Structure and Reproduction of Micro-Organisms

Microorganisms encompass a diverse group of organisms, including bacteria, fungi, viruses, and parasites. Each has unique structural characteristics:

• Bacteria: unicellular (single-celled) organisms that have a simple cellular structure. They are characterised by their lack of a nucleus and the presence of a cell wall.

• Fungi: can be unicellular (like yeast) or multicellular (like mould). They have a complex structure with a defined nucleus and cell wall.

• Viruses: are not cells but particle-like entities that can only replicate inside a host organism’s cells. Their structure includes genetic material (DNA or RNA) surrounded by a protein coat.

• Parasites: organisms that live on or inside a host organism and cause it harm. They can be unicellular (like Plasmodium, which causes malaria) or multicellular (like tapeworms).

• Structure of bacteria: Bacteria have three basic shapes - sphere (coccus), rod (bacillus), and spiral (spirochete). They lack a nucleus but have a nucleoid region where their DNA is located. Other features include a rigid cell wall, a cytoplasm with various enzymes, and ribosomes for protein synthesis. Some bacteria also have flagella for movement.

• Structure of viruses: Viruses are composed of an outer protein coat called a capsid and an inner core of genetic material (either DNA or RNA). Some viruses also have a lipid envelope derived from the host cell membrane. They lack the standard cellular components as they are not cells.

• Microbial reproduction: Bacteria and fungi typically reproduce asexually through a process called binary fission. This involves the organism duplicating its DNA and then splitting into two identical daughter cells. Viruses, on the other hand, replicate by invading a host cell and taking over its machinery to make more virus particles.

• Parasitic reproduction: Parasites can reproduce both sexually and asexually, depending on the species and life stage. They often have complex life cycles requiring multiple hosts.

• Fungal reproduction: Fungi can reproduce both sexually and asexually. Asexual reproduction often involves the production of spores, which are dispersed and grow into new organisms. Sexual reproduction involves the fusion of male and female cells to produce spores.

• Viral reproduction: Viruses reproduce by invading a host cell and using its machinery to produce more viruses. This can occur through a lytic cycle (which kills the host cell) or a lysogenic cycle (which incorporates the viral DNA into the host’s genome).

• Antibiotics are drugs that kill bacteria or stop them from reproducing but they are ineffective against viruses.

• Vaccines can provide immunity against many viral and bacterial infections. They work by stimulating the immune system to recognise and fight specific viruses or bacteria.

• Microorganisms play a crucial role in ecosystems, acting as decomposers and participating in nutrient cycling. Additionally, they can be beneficial for human health, as is the case with the microbiota living in our gut.

• Pathogenic microorganisms cause diseases in humans and other organisms. They can be spread in several ways, including through direct contact, through the air, through food and water, or via vectors like insects.

• Microorganisms can also develop resistance to antimicrobial drugs. This process, known as antimicrobial resistance (AMR), can make treatment of certain infections very challenging.

These points should provide a sound basis for understanding the structure and reproduction of microorganisms and their interactions with human health. To get the most out of this revision, make sure to also practise identifying different types of microorganisms and understanding their roles in disease and health. Active recall and spaced repetition are techniques that can further assist your revision process.