Botany - B.Ye. Yakubenko 2017

Part One. Plant Anatomy and Morphology
Chapter I. Cytology
Laboratory Class Topic 1.2. Structure of the Prokaryotic Cell

General Remarks. Modern and fossil organisms share two MAIN TYPES OF Cells: prokaryotic and eukaryotic. Differences in their Structure served as the basis for establishing two superkingdoms of the living world: prokaryotes (pre-nuclear organisms) and eukaryotes (true-nucleated organisms). The structure of prokaryotes is significantly simpler than that of eukaryotes, and their overall Abundance is relatively low compared to nuclear organisms. Unlike eukaryotes, a Introduction/4.html">Prokaryotic Cell lacks a defined Nucleus; instead, it is replaced by a specialized nuclear region in the Cytoplasm known as the nucleoplasm. Prokaryotes lack typical Chromosomes, and their genetic material is represented solely by a DNA molecule that is not associated with Proteins. Prokaryotes lack many cell Organelles characteristic of Eukaryotic cells, such as the Golgi apparatus, Endoplasmic reticulum, Mitochondria, Plastids, and Lysosomes. Prokaryotic Ribosomes are smaller than eukaryotic ones. The Functions of Mitochondria and Plastids are performed by simply structured membrane formations, such as mesosomes and proplastids.

Objects: fixed or living material of the blue-green alga common nostoc (Nostoc commune Vauch.)

Tasks:

1. Prepare a temporary mount of the common nostoc alga on your own.

2. Examine the STRUCTURE OF THE prokaryotic alga under low and high Microscope magnification.

3. Sketch the general appearance of the colony under low magnification, and a single filament with heterocysts and a vegetative cell under high magnification, labeling their main structural components.

Equipment and Materials: MBR-1 or Biolam microscope, microscope slides and coverslips, dissecting needles, fixed or living culture material, and other accessories.

Procedure for preparing a microscopic mount of common nostoc. Wipe the microscope slide and coverslip thoroughly clean and dry. Place the slide on a staining rack and apply a drop of Water onto it. Using a dissecting needle, take a tiny piece of the mucous mass of nostoc, place it into the drop of water on the slide, and cover it with a coverslip.

Microscopic Examination of the Mount. Examine the mount first under low microscope magnification. Locate and observe the mucilaginous colony of nostoc in the field of view, which appears as a mass of convoluted filaments (Fig. 12) often intertwined and composed of spherical or barrel-shaped blue-green cells. The Cell wall of each individual consists of pectic substances and easily mucilaginates. The characteristic pigments that impart the blue-green color to the alga are phycocyanin and chlorophyll.

Next, examine the object under high microscope magnification. Focus on the presence of different cell types—heterocysts and vegetative cells. In the latter, the following structural elements can be distinguished: The Cell wall, granular chromatoplasm, and centroplasm (Fig. 12).

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Figure 12. General appearance of the colony and an individual filament of Nostoc commune

Conclusions. 1. Prokaryotes represent one of the oldest groups of organisms, encompassing Bacteria and blue-green Algae (cyanobacteria).

2. Cells of prokaryotic organisms lack a differentiated nucleus, METABOLISM/14.html">Chloroplasts, mitochondria, and several other organelles.

Self-Control Questions

1. What prokaryotic organisms do you know, and where are they distributed?

2. What are the Structural Features of prokaryotes?

3. What is the colorless region of a prokaryotic cell called that contains

Nucleic Acids?

4. Which organisms are characterized by the presence of a chromatoplasm that performs

the function of Photosynthesis?

5. How do prokaryotic and eukaryotic cells differ in structure?