Asexual Reproduction in Amoeba and Yeast

Objective

Our objective is to study using the prepared slides;

  1. Binary fission in Amoeba.
  2. Budding in Yeast.

The Theory

Reproduction

All living things produce their own kind through the process called reproduction. Reproduction takes place sexually and asexually.

Sexual reproduction

Sexual reproduction is the primary method of reproduction for the vast majority of macroscopic organisms, including almost all animals and plants. Here are two main processes during sexual reproduction in eukaryotes: meiosis, involving the halving of the number of chromosomes; and fertilisation, involving the fusion of two gametes and the restoration of the original number of chromosomes. During meiosis, the chromosomes of each pair usually cross over to achieve homologous recombination that helps produce genetic diversity when cells divide in meiosis.

Asexual reproduction

Asexual reproduction is the primary form of reproduction for single-celled organisms such as the archaea, bacteria, and protists. Many plants and fungi reproduce asexually as well. Asexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only. The offspring will be the exact genetic copies of the parent.

New organisms are produced in rapid multiplication by the process of amitotic or mitotic divisions. Amitosis is the process by which a cell directly separates, as the nucleus and cytoplasm are directly cut in two. Mitosis is the process by which a cell, which has previously replicated each of its chromosomes, separates the chromosomes in its cell nucleus into two identical sets of chromosomes, each set will have its own new nucleus. It is a form of nuclear division.

Binary fission and budding are two common method of asexual reproduction. Binary fission is found in unicellular organisms like Amoeba, Paramaecium and Euglena, to name and few. Budding is found in Yeast and Hydra.

Binary fission in Amoeba

Amoeba is a shapeless tiny unicellular organism that has a porous cell membrane which encloses the cell organelles and cytoplasm. Amoeba reproduces by the common asexual reproduction method called binary fission. After replicating its genetic material through mitotic division, the cell divides into two equal sized daughter cells. The genetic material is also equally partitioned; therefore the daughter cells are genetically identical to each other and the parent cell. In this process, the nucleus of the Amoeba first divides to form two daughter nuclei by the process of Karyokinesis. After the nucleus has divided into two, the process of Cytokinesis takes place in which the cytoplasm in the mother cell divides into two daughter cells. This leads to the formation of the two daughter Amoebae cell having a nucleus and its own cell organelles.

Karyokinesis is the process of the division of the nucleus. It corresponds to the separation of the daughter chromosomes into two daughter nuclei. Karyokinesis is usually followed by Cytokinesis.

Cytokinesis is the process of the division of the cytoplasm. It corresponds to the separation of the daughter nuclei into two daughter cells. Cytokinesis occurs immediately after mitosis.

 

Budding in Yeast

Yeast are unicellular (some are multicellular) eukaryotic micro-organisms belonging to the kingdom fungi. Yeast size can vary greatly depending on the species, typically measuring 3-4 µm in diameter. Most yeasts reproduce asexually by an asymmetric division process called budding. First it produces a small protuberance on the parent cell that grows to a full size and forms a bud. The nucleus of the parent cell splits into a daughter nucleus and migrates into the daughter cell. The bud detaches from the mother’s body by forming a constriction at the base. Budding will repeat to form a chain of bud cells. The daughter cell produced during the budding process is generally smaller than the mother cell.

 

Learning Outcomes

  1. Students understand the terms budding, binary fission and a few other terms.
  2. Students understand the different stages of binary fission in Amoeba.
  3. Students understand the different stages of budding in Yeast.
  4. Students understand the experiment better through the animated demonstration.

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