Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Define 'micro-organism' and give examples.
• Describe the five-kingdom classification system and where microbes fit.
• Explain the basic structures of bacteria and protists.
• Differentiate between beneficial and harmful microbes with South African examples.
• Discuss the importance of controlling microbial growth.

Lesson summary

Micro-organisms (or microbes) are tiny living things that are all around us – in the air, soil, water, and even inside our bodies. They're a crucial part of our ecosystem, playing essential roles in nutrient cycling, food production, and even human health. Understanding their biodiversity and how they are classified is vital because it impacts everything from preventing diseases to developing new medicines and ensuring food security. In South Africa, where we face unique challenges related to infectious diseases and food production, grasping these concepts is particularly important for informed decision-making about health, agriculture, and conservation.

Lesson notes

What are Micro-organisms? Micro-organisms are organisms that are too small to be seen with the naked eye. They are typically unicellular (single-celled) but can sometimes form colonies. The main groups of micro-organisms include: Bacteria: Prokaryotic cells (lacking a nucleus) with a cell wall made of peptidoglycan.

Archaea: Also prokaryotic cells, but with cell walls made of different substances (not peptidoglycan) and distinct metabolic pathways. Often found in extreme environments.

Protists: Eukaryotic cells (containing a nucleus) that are mostly unicellular.

Fungi: Can be unicellular (like yeast) or multicellular (like mushrooms). They are eukaryotic and have cell walls made of chitin.

Viruses: Technically not living organisms as they require a host cell to replicate. They consist of genetic material (DNA or RNA) enclosed in a protein coat. The Five-Kingdom Classification System and Micro-organisms: The five-kingdom classification system, although now often superseded by more modern systems involving domains, is still useful for illustrating the basic relationships of living organisms and their major groups. It divides all living organisms into five kingdoms: Monera: This kingdom consists of prokaryotic organisms, meaning their cells lack a true nucleus.

It includes: Bacteria: These are the most abundant organisms on Earth. They play crucial roles in nutrient cycling (e.g., nitrogen fixation), decomposition, and can be both beneficial (e.g., gut bacteria) and harmful (e.g., Mycobacterium tuberculosis, the cause of TB).

Structure of Bacteria: Bacteria have a cell wall, cell membrane, cytoplasm, ribosomes, and DNA (in a circular chromosome called a plasmid). Some have flagella for movement and capsules for protection.

Reproduction: Bacteria reproduce asexually through binary fission (cell division).

Archaea: Similar in appearance to bacteria, but genetically and biochemically distinct. They are often found in extreme environments like hot springs or salt lakes.

Protista: This kingdom consists of eukaryotic, mostly unicellular organisms.

They are incredibly diverse and include: Protozoa: Animal-like protists, such as Amoeba and Paramecium. They are heterotrophic (obtain nutrients by consuming other organisms).

Algae: Plant-like protists, such as Euglena and diatoms. They are autotrophic (produce their own food through photosynthesis).

Structure of Protists: Protists have a cell membrane, cytoplasm, nucleus, and other organelles like mitochondria and chloroplasts (in algae). Some have flagella or cilia for movement.

Reproduction: Protists reproduce both asexually (e.g., binary fission, budding) and sexually (e.g., conjugation).

Fungi: Eukaryotic organisms with cell walls made of chitin. Can be unicellular (yeasts) or multicellular (mushrooms). They are heterotrophic and obtain nutrients by absorbing organic matter.

Example: Yeast used in bread making, Penicillium (source of penicillin).

Plantae: Multicellular, eukaryotic organisms with cell walls made of cellulose. They are autotrophic and produce their own food through photosynthesis.

Animalia: Multicellular, eukaryotic organisms that lack cell walls. They are heterotrophic and obtain nutrients by consuming other organisms. Beneficial and Harmful Micro-organisms (South African Examples): Beneficial: Bacteria in Yoghurt Production: Lactobacillus bacteria are used to ferment milk and produce yoghurt, a popular and nutritious food source in South Africa.

Nitrogen-fixing Bacteria: Rhizobium bacteria in the root nodules of legumes (beans, peas) convert atmospheric nitrogen into ammonia, which plants can use. This is essential for soil fertility in South African agriculture.

Decomposers: Bacteria and fungi decompose dead organic matter, returning nutrients to the soil. This is vital for maintaining healthy ecosystems.

Harmful: Mycobacterium tuberculosis: Causes tuberculosis (TB), a major public health challenge in South Africa.

Vibrio cholerae: Causes cholera, a waterborne disease that can be a problem in areas with poor sanitation.

Fungi causing crop diseases: Various fungi can infect crops like maize and wheat, leading to significant yield losses and impacting food security.

Controlling Microbial Growth: Controlling microbial growth is essential to prevent diseases, preserve food, and maintain hygiene.

Methods include: Sterilization: Kills ALL micro-organisms, including spores. Examples include autoclaving (using high-pressure steam), radiation, and filtration.

Disinfection: Kills most, but not all, micro-organisms. Examples include using disinfectants like bleach and alcohol.

Antiseptics: Disinfectants that are safe to use on living tissue, like skin. Examples include alcohol-based hand sanitizers.

Pasteurization: Heating liquids to a specific temperature for a specific time to kill harmful micro-organisms without significantly altering the taste or nutritional value.

Example: Milk pasteurization.