Micro-organisms our friends and foes

Micro-organisms – friend or foe?

Hookworm

We can’t see them. We can’t hear them or feel them, but they are with us. There are 10 trillion (10 x 1,000,000,000,000 or a million million) cells in the average body. For every cell, we have 10 times as many micro-organisms – that’s 100 trillion micro-organisms on and in our bodies! We are a walking, talking ecosystem.

But don’t worry – without micro-organisms, