Grade 9 Science Unit #3: Reproduction Topic #3 Asexual and Sexual Reproduction

Transcription

1 Grade 9 Science Unit #3: Reproduction Topic #3 Asexual and Sexual Reproduction Lesson Topic What you will learn: 1 Asexual Reproduction - Asexual reproduction involves only one parent - Plants can reproduce asexually by binary fission, spore production, vegetative reproduction, fragmentation, or grafting. Animals can reproduce asexually by budding or parthenogenesis - Asexual reproduction can produce lots of identical individuals very quickly but produces entire populations of individuals that may not survive if the environmental conditions are not optimal - Asexual reproduction is a fundamental part of the agriculture 2 Sexual Reproduction and forestry sectors in Saskatchewan - Sexual reproduction in animals is achieved by the union of male and female gametes - Gametes are produced through the process of meiosis - Sexual reproduction produces individuals with many variations of characteristics, so they are very rarely identical; this form of reproduction may require a large amount of energy to produce only a small number of offspring

2 Grafting Budding A. Asexual Reproduction Asexual reproduction is a method of reproduction where a single parent reproduces its offspring. There is no genetic recombination; therefore the DNA of the offspring is identical to that of its parent. Offspring that are identical copies of each other are called clones. In some cases, asexual reproduction can produce lots of identical individuals very quickly. Over a 12-hour period, a single bacterium can divide to produce 10 million copies of itself. This is a great advantage in environments that do not change very much. Ex. Bacteria that live in the gut of an animal will always have a warm, moist environment to live in while the animal is alive. Producing many copies of a bacterial cell that is suited to that environment is a safer bet for survival than producing a smaller number of bacteria with many variations that may never be needed. The main disadvantage of asexual reproduction is that all the offspring are identical to the parent. Any factor that negatively affects the parent, such as disease or drug, will also affect all the offspring. Also, if the environmental conditions become unfavorable, the entire population may be wiped out. Definition/Process Diagram Examples of plants The parent produces a small bud, or a miniaturized clone. In some parents, the buds eventually detach and become separate individuals. In other animals, the offspring remain attached to the parent, forming a large structure composed of many identical individuals. One plant is joined with another plant, called the parent tree or the root stock. The two plants heal together and grow as a single plant, but the two plants maintain their own characteristics. Can be used to strengthen the stem of a plant to ensure that it grows and develops a strong, healthy stem. Hydra Yeast Coral This is commonly used by gardeners to produce flowers with certain colours or trees that grow different types of apples on different branches.

3 Vegetative Reproduction Fragmentation Spore Production Binary Fission Occurs when single-celled organisms divide into two identical daughter cells to produce two new individuals that are identical to each other and are clones of the parent cell. Bacteria Amoeba algae Spores are haploid cells that can develop into new organisms. Spores are similar to seeds because they contain and protect the DNA of the organism against unfavourable conditions. Spores remain alive, but they do not grow until environmental conditions are suitable for growth. Fungi Green algae Mould Non-flowering plants New individuals are formed from a piece of the existing parent organism. Some animals can grow two identical individuals after being cut into two pieces. Worms Starfish Many plants Method 1 take a cutting from a coleus plant and place it in water, the cutting will grow roots and eventually develop into a whole new plant. Method 2 Plant produce modified stems that run horizontally over the ground (runners) or under the ground (rhizomes) and produce new plants along their length. Coleus plants Strawberries Spider plants Potatos Onions Tulips

4 Plant Tissue Cultures Parthenogenesis An unfertilized haploid egg matures into new organisms. In some species unfertilized eggs become male drones and fertilized eggs become female workers and queens. Ants Bees Snakes Lizards Plant cells are placed in a petri dish or a bottle containing nutrients and other chemicals and grown into a new individual. Once the cells develop into seedlings, they can be transplanted into soil and grown like a normal plant. Often happens with plants that have desirable features such as disease resistance or good fruit production. Or to conserve endangered plant species. Potatoes are an excellent example of how different methods of asexual reproduction are used in agriculture in Saskatchewan. A parent plant with desirable features is selected, cuttings are taken and either planted and grown or used to create plant tissue cultures. The clones are grown and produce seed potatoes. Seed potatoes are potatoes that are grown for replanting, not eating. The plants grown from seed potatoes produce potatoes sold for eating. Assignment: Page 23 # 1 6, 8, 11, 12

