Learning Objective:
To study (a) binary fission in Amoeba and (b) budding in yeast with the help of prepared slides.
Materials Required:
Light/compound microscope
Prepared slides(of amoebas and yeast reproducing)
Safety Precautions:
1. HANDLE MICROSCOPE WITH CARE
Experimental Accuracy:
1. Ensure that the microscope is clean
2. Ensure that the most promising region of the slide is in the centre of the stage
3. Ensure that low power is used first, before higher power
Processes:
Binary Fission: a mode of asexual reproduction, commonly observed in bacteria, in which genetic material is duplicated in a cell, before the organism undergoes cytokinesis to produce two viable progeny cells that are genetically identical. Binary fission is a form of amitosis, where unlike mitosis, spindle and chromosome formation is not observed.
Budding: a mode of asexual reproduction which sees a new organism growing from a parent organism via an extension growth/outgrowth out of the parent organism, at a site of cell division.
Methodology:
1. Place the prepared slides sequentially on the microscope’s stage by attaching them to stage clips
2. Focus the microscope on low power, before choosing the appropriate power
3. Observe the image of the cells and make a clean sketch in your notebook
General Preparation of a Temporary Mount:
1) Place a one cell thick layer of cells on the slide
2) Add a drop of water or stain
3) Lower a coverslip onto the drop(carefully so as to prevent the formation of air bubbles)
4) Place the slide inside folded paper towel/blotting or filer paper to drain excess fluid. Press on the coverslip lightly/gently from the outside of the paper towel
Observation - Amoeba:
Stage 1: Pseudopodia (extensions of the cell for locomotion) retreat inwards, to make the cell more rounded
Stage 2: The nucleus divides, followed by the division of the cytoplasm
Stage 3: A cleavage furrow forms at the site of invagination/division/fission
Stage 4: The furrow grows, dividing the cell, giving rise to two distinct daughter cells
Observation - Yeast:
Stage 1: A tiny protuberance is seen due to an outgrowth
Stage 2: The nucleus divides, before moving to the outgrowth
Stage 3: This budding repeats, producing a chain of cells
We’ll have to include a diagram similar to the one above that corresponds with the given stages
Experiment in Context:
While asexual reproduction has been demonstrated in unicellular organisms such as amoeba and yeast, it can also happen in multicellular organisms such as plants.
Asexual Reproduction in plants: All flowering plants produce sexually, however some also have asexual means which come under the term vegetative propagation.
Generally, it is a lateral bud which grows from a stem(which may be close to or under the soil ) and produces an independent organism when the parent dies
1. Rootstock: The rootstocks bear leaves and flowers. After the main shoot flowers, the rootstock grows a lateral bud, which grow a shoot horizontally over the ground(and are called stolons or runners)
At each node, there is a bud which can grow into a plant, and while the parent is alive, it ensures that the bud at each stolon node is well nourished. The stolen eventually dries up and withers, leaving an independent daughter plant.
2. The plant has lateral buds near the stem base which grows a shoot horizontally, but unlike stolons, these shoots are underground(and are called rhizomes).Rhizomes contain buds at nodes which may develop above-ground shoots. The rhizome eventually dies out and an independent bud, whose shoots can develop into a plant is left.
3. Bulbs and corms: The leafy bases(or stems in the case of corms) take in food , especially during growing season, and then form a new bulb by swelling. The lateral bud initially grows in the parent plant but when the new bulb forms, it grows in that.
4. Tubers: Lateral buds at the base of shoots produce rhizomes which swell up with stored starch to become tubers. The tubers are stems which have buds and if the tuber is left underground, it can grow the shoots upwards.
There are also some artificial modes of vegetative reproduction that exist, which allow it to take place in vitro.
