Ch 5Cell Structure and Organization — Class 11 Biology, concept-first.

The cell is the structural and functional unit of life. Every living organism -- whether a single-celled microbe or a large multicellular plant or animal -- is built of cells, and a cell on its own is…

Based on how their cells are organised, all living organisms fall into two broad groups: the Prokaryotes and the Eukaryotes.

Prokaryotic cells are the simpler of the two basic cell types. They have a chemically complex, protective cell envelope, but they lack a well-defined nucleus and lack the membrane-bound cell organelle…

Cells in which the nucleus is enclosed by a definite nuclear membrane are called eukaryotic cells. These cells also show a range of membrane-bound cell organelles, unlike prokaryotic cells.

A eukaryotic cell is built from a shared set of basic components -- a plasma membrane enclosing the cytoplasm, and within the cytoplasm a range of organelles, along with, in plants, fungi and some pro…

The cell wall is the rigid, supportive and protective outer covering that lies external to the plasma membrane of plant cells, fungi, and some protists; it is absent in animal cells.

The cell membrane, also called the plasma membrane or biomembrane, is a thin, quasi-fluid structure. It is found both extracellularly, around the entire protoplast of the cell, and intracellularly, ar…

The cell is filled with a ground substance called the cytoplasmic matrix, or cytosol. This colloidal, jelly-like material is not static -- it shows a streaming movement within the cell known as cyclos…

The endoplasmic reticulum (ER) is a fine network of membranous tubules and sacs, called cisternae, running through the cytosol.

The Golgi complex -- also called the Golgi apparatus or Golgi body -- is the manufacturing-cum-packaging-and-transport unit of the cell.

Lysosomes can be thought of as the dismantling and restructuring units of the cell. They are membrane-bound vesicles containing hydrolytic enzymes -- a full set of hydrolases including amylases, prote…

Vacuoles Vacuoles are membrane-bound, fluid-filled sacs found prominently in plant cells; in animal cells, when present, they tend to be fewer in number and smaller in size.

Glyoxysomes are membrane-bound organelles that contain enzymes able to convert fatty acids into sugar.

Mitochondria (singular: mitochondrion) are important organelles involved in aerobic respiration. They are absent from prokaryotic cells and from red blood corpuscles, and their shape may be oval, sphe…

Like mitochondria, plastids are double-membraned organelles that contain their own DNA, RNA and 70S ribosomes, but they are larger than mitochondria and can be seen under a light microscope.

Ribosomes are often described as the protein factories of the cell -- they use the genetic information carried to them to synthesise proteins.

The structure of a eukaryotic cell's nucleus becomes clearly distinct in a non-dividing cell, or during interphase.

With advances in light and electron microscopy, scientists discovered a network of fine fibrils running throughout the cytoplasm of a cell.