UNIT 3 – ASEXUAL REPRODUCTION IN PLANTS –PART 1 CAPE BIOLOGY

OBJECTIVES You should be able to: Explain the term asexual reproduction. Discuss the advantages and disadvantages of asexual reproduction. Discuss the genetic consequences of asexual reproduction.

INTRODUCTION Reproduction: the formation of a new organism from one or two individuals. It involves the passing on of genetic material which ensures the survival of a species. There are two types of reproduction, asexual and sexual reproduction. Reproduction involves cell division, growth and development.

COMPARISON OF TYPES OF REPRODUCTION ASEXUAL REPRODUCTION SEXUAL REPRODUCTION An organism grows an offspring from itself Two parents There is no joining of gametes There is joining of gametes (fertilization) The new organism is genetically identical to its parent i.e. it does not produce variation. It is ideal for stable environments if the organisms is adapted to the environment. The new organism is genetically different to its parent thus it produces variation. This makes it good for an unstable environment where new adaptations are necessary for survival of offspring. It involves mitosis The formation of gametes involves meiosis Examples – binary fission in the Amoeba, spore production in fungi, bud growth in potatoes Examples – all vertebrates and most plants

ASEXUAL REPRODUCTION Asexual reproduction involves only one individual. There is no exchange of sex cells or gametes. The cell division associated with asexual reproduction is mitosis. Cells produced by this type of division are identical to the original*. The resulting offspring of asexual reproduction are therefore identical to the original organism or clones of the original. *There may be slight variation due to mutations e.g. bacteria

ADVANTAGES OF ASEXUAL REPRODUCTION It requires only one organism thus no effort is needed to create ways to exchange gametes. It can lead to the rapid dispersal of species e.g. fungus and grass It can be a quick way to reproduce e.g. bacteria and parasites. In some cases there are more food reserves for the offspring and these have a better chance of surviving.

GENETIC SIGNIFICANCE OF IDENTICAL OFFSPRING Since the offspring of asexual reproduction are genetically identical to the original organism, this type of reproduction is advantageous for those organisms living in stable environments. AGRICULTURAL APPLICATION This is also an advantage for farmers who use asexual reproduction to propagate crops. If the original plant has all the features e.g. disease resistance, grows to good size, tasty, looks good – the offspring will have these features as well.

DISADVANTAGES OF ASEXUAL REPRODUCTION It does not produce genetic variation. Overcrowding may occur. If the offspring are dispersed e.g. in the form of spores, some may land where they cannot grow or thrive.

SIGNIFICANCE OF LACK OF GENETIC VARIATION If used for propagation of crop plants, the quality of the crop cannot be improved. The lack of variation means weaknesses show in the offspring after several generations. Diseases are automatically passed onto the offspring.

REVIEW QUESTIONS Define reproduction. Why is reproduction important? Compare asexual and sexual reproduction. What are the advantages and disadvantages of asexual reproduction? What is the genetic significance of the lack of variation in asexual reproduction?

TYPES OF ASEXUAL REPRODUCTION BINARY FISSION, ASEXUAL SPORE FORMATION, BUDDING, FRAGMENTATION TYPES OF ASEXUAL REPRODUCTION

BINARY FISSION This occurs in unicellular organisms where two or more identical daughter cells are produced from a single cell. Sometimes the process can occur multiple times and create many offspring e.g. bacteria and the malaria parasite Plasmodium.

DISCUSSION QUESTION Q. Why do you think this is an advantage to bacteria and other parasites? A. Many offspring are lost or destroyed between hosts or by the organism’s immune system. Being able to create large amounts of offspring ensures survival of the species.

http://aark. portal. isis http://aark.portal.isis.org/Amphibian%20photos/Forms/DispFohttp://aark.portal.isis.org/Amphibian%20photos/Forms/DispForm.aspx?ID=179ttp://aark.portal.isis.org/Amphibian%20photos/Forms/DispForm.aspx?ID=179m.aspx?ID=179 TADPOLES AND FISH SOURCES OF PICTURES OF FISH AND TADPOLES http://aark.portal.isis.org/Amphibian%20photos/Forms/DispForm.aspx?ID=179 http://sashaintaiwan.blogspot.com/

EXAMPLE - AMOEBA The Amoeba reproduces by binary fission, a form of asexual reproduction. The Amoeba stops all activities. The nucleus begins to divide. When the division of the nucleus has been completed, the cytoplasm begins to divide. This division process continues until completion when two daughter Amoebae are formed.

EXAMPLE - AMOEBA

VIDEO CLIP http://www.youtube.com/watch?v=fUxPL8cySwY

Encystment occurs when the pond or ditch in which an Amoeba lives in dries up, it forms a cyst around itself to protect it from drying up. When the pond fills with water again, the cyst breaks open releasing many Amoebae into the water. EXCYSTATION is the process where the cyst wall breaks down.

ASEXUAL SPORE FORMATION Spores are small structures which form new organisms. They contain a cell and a small amount of food. Large quantities of spore are produced since so many will land on inhospitable areas.

DIAGRAM OF FUNGUS

LIFE CYCLE OF FUNGUS – Pencillium sp Hypha Conidia produced asexually. Spores from conidia Germinating spores with hyphae. Sexual reproduction stage when male nuclei fuse in male hypha (6) with female nuclei in female hyphae (7). Fusion shown in (8). Structure (9) asci contain ascospores (10) are produced after fusion of male and female nuclei. A vesicle is formed (11) which produces conidia which in turn produces asexual spores.

BUDDING A new organisms is formed from an outgrowth of the original. This occurs in plants and some simple organisms

DIAGRAM OF HYDRA http://www.youtube.com/watch?v=a5oHMjGqjyo&NR=1

FRAGMENTATION An organism breaks into two parts, each of which forms new individuals. Examples Ribbon worms Starfish Video clip of fragmentation http://www.youtube.com/watch?v=d5dOSyaKWTQ