BIOLOGY · Stage 7 · Chapter 3: Microorganisms and Decomposers
Biology 3.8 Chapter 3 Review: Microorganisms and Decomposers — Alhussan International Academy - Biology (Stages 7-9) Revision Notes & Topical Questions
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Lesson summary
3.8 Chapter 3 Review: Microorganisms and Decomposers — Alhussan International Academy — Biology (Stages 7–9) notes: Revise the types of microorganism, their uses and harms, disease prevention and the role of decomposers in food webs.Bacteria — single cells with no nucleus.Fungi —…
- Protoctists
- Lactobacillus
- Other products
- Body defences
- Antibiotic resistance
- Herd immunity
Section 1 of 7Types of microorganism
- Bacteria
- single cells with no nucleus.
- Fungi
- yeast and moulds have cells with a nucleus and a chitin cell wall.
- Protoctists
- a varied group of mostly single-celled organisms with a nucleus.
- Viruses
- not cells, but genetic material inside a protein coat.
Section 2 of 7Useful microorganisms
- Yeast
- it ferments sugar to make carbon dioxide for bread and ethanol for drinks.
- Lactobacillus
- it turns lactose into lactic acid to make yoghurt.
- Cheese
- bacteria make lactic acid, so milk separates into curds and whey.
- Other products
- fungi and some bacteria are used to make antibiotics, insulin, biofuels and food proteins.
Section 3 of 7Disease and how it spreads
- Pathogen
- a microorganism that causes disease.
- Spread
- by droplets, direct contact, contaminated food and water, breaks in the skin, body fluids and vectors such as mosquitoes.
- Body defences
- barriers, and white blood cells that make antibodies.
- Pasteur
- his anthrax experiment supported the germ theory of disease.
Section 4 of 7Preventing and treating disease
| Measure | Works on | Key idea |
|---|---|---|
| Hygiene | All pathogens | Stops spread |
| Antibiotics | Bacteria only | Kill or stop bacteria; resistance can develop |
| Vaccines | Specific pathogens | Memory cells give a fast response |
- Antibiotic resistance
- resistant bacteria survive treatment, reproduce and become the population.
- Herd immunity
- a vaccinated majority protects people who cannot be vaccinated.
Section 5 of 7Decomposers
- Decomposers
- bacteria and fungi that release enzymes onto dead material and absorb the soluble products.
- Recycling
- they return minerals to the soil and release carbon dioxide by respiration.
- Fastest decay
- warm, moist and oxygen-rich conditions.
- Slowest decay
- cold, dry or airless conditions.
Section 6 of 7Food chains and webs
- Food chain
- begins with a producer and passes through consumers.
- Arrows point from food to feeder and show the flow of energy and biomass.
- Food web
- links food chains and is more realistic than one chain.
- Energy transfer
- only about 10% of the energy is passed to the next level, so chains are short.
- Decomposers
- they return nutrients to the soil so that new producers can grow.
Section 7 of 7Investigation skills
- Practicals
- chapter investigations use yeast, mould on bread, leaf decay or souring milk.
- Variables
- name the independent, dependent and control variables.
- Reliability
- repeat measurements and calculate a mean.
- Example variables
- in a milk souring test, temperature is independent, time or pH change is dependent, and milk volume and bacteria amount are controlled.
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