Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Define 'micro-organism' and list the major groups.
• Describe the structure and characteristics of bacteria.
• Explain the role of bacteria in the nitrogen cycle.
• Discuss beneficial and harmful impacts of bacteria in South Africa.
• Explain the basic structure of viruses.

Lesson summary

Micro-organisms are all around us, in the air we breathe, the food we eat, and even inside our bodies. They play a vital role in various processes, from nutrient cycling in the environment to the production of essential foods like yogurt and bread. Understanding the biodiversity and classification of these tiny organisms is crucial because it helps us appreciate their impact on our lives, both positive and negative. In South Africa, understanding micro-organisms is particularly important as some are responsible for diseases prevalent in our communities (e.g., tuberculosis caused by bacteria) and in the agricultural sector (e.g., plant diseases caused by fungi).

Lesson notes

2.1 What are Micro-organisms? Micro-organisms, also known as microbes, are microscopic organisms that are too small to be seen with the naked eye. They include bacteria, viruses, fungi (some), and protists (some). Studying them requires microscopes. 2.2 Bacteria: The Tiny Powerhouses Bacteria are single-celled prokaryotic organisms (they lack a nucleus and other membrane-bound organelles). They are incredibly diverse and can be found in almost every environment on Earth.

Structure: A typical bacterium consists of: Cell Wall: Provides shape and support. Bacterial cell walls are made of peptidoglycan, a unique polymer of sugars and amino acids. This is an important distinction from plant cell walls (cellulose) and fungal cell walls (chitin).

Cell Membrane: Controls the movement of substances in and out of the cell.

Cytoplasm: A gel-like substance containing the cell's DNA (in a nucleoid region, not enclosed by a membrane), ribosomes (for protein synthesis), and plasmids (small circular DNA molecules carrying extra genes).

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

Pili: (Some bacteria) Hair-like structures used for attachment to surfaces or for transferring genetic material during conjugation.

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

Shapes: Bacteria come in various shapes: Cocci: Spherical (e.g., Streptococcus)

Bacilli: Rod-shaped (e.g., Bacillus)

Spirilla: Spiral-shaped (e.g., Spirillum)

Vibrios: Comma-shaped (e.g., Vibrio)

Reproduction: Bacteria reproduce primarily through binary fission, a type of asexual reproduction where one cell divides into two identical daughter cells. Under optimal conditions, some bacteria can divide every 20 minutes! Some bacteria can also exchange genetic material through conjugation, using pili.

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

Example: Escherichia coli (E. coli) is a bacterium commonly found in the human gut. It's mostly harmless and even beneficial, aiding in digestion.

However, some strains of E. coli can cause food poisoning. 2.3 The Nitrogen Cycle and Bacteria Bacteria play a crucial role in the nitrogen cycle, which is essential for plant growth and therefore vital for agriculture in South Africa.

Key processes include: Nitrogen Fixation: Certain bacteria (e.g., Rhizobium in root nodules of legumes like beans and peas) convert atmospheric nitrogen (N 2 ) into ammonia (NH 3 ), a form plants can use. This is incredibly important because plants cannot directly use atmospheric nitrogen.

Equation: N 2 + 8H + + 8e - + 16 ATP → 2NH 3 + H 2 + 16 ADP + 16 Pi Nitrification: Other bacteria (e.g., Nitrosomonas and Nitrobacter) convert ammonia (NH 3 ) into nitrites (NO 2 - ) and then into nitrates (NO 3 - ), which are also readily absorbed by plants.

Step 1 (Nitrosomonas): 2NH 3 + 3O 2 → 2NO 2 - + 2H + + 2H 2 O Step 2 (Nitrobacter): 2NO 2 - + O 2 → 2NO 3 - Denitrification: Some bacteria (e.g., Pseudomonas) convert nitrates (NO 3 - ) back into atmospheric nitrogen (N 2 ), completing the cycle. This can be a problem in agriculture if too much nitrate is lost. 2.4 Beneficial and Harmful Impacts of Bacteria Beneficial: Food Production: Bacteria are used to make yogurt, cheese, sauerkraut, and other fermented foods. Lactobacillus bacteria are used in yogurt production.

Digestion: Bacteria in our gut help us digest food and produce vitamins.

Decomposition: Bacteria decompose dead organisms and organic matter, recycling nutrients back into the environment.

Bioremediation: Some bacteria can break down pollutants, cleaning up contaminated sites.

Nitrogen Fixation: As explained above, essential for agriculture.

Harmful: Diseases: Many bacteria cause diseases, such as tuberculosis (caused by Mycobacterium tuberculosis), cholera (caused by Vibrio cholerae), and food poisoning (caused by Salmonella, E. coli, etc.). The spread of TB is a major health concern in South Africa.

Spoilage: Bacteria can spoil food, making it unsafe to eat. 2.5 Viruses: The Acellular Intruders Viruses are acellular (not cells) entities that are much smaller than bacteria. They consist of genetic material (DNA or RNA) enclosed in a protein coat called a capsid. Viruses are obligate intracellular parasites, meaning they can only reproduce inside a living host cell.

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

Capsid: Protein coat that protects the genetic material.

Envelope: (Some viruses) A lipid membrane derived from the host cell that surrounds the capsid.

Replication: Viruses cannot replicate on their own. They must infect a host cell and use the host cell's machinery to produce more virus particles.

Diversity: Viruses come in various shapes and sizes, and they can infect a wide range of organisms, including bacteria, plants, and animals.