary in their shape – from a disc shape to spherical, discoid, oval and ribbon. They are present in mesophyll cells of leaves, which store chloroplasts and other carotenoid pigments. These pigments are responsible for trapping light energy for photosynthesis. The inner membrane encloses a space called the stroma. Flattened disc-like chlorophyll-containing structures known as thylakoids are arranged in a stacked manner like a pile of coins. Each pile is called a granum (plural: grana) and the thylakoids of different grana are connected by flat membranous tubules known as stromal lamella. Just like the mitochondrial matrix, the stroma of chloroplast also contains a double-stranded circular DNA, 70S ribosomes, and enzymes which are required for the synthesis of carbohydrates and proteins. 2. Chromoplasts – The chromoplasts include fat-soluble, carotenoid pigments like xanthophylls, carotene, etc. which provide the plants with their characteristic color – yellow, orange, red, etc. 3. Leucoplasts – Leucoplasts are colorless plastids which store nutrients. Amyloplasts store carbohydrates (like starch in potatoes), aleuroplasts store proteins, and elaioplasts store oils and fats. Ribosome Ribosomes are non membrane-bound and important cytoplasmic organelles found in close association with the endoplasmic reticulum. Ribosomes are found in the form of tiny particles in a large number of cells and are mainly composed of 2/3rd of RNA and 1/3rd of protein. They are named as the 70s (found in prokaryotes) or 80s (found in eukaryotes) The letter S refers to the density and the size, known as Svedberg’s Unit. Both 70S and 80S ribosomes are composed of two subunits. Ribosomes are either encompassed within the endoplasmic reticulum or are freely traced in the cell’s cytoplasm. Ribosomal RNA and Ribosomal proteins are the two components that together constitute ribosomes. The primary function of the ribosomes includes protein synthesis in all living cells that ensure the 21  BIO 101 – GENERAL BIOLOGY(FUTIA) survival of the cell. Golgi Apparatus Golgi Apparatus is also termed as Golgi Complex. It is a membrane-bound organelle, which is mainly composed of a series of flattened, stacked pouches called cisternae. This cell organelle is primarily responsible for transporting, modifying, and packaging proteins and lipids to targeted destinations. Golgi Apparatus is found within the cytoplasm of a cell and is present in both plant and animal cells. Microbodies Microbodies are membrane-bound, minute, vesicular organelles, found in both plant and animal cells. They contain various enzymes and proteins and can be visualized only under the electron microscope. Cytoskeleton It is a continuous network of filamentous proteinaceous structures that run throughout the cytoplasm, from the nucleus to the plasma membrane. It is found in all living cells, notably in the eukaryotes. The cytoskeleton matrix is composed of different types of proteins that can divide rapidly or disassemble depending on the requirement of the cells. The primary functions include providing the shape and mechanical resistance to the cell against deformation, the contractile nature of the filaments helps in motility during cytokinesis. Centrosome and Centrioles 22  BIO 101 – GENERAL BIOLOGY(FUTIA) The centrosome organelle is made up of two mutually perpendicular structures known as centrioles. Each centriole is composed of 9 equally spaced peripheral fibrils of tubulin protein, and the fibril is a set of interlinked triplets. The core part of the centriole is known as a hub and is proteinaceous. The hub connects the peripheral fibrils via radial spoke, which is made up of proteins. The centrioles from the basal bodies of the cilia and flagella give rise to spindle fibres during cell division. Vacuoles Vacuoles are mostly defined as storage bubbles of irregular shapes which are found in cells. They are fluid-filled organelles enclosed by a membrane. The vacuole stores the food or a variety of nutrients that a cell might need to survive. In addition to this, it also stores waste products. The waste products are eventually thrown out by vacuoles. Thus, the rest of the cell is protected from contamination. The animal and plant cells have different size and number of vacuoles. Compared to the animals, plant cells have larger vacuoles. CELL CYCLE Cell cycle refers to the series of events that take place in a cell, resulting in the duplication of DNA and division of cytoplasm and organelles to produce two daughter cells.” Phases of Cell Cycle Cell cycle or cell division refers to the series of events that take place in a cell leading to its maturity and subsequent division. These events include duplication of its 23  BIO 101 – GENERAL BIOLOGY(FUTIA) genome(Gap phase) and synthesis of the cell organelles(S phase) followed by division of the cytoplasm (Citokinesis). Human cells exhibit typical eukaryotic cell cycle and take around 24 hours to complete one cycle of growth and division. The duration of the cycle, however, varies from organism to organism and cell to cell. A typical eukaryotic cell cycle is divided into two main phases:- Namely: Interphase and Mphase (Mitotic phase) The interphase Also known as the resting phase of the cell cycle; interphase is the time during which the cell prepares for division by undergoing