THE CELL:

The basic structural and functional unit of all organisms is called cell.
The cell is one of the most basic units of life. There are millions of different types of cells. There are cells that are organisms onto themselves, such as microscopic amoeba and bacteria cells. And there are cells that only function when part of a larger organism, such as the cells that make up our body. The cell is the smallest unit of life in our bodies. In the body, there are brain cells, skin cells, liver cells, stomach cells, and etc. All of these cells have unique functions and features. And all have some recognizable similarities.

SIMILARITIES:
All cells have a 'skin', called the plasma membrane, protecting it from the outside environment. The cell membrane regulates the movement of water, nutrients and wastes into and out of the cell. Inside of the cell membrane are the working parts of the cell. At the center of the cell is the cell nucleus. The cell nucleus contains the cell's DNA, the genetic code that coordinates protein synthesis. In addition to the nucleus, there are many organelles inside of the cell - small structures that help carry out the day-to-day operations of the cell. One important cellular organelle is the ribosome. Ribosomes participate in protein synthesis. The transcription phase of protein synthesis takes places in the cell nucleus. After this step is complete, the RNA leaves the nucleus and travels to the cell's ribosomes, where translation occurs. Another important cellular organelle is the mitochondria. Mitochondria are often referred to as the power houses of the cell because many of the reactions that produce energy take place in mitochondria. Also important in the life of a cell are the lysosomes. Lysosomes are organelles that contain enzymes that aid in the digestion of nutrient molecules and other materials.

TYPES:
There are many different types of cells. One major difference in cells occurs between PLANT CELLS and ANIMAL CELLS.
While both plant and animal cells contain the structures discussed above, plant cells have some additional specialized structures. Many animals have skeletons to give their body structure and support. Plants do not have a skeleton for support and yet plants don't just flop over in a big spongy mess. This is because of a unique cellular structure called the CELL WALL.

The cell wall is a rigid structure outside of the cell membrane composed mainly of the polysaccharide cellulose. The cell wall gives the plant cell a defined shape which helps support individual parts of plants. In addition to the cell wall, plant cells contain an organelle called the CHLOROPLAST. The chloroplast allow plants to harvest energy from sunlight. Specialized pigments in the chloroplast (including the common green pigment chlorophyll) absorb sunlight and use this energy to complete the chemical reaction.


CHROMOSOMES:

A threadlike body in the cell nucleus that carries the genes in a linear order are called chromosomes.
Chromosomes are composed of depxyribonucleic acids (DNA) and are blue prints in the cell structure in the form of genetic code.
Chromosomes appear thickened rod when a cell is dividing but in the phase between the divisions the DNA is distributed throughout teh nucleoplasm and only fine threads of chromatin can be seen.These threads thicken again prior to cell division.

GENES:

The fundamental unit of heredity formed as a sequence of basis in a DNA chain .
Genes determine all the functional and structural chracters of an individual like eye colour,intelligence ,temperament etc.
The genes transfer from one living organism to another through the process of reproduction.Genes are very stable which gurantee the similarity of the offsprings generation after generation.The accurate structure of the proteins and enzymes in the body is also determined by genes.

NUCLEIC ACIDS:

By definition, nucleic acids are biomolecules that store genetic information in cells or that transfer this information from old cells to new cells. There are two groups of nucleic acids: DeoxyRiboNucleic Acid and RiboNucleic Acid, DNA and RNA, respectively. DNA codes for the functioning of the cell and RNA is the "worker" that helps get the DNA message out to the rest of the cell. DNA is located mainly in the nucleus of the cell .RNA is primarily in the cytosol of the cell. DNA is double stranded and RNA is single stranded. BOTH are "codes" for the cell and , hence, the body's activities at the cellular level.