Exploring the world of bacteria reveals fascinating insights into these...
Biology184 views·Updated 19 Jun 2026·2 pagesComprehensive WJEC A Level Biology Unit 3.4: Microbiology Mind Map
Caitlin Ellis@caitlinellis0312
1
of 2
Bacterial Classification and Characteristics
Ever wondered how scientists tell different bacteria apart? Bacteria can be distinguished by their shape, size, metabolism, and genetics. Their distinctive shapes—bacilli , cocci (spherical), and spirilli —are maintained by their cell wall structure.
Bacteria have different oxygen requirements that affect where they can survive. Obligate aerobes must have oxygen to metabolise and reproduce, while obligate anaerobes require oxygen-free environments. Facultative anaerobes are the adaptable middle-grounders that can function with or without oxygen, though they prefer having it.
The Gram staining technique is crucial for classifying bacteria into two main groups. Gram-positive bacteria have a thick peptidoglycan layer that retains crystal violet stain, appearing purple under a microscope. Gram-negative bacteria have a thinner peptidoglycan layer and an extra lipopolysaccharide layer, which makes them appear red after counterstaining with safranin.
Did you know? The extra lipopolysaccharide layer in gram-negative bacteria provides protection against many antibiotics, making some infections particularly challenging to treat!
2
of 2
Culturing and Measuring Bacterial Growth
Working with bacteria in the lab requires strict aseptic technique to prevent contamination. This includes washing hands, sterilising work surfaces with disinfectant, using a Bunsen burner to create a sterile area, and properly sterilising all equipment before and after use.
Bacteria need specific growth conditions to thrive in the laboratory. The most common medium is agar, which contains carbon, nitrogen, water, vitamins, and mineral salts. Some bacteria have special requirements – they might need blood agar or specific temperatures to grow. In schools, bacteria are cultured at 25°C to avoid growing human pathogens.
Scientists measure bacterial growth using two main methods: total count and viable count. Total count measures all cells present (living and dead), while viable count only measures living cells capable of reproducing. Before counting, scientists perform serial dilutions (1:10, 1:100, etc.) to make the bacterial population manageable to count.
Pro tip: When conducting a viable count, always choose the plate with the largest number of distinct, non-overlapping colonies to increase the reliability of your count!
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Biology184 views·Updated 19 Jun 2026·2 pagesComprehensive WJEC A Level Biology Unit 3.4: Microbiology Mind Map
Caitlin Ellis@caitlinellis0312
Exploring the world of bacteria reveals fascinating insights into these microscopic organisms. This summary covers their shapes, characteristics, and the essential lab techniques used to study them, providing a practical foundation for understanding microbiology in your science classes.
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Bacterial Classification and Characteristics
Ever wondered how scientists tell different bacteria apart? Bacteria can be distinguished by their shape, size, metabolism, and genetics. Their distinctive shapes—bacilli , cocci (spherical), and spirilli —are maintained by their cell wall structure.
Bacteria have different oxygen requirements that affect where they can survive. Obligate aerobes must have oxygen to metabolise and reproduce, while obligate anaerobes require oxygen-free environments. Facultative anaerobes are the adaptable middle-grounders that can function with or without oxygen, though they prefer having it.
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Culturing and Measuring Bacterial Growth
Working with bacteria in the lab requires strict aseptic technique to prevent contamination. This includes washing hands, sterilising work surfaces with disinfectant, using a Bunsen burner to create a sterile area, and properly sterilising all equipment before and after use.
Bacteria need specific growth conditions to thrive in the laboratory. The most common medium is agar, which contains carbon, nitrogen, water, vitamins, and mineral salts. Some bacteria have special requirements – they might need blood agar or specific temperatures to grow. In schools, bacteria are cultured at 25°C to avoid growing human pathogens.
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