Microorganisms Chapter Notes | IGCSE Cambridge Science for Year 7 - Class 6 PDF Download

Types of Microorganism

Microorganisms Introduction

• Microorganisms, or microbes, are tiny living organisms that include bacteria, viruses, fungi, and the microbes found in yoghurt. These organisms are usually too small to be seen without a microscope. 
• They are termed 'micro' due to their very small size.

• Microorganisms are unicellular, meaning they consist of a single cell. They carry out essential life processes and are a fundamental part of ecosystems.
• Microbes are vital in nutrient cycling, decomposition, and as part of the human microbiome.

Microorganisms

Fungi

• Fungi are not plants; they do not photosynthesize but instead absorb nutrients from organic materials.
• Fungi can be multicellular (like mushrooms) or unicellular (like yeasts). Moulds, a type of fungi, grow by reproducing through spores, which are capable of traveling through air and growing on new sources.
• Some fungi are beneficial and used in cooking, while others, like certain moulds, can produce toxins and are hazardous.

Bacteria

• Bacteria are unicellular organisms that can reproduce quickly. They can be found in every environment on Earth.
• Bacterial structure is simple, yet they are involved in both beneficial processes (like digestion and fermentation) and pathogenic activities.

Viruses

• Viruses are not cells but are tiny particles that infect living cells. 
• Viruses must enter into a living cell to replicate (copy) themselves.
• Viruses can infect all types of life forms, from plants and animals to bacteria.

Microorganisms and Decay

History and Discovery of Microorganisms

• Antonie van Leeuwenhoek first observed microorganisms in 1674.
• Initial scientific belief was that microorganisms spontaneously generated from the materials they were found in, such as bread creating mold.

Louis Pasteur's Experiments

• Louis Pasteur, a French scientist in the 19th century, questioned why clear soup would turn cloudy and start to smell when left open.
• He hypothesized that microorganisms in the air were responsible for spoiling food.
• Pasteur's experiments involved boiling soup in glass containers to kill any existing microorganisms and then allowing air to contact some of the soup while keeping other samples isolated. Only the soup exposed to air spoiled, supporting his hypothesis.

Scientific Method

• Involves asking questions, formulating hypotheses, and conducting experiments to test these hypotheses.
• A hypothesis must be testable, meaning experiments can be conducted to prove it right or wrong.
• The results from these experiments provide evidence to support or reject the hypothesis.

Decay

• Decomposers like bacteria and fungi cause decay/breakdown of materials.
• They also play a role in recycling nutrients from dead matter back into the soil.

Food Chain

• A food chain is a diagram showing feeding relationships in a habitat

• It consists of producers (organisms that make their own food, like plants using sunlight) and consumers (animals that eat producers).
• Consumers can be classified as:
  • Herbivores: Animals that eat only plants (primary consumers)
  • Carnivores: Animals that eat other animals (secondary/tertiary consumers)
  • Omnivores: Animals that can eat plants or animals
  • Predators: Animals that hunt and eat other animals
  • Prey: Animals that are hunted and eaten by other animals

Food Web

A food web is a diagram that shows how different food chains all interact in a habitat.

For example : 

Food Web

Energy Flow in Ecosystems

• Energy flows from producers to various levels of consumers. Not all energy consumed by one level is transferred to the next; some is lost a through respiration, waste, and organism death.
• Decomposers ensure that no energy is wasted by breaking down dead matter and recycling it into the ecosystem.