The nerve cell receives and transfers messages, thereby helping to control and coordinate the working of different parts of the body. Components of the cell are enclosed in a membrane.
19 RAJESH NAYAK This membrane provides shape to the cells of plants and animals. Cell wall is an additional covering over the cell membrane in plant cells. It gives shape and rigidity to these cells. Bacterial cell also has a cell wall. The smallest cell is 0.1 to 0.5 micrometre in bacteria. The largest cell measuring 170 mm ×130 mm, is the egg of an ostrich. Each organ is further made up of smaller parts called tissues. A tissue is a group of similar cells performing a specific function. The basic components of a cell are cell membrane, cytoplasm and nucleus. The cytoplasm and nucleus are enclosed within the cell membrane, also called the plasma membrane. The membrane separates cells from one another and also the cell from the surrounding medium. The plasma membrane is porous and allows the movement of substances or materials both inward and outward. The jelly-like substance between the nucleus and the cell membrane is called cytoplasm. Cytoplasm is the jelly-like substance present between the cell membrane and the nucleus. Various other components, or organelles, of cells are present in the cytoplasm. These are mitochondria, golgi bodies, ribosomes, etc. Nucleus is separated from the cytoplasm by a membrane called the nuclear membrane. This membrane is also porous and allows the movement of materials between the cytoplasm and the inside of the nucleus. With a microscope of higher magnification, we can see a smaller spherical body in the nucleus. It is called the nucleolus. In addition, nucleus contains thread-like structures called chromosomes. These carry genes and help in inheritance or transfer of characters from the parents to the offspring. The chromosomes can be seen only when the cell divides. Gene is a unit of inheritance in living organisms. It controls the transfer of a hereditary characteristic from parents to offspring. The entire content of a living cell is known as protoplasm. It includes the cytoplasm and the nucleus. Protoplasm is called the living substance of the cell. The cells having nuclear material without nuclear membrane are termed prokaryotic cells. The organisms with these kinds of cells are called prokaryotes (pro : primitive; karyon: nucleus). Examples are bacteria and blue green algae. The cells, like onion cells and cheek cells having well organised nucleus with a nuclear membrane are designated as eukaryotic cells. All organisms other than bacteria and blue green algae are called eukaryotes. (eu: true; karyon: nucleus).
You've reached the end of your free preview.
Want to read all 23 pages?