Biology Chemistry Physics Controlled Assessments Long Answer Questions 11-14 Science Big Moments in Science Linkup

 Microbes and Diseases

Microbes are Micro-organisms

These are tiny living things that can only be seen using microscope

There are 4 main groups of microbes that are of interest to human beings, these are:

  • Bacteria
  • Fungi
  • Viruses
  • Protozoans

Most micro-organisms are harmless e.g.

  • We have millions of bacteria living on our skin and digestive systems
  • We also eat products made using bacteria and fungi e.g. Yoghurt may contain living bacteria, Yeast (a fungi) is used to make bread and wine.

Pathogens- are microbes that cause disease (the harmful ones)

1. Bacteria

Structure- Bacteria are made of single cells. They have:

  • A cell wall
  • Cell membrane
  • Cytoplasm
  • Flagella- a tail-like structure for movement
  • A slimy capsule outside
  • DNA that lies in the cytoplasm
  • Small ribosomes

Reproduction: Bacteria reproduce by Cell division. Once a cell is big enough, it splits in two.

How they cause disease: Most bacteria produce toxins (poisons) which make us ill.

2. Fungi

Structure- Fungi are made of cells, from single celled yeast (unicellular) to many cells (multicellular) in Bread mould and mushrooms.

The cells have:

  • A cell wall
  • Cell membrane
  • Cytoplasm
  • Nucleus
  • Large ribosomes
  • Mitochondria

How they cause disease

  • Most fungi cause disease by being parasitic. they release enzymes to digest the host cell and then absorb the products.

Examples of Fungal diseases: thrush, athletes foot, ringworm

Importance of Fungi

  • They are used to make food products e.g. bread, alcohol, blue cheese
  • They are food e.g. mushrooms
  • They help decay ang recycle plant and animal matter e.g. in compost heaps.

3. Viruses

Viruses are the tiniest microbes

They live inside living cells only


  • The virus particle (not a cell) is surrounded by a protein coat
  • Inside is a single coil of DNA
  • At the base are tail spikes for attaching to a host cell

Reproduction and how they cause disease

The way viruses reproduce is the way that they use to cause disease.

  • They inject their DNA into a cell
  • They then take over the cell's DNA and use it to make their copies
  • Then cause the cell to burst and release more of themselves which can infect other cells

The nuisance of viruses

It is hard to treat viral diseases as:

  • They live inside cells- you may end up killing the cell instead of the virus
  • They mutate- change their DNA and proteins every now and then so are difficult to detect by the immune system and medicines.

Examples of viral diseases

Chicken pox, measles, Flu, AIDS


4. Protozoans

Protozoans are single celled, water-borne micro-organisms


They have:

  • A cell membrane
  • Cytoplasm
  • Nucleus
  • Ribosomes
  • Mitochondria
  • They move by crawling on the surface using false-feet (pseudopoda)


They mainly cause diseases that are a result of drinking dirty water.


 Key terms

Micro = Tiny

Organism = Living thing

Scope = to see

Bacteria living on our skin and digestive systems is called our Microflora (more like a forest of bacteria)

Our microflora helps get rid of dead cells on our skin.


Scientists also think that these bacteria in our digestive system may help with our immune system and may possibly affect how we feel (our mood?) and think. Wow!


Ribosomes are tiny particles in a cell that make proteins.

Mitochondria carry out respiration. They release energy.


Challenge yourself:

1. What are antibiotics? Which of these microbes do they kill?

2. Find out about bacteria and Antibiotic resistance. Why should we be very concerned about it?