b. Cell Membranes:
Different kinds of cells are being enclosed with the help of a thin covering, which is known as cell membrane. Outer boundary of the cell as well as its internal parts is being made up of cell membranes.
These are organisms which are small in size. A cell is made up of various little organs. Some of these organisms are covered with the help of thin covering, and some are without any kind of covering.
The part of a cell between its membrane and nucleus is called the Cytoplasm. Between cell membrane and nuclei, there lies protoplasm.
Within the cytoplasm of cells there are generally found certain essential elements called organelles which are now known to be of considerable functional significance, even though their function is not always clear.
Throughout the cytoplasm, small microscopic sacs are being found, which are called the Mitochondria.
Outer smooth membrane and an inner membrane is main constituent of the mitochondria. Inner membrane is consisted of various folds, which consists of a number of enzymes. These enzymes perform different kinds of functions in human body.
These are the small membrane enclosed sacs, which consist of enzymes. These enzymes can break down various kinds of proteins and lipids.
g. Golgi Apparatus:
The Golgi apparatus has been described as a protoplasmic reticulum common to all types of cell. Usually situated around or in close proximity to the nucleus, it undergoes a characteristic displacement in glandular cells in relation of their secretory activity.
In other cases it may become dispersed throughout the cytoplasm in the form of fine granules, and it undergoes rapid disintegration in degenerative conditions.
An individual cell is composed of number of ribosomes. These are the small spherical organs which remain attached to the endoplasmic reticulum and it is through the cytoplasm that they remain scattered.
These are sac like structures. These consist of water and water soluble substances. Various kinds of excretory functions are being done by this organ.
j. Cilia and Flagella:
These are tiny hairs, the main purpose or function of which is to pull the cell through a fluid environment or to move the fluid surrounding the cell. Cilia have a short length and they are being present in the human body in a great number. Generally, in the human respiratory tract, they are being found.
The nucleus of a generalized type of cell occupies an approximately central position in the cytoplasm, and it is enclosed in a definite membrane, the nuclear membrane.
This is a double membrane and is not complete, for it may be interrupted at frequent intervals by small gaps, nuclear poses that permit the transport of nuclear material into the surrounding cytoplasm and of cytoplasmic material in the reverse direction.