Chemical reactions occur when atoms or molecules interact to form new substances. This process involves the breaking and forming of chemical bonds, leading to changes in the arrangement of atoms. Here’s a step-by-step overview of how chemical reactions happen:

1. Collision of Reactants: For a chemical reaction to occur, the reactant molecules or atoms must collide with one another. These collisions provide the opportunity for bonds to break and form new ones.

2. Activation Energy: Not all collisions lead to a reaction. The colliding particles must have enough energy to overcome the activation energy, which is the minimum energy required to initiate the reaction. This energy barrier must be surpassed for the reaction to proceed.

3. Formation of Transition State: When the reactants collide with sufficient energy, they form an intermediate structure called the transition state. In this state, bonds in the reactants are partially broken, and new bonds in the products are partially formed.

4. Breaking and Forming Bonds: In the transition state, existing bonds are broken, and new bonds are formed, resulting in the conversion of reactants into products. The arrangement of atoms changes, leading to the creation of new substances with different properties.

5. Energy Change: Chemical reactions either release energy (exothermic reactions) or absorb energy (endothermic reactions). In exothermic reactions, energy is released, usually as heat or light, while in endothermic reactions, energy is absorbed from the surroundings.

6. Products Formation: Once the reaction is complete, the transition state collapses into the final products. These products are the new substances formed as a result of the chemical reaction.

7. Equilibrium (in Reversible Reactions): Some reactions are reversible, meaning they can proceed in both forward and backward directions. Over time, these reactions may reach a state of equilibrium, where the rates of the forward and reverse reactions are equal, and the concentrations of reactants and products remain constant.

Chemical reactions are fundamental to all biological and chemical processes, driving everything from the metabolism in living organisms to industrial manufacturing processes.

Mitosis is the process by which a single eukaryotic cell divides to produce two genetically identical daughter cells. It is essential for growth, tissue repair, and asexual reproduction. The process can be broken down into several distinct stages:

1. Interphase (Preparation phase):

G1 phase (Gap 1): The cell grows and carries out its normal metabolic functions. It also prepares the necessary proteins and organelles for DNA replication.

S phase (Synthesis): DNA replication occurs, resulting in two identical copies of each chromosome, now called sister chromatids.

G2 phase (Gap 2): The cell continues to grow and prepares for mitosis by synthesizing proteins and other components needed for division.

2. Prophase:

Chromosomes condense and become visible under a microscope as tightly coiled structures.

The nuclear membrane begins to break down.

The mitotic spindle (a structure made of microtubules) begins to form, extending from the centrosomes (regions in the cell that organize the microtubules).

Centrioles (in animal cells) move to opposite poles of the cell.

3. Metaphase:

The chromosomes align along the metaphase plate, an imaginary line in the middle of the cell.

The spindle fibers attach to the centromeres of the chromosomes via kinetochores, specialized protein complexes.

4. Anaphase:

The sister chromatids are pulled apart toward opposite poles of the cell. This happens when the centromere splits, and the spindle fibers shorten, separating the chromatids.

Each chromatid is now considered a separate chromosome.

5. Telophase:

Chromosomes reach the opposite poles of the cell and begin to de-condense back into chromatin.

The nuclear membrane reforms around each set of chromosomes, creating two distinct nuclei in the cell.

The spindle fibers disintegrate.

6. Cytokinesis:

Cytokinesis is the division of the cytoplasm that occurs at the end of mitosis.

In animal cells, a contractile ring of actin filaments forms and pinches the cell membrane, dividing the cell into two daughter cells.

In plant cells, a cell plate forms between the two nuclei, eventually developing into a new cell wall, dividing the cell into two.

At the end of mitosis and cytokinesis, two genetically identical daughter cells are produced, each with the same number of chromosomes as the original cell.