Asexual Reproduction Only one parent is involved in asexual reproduction. The offspring is genetically identical to the parent. The offspring inherits all of its traits from one parent. Therefore, the offspring is exactly the same as the parent. Some scientists call asexual reproduction cloning. Cloning produces genetically identical organisms. Most unicellular (singlecelled) organisms reproduce asexually. Bacteria and Protista reproduce asexually. Some plants and fungi and many insects, such as ants and bees, can reproduce asexually too. Types of Asexual Reproduction There are different types of asexual reproduction. The most common types of asexual reproduction in unicellular organisms are binary fission and budding. Multicellular organisms can reproduce asexually by vegetative propagation and fragmentation (regeneration). Asexual Reproduction synonyms: Identical, clone, uniform
Binary Fission Binary Fission occurs when a parent organism divides in half. The parent cell splits in half to form two daughter cells. This is the most common form of asexual reproduction in unicellular organisms. Bacteria, Protista and unicellular fungi reproduce by binary fission. The Amoeba is a common single celled eukaryotic organism that reproduces by binary fission.
Budding Budding occurs when an offspring develops from an outgrowth or bud of a parent. The bud separates from the parent to form an offspring. The offspring is also called a daughter cell. The daughter cell is smaller than the parent but identical to the parent. Over time, the bud grows larger and becomes equal in size to the parent. Many unicellular organisms reproduce by budding. Protista and fungi, such as yeast, reproduce by budding. Some multicellular animals reproduce by budding as well. Hydra are small and simple fresh-water animals that reproduce by budding. Corals and sponges reproduce by budding too. Corals and sponges are marine organisms.
Regeneration - Fragmentation Regeneration occurs when a new organism grows from a fragment of the parent. The fragment develops into a full-grown mature adult that is identical to the parent. This form of asexual reproduction is seen in animals such as worms and sea stars. Regeneration is also fragmentation. Sometimes fragments of an animal are not intentionally broken off. The fragment develops into a new organism and the parent organism regenerates the fragment. Fungi and plants can reproduce by fragmentation as well. Some fungi form filaments called hyphae. The hyphae break off and grow into new organisms.
Vegetative Propagation Most plants reproduce sexually with seeds. Some reproduce sexually with pollen or spores. Some plants have the ability to reproduce without seeds. Vegetative propagation is asexual reproduction in plants. There are different ways plants reproduce by vegetative propagation. Some plants grow a stem from the side of the plant. This is called a runner. The runner grows horizontally across the ground. Buds form along the runner. Each bud grows into a new plant. The runner dies and dries out. The plants along the runner survive on their own. Strawberry plants reproduce this way. Some plants grow swollen, underground stems called tubers. A tuber is not a root. It grows buds. The buds develop into new plants. An example of a tuber is a potato. The eyes of a potato are buds. Scientists can artificially reproduce a plant asexually. For example, scientists can take a cutting from a plant and grow a new plant from the cutting. When placed in soil, the cutting will grow new roots and leaves. The plant will be identical to the plant from which the cutting came from.
Sexual Reproduction Plant The life of a flower begins as a seed. A seed contains a plant embryo and a food store. The plant embryo will grow into a new plant. This is called germination. The food store will provide energy to help the embryo germinate. It provides food until the plant can make food on its own. The new plant that grows from the seed is called a seedling. The seedling grows into a mature flowering plant. A mature flowering plant has petals and male and female parts. A mature flowering plant can reproduce. Pollination Reproduction begins with pollination. Pollination is the transfer of pollen from the anther to the stigma. In other words, it is the transfer of pollen from the male to the female part of the flower. Most angiosperms are pollinated by animals. Animals such as bees, butterflies and birds are attracted to flowers. They are attracted to the bright colors of petals and scent of the flower. Insects feed on pollen. Some flowers produce a sugary liquid called nectar.
Sexual Reproduction Two parents are needed for sexual reproduction. Each parent contributes half of its DNA to the offspring so that the offspring has a full set of genetic material. Unlike offspring formed from asexual reproduction, offspring formed from sexual reproduction are different from the parents. Sexual Reproduction synonyms: Variation, different, unique Gametes Each parent contributes DNA to the offspring through a gamete. A gamete is a special cell. It contains half of the amount of DNA as normal cells in the parent. Gametes are produced through a special type of cell division called meiosis. Females produce gametes called eggs. Males produce gametes called sperm. An egg and sperm fuse during sexual reproduction. This is called fertilization. Fertilization forms a cell called a zygote. The zygote contains a full set of genetic material half from the female parent and half from the male parent.
Zygote to Embryo The zygote divides by mitosis to form two cells. These two cells divide by mitosis to form four cells. The cells continue to divide to form a cluster of cells called an embryo. The cells of the embryo differentiate and specialize. In other words, the cells develop into all the different and special cells of the organism. These cells form tissues and organs of the organism. The embryo develops into an offspring. The offspring has a combination of traits from both of its parents. Variations in Sexual Reproduction Fertilization and development in sexual reproduction occurs differently in organisms. Fertilization and development can take place internally or externally. In other words, sperm can fertilize an egg inside the body of the female or sperm can fertilize an egg outside the body of the female. The embryo can grow and develop inside the female body or outside the female body.
Comparing Asexual and Sexual Reproduction There are some similarities between asexual and sexual reproduction. Both types of reproduction produce offspring. In order to produce the offspring, at least one parent is involved. Asexual and sexual reproduction occur for the same purpose. The purpose of reproduction is to produce offspring in order to continue survival of a species. Life Span Asexual reproduction usually occurs in less complex organisms resulting in a shorter life span. Sexual reproduction occurs in complex organisms resulting in a longer life span. Cell Division Asexual reproduction uses mitosis to produce offspring. Mitosis is a form of cell division. Sexual reproduction uses meiosis and mitosis to produce offspring. Meiosis is a special form of cell division that produces gametes. Differences between Asexual and Sexual Reproduction Asexual reproduction requires one parent. All of the offspring are genetically identical to the parent or uniform. In other words, the offspring are clones of the parent. Sexual reproduction requires two parents. The offspring are genetically different from the parents or have genetic variety. In other words, the offspring have a unique combination of genetic traits. Some traits came from the female parent and other traits came from the male parent.
Comparing Asexual and Sexual Reproduction Asexual Reproduction ADVANTAGES Offspring grow and develop quickly. It requires less energy. There is no need for a partner to produce offspring; all organisms reproduce. DISADVANTAGES Do not increase variation. Offspring are genetically identical to the parent. Not able to adapt to change. Sexual Reproduction Major ADVANTAGE Variation is the differences between organisms in a species. - increases a species survival. (Adapt to survive.) - offspring may have a better combination of traits than their parents. - increase the chance of the offspring s survival. - protects the organisms. - evolution is change in species over time. DISADVANTAGES Takes longer. It requires more energy It requires two organisms. Takes longer for offspring to grow and develop.