Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Describe the main groups of micro-organisms: Bacteria, Archaea, Fungi, and Viruses.
• Explain the criteria used to classify them (e.g., cell structure).
• Compare the structure and reproduction of Bacteria and Viruses.
• Explain their role in ecosystems and human health.
• Evaluate the importance of hygiene in South Africa.

Lesson summary

Micro-organisms, despite their tiny size, play a colossal role in our lives and the environment. They are involved in everything from the air we breathe and the food we eat to the breakdown of waste and the cycling of nutrients in ecosystems. Understanding their biodiversity and how we classify them is crucial for comprehending the complex web of life. This knowledge allows us to develop strategies for combating diseases, improving agricultural practices, and maintaining environmental sustainability – all incredibly relevant in the South African context, given our challenges with disease prevalence, food security, and environmental degradation.

Lesson notes

Micro-organisms, also known as microbes, are microscopic organisms that are too small to be seen with the naked eye. They are incredibly diverse and are found in virtually every habitat on Earth. The major groups of micro-organisms we will focus on are Bacteria, Archaea, Fungi, and Viruses. 2.

1. Bacteria: Bacteria are prokaryotic organisms, meaning their cells lack a true nucleus and other membrane-bound organelles. They are typically single-celled and come in a variety of shapes, including spherical (cocci), rod-shaped (bacilli), and spiral (spirilla). Bacteria are found everywhere – in soil, water, air, and even inside other organisms (including humans!).

Structure: Cell Wall: Provides shape and support (made of peptidoglycan). Gram-positive bacteria have a thick peptidoglycan layer, while Gram-negative bacteria have a thin layer and an outer membrane. This difference is crucial for antibiotic targeting.

Cell Membrane: Controls what enters and exits the cell.

Cytoplasm: Contains the genetic material (DNA) and ribosomes.

DNA: A single, circular chromosome.

Plasmids: Small, circular DNA molecules that carry extra genes (e.g., antibiotic resistance).

Flagella: Whip-like structures used for movement.

Pili (Fimbriae): Hair-like structures used for attachment to surfaces.

Capsule: A sticky outer layer that protects the bacteria from phagocytosis (being engulfed by immune cells).

Reproduction: Bacteria primarily reproduce asexually through binary fission, a process where the cell divides into two identical daughter cells. They can also exchange genetic material through conjugation, transformation, and transduction, leading to genetic variation.

Nutrition: Bacteria exhibit diverse modes of nutrition: Autotrophs: Produce their own food through photosynthesis (using sunlight) or chemosynthesis (using chemical energy).

Examples: Cyanobacteria.

Heterotrophs: Obtain food from other organisms (either living or dead).

Saprophytes: Decomposers, feeding on dead organic matter.

Parasites: Live on or in a host organism, causing harm.

Example: Mycobacterium tuberculosis, the bacterium that causes tuberculosis (TB), is a significant health concern in South Africa. Understanding its structure, reproduction, and transmission is crucial for developing effective treatment and prevention strategies. 2.

2. Archaea: Archaea are also prokaryotic organisms, but they are distinct from bacteria in terms of their cell wall composition, membrane lipids, and ribosomal RNA. They were initially classified as bacteria, but advances in molecular biology revealed their unique evolutionary lineage. Many archaea are found in extreme environments, such as hot springs, salt lakes, and acidic conditions.

Structure: Similar to bacteria in lacking a nucleus, but with key differences in cell wall composition (lacking peptidoglycan) and membrane lipids.

Reproduction: Primarily asexual through binary fission, fragmentation, or budding.

Nutrition: Like bacteria, archaea can be autotrophic or heterotrophic. Some archaea are methanogens, producing methane as a byproduct of their metabolism.

Example: Methanobrevibacter smithii is an archaeon found in the human gut. It plays a role in breaking down complex carbohydrates, but excessive methane production can contribute to bloating and discomfort. 2.

3. Fungi: Fungi are eukaryotic organisms, meaning their cells contain a true nucleus and other membrane-bound organelles. They can be unicellular (e.g., yeasts) or multicellular (e.g., molds and mushrooms).

Structure: Cell Wall: Made of chitin.

Hyphae: Thread-like filaments that make up the body of multicellular fungi.

Mycelium: A network of hyphae.

Spores: Reproductive cells that are dispersed to form new fungi.

Reproduction: Fungi reproduce both sexually and asexually, often through the production of spores.

Asexual Reproduction: Budding (in yeasts), fragmentation, and spore formation.

Sexual Reproduction: Involves the fusion of hyphae from two different mating types.

Nutrition: Fungi are heterotrophic and obtain nutrients by absorbing organic matter from their surroundings.

Saprophytes: Decomposers, playing a crucial role in nutrient cycling.

Parasites: Live on or in other organisms, causing diseases.

Example: Candida albicans is a yeast that can cause infections such as thrush and vaginal yeast infections, particularly in individuals with weakened immune systems. In South Africa, where HIV prevalence is high, Candida infections are common opportunistic infections. 2.

4. Viruses: Viruses are not cells; they are infectious agents that consist of genetic material (DNA or RNA) enclosed in a protein coat called a capsid. They are obligate intracellular parasites, meaning they can only replicate inside a living host cell.

Structure: Genetic Material: DNA or RNA (single-stranded or double-stranded).

Capsid: A protein coat that protects the genetic material.

Envelope: A lipid membrane derived from the host cell (present in some viruses).