both cell growth and DNA replication. It occupies around 95% time of the overall cycle. The interphase is divided into three phases:- G1 phase (Gap 1) – G1 phase is the phase of the cell between mitosis and initiation of replication of the genetic material of the cell. During this phase, the cell is metabolically active and continues to grow without replicating its DNA. S phase (Synthesis) – DNA replication takes place during this phase. If the initial quantity of DNA in the cell is denoted as 2N, then after replication it becomes 4N. However the number of chromosomes does not vary, viz., if the number of chromosomes during G1 phase was 2n, it will remain 2n at the end of S phase. The centriole also divides into two centriole pairs in the cells which contain centriole. G2¬ phase (Gap 2) –During this phase, the RNA, proteins, other macromolecules required for multiplication of cell organelles, spindle formation, and cell growth are produced as the cell prepares to go into the mitotic phase. Some cells like cardiac cells in the adult animals do not exhibit division and some others only divide to replace those cells which have been either damaged or lost 24  BIO 101 – GENERAL BIOLOGY(FUTIA) due to cell death. Such cells which do not divide further attain an inactive G0 phase also known as Quiescent Phase after they exit the G1 phase. These cells remain metabolically active but do not divide unless called upon to do so. M phase This is the mitotic phase or the phase of the equational division as the cell undergoes a complete reorganization to give birth to a progeny that has the same number of chromosomes as the parent cell. The oTther organelles are also divided equally by the process of cytokinesis which is preceded by mitotic nuclear division. The mitotic phase is divided into four overlapping stages:- Prophase, Metaphase, Anaphase, and Telophase mitosis The process by which a eukaryotic cell separates the nuclear DNA and chromosomes and divides into two different but similar sets of nuclei is known as mitosis. The chromosomes are pulled apart by a mitotic spindle, which is a specialized structure consisting of microtubules. Cytokinesis 25  BIO 101 – GENERAL BIOLOGY(FUTIA) In this phase, the cytoplasm of the cell divides. It begins as soon as the mitosis ends. Plant cells are much tougher than animal cells, as they have a rigid cell wall and high internal pressure. Thus, cytokinesis occurs in plant and animal cells differently. M Phase  This is also known as the Equational division, as during this phase the number of chromosomes in the parent and daughter cells remain the same.  The most dramatic period of the cell cycle is when the reorganization of all the organelles takes place.  This phase is further divided into 4 phases, namely, Prophase Metaphase Anaphase Telophase Prophase  The first stage of mitosis is when the condensation of chromosomal material begins that leads to untangling of chromosomal material.  The centriole begins to move towards opposite poles of the cell.  Mitotic spindle initiates to assemble which is helped by the microtubules.  Chromosomes seem to be composed of two chromatids attached to the centromere.  The nuclear envelope, Golgi bodies, endoplasmic reticulum, and nucleolus disappear. 26  BIO 101 – GENERAL BIOLOGY(FUTIA) Metaphase Condensed chromosomes, which are now clearly visible in the microscope, spread in the cytoplasm because of the disintegration of the nuclear membrane and move to the centre or the equator of the cell forming a plane of alignment of the chromosomes known as the metaphase plate. The chromosomes are made up of 2 sister chromatids which are attached by a centromere. Centromeres have a disc-shaped structure known as kinetochores, which help in the attachment of spindle fibers to the chromosomes. Anaphase Each chromosome starts to split simultaneously and forms two sister chromatids (chromosomes of future daughter nuclei). These chromatids begin to move towards opposite poles. Centromeres which were at the poles until now, start to lead the way of chromatids towards the poles and begin to split. Telophase Chromosomes that have reached their respective poles start to decondense and cannot be seen individually anymore. Nuclear membrane, nucleolus, Golgi complex and ER appear. CYTOKINESIS This is the phase in which the cell divides into two daughter cells. In animal cells, a furrow in the plasma membrane appears which gradually 27  BIO 101 – GENERAL BIOLOGY(FUTIA) deepens and joins in the centre dividing the cell cytoplasm into two. In a plant cell, due to the presence of a cell wall, a cell plate starts to form at the centre of the cell which later forms a cell wall. Mitochondria, plastids and other cell organelles get distributed between the two daughter cells. In some organisms, the phenomenon of syncytium (multinucleate condition) takes place due to the absence of cytokinesis after karyokinesis. E.g., liquid endosperm in coconut. Significance of Mitosis Restricted to diploid cells in higher organisms and haploid cells of some lower plants and some insects like male bees (drones), wasps and ants. Produces diploid daughter cells with identical genetic material. The growth of multicellular organisms depends on mitosis. Helps in cell repair by dividing the cell to restore the nucleo-cytoplasmic ratio of the cell which is disturbed by cell growth. Helps in the replacement of the cells of the upper epidermis, blood cells, and cells of the lining of the gut. In plants, mitosis takes place in the apical and the lateral cambium which results in plant growth. Living And Non Living Things Introduction We can find many things around us, from mountains and oceans to plants and animals. 