Mechanisms of Reproduction PDF

Mechanisms of Reproduction  Explain the mechanisms of reproduction that ensure the continuity of a species, by analysing sexual and asexual methods of reproduction in a variety of organisms, inclu...

Mechanisms of Reproduction  Explain the mechanisms of reproduction that ensure the continuity of a species, by analysing sexual and asexual methods of reproduction in a variety of organisms, including but not limited to: - Animals: advantages of external and internal fertilisation - plants: asexual and sexual reproduction - fungi: budding, spores - bacteria: binary fission - protists: binary fission, budding Asexual Reproduction: o Offspring created is identical as it comes from one parent. o Use of mitosis. o Individuals have a short lifespan, so for a population or species to survive, genetic material must be passed from one generation to the next. Types of asexual reproduction in plants – o Runners  side branches with clumps of leaves and roots which grow on the ground, the roots dig down and establish the plant as its own individual plant, i.e.. Strawberries. o Bulbs  bulbs are underneath certain plants which allow buds to grow from them and then flourish their own individual plant eg. Daffodil o Cutting  branch off a tree is cut and stripped down, then is planted again to grow as its own individual plant. o Spores  Airborne cells that are released from the parent. They are enclosed and developed when the environment is appropriate. E.g., Fungi → Mushrooms. o Binary Fission  A parent cell divides, resulting in two identical cells, each having the potential to grow to the size of the original cell. E.g., Amoeba, Bacteria, Paramecium. Asexual Reproduction in Unicellular Life – o Single-celled organisms such as bacteria reproduce by simply dividing in two by mitosis. The offspring cells are genetically identical to each other, and to the “parent cell”. o Among the single-celled, eukaryotic protists such as Amoeba & Paramecium species binary fission (splitting in two) is also common but is often more complex than simple mitosis division. o In single-celled fungi (yeasts) a process called “budding” is very common. This is a form of binary fission in which a new cell is formed as a small “bud” growing on the parent cell. It separates as a new cell and grows to full size. Each budding cycle doubles the population, so a few cells can become millions very quickly. Asexual Reproduction in Multicellular Life – o Many multi-cellular organisms are also able to reproduce asexually. o Even some animals can reproduce asexually. Perhaps the best-known example is the small aquatic animal Hydra. This is a relative of jellyfish & coral animals. o Hydra can reproduce sexually by releasing eggs or sperm into the water but can also reproduce asexually by a “budding” process. A small out-growth appears on its body and grows into a new little hydra. Eventually this “baby” separates from the parent to live freely as a separate individual.  Asexual Reproduction Advantages Disadvantages  Asexual reproduction can produce large  By producing genetically identical offspring, numbers of offspring quickly, to take advantage there is less variation in the population. If an of a sudden or temporary increase in some environmental change occurs, a low-variation environmental resource such as food. species is at risk of extinction. Sexual Reproduction: o Involves fusion of genetic material which is the combination of two parents to form an offspring causing high genetic variation. o Use of meiosis. Methods of Sexual Reproduction –  Process of Pollination  insects, birds or wind carry pollen (male sex gamete) from a flower to another. The pollen attaches to the stigma where the fusion of the two gametes causes a seed to grow where the ovules once were > grows into a fruit. Sexual Reproduction Advantages Disadvantages  Sexual reproduction produces more variation  Sexual reproduction is more complex, and in a population, by mixing genes in new often takes more time and energy to achieve. combinations. This helps a species survive when environments change. Internal Fertilisation External Fertilisation o The union of an egg and a sperm cell o Fertilisation that occurs outside of the internally through sexual reproduction. organisms. The sperm cell meets the egg cell outside of the body. Advantages –  Increased possibility of gamete union. Advantages –  Higher birth rates as foetus grows  Generally, many offspring are formed. within an organism not outside of.  More genetic variation.  More selective of mates.  Easier to fertilise as they don’t need to mate. Disadvantages – Disadvantages –  Time must be sent trying to attain a  Fusion of gametes may not occur.  mate.  Must occur in water.  Increased energy must be used to fuse  Decreased chance of fertilisation. gametes.