rasheeda

                                    CELLS-THE UNIT OF LIFE   Q.1 What is the importance of a vacuole in a plant cell? A.1.  The vacuole is a membrane-bound space in the cytoplasm of a plant cell. It contains sap, water, excretory products and other materials not useful for the cell. Vacuoles occupy 90% of the cell volume during osmosis. They maintain the turgor pressure against the cell wall thereby maintaining the shape of the cell and cell fluid balance. Q.2. What is a satellite chromosome? A.2.  The chromosomes that have an additional or secondary constriction at the distal part of the arm formed by a chromatin thread are known as satellite chromosomes. These appear as an outgrowth or a small fragment. These are also known as marker chromosomes. The chromosomes 13, 14, 15, 16, 21, and 22 are satellite chromosomes. Q.3. Match the following: Column I Column II Cristae Fat membranous sacs in the stroma Cisternae Infoldings in mitochondria Thylakoids Disc-shaped sacs in Golgi apparatus

                                      CELLL-THE UNIT OF LIFE Study of form, structure, and composition of cell is called  cytology . Cell is the structural and functional unit of life. In unicellular organism (amoeba, paramecium, yeast, bacteria) single cell performs all the essential functions of life. In multicellular organism, different kinds of tissues perform different function and have division of labour. Anton Von Leeuwenhoek first saw and described a live cell. Robert Brown later discovered the nucleus. Metthias Schleiden and Theodore Schwann( 1938) proposed the cell theory which was later modified by Rudolf Virchow(1855)- 1.      All living organisms are composed of cells and products of cells. 2.      All cells arise from pre-existing cells. Prokaryotic cells Eukaryotic cells 1.      Membrane-bound nucleus is absent. 2.      Cells are smaller in size. 3.      Single chromosome is pres