5 B. Sexual Reproduction Sexual reproduction is a method of reproduction that typically involves two parents, a male and female such as with humans and other animals, but can occur with species that we wouldn t consider male and female, such as in plants and coral. Sexual reproduction is the combination of two gametes, male and female sex cells, to produce an offspring. Gametes in females are called eggs or ova, whereas sex cells from a male are called sperm. These cells are produced through meiosis. The union of the sperm cell with the egg cell occurs during mating and is called fertilization. DNA recombines to create offspring with a combination of characteristics from both parents. So offspring are not clones of their parents. Variation helps a species survive by giving it the ability to survive changes in its environment. Although, a major disadvantage or sexual reproduction is that the gametes need to meet. Flowering plants must have wind or attract insects to move pollen to the stigma. Also, the embryo must be protected and nurtured during development. In mammals, the embryo grows within the body of the female parent. Because this takes a large amount of time and energy needed for this development, only a limited number of offspring can be produced. Flowering Plant Structures

6 Pollination is the transfer of pollen grains to the stigma. Pollen transferred to the stigma of the same flower is called self-pollination. If pollen grains are transferred to the stigma of another flower, it is called cross-pollination. Cross-pollination can be caused by various sources, such as: wind, water, bees, birds, bats or other animals (including humans). Fertilization is the process that occurs after pollination. If the pollen grain has landed on a compatible stigma, a pollen tube grows to transport the pollen to the egg. Once the pollen reaches the egg, the two gametes fuse and create a zygote. The zygote then forms into a seed. Germination is the process a plant undergoes as the seed grows into a new plant. Once the seed absorbs water, it begins to expand and open as the new plant grows within it. Sexual Reproduction in Animals In animals, sexual reproduction uses eggs (female gamete) and sperm (male gamete) as the reproductive cells. After the two gametes fuse, a zygote is formed. Fertilization can occur within and exterior to the animal body depending on the specific animals form of reproduction. Once the zygote has undergone cellular division, it forms an embryo, which is a multi cellular structure. The embryo will begin to form small organs and appendages. Once the organs begin to function, it is called a fetus this occurs at approximately the nine week mark in humans. The fetus is final structure an organism will take before birth. Hermaphrodites can produce both male and female gametes. Worms and slugs are examples of hermaphrodites. Although hermaphrodites usually mate with other individuals of their species, in time of environmental stress, members of some species can fertilize themselves. Sequential hermaphrodites are species that are born as one sex, but then become the opposite sex. One example is the clownfish. Clownfish travel in packs that consist of a large reproductive female, a smaller reproductive male as well as numerous smaller nonreproductive males. If the female dies or leaves, the large reproductive male becomes a female and the largest of the non-reproductive males becomes the new reproductive male. Organisms that Reproduce Both Sexually and Asexually Some species have the ability to reproduce both sexually and asexually. Most plants that produce seeds by sexual reproduction can also reproduce asexually, either from cuttings or by producing structures such as bulbs or runners. Some plants can use their seeds to reproduce both asexually and sexually. In the asexual method, embryos develop in the seeds without the contribution of sperm cells. These offspring are genetically identical to their parent.

7 Some animal species can also reproduce both ways. Aphids are small insects that feed on the sap of certain plants. Throughout the growing season, females produce live female young through asexually. Over the summer, several generations are produced. In the fall, when days shorten and the temperature drops, the females produce a generation that includes both males and females. These males and females reproduce sexually and lay eggs that will hatch in the spring to produce new colonies. Sponges can also produce sexually and asexually. Assignment: Page 34 #3, 4, 6 9, 11, 12