All living things need to make more of their species in order for the species to survive.
New living things can only come from other living things. We call this process reproduction.
Most unicellular organisms, and a few multicellular organisms, use cell division to reproduce, in a process called asexual reproduction. In asexual reproduction, one organism produces one or more new organisms that are identical to itself and that live independently of it. The organism that produces the new organism or organisms is the parent. Each new organism is an offspring. The offspring produced by asexual reproduction are genetically identical to the parent. Asexual reproduction is a simple way for cells to reproduce.
CELL DIVISION IN UNICELLULAR ORGANISMS
Cell division and reproduction are the same thing in all singlecelled organisms. However, the process of cell division in prokaryotes and in single-celled eukaryotes differs.
Binary fission is one form of asexual reproduction that occurs in prokaryotes. Binary fission occurs when the parent organism splits in two, producing two completely independent daughter cells. Genetically, the daughter cells are exactly like the parent cell. Since all prokaryotic organisms are single-celled, cell division and reproduction by binary fission are the same process for them. Budding is another form of asexual reproduction. In budding, the parent organism forms a bulge that eventually falls off and continues to grow developing a new organism that is an exact copy of the parent. Many plants use budding as a form of reproduction. Regeneration is a process that can also be used for asexual reproduction. In regeneration, a part of an organism regrows, such as when a lizard regrows a tail. When a part of the parent organism re-grows to create an entirely new organism, the result is asexual reproduction. The regeneration of a whole new starfish from one arm of a parent starfish is an example of this.

Sexual reproduction occurs when the offspring is the result of the mixing of genetic information from two parents. This requires special cell division in the organism that results in either male or female sex cells (sperm and eggs in animals, pollen and ovules in plants). Fertilization of the female sex cell is required by a male sex cell. This is a random process that results in genetic variety.
Sexual reproduction requires two parents of the same species. The genetic information from the mother and the father in the offspring must combine properly to make a new organism. This cannot happen if the egg is from one species and the sperm is from another.
Summary of differences between asexual and sexual reproduction
Number of parents 1
Make up of offspring Genetically identical to parent and other offspring
Advantages
2 (one male, one female)
Genetically unique
(child is different from either
(child is exact copy of parent) parent)
Rapid reproduction – quickly builds population numbers
Produces variation which allows for changes in
Disadvantages Disease or other conditions may kill off the entire population organisms for adaptations to environments
Slower process so reproduction may not be at a rate fast enough to re-populate an area