28  BIO 101 – GENERAL BIOLOGY(FUTIA) The earth in which we live is made up of several things. These “things” can be categorized into two different types – Living and Non-living Things. All living things breathe, eat, grow, move, reproduce and have senses. Non-living things do not eat, grow, breathe, move and reproduce. They do not have senses. Living things have “life,” though some might not show its evident signs. For instance, a tree would probably not react the same way a human would. It would not react when we hit it, and it might not be able to walk around. Though the signs of life displayed by them are not very observable, it does not make them non-living. Let us have a detailed look at the important characteristics of living and non-living things and the difference between the two. Living things Living things exist and are alive and are made of microscopic structures called cells. They grow and exhibit movement or locomotion. They experience metabolism, which includes anabolic and catabolic reactions. Living things are capable of producing a new life which is of their own kind through the process of reproduction. Living things have a particular life span and are not immortal. Cellular Respiration enables living organisms to acquire energy which is used by cells to perform their functions. They digest food for energy and also excrete waste from the body. Their life cycle can be summarised as follows – birth, growth, reproduction and death. Characteristics of Living Things Following are the important characteristics of living things: Living things exhibit locomotory motion, they move. Animals are able to move as they possess specialized locomotory organs, for example – Earthworms move through the soil surface through longitudinal and circular muscles. Plants move in order to catch 29  BIO 101 – GENERAL BIOLOGY(FUTIA) sunlight for photosynthesis Living things respire. Respiration is a chemical reaction, which occurs inside cells to release energy from the food. Transport of gases takes place. The food that is ingested through the process of digestion is broken down to release energy that is utilized by the body to produce water and carbon dioxide as by-products. Living things are sensitive to touch (and other stimuli as well) and have the capability to sense changes in their environment. They grow. Living things mature and grow through different stages of development. One of the striking features is that living things are capable of producing offspring of their own kind through the process of reproduction, wherein genetic information is passed from the parents to the offspring. They acquire and fulfil their nutritional requirements to survive through the process of nutrition and digestion, which involves engulfing and digesting the food. Some living organisms are also autotrophic, which means they can harness the sun’s energy to make their food (also known as autotrophs). The digested food is eliminated from the body through the process of excretion. Non-living things Non-living things are not alive. They do not possess life. They do not have cells and do not grow or show locomotion/movement. They do not undergo metabolism with anabolic and catabolic reactions. They do not reproduce. Non-living things do not have a life span. They do not respire as they do not require food for energy and hence do not excrete. They do not fall into any cycle of birth, growth or death. They are created and destroyed by external forces. Examples of non-living things include stones, pens, books, cycles, bottles, etc. Characteristics Of Non-living Things 30  BIO 101 – GENERAL BIOLOGY(FUTIA) The important characteristics of non-living things are mentioned below: Non-living things are lifeless. They do not have cells, and there is no protoplasm which forms the basis for life to exist. Lack of protoplasm leads means no metabolic activities. They do not have a definite and certain size of their own. They take the shape of the substance they are contained in, for example, a liquid takes the shape of its container. Stones, rocks and boulders are moulded by the changing environment and landscape. The change in the state of a non-living thing is due to an external influence. Non-living things “grow” by accretion. It occurs through adding materials externally. For example, A snowball may increase in size due to the accumulation of smaller units of its own on its outer surface. Non-living things never die as they do not have cells with a definite lifespan. Immortality is a distinguishing factor. Fundamental life processes such as reproduction, nutrition, excretion, etc. are absent in non-living things. Difference between living and non-living things Here are some of the major differences between living and non-living things: Living Things Non-Living Things They possess life. They do not possess life. Living things are capable of giving birth to their young ones. Non-living things do not reproduce. 