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Downloaded from https:// www.studiestoday.com, , Cell - The Structural and Functional, Unit of Life [For Revision Only], , , , , , , , — — aa All organisms, including ourselves, are made of microscopic cells. These cells, perform activities which contribute to the overall tasks of an individual. It is also, to. that every organism starts its life as a single cell. The same cell undergoes, repeated divisions to give rise to a large mass of cells. Further, the cells get, specialised for various tasks such as those of giving support, producing digestive, | enzymes and carrying out photosynthesis., , , , , , , , , , , , , , , 1.1 CELLS - A BASIC STUDY IN BIOLOGY, You have already read about cells in some detail * Longest cells are the nerve cells., , cells in the human body, etc., , in Class IX. However, it is necessary to refresh your + Largest cells are the birds’ eggs (actually the, , knowledge for a proper understanding of several, aspects of biology which specially constitute the, Class X syllabus. Some of the main points about cells, are as follows :, , * All living beings are made up of cells., , * The cell is the structural and functional unit of, , the body., , ¢ All living beings develop from a pre-existing, , cell., , 1.2 CELLS - HOW NUMEROUS?, , central yellow sphere). Ostrich egg, before, development begins in it, is the largest single, cell of the living world today. The white, (albumen) of the egg and the egg-shell are, extra parts added on the actual egg as it, passes down the reproductive tract., , , , An average-sized adult human constitutes, approximately:, , - 1000 million million cells in the whole body., — 10,000 million nerve cells in the brain cortex., , , , , , Larger an organism, greater the - 25 million million red blood cells., number of cells in its body. — 30 thousand million white blood cells., , , , , , , , Single-celled : Many small organisms are made, up of just one single cell., , , , , , 14 CELL SHAPES, Different shapes of cells are often related to the, , Examples : Bacteria, yeast and amoeba., , Few-celled : Some very small organisms are made, up of just a few hundred or a few thousand cells., , Examples : Spirogyra, Volvox., , different functions they perform., * Human red blood cells are circular and, , biconcave, for easy passage through blood, capillaries and to transport oxygen., , Multi-celled : Most plants and animals we see * White blood cells are amoeboid (amoeba-like, , around are made up of millions and billions of cells., , Examples :, , 1.3 CELLS — HOW SMALL?, Cells are very small and can be seen only with a, , microscope., , * Smallest cells are certain bacteria, red blood, , Humans, mango., , movement, with pseudopodia) that can squeeze, out through capillary walls., , * Nerve cells are long to conduct “impulse” from, distant parts of the body to the brain and viceversa., , ¢ Guard cells of stomatal pore in the leaves are, bean-shaped to open and close it., , ——Downloaded trom https: www.studiestodayprarn Booey

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Downloaded from https:// www.studiestoday.com, S 0 am, , Cell, membrane, , , , , , , , , , NUCLEUS, , , , Mitochondria, , CYTOPLASM Rough, , endoplasmic, reticulum, , Nuclear pore Golgi body, , , , Smooth, endoplasmic, reticulum Vacuole, , Nucleolus, , Nuclear, , NUCLEUS, , MmeiGrane Rough Mitochondrion. Smooth, endoplasmic endoplasmic, reticulum reticulum, , CYTOPLASM, CELL Lysosome, MEMBRANE, , A— ANIMAL CELL B — PLANT CELL, Fig. 1.1: A generalised animal cell and a generalised plant cell. (Note the parts common to both cells and the parts, which are found exclusively in an animal cell or in a plant cell), 15 GROSS STRUCTURE OF CELL -. THE * It is surrounded by a double layered nuclear, , THREE ESSENTIAL PARTS membrane with nuclear pores (Fig. 1.2)., , 1. Cell membrane (or plasma membrane) Nuclear Membrane, encircles the cell., , ¢ It is a living membrane having fine pores., , ° It is semi-permeable (also called selectively, permeable or differentially permeable) meaning, that it allows only certain substances to pass, through while preventing others., , In the plant cell (Fig. 1.1 B), an additional, outermost non-living layer called the cell, wall, surrounds the cell membrane., , , , , , , , , , Nuclear Pore, » Nucleolus, , Nucleoplasm, , Chromatin Network, , Fig. 1.2 : Structure of nucleus, , — The cell wall is mostly made up of cellulose. * The ground substance of the nucleus is a semi, — It gives shape and rigidity to the cell. solid substance (nucleoplasm) containing one, , — It is freely permeable (allowing substances or more round-shaped nucleoli (sing. nucleolus)., , in solution to enter and leave the cell without * The nucleoplasm contains a network of dark, hindrance). coloured fibres called chromatin fibres. These, , 2. Cytoplasm is the part of the cell inside the cell chromatin fibres condense into short thick, membrane and outside the nucleus. chromosomes (Fig. 1.3) during cell division., , * It is a semiliquid substance., * Many chemical reactions catalyzed by, enzymes occur in it., , * Itcontains several organelles, each concerned, with some specific function., , Nucleus, , Cytoplasm, , , , , Centrioles 4, moving apart, , ° The part of the cytoplasm other than the nate, organelles (mitochondria, etc.) is called, cytosol, which constitutes mainly the liquid _ Fig, 1.3 : An early stage of cell division in an animal cell, medium. showing two pairs of chromosomes that have condensed, , " 5 . from the chromati network, inside the nucleus, 3. Nucleusis a large somewhat spherical body lying —_ (diagrammatic). Chromosome number varies from one, , nearly in the centre of the cytoplasm. organism to another., , [2 Cell—The Bresiye ELSE TOM HHS A WAN Stidiestoday.com —~—~S~S, , Chromosomes

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Downloaded from https:// www.studiestoday.com, , 16 FINER STRUCTURE OF CELL - THE, ORGANELLES, , , , Organelles are the specialised membrane-bound, structures in a cell, concerned with definite functions., , , , , , ORGAN and ORGANELLE, Just as there are organs in the body, so are the organelles, inside a cell., Just as each body organ performs one or more special, functions, similarly, each organelle has a specific function, in a cell., , , , , , , , The living parts of a cell which consist of, cytoplasm, nucleus and other living bodies are, collectively called protoplasm or protoplast. The, latter term protoplast is more appropriately used for a, plant cell after the removal of cell wall. The living, bodies called organelles are the same in both plant, and animal cells except cell wall in plants and, centrosome with centrioles in animals. The various, organelles are : Nucleus, nucleolus, mitochondria,, endoplasmic reticulum, ribosomes, Golgi bodies,, lysosomes, chloroplasts, vacuoles, cell membrane., , Table 1.1 Parts of cell and their main characteristics and chief functions, , , , 1. Cell membrane (also called 1. Outermost in animal cells. 1. Separates contents of cell from its surroundings, plasma membrane) 2. Lies next to cell wall in plant cells. 2. Regulates the entry of certain solutes and ions., 3. Very thin, flexible, living membrane. 3. Maintains shape of the cell (in animal cells)., 4. Possesses fine pores., 5, Semi-permeable., 6. Made up of lipoproteins., , , , , , , , plasma membrane, , 3. Freely permeable., , , , , , 1. Non-living rigid layer surrounding, , 2. Mainly composed of cellulose., , . Gives rigidity and shape to the plant cell., , 2, Allows substances in solution to enter and leave, the cell without hindrance., , 3. Provides protection., , , , , , , , , , , , , , 3. Cytoplasm 1. All the parts together inside the plasma 1. Different organelles contained in it perform, Sl membrane excluding nucleus. different functions., 2. Contains a mixture of water and soluble 2. All metabolic activities occur in it., inorganic and organic compounds, and 3. Medium of earlier steps of respiration (production, various organelles. of pyruvic acid) (anaerobic respiration)., 4, Endoplasmic reticulum (ER) 1, Irregular network of tubular double 1. Supportive framework for the cell., , membrane., , 2. Synthesis and transport of proteins and fat., , 2. It is continuous with the plasma membrane, , on the outside and the nuclear membrane, on the inside., , . May be smooth or rough, , (attached ribosomes)., , , , , , , , , , , , , , . Various shapes but usually sausage-like., , . Release of energy from pyruvic acid produced, , , , , , 2. Double walled; inner wall thrown into in cytoplasm in the form of ATP. (Seat of cellular, folds (cristae). aerobic respiration & stores energy)., 3. Have their own DNA (containing several | 2. Synthesis of respiratory enzymes., genes), 4. Also, contain their own ribosomes, 6. Golgi apparatus (In animal cells) | 1. Stacks of flattened membrane 1. Synthesis and secretion of, (called dictyosomes sacs. enzymes, hormones, etc., in plant cells) 2. Consists of tubules, vesicles 2. Formation of acrosome of, , , , , , , , , , and vacuoles., , , , sperm., , , , (Contd.), , , , CONCISE BIOLoGy —{_3_ |, , Downloaded from https:// www.studiestoday.com

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Downloaded from https:// www.studiestoday.com, , 7. Ribosomes, , 1. Small granules either scattered in the, , , , , , cytoplasm or attached to the outside of, endoplasmic reticulum., , 2. Single walled dense, spherical bodies, composed mainly of RNA., , , , 1. Protein synthesis., , , , , , , , , , 1, Membranous sacs budded off from, Golgi body. ‘, 2. Contain 40 different types of enzymes., , , , 1. Intracellular digestion., , 2. Destroy foreign substances., , 3. When cell is old or injured, these rapidly, destroy organelles, (hence called “suicide bags”)., , 4. Digest cartilages during formation of bones., , , , , , 9. Centrosome —_[yaige i,, , (Animal cells, only), , , , , , 1. A region surrounding the centrioles,, located near nucleus., , 2. Contains one or two centrioles, , 3. Centrioles are surrounded by microtubules., , , , , , 1. Initiates and regulates cell division., 2. Forms spindle fibres, with the help of asters., , , , 10. Plastids (Plant cells only), , 1. Several kinds, most common ones, are chloroplasts containing the, green pigment chlorophyll., , 2. Double membraned, proteinaceous, matrix, contain DNA., , 3. Disc-like structures called, thylakoids contain chlorophyll., , , , 1. Chloroplast (green) trap solar energy for, photosynthesis, contans the pigment chlorophyll., , 2. Leucoplast — stores starch., , 3. Chromoplast — imparts colour to flowers and, fruits, contains the pigment Xanthophyll (yellow, coloured pigment); Carotene (orange-red pigment)., , 4. Anthocyanin pigment is dissolved in cytoplasm, (blue-violet colour)., , , , , , , , 11. Nucleus, , , , 1. Largest cell organelle., . Mostly spherical and dense., , 2., , 3. Nuclear membrane with pores to allow, substances to enter and leave., , 4. Contains network of thread-like structures, , , , called chromatin fibres which contain DNA., , 1, Regulates cell functions., , 2. If removed, the cell dies., , 3. Contains chromosomes (bearers of genes that, control hereditary characters)., , , , , , 12. Nucleolus, coe, , , , , , 1. One or more round-shaped nucleoli inside, the nucleus., , , , 1, Produces ribosomes, 2. Participates in protein synthesis, by forming and storing RNA., 3. Dictates ribosomes to synthesise proteins., , , , 13, Chromatin fibres, , 1, The network in resting stage of the nucleus, , , , , , , , condenses into chromosomes during cell, division. r, 2. Made up of DNA threads., , , , 1. Chromosomes carry hereditary information, or the genes., , , , , , , , , , , , , , 14. Vacuoles 1. Clear spaces with water or other 1. Storage of water and other substances, food,, substances in solution. pigments, and waste products., 2. Plant cells have larger vacuoles, while the | 2. Give turgidity to the plant cells by pressing, animal cells have fewer and smaller ones. against cell wall., 3. Covered by a covering called tonoplast., 15. Granules 1. Small particles, crystals or droplets. 1. Starch (in plant cells), glycogen (in animal cells), , , , , , , , , , , , , , and fat-containing granules serve as, food for the cell., , , , [a cal the sce aye Fron htips:// www. Studiestoday.com, , own

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Downlgaded from https:// www.studiestoday.com, , eren, , between Plant and A:, , , , FEATURE, , 1. Cell wall, 2. Centrosome, 3. Vacuoles, , 4. Plastids, 5. Size, 6. Cytoplasm, 7, Arrangment of, cytoplasm, , , , , , , , , , , , , , , ANIMAL CELLS, , No cell wall, , Present., , Vacuoles, if any, are small and temporary;, concerned with excretion or secretion., , No plastids., , Usually smaller., , Cytoplasm denser and more granular., Cytoplasm fills almost the entire cell., , , , eye, , rays, , , , , , , , 1.7 MICROSCOPIC EXAMINATION OF ONION, PEEL, , Epidermal cells of onion, , The epidermal peel from onion is easy to prepare., You can proceed as follows :, , Cut the onion bulb into four pieces (quarters), lengthwise (Fig. 1.4)., , Cc, , , , Fig. 1.4: Preparation of an onion peel, , From one of these quarters, remove one thick scale, leaf. Take the fleshy scale of onion in your hand and, tear it from the inner (concave) side so as to get a thin, transparent strip (Fig. 1.4B). Using a pair of forceps,, remove this strip (peel) (Fig. 1.4 C) and put itin a watch, glass containing water. Cut a square piece of this peel, (about 5 x 5 mm) and mount it on a slide in a drop of, water as shown in Fig. 1.5. Cover the peel with a, coverslip carefully so that the tissue does not get, wrinkled. Examine the preparation under a low power, microscope. You may as well stain the material with, iodine or eosin solution, which will make the nucleus, , , , , , Fig. 1.5 : Preparation of a slide of onion peel, , more distinct. More details of the cell structure will, be seen under a high power microscope., , The cells of onion peel have a somewhat regular, shape, linear or rectangular (Fig. 1.6). Each cell has a, prominent cell wall, a nucleus and the cytoplasm, encircling one or two large vacuoles. The details are better, seen in high power, especially the thick cell wall. Note, that the cells are, , * firmly bound together and, ¢ the nucleus is placed towards one side, which is, usually the case in almost all plant cells., , NUCLEUS CELLS ._, , , , Fig. 1.6 : Cells from a peeling of onion scale leaf as, seen under the low power of microscope, , 1.8 THE NUCLEUS — KEY TO THE LIFE OF A, CELL, , Although every part of a cell contributes to the life, of the cell as a whole, yet the key performer or the, , , , Downloaded from https:// www.studiestodaf Sort #0Locr