Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

This page supports the lesson note with a companion video and a short classroom-ready summary.

For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.

Performance objectives

• Define 'micro-organism' and their importance.
• Describe the five-kingdom classification system.
• Explain the characteristics and roles of bacteria.
• Distinguish between viruses and bacteria.
• Describe the economic and environmental importance of micro-organisms.

Lesson summary

Micro-organisms, often invisible to the naked eye, play a pivotal role in our lives and the ecosystems around us. From the food we eat to the air we breathe, microbes are constantly at work. Understanding their diversity and how we classify them is crucial for fields like medicine, agriculture, and environmental science. In South Africa, micro-organisms have a significant impact on our health (think of diseases like Tuberculosis and HIV, both caused by micro-organisms), our food production (think of fermentation processes used to make amahewu or mageu), and our environment (think of the role of bacteria in cleaning up pollution).

Lesson notes

What are Micro-organisms? Micro-organisms (or microbes) are microscopic organisms, meaning they are too small to be seen with the naked eye. They include bacteria, archaea, fungi, protozoa, algae, and viruses. While viruses are not technically living organisms (they require a host cell to reproduce), they are often studied alongside micro-organisms due to their small size and significant impact on living things.

The Five-Kingdom Classification System: Biologists classify living organisms into different groups based on their characteristics and evolutionary relationships. A widely used system is the Five-Kingdom Classification, proposed by Robert Whittaker in

1

9

6

9. This system divides organisms into five kingdoms: Monera (Prokaryotes): This kingdom includes all bacteria and archaea. These are single-celled organisms that lack a membrane-bound nucleus and other complex organelles. Their DNA is typically a single, circular chromosome.

Protista: This kingdom includes a diverse group of mostly single-celled eukaryotic organisms (organisms with a nucleus). Examples include protozoa (like amoeba and paramecium) and algae (like euglena and diatoms). They exhibit a wide range of nutritional strategies (autotrophic and heterotrophic).

Fungi: This kingdom includes organisms like mushrooms, molds, and yeasts. Fungi are eukaryotic, mostly multicellular (except for yeasts), and heterotrophic. They obtain nutrients by absorbing organic matter from their environment (saprophytes) or by parasitizing other organisms.

Plantae: This kingdom includes all plants. Plants are eukaryotic, multicellular, and autotrophic, meaning they produce their own food through photosynthesis.

Animalia: This kingdom includes all animals. Animals are eukaryotic, multicellular, and heterotrophic, meaning they obtain nutrients by consuming other organisms.

Micro-organisms and the Five Kingdoms: Kingdom Monera: All members are micro-organisms (Bacteria and Archaea).

Kingdom Protista: Many members are micro-organisms (e.g., Protozoa, some algae).

Kingdom Fungi: Some members are micro-organisms (e.g., Yeasts, some molds).

Bacteria: Structure and Function Bacteria are prokaryotic, single-celled organisms. They are found everywhere, from the soil and water to the inside of our bodies.

Structure: Cell Wall: Provides shape and support. Bacterial cell walls are typically made of peptidoglycan, a unique molecule not found in eukaryotic cell walls. This difference is important because many antibiotics target peptidoglycan synthesis, selectively killing bacteria without harming our own cells.

Cell Membrane: Encloses the cytoplasm and regulates the passage of substances in and out of the cell.

Cytoplasm: The jelly-like substance inside the cell, containing the DNA, ribosomes, and other essential molecules.

DNA: A single, circular chromosome located in the cytoplasm (not enclosed in a nucleus). Some bacteria also have plasmids, small circular DNA molecules that can carry genes for antibiotic resistance or other special functions.

Ribosomes: Structures responsible for protein synthesis.

Flagella (optional): Whip-like structures used for movement.

Pili (optional): Hair-like appendages used for attachment to surfaces.

Reproduction: Bacteria reproduce asexually through a process called binary fission. The cell divides into two identical daughter cells. Under optimal conditions, some bacteria can divide every 20 minutes.

Nutrition: Bacteria can be autotrophic (making their own food through photosynthesis or chemosynthesis) or heterotrophic (obtaining nutrients from other organisms or organic matter).

Ecological Roles: Bacteria play crucial roles in ecosystems: Decomposition: Breaking down dead organic matter and recycling nutrients.

Nutrient Cycling: Converting nitrogen into usable forms for plants (nitrogen fixation).

Food Production: Used in the production of yogurt, cheese, and other fermented foods.

Disease: Some bacteria are pathogens, causing diseases like pneumonia, tuberculosis, and cholera.

Viruses: Structure and Function Viruses are not cells; they are infectious agents consisting of genetic material (DNA or RNA) enclosed in a protein coat called a capsid. They are much smaller than bacteria and require a host cell to replicate.

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

Capsid: A protein coat that protects the genetic material and helps the virus attach to host cells. The capsid is made up of smaller units called capsomeres.

Envelope (optional): Some viruses have an outer envelope derived from the host cell membrane. This envelope may contain viral proteins that help the virus attach to and enter host cells.

Reproduction: Viruses cannot reproduce on their own. They must infect a host cell and hijack its cellular machinery to produce new viral particles. The viral replication cycle typically involves the following steps: Attachment: The virus attaches to the host cell.

Entry: The virus enters the host cell.