Asexual and Sexual Reproduction

Mitosis Have you ever been stuck in a crowded parking lot? It is probably crowded because there are a lot of parking spaces and few exits. Cells let materials exit and enter through the cell mem- brane. If a cell is really big, materials cannot enter and leave quickly. Cells must remain small to survive. When they grow too large, cells divide. Cell division starts with mitosis. Mitosis is the division of the cell’s nucleus. The nucleus contains DNA, the material that stores information about an organism’s growth and development. Before mitosis begins, the DNA is copied. During mitosis, DNA winds up tightly. The cell divides the DNA. One complete set of DNA is at one side of the cell. The other set of DNA is at the opposite side. The cell membrane then splits apart, forming two cells. Each cell gets one full set of DNA. The new cells are the same as the original cell. Asexual reproduction Species survive because parents pass traits to their offspring. Organisms can reproduce by asexual reproduction. In asexual reproduction, only one parent makes offspring. The parent makes a copy of itself through mitosis. All offspring have the same DNA as the parent. Many species use asexual reproduction. Bacteria reproduce asexually. They go through mitosis once to make two cells from the original cell. Hydra reproduce asexually, too. They grow a baby hydra on their side. When the new hydra grows big enough, it falls off and starts a life of its own. In both examples, offspring have exactly the same DNA as the parent and the same characteristics. Many other organisms reproduce asexually. For example, strawber- ries, starfish, and tulips can reproduce asexually. Sexual reproduction In sexual reproduction, sex cells from two parents join. The female parent makes an egg cell. The male parent makes a sperm cell. Each sex cell has half the usual amount of DNA. When the egg and sperm join, the resulting off- spring have unique combinations of DNA. The DNA is a mixture from both parents. Because of this, offspring have a unique combi- nation of traits. Good and Bad Asexual reproduction has many good points. It can be completed quickly. It does not use up much of the parent’s energy. A parent can have lots of offspring in a short time. Asexual reproduction requires one parent. The species can grow even if only one organism is present. Asexual reproduction makes offspring that are exact copies of the parent. Offspring will survive in environ- ments where the parent survives. Environments change over time. Offspring of asexual reproduc- tion are all the same. Sometimes they are not adapted to new condi- tions. If conditions change too much, the parents and offspring may die. Sexual reproduction takes more energy and time. It requires two parents of opposite sexes. This can be a problem if there are few organisms in an area. Sexual reproduction has one big advantage. Offspring have a unique combination of DNA. Every new offspring has a different set of traits. Some individuals are better suited to one environment. Other organisms are better suited to a different environment. If conditions change, some members of the species are likely to do well in the new situation.