Classification of Microorganisms (Leaving Cert Home Economics): Revision Notes

Classification of Microorganisms

Introduction to microbiology

Microbiology focuses on the study of tiny organisms that can only be seen under a microscope. These microscopic life forms include bacteria, fungi, and yeasts. You'll find these organisms everywhere in nature, and they play crucial roles in many important processes such as food production, breaking down organic matter, and causing diseases.

Main types of microorganisms

Scientists group microorganisms into three primary categories based on their structure and characteristics. Understanding these differences helps us learn how they behave and affect our daily lives.

Fungi

Fungi have several distinctive features that set them apart from other microorganisms:

Cell structure and organisation:

• Possess a well-organised nucleus and internal compartments
• Usually made up of multiple cells working together
• Have complex internal structures similar to plant and animal cells

How they reproduce:

• Can reproduce both sexually (involving two parents) and asexually (from one parent)
• This flexibility helps them spread effectively in different environments

How they obtain nutrition:

• Feed on dead organic material (saprophytic) or live as parasites
• Cannot photosynthesise like plants, so they must consume other organisms

Common examples you might encounter:

• Moulds: Found in damp environments like bathrooms; Penicillium is used to make antibiotics
• Mushrooms: Some varieties are edible and used in cooking, whilst others can be poisonous
• Yeasts: Single-celled fungi essential for baking bread and brewing alcoholic beverages

Bacteria

Bacteria are fundamentally different from fungi in several key ways:

Cell structure and organisation:

• Do not have a defined nucleus or organised internal compartments
• Exist as individual single cells
• Have a simpler structure compared to fungi

How they reproduce:

• Primarily reproduce through binary fission, where one cell splits into two identical cells
• This process allows rapid multiplication under favourable conditions

How they obtain nutrition:

• Some can make their own food using sunlight or chemicals (autotrophic)
• Others must consume organic matter from their environment (heterotrophic)

Common examples in daily life:

• Lactobacillus: Beneficial bacteria used to produce yoghurt and other fermented foods
• E. coli: Normally lives harmlessly in human intestines, but certain strains can cause serious food poisoning

Viruses

Viruses are unique among microorganisms because they cannot survive independently:

Structure and composition:

• Consist of genetic material (DNA or RNA) surrounded by a protective protein shell
• Much smaller than bacteria or fungi
• Do not have cellular structures like other microorganisms

How they reproduce:

• Cannot reproduce on their own
• Must infect a host cell and use the host's resources to make copies of themselves
• This dependency makes them different from true living organisms

How they obtain energy:

• Do not have their own metabolic processes
• Completely depend on their host cells for energy and raw materials

Examples that affect human health:

• Influenza virus: Causes seasonal flu, a common respiratory illness
• Human Immunodeficiency Virus (HIV): Attacks the immune system and can lead to AIDS
• Norovirus: A common cause of foodborne illness and gastroenteritis

Conditions needed for microorganism growth

Microorganisms require specific environmental conditions to survive and multiply. Understanding these requirements helps us both encourage beneficial microorganisms and prevent harmful ones.

Nutritional requirements

All microorganisms need basic nutrients to build their cellular components and obtain energy. The main food sources include sugars for quick energy, amino acids for building proteins, and fatty acids for cell membranes.

Oxygen availability

Different microorganisms have varying oxygen needs:

• Aerobic organisms: Require oxygen to survive, similar to humans
• Anaerobic organisms: Can only grow in oxygen-free environments
• Facultative anaerobes: Can adapt to grow with or without oxygen (yeasts are a good example)

Temperature preferences

Each type of microorganism thrives within specific temperature ranges:

• Mesophiles: Prefer moderate temperatures (20-45°C) and include most disease-causing bacteria
• Thermophiles: Thrive in hot environments and are often found in hot springs
• Psychrophiles: Prefer cold temperatures and can grow in refrigerated conditions

Moisture content

Water is essential for all metabolic processes in microorganisms. Foods with high water content provide ideal conditions for microbial growth, which is why proper food storage and preservation techniques focus on controlling moisture levels.

Acidity levels (pH)

Most bacteria prefer neutral conditions (pH around 7), similar to the pH of pure water. However, fungi can tolerate and even thrive in acidic environments, which is why acidic foods may still develop mould growth.

Time for multiplication

Given the right conditions, microorganisms can multiply at remarkable rates. Some bacteria can double their population every 20-30 minutes, which explains how food contamination can become serious very quickly.