Cells are the building blocks of life. It is the smallest unit that contains life on earth. The study of cells is termed ‘cell biology,’ ‘cellular biology,’ or ‘cytology.’ Cells are made up of many substances, like water, inorganic ions, or carbon-containing compounds. Water is one of the major constituents of cells. Water accounts for more than 70% of the substance inside the cells. 

There are different kinds of organisms in terms of their cell structure. Some organisms have a single cell structure and are termed unicellular, whereas others contain multiple cells and are called multicellular. For instance, bacteria are unicellular, whereas plants and most animals, and even humans, are multicellular.

There is a fragile line between the cell cycle and cell division. The cell cycle is the series or continuation of a cell’s life, whereas cell division implies splitting a cell into two or more offsprings. 

The cell cycle is the series of a period in a cell’s life. 

The cell cycle has four major stages – 

1. G1 – Here, the cellular content, excluding the chromosomes, is duplicated. 
2. S (synthesis phase) – Each of the 46 chromosomes is duplicated by the cell. 
3. G2 – Here, the duplicated chromosomes are double-checked by the cells. In case of any errors, the same is rectified. 
4. M (mitosis phase) – Finally, the mitosis partitions the genetic material, and the cells get divided. 

Cell division is the process by which the cell multiplies. It includes both nuclear as well as cytoplasmic division. 

Cell division is a major of two types – 

• Mitosis – Mitosis is the cell division process when the offspring cell’s traits are derived from the parent cell. For instance, in mitosis, the parent cell gets divided into two daughter cells. These daughter cells have similar characteristics to each other and that of the parent cell too. Mitosis is also termed as equational division, as here, both the parent and the daughter cell have the same number of chromosomes. 
• Meiosis – Meiosis is the cell division process where the parent cell chromosomes are reduced by half, and then four new daughter cells are formed. Meiosis further can be divided into two major cell divisions—meiosis I and meiosis II. Meiosis I can further be divided into four stages—prophase I, metaphase I, anaphase I, and telophase I. Whereas meiosis II can be divided into prophase II, metaphase II, anaphase II, and telophase II.

Chromosomes are the minute thread-like part of the cells known to pass characteristics or hereditary information in the form of genes. One of the essential features of a chromosome is its compactness. 

When it comes to the structure of a chromosome, it is made up of DNA that is tightly seen around the protein structure and is termed histones. Each chromosome contains a centre point, which is known as the centromere. It is the point where the chromosome is divided into two major sections. The long section is termed the ‘Q’ arm, whereas the short section is termed the ‘P’ arm. It is the location of the centromere, which defines the structure and location of the chromosome.

The significance of inheritance was first studied and brought into light by George Mendel during 1856-1863. As a part of his experiment on peas, three major laws were derived, which are as follows:

• Law of Dominance – This is the first law that states that the hybrid inherits only their parents’ dominant traits. The traits that are not dominant are called recessive traits. 
• Law of Segregation – As per this law, during reproduction, two copies of hereditary factor get separated, and then each part is absorbed by each offspring.
• Law of Independent Assortment – This law states that any trait is free to segregate into the offspring during the formation of gamete.

Basic biology is the science of life. It is about living organisms that we can see and some we cannot see through our naked eyes. The science behind genetics, cell division and cell cycle is quite interesting and eye-opening. This chapter helps in understanding the concepts behind inheritance and different theories surrounding the same.

1. What do you understand by chromosomes?
   Chromosomes are made up of DNA and are responsible for carrying genetic information from one cell to another.
   
2. What is meant by cell division?
   The process by which a parent cell divides into two equal daughter cells.
   
3. How many chromosomes does a human body have?
   The human body has 46 chromosomes.
4. In which cells in the process of mitosis seen?
   The process of mitosis is seen in the somatic cells.
5. Which part of the cell is associated with hereditary?
   Chromosomes are associated with hereditary.
6. What is the result of an alarming cell division?
   The result of an alarming cell division is cancer.