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Microbiology & Bacteria Cheat Sheet
A printable reference covering bacterial structure, cell types, growth, classification, infection, antibiotics, and lab safety for grades 10-11.
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Microbiology is the study of microscopic organisms, including bacteria, viruses, fungi, and protists. This cheat sheet focuses on bacteria because they are important in health, disease, ecosystems, food production, and biotechnology. Grade 10 and 11 biology students need a clear reference for comparing cell types, identifying bacterial structures, and understanding how bacteria grow and spread. It also supports safe lab work and careful interpretation of microbiology data. Bacteria are prokaryotic cells, meaning they lack a nucleus and membrane-bound organelles. Their main structures include a cell wall, plasma membrane, cytoplasm, ribosomes, DNA in a nucleoid, and sometimes plasmids, capsules, pili, or flagella. Important formulas include magnification = image size / actual size and number after n divisions = starting number x 2^n. Bacterial classification often uses shape, arrangement, Gram stain result, oxygen use, and method of obtaining energy.
Key Facts
- Bacteria are prokaryotes, so their DNA is in a nucleoid region instead of inside a nucleus.
- Magnification is calculated using magnification = image size / actual size, with both sizes in the same units.
- During binary fission, one bacterial cell divides into two genetically identical cells under favorable conditions.
- The number of bacteria after n divisions is calculated by final number = starting number x 2^n.
- Population growth rate over a time interval can be estimated by growth rate = change in population / change in time.
- Gram-positive bacteria stain purple because they have a thick peptidoglycan cell wall, while Gram-negative bacteria stain pink because they have a thin peptidoglycan layer and an outer membrane.
- Antibiotics treat bacterial infections by targeting bacterial structures or processes, such as cell wall synthesis or protein synthesis.
- Aseptic technique reduces contamination by keeping cultures, tools, hands, and work surfaces as free from unwanted microbes as possible.
Vocabulary
- Prokaryote
- A cell type that lacks a nucleus and membrane-bound organelles, such as a bacterial cell.
- Nucleoid
- The region of a prokaryotic cell where the main circular DNA molecule is located.
- Plasmid
- A small circular DNA molecule in bacteria that often carries extra genes, such as antibiotic resistance genes.
- Binary fission
- The asexual process in which one bacterial cell copies its DNA and divides into two cells.
- Gram stain
- A staining method used to classify bacteria as Gram-positive or Gram-negative based on cell wall structure.
- Antibiotic resistance
- The ability of bacteria to survive exposure to an antibiotic that would normally kill them or stop their growth.
Common Mistakes to Avoid
- Confusing bacteria with viruses is wrong because bacteria are living cells with ribosomes and membranes, while viruses are noncellular particles that must use host cells to reproduce.
- Forgetting to use the same units in magnification calculations is wrong because magnification = image size / actual size only works when both measurements are in matching units.
- Assuming all bacteria cause disease is wrong because many bacteria are harmless or helpful in digestion, decomposition, nitrogen cycling, and food production.
- Thinking antibiotics work on viruses is wrong because antibiotics target bacterial structures or processes that viruses do not have.
- Calling Gram-negative bacteria weaker because they stain pink is wrong because Gram-negative bacteria often have an outer membrane that can make them harder to treat.
Practice Questions
- 1 A bacterial cell is 2 micrometers long, and its image is 40 millimeters long. What is the magnification?
- 2 A culture starts with 50 bacterial cells. If the cells divide 6 times by binary fission, how many cells are present?
- 3 A bacterial population increases from 2,000 cells to 18,000 cells in 4 hours. What is the average growth rate in cells per hour?
- 4 Explain why using the full course of an antibiotic helps reduce the chance of antibiotic resistance developing in a bacterial population.