31  BIO 101 – GENERAL BIOLOGY(FUTIA) For survival, living things depend on water, air and food. Non-living things have no such requirements Living things are sensitive and responsive to stimuli. Non-living things are not sensitive and do not respond to stimuli. Metabolic reactions constantly occur in all living things. There are no metabolic reactions in Non-living things. Living organisms undergo growth and development. Non-living things do not grow or develop. They have a lifespan and are not immortal. They have no lifespan and are immortal. Living things move from one place to another. Non-living things cannot move by themselves. They respire and the exchange of gases takes place in their cells. Non-living things do not respire. Example: Humans, animals, plants, insects. Example: Rock, pen, buildings, gadgets. Criteria for differentiating living things from non-living things For easy differentiation between living things and non-living things, scientists have come up with traits or characteristics that are unique to them. The criterion for classification is necessary to avoid the wrong grouping. Hence, science developed a basis for classification. Anything that has life is considered a living being. For example– humans, trees, dogs, etc. Things which have no life in them are considered non-living. For example– stone, mountain, watch, etc. Scientists have discovered a few criteria for differentiating living things from non-living 32  BIO 101 – GENERAL BIOLOGY(FUTIA) things. Here are some of them: Living beings can grow and develop. Living beings obtain and use energy. Living beings adapt to their environment. All living beings are made of one or more cells. Living beings respond to their environment or stimuli. All living things excrete to remove waste material from the body. Living beings have the ability to give birth to their young ones through the process of reproduction. All living beings require energy to perform different metabolic activities, and they gain energy from food/ nutrition. All living beings, apart from plants, move from one place to another. This type of movement is called locomotion. If something obeys a few of the rules, it cannot be categorized as a living thing. It has to follow all the given rules stringently. For example, an icicle, although it grows (increases its mass or length), is still a non-living thing since it cannot reproduce or respond to stimuli. Non-living things do not have any of the life processes, unlike living beings. Darwins Contribution Theory Evolution Darwin's Contribution: The Theory of Evolution Charles Darwin, an English naturalist of the 19th century made an extensive study of 33  BIO 101 – GENERAL BIOLOGY(FUTIA) nature for over 20 years. He collected the observations on animal distribution and the relationship between the living and extinct animals and finally found that the present living animals share similarities to some extent not only between them but also with the other species that existed millions of years ago and among which some have become extinct. Carles Darwin is known as the father of evolution due to his contribution to the establishment of the theory of evolution. His theory helped in removing all the conventional old beliefs which said that the formation of various species was a supernatural phenomenon or act of the Almighty. Darwin’s evolutionary theory of natural selection gave a more rational explanation of the formation of new species. As per natural selection, various species originated from a single species as a result of adaptation to the changing environment. Genetics Genetics is the branch of biology that deals with the study of heredity and its biological process. It also involves the study of genes, genomes and the cell cycle. What is Genetics? Genetics is termed as the study to understand the functioning of inheritance of traits from parents to offspring. The groundwork on which heredity stands is known as inheritance. It is defined as the procedure by which characteristics are handed down from one generation to the other. Gregor Johann Mendel is known as the “Father of Modern Genetics” for his discoveries on the basic principles of heredity. Variation, as the name suggests is the amount of dissimilarity that exists between children and their parentages. It can be determined to keep in view the behaviouristic, cytological, physiological, and morphological characters of individuals fitting into similar species. Genetics 34  BIO 101 – GENERAL BIOLOGY(FUTIA) Law of Inheritance by Gregor Mendel Garden Pea (Pisum Sativum) was the plant that Mendel experimented on for 7 years to get to the point to propose the laws of inheritance in live creatures. Mendel carefully chose seven distinct characteristics of Pisum Sativum for the investigation concerning hybridization. Mendel used true-breeding lines i.e. those that go through constant self- pollination and display steady characteristic inheritance. Principles of Inheritance When Mendel observed the monohybrid cross he proposed two laws of inheritance- Law of Dominance – Distinct elements termed as factors control the characteristics. These factors at all times exist as a couple. One of the constituent genes of the couple dominates over the former. Law of Segregation – Alleles don’t blend and the two characteristics are recuperated all through the gamete formation (in the F2 generation). The characters are apart from each other and pass on to diverse gametes. Comparable types of gametes are produced by Homozygous and Heterozygous produces diverse sorts of a gamete with varied characteristics. Incomplete Dominance It is the discovery that was done after Mendel’s work. Incomplete dominance is the situation in which both the alleles do not display a dominant trait resulting in a fine combination or a midway amid the characteristics of the alleles. Codominance When two alleles lack the dominant-recessive association and thus the duo affects the creature together. Law of Independent Assortment The separation of one set of characteristics is autonomous of the other set of characters when they are pooled in a hybrid. 35  BIO 101 – GENERAL BIOLOGY(FUTIA) The Chromosomal Theory of Inheritance Both genes and chromosomes exist in sets of two. The homologous chromosome contains the two alleles of a gene pair in the homologous sites. The coupling and split of a set of chromosomes will cause a split in the set of genes (factor) they carry. This united knowledge is termed the Chromosomal Theory of Inheritance. Sex Determination A particular nuclear arrangement was perceived by Henking. He perceived that this particular nuclear arrangement was found in only fifty per cent of sperms. He termed this body as x. Later, it was observed that the ova which only obtained the X chromosome matured and were born as females and those that didn’t receive only X chromosomes were born as males. Thus, the X- chromosome was termed a sex chromosome and the remaining ones were termed autosomes. The occurrence due to which a modification in DNA happens and causes a variation in the phenotype and genotype of a creature is termed a Mutation. Principles of Heredity What is Heredity? In Biology, heredity is the term used for transmission of the traits from one generation to the next generation. It is due to heredity that the offsprings look similar to their parents. It also explains why dogs always give birth to puppies and never to kittens. The process of heredity is universal among all living organisms. Genetic variation refers to the variation in a population or species. Genetics is the study of heredity and variation in living organisms. Transmission genetics and cytogenetics have helped scientists investigate the biological basis of heredity. In transmission genetics, organisms are crossed to study the inheritance pattern in offsprings. Cytological techniques help in understanding cellular reproduction. With the advancement of molecular biology and its tools and techniques, geneticists are able to understand the genetic basis of the inheritance of 36  BIO 101 – GENERAL BIOLOGY(FUTIA) traits and variations present in various organisms. Genetics Genetics is the science which deals with the mechanisms responsible for similarities and differences among closely related species. The term ‘genetic’ was coined by William Bateson in 1905. It is derived from the Greek word ‘genesis’ meaning grow into or to become. So, genetics is the study of heredity and hereditary variations, it is the study of the transmission of body features: i.e., similarities and difference, from parents to offspring and the laws related to this transmission. Variation Any differences present between individuals of any species, caused either by genetic difference or by the effect of environmental factors, is called variation. Variation can be shown in physical appearance, metabolism, behaviour, learning and mental ability, and other obvious characters. Types of Variation Variations can be categorised into two types: Genotypic variations: – Genotypic variations refer to the differences in the genome, it may be due to structure or number of chromosomes present in the cells or difference in the genetic constituents of the chromosomes. Skin, hair, eye colour, height are some of the genotypic variations in animals. A variation can only be confirmed as genotypic by doing cross-breeding experiments. Somatic variations: – Somatic variations are not hereditary. These are not due to changes in the alleles or chromosomes. These are due to various factors such as nutrition, climate and due to other social interactions. Heredity Heredity refers to the transmission of traits from parents to offsprings. Heredity is 37  BIO 101 – GENERAL BIOLOGY(FUTIA) responsible for the resemblance among individuals of the same species. Mendel’s Laws of Heredity Gregor Johann Mendel is known as the father of genetics. He was the first to show the inheritance pattern of traits from one generation to the next generation. He did his research on the garden pea, Pisum sativum. He selected 7 pairs of contrasting traits like the red and yellow colour of the pod, round and wrinkled seeds, tall and short plants, etc. and crossbred the plants to understand their inheritance pattern. Mendel gave three fundamental laws of inheritance. Law of dominance: States that in the heterozygous condition of the genotype for a pair of alleles, the alleles which express itself phenotypically is dominant and the one which can’t express is recessive. Law of segregation: States that although the alleles of a character remain together for a long time, they do not mix with each other and separate at the time of gametogenesis so that each gamete receives only one allele of a trait, which is either dominant or recessive. When tall pea plants of the F1 generation (obtained by crossing homozygous tall and dwarf pea plants), are self-fertilised, we get tall and dwarf plants in the ratio of 3:1. Law of Independent assortment: States that when more than a pair of characters are taken into consideration, alleles of a character can undergo any sort of combination to give rise to a phenotype differing from both the parents. Notations used in Breeding Experiments The dominant trait – Upper case letter, e.g. Tallness is represented by ‘T’ The recessive trait – Lower case letter, e.g. Dwarfness by ‘t’ Homozygous – A pair of same alleles, e.g. TT (homozygous dominant) or tt (homozygous recessive) Heterozygous – Having different alleles of a trait, e.g. Tt 38  BIO 101 – GENERAL BIOLOGY(FUTIA) The Theory of Evolution Darwin had the following ideas regarding the theory of natural selection: Species keep on evolving or changing with time. As the environment changes, the requirements of an organism also change and they adapt to the new environment. This phenomenon of changing over a period of time as per the natural requirements is called adaptation. As per Darwin’s theory, only the superior changes are naturally selected and the inferior ones are eliminated. Thus, not all adaptations contribute to progressive evolution. For example, people living in tropical countries have more melanin in their bodies to protect them from the sunlight. Almost all organisms share common ancestry with some organisms. According to Darwin, all organisms had one common ancestor at some point in time and kept on diverging ever since. His evolutionary theories support the convergent theory and divergent theory of evolution with examples. He also studied that the birds of Galapagos Island (Darwin’s finches) developed different beaks as per the availability of the food. This proved adaptive radiation. Similarly, he also observed the Australian Marsupials which showed a number of marsupials emerging from an ancestor. According to Charles Darwin, evolution is a very slow and gradual process. He concluded that evolution took place over a very long period of time. As we talk about the time period in evolution we usually refer to billions of years. The generation of a species from another takes a long period of time. It is a very steady process as the changes and adaptation take a long time to stabilize and give rise to a new species. Natural selection takes place in four different ways as follows: Variation – The changes accumulated over a period of time in an organism usually give rise to a new species. Inheritance – It is the passing on of the variations over generations which ultimately 39  BIO 101 – GENERAL BIOLOGY(FUTIA) leads to speciation. A high rate of growth of population – This gives rise to more organisms being reproduced by a species than the environment can support. Differential survival and reproduction – The superior variations lead to the survival of a particular organism and the inferior or negative variations lead to extinction. The superior variations are the ones inherited during reproduction. 40  BIO 101 – GENERAL BIOLOGY(FUTIA) Biological Evolution Table of Contents Introduction Biological Evolution Natural Selection and Genetic Drift Introduction The word ‘evolution’ was first mentioned in the book ‘The Origin of Species’ in 1859, by Charles Darwin. Darwin put forward the concept of evolution during his journey to the Galapagos Islands. He noted that all living species change both their physical and anatomical structure over a long period of time for better adaptations to the developing environment. The difference is by natural process and the species which do not get adjusted will find it difficult to survive. This was the proposed concept of natural selection and Darwin called it ‘Survival of the fittest. Biological evolution Evolution is a scientific theory mainly used by biologists to explain how living species change their characteristics for their better adaptations to the changing environment. It is the successive adjustment of inherited traits over a huge span of time, usually over generations. Researchers consider it as a process as well as the outcome of a process. Evolution as a process explains how the world came to exist. Sometimes it is explained as the outcome of various processes which resulted in biodiversity. Natural selection is one among them. Darwin’s concept of evolution is natural selection. Darwinian Theory of Evolution explains that evolution is the result of natural selection, and natural selection is biased by the inherited characteristics of organisms. The adaptive ability of organisms is the one which helps organisms in evolution through natural selection. Biological evolution According to Jean-Baptiste Lamarck – a French naturalist, he explained evolution is all about the law of use and disuse by the organs. He also explained that the characteristic feature of certain living creatures such as giraffes, and the long necks, is the result of their adaptation to their nature. The elongated necks are the outcome of their attempt 41  BIO 101 – GENERAL BIOLOGY(FUTIA) to feed leaves on tall trees. This character is passed on from generation to generation. Natural Selection and Genetic Drift According to Darwin’s Theory of Evolution, branching descent and natural selection are the two factors for evolution. Environmental factors like climate, temperature, availability of resources, etc. had a great impact on the evolutionary process. Suppose a colony of bacteria is growing in a medium A. They feed on, reproduce and find themselves fit for that particular medium A. If you change the composition of medium A to B, every bacterium wouldn’t make it. Only a portion, which can adapt to new conditions, will survive in medium B. Eventually, they separate out and arise as new species. Here, the nature of the medium filters the fittest and marks an onset for evolution. Another factor which can lead to natural selection is inheritance. Two organisms compete for the same resource. If one can multiply much faster than the other, it will dominate over the other. Thus, the inherited gene in organisms helps them in getting selected and evolve. In other words, the more you adapt to the changing environment, the more chance you have to get selected by nature. Natural Selection The inadequate climatic changes, natural resources, predators, competition, etc., are amazing challenges given by nature to select the fittest. The one which has more inherited adaptations will have more chances of survival and others won’t flourish. The one which is selected by nature grows, reproduces and a new population will arise at the cost of others. Thus, we can conclude that during the course of evolution there is ‘survival of the fittest. Lamarckism Lamarckism was proposed by Jean-Baptiste de Monet Lamarck in the year 1744-1829. This theory was based on the principle that all the physical changes occurring in an individual during its lifetime are inherited by its offspring. For eg., the development of an organ when used many times. This theory has been explained here. 42  BIO 101 – GENERAL BIOLOGY(FUTIA) Lamarck’s Theory Lamarck’s theory includes four main propositions: Change Through Use And Disuse The organs which are used frequently by the organism develop and the characteristics that are used seldom are lost in the succeeding generations. For eg., a giraffe stretches its neck to eat leaves, a “nervous fluid” would flow in its neck and it enlarges. The organs which the organisms have stopped using would shrink with time. Organisms Driven To Greater Complexity As the organisms adapted to their surroundings, they became increasingly complex from the simpler forms. Lamarck believed in the spontaneous generation of life. Inheritance of Acquired Characters An individual acquires certain characteristics during its lifetime. These characters are inherited by their offspring as well. He explained this with an example of a blacksmith. A blacksmith has strong arms due to the nature of their work. He proposed that any children a blacksmith conceives will inherit the development of strong muscles. Effect of Environment and New Needs The environment influences all the organisms. A slight change in the environment brings about changes in the organisms. This gives rise to new needs which in turn produces new structures and changes the habits of the organisms. Examples of Lamarckism Few of the examples of Lamarckism are mentioned below: Evolution of giraffe The ancestors of the giraffe looked like horses with small necks and forelimbs. They lived in areas where there was no surface vegetation. Therefore, they had to stretch 43  BIO 101 – GENERAL BIOLOGY(FUTIA) their neck and forelimbs to eat leaves from tall plants. Consequently, these parts got elongated. This trait was transmitted in the successive generations. Aquatic Birds with Webbed Toes Aquatic birds such as ducks are believed to have evolved from terrestrial animals. Extinction of Limbs in Snakes The snakes are believed to have evolved from lizard-like ancestors that have two pairs of limbs. Flightless Birds It is believed that the ancestors of birds such as Ostrich were able to fly. Due to some environmental changes, they had a lot of food and were well protected. They stopped using their wings and as a result, the wings became vestigial. Cave Dwellers The ancestors of the animals living in caves are believed to have powerful eyesight. Due to living under continuous dark conditions, they lost their power to see. Lamarckism v/s Darwinism Lamarck proposed theories like the inheritance of acquired characters, use and disuse, increase in complexity, etc. whereas Darwin proposed theories like inheritance, different survival, species variation, and extinction. Darwin did not completely believe in his theory of acquired characters and proposed that the complexity in the organisms arise by the adaptation to the environment for 44  BIO 101 – GENERAL BIOLOGY(FUTIA) several generations. Whereas Lamarck proposed that complexity arises due to usage or disuse of particular characters. As the environment of an organism changes, so does his basic needs. The behaviour of the individual changes that eventually change organ usage and organism development. This gradual change in the species in response to the environment is known as “transmutation of species”. Lamarckism was reformed by Giard and Cope by incorporating a few points of the opponents. This theory is known as Neo-Lamarckism. 45