Cell can be best defined as the basic structural unit of an organ. The organisms made up of a single cell are called unicellular. Examples-a) Amoeba b) Paramecium.
A single-celled organism performs all the necessary functions that multicellular organisms perform. Organisms made up of more than one cell are called multicellular organisms.
The parts of cell are as following:-
b. cytoplasm and
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.
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, ribosomes etc.
Nucleus is an important component of the living cell. It 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 nucleus.
Nucleus in addition to its role in inheritance acts as control centre of the activities of the cell. Using a sophisticated microscope, 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.
Mitosis is a process of cell duplication, or reproduction, during which one cell gives rise to two genetically identical daughter cells.
Meiosis, on the other hand, is a division of a germ cell involving two fissions of the nucleus and giving rise to four gametes, or sex cells, each possessing half the number of chromosomes of the original cell.
Mitosis is used by single celled organisms to reproduce; it is also used for the organic growth of tissues, fibres, and membranes. Meiosis is useful for sexual reproduction of organisms; the male and female sex cells, e.g. the spermazoa and egg, fuse to create a new, singular biological organism.
Tissue can be categorized as a group of cells similar in structure and function. It can be categorized under animal and plant tissues. Plant tissues are of two main types-meristem tic and permanent. Meristem tic tissue is the dividing tissue present in the growing regions of the plant.
Meristem tic tissues are classified as apical, lateral and intercalary depending on the region where they are present. Apical meristem is present at the growing tips of stems and roots and increases the length of the stem and the root. The girth of the stem or root increases due to lateral meristem (cambium). Intercalary meristem is the meristem at the base of the leaves or internodes on twigs.
Permanent tissues are derived from meristem tic tissue once they lose the ability to divide. They are classified as simple and complex tissues. Parenchyma, collenchymas and sclerenchyma are three types of simple tissues. Xylem and Phloem are types of complex tissues.
Animal tissues can be epithelial, connective, muscular and nervous tissue. Depending on shape and function, epithelial tissue is classified as squamous, cuboidal, columnar, ciliated and glandular. The different types of connective tissues in our body include areolar tissue, adipose tissue, bone, tendon, ligament, cartilage and blood. Striated, unstrained and cardiac are three types of muscle tissues. Nervous tissue is made of neurons that receive and conduct impulses.
Sometimes a portion of the epithelial tissue folds inward and a multicellular gland is formed. This is glandular epithelium. Two bones can be connected to each other by another type of connective tissue called the ligament. This tissue is very elastic.
Muscular tissue consists of elongated cells are also called muscle fibres. This tissue is responsible for movement in our body. Muscles contain special proteins called contractile proteins, which contract and relax to cause movement.
SEX DETERMINATION IN HUMANS
The sex determining mechanism in case of humans is XY type. Out of 23 pairs of chromosomes present, 22 pairs are exactly same in both females and males; these are the autosomes.
A pair of X chromosomes is present in the female, whereas the presence of an X and Y chromosome are determinant of the male characteristic. During spermatogenesis among males, two types of gametes are produced. Fifty percent of the total sperm produced carry the X chromosome and the rest 50 percent has Y chromosome besides the autosomes.
Females however produce only one type of ovum with an X chromosome. There is an equal probability of fertilization of the ovum with the sperm carrying either X or Y chromosome. In case the ovum fertilizes with a sperm carrying X chromosome the zygote develops into a female and the fertilization of ovum with Y chromosome carrying sperm results into a male offspring.
SEX DETERMINATION IN BIRDS
In birds, a different mechanism of sex determination is observed. In this case, the total number of chromosome is same in both males and females. But two different types of gametes in terms of the sex chromosomes are produced by females. In order to have a distinction with the mechanism of sex determination described earlier, the two different sex chromosomes of a female bird has been designated to be the Z and W chromosomes. In these organisms the females have one Z and one W chromosome, whereas males have a pair of Z-chromosomes besides the autosomes.
14. MONOCLONAL ANTIBODIES
Monoclonal antibodies (mAb or Moab) are nonspecific antibodies that are the same because they are made by identical immune cells that are all clones of a unique parent cell, in contrast to polyclonal antibodies which are made from several different immune cells. Monoclonal antibodies have monovalent affinity, in that they bind to the same epitope.
Given almost any substance, it is possible to produce monoclonal antibodies that specifically bind to that substance; they can then serve to detect or purify that substance. This has become an important tool in biochemistry, molecular biology and medicine.