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Asexual vs. Sexual Reproduction Part 2 of 3 Sexual Reproduction Sexual Reproduction 1. 2 parents 2. Sex cells: sperm and egg 3. Sperm and egg join= fertilization 4. Offspring look different from parent (mixed DNA) Sexual Reproduction Sexual Reproduction Examples – Humans, some plants, mammals, fish, reptiles, etc. Read: Sexual Reproduction: Gametes, External/Internal Fertilization, Male/Female Sexual Reproduction Sexual Reproduction in Animals • involves specialized sex cells called gametes • the union of a male and female gamete results in the formation of a zygote that develops into a new individual Sexual Reproduction in Plants Female Parts Male Parts (Pistil) pollen (male) + ovule (female) → single-celled zygote → multi-celled embryo (contained in a seed) → new individual Sexual Reproduction in Plants • The stamen is the male part and contains pollen • The carpels or pistil is the female part and contains the ovule (eggs) • Pollen grains from the anther are transferred to the stigma by the process of pollination – self pollination (plant pollinates its own eggs) – Assisted Pollination of a Flower (1:11) – cross pollination (pollen from one plant pollinates another plants eggs) Pollination • Flowers are designed (bright colors, stripes, sweet smell, food) to attract insects to help with the pollination process – also wind, animals, birds can transport pollen Plant Reproduction (1:30) Plant Reproduction: Methods of Pollination (3:58) Sexual Reproduction Summary Male Gamete Female Gamete Type of Union Result of Union Final Result Plants pollen ovule (egg) pollination single cell zygote multi-cell embryo (in seed) Animals sperm egg fertilization single cell zygote multi-cell embryo Asexual vs. sexual reproduction Organisms that reproduce through asexual reproduction tend to grow in number exponentially. However, because they rely on mutation for variations in their DNA, all members of the species have similar vulnerabilities. Organisms that reproduce sexually yield a smaller number of offspring, but the large amount of variation in their genes makes them less susceptible to disease. Many organisms can reproduce sexually as well as asexually. Aphids, slime molds, sea anemones, some species of starfish (by fragmentation), and many plants are examples. When environmental factors are favorable, asexual reproduction is employed to exploit suitable conditions for survival such as an abundant food supply, adequate shelter, favorable climate, disease, optimum pH or a proper mix of other lifestyle requirements. Populations of these organisms increase exponentially via asexual reproductive strategies to take full advantage of the rich supply resources. When food sources have been depleted, the climate becomes hostile, or individual survival is jeopardized by some other adverse change in living conditions, these organisms switch to sexual forms of reproduction. Sexual reproduction ensures a mixing of the gene pool of the species. The variations found in offspring of sexual reproduction allow some individuals to be better suited for survival and provide a mechanism for selective adaptation to occur. In addition, sexual reproduction usually results in the formation of a life stage that is able to endure the conditions that threaten the offspring of an asexual parent. Thus, seeds, spores, eggs, pupae, cysts or other "over-wintering" stages of sexual reproduction ensure the survival during unfavorable times and the organism can "wait out" adverse situations until a swing back to suitability occurs. Some Organisms do Both • Most plants that produce seeds (sexual reproduction) can also reproduce asexually by things like cuttings or runners • This gives them an advantage for survival sponges and hydra mosses onions Asexual and Sexual Reproduction - I can do both! Aphids Asexual and Sexual Reproduction - I can do both! Fuligo septica, the "dog vomit" slime mold Slime mold growing out of a bin of wet paper Mycetozoa from Ernst Haeckel's 1904 Kunstformen der Natur (Artforms of Nature) Mycetozoa is a grouping of slime molds. Slime mold (Physarum polycephalum) Sea anemone Asexual Reproduction – Grade Six Attachment Organisms and Types of EAsexual Reproduction Asexual Reproduction Resource Page Any of the following could be used in the science lab to reinforce content. Organism Whiptail lizards Type of Asexual Reproduction Parthenogenesis Bacteria Fission Spider plant Vegetative Propagation Strawberries Vegetative Propagation Fragmentation Some flatworms Paramecium Mint Blue-green algae Protists Hydra Fission Vegetative Propagation Fission Fission Budding Description A female whiptail lizard may produce eggs that develop into genetically identical versions of itself. In some species, there are entire clonal populations of this lizard. Most whiptail lizard species do reproduce sexually, though. A single-celled organism that has no nuclei or cell walls and reproduce by splitting in two. Spider plants reproduce new plants by the division of cells from roots or runners. These can be placed in water or soil to produce another plant. Spider plants also reproduce sexually. Strawberries reproduce new plants by the division of cells from runners or roots. Strawberries also reproduce sexually. Some flatworms can grow by cell division from a fragmented section of its body. Paramecium is a single-celled organism that reproduces by splitting in two. Division of the roots reproduces new mint. Mint also reproduces sexually. A single celled organism that reproduces by splitting in two. Protists have a nucleus and are therefore eukaryotic. Some protists contain chloroplasts and make their own food, and others don't. But all reproduce by fission-the process of splitting in two. Cell division forms a bud that is an identical copy of its single parent that separates from the parent and becomes independent. Which is Better? It depends! Asexual Reproduction • advantages – does not require special cells or a lot of energy – can produce offspring quickly – in a stable environment creates large, thriving population • disadvantages – limited ability to adapt – face massive die-off if environment changes Sexual Reproduction • advantages – lots of variation within a species – able to live in a variety of environmental settings – able to adapt to changes in the environment • disadvantages – needs time & energy – produce small populations