question_answer 48)

    Eukaryotic cells have organelles which may (a) not be bound by a membrane (b) bound by a single membrane (c) bound by a double membrane Group the various sub-cellular organelles into these three categories.

Answer:

                  (a) Cell organelles with no membraneIn eukaryotic cell, ribosomes occur freely in thecytoplasmic matrix and are attached to the outer cytoplasmic surface of the roughendoplasmic reticulum and nuclear envelope. The ribosomes are also found in thematrix of mitochondria and stroma of plastids called as mitoribosomes and plastidoribosomes, respectively. (b) Cell organelles with single membraneA lysosome is a tiny sac bounded by a singleunit membrane of lipoprotein. The lysosomes occurs in all animal cells and protozoans. Prokaryotic cell lack lysosomes. Number of lysosomes varies with the cell type. Lysosome contain a dense, finelygranular fluid consisting of glycoproteinaceous hydrolytic (digestive) enzymes calledacid hydrolases. Cell organelles like sphaerosomes and microbodies also possesssingle membranes. (c) Cell organelles with double membrane Mitochondria are double membrane boundstructures with the outer membrane and inner membrane dividing its lumen distinctlyinto two aqueous compartments. The inner compartment is called the matrix whereas the outer membrane forms the continuous limiting boundary of the organelle. Chloroplast and nucleus are also double membrane bound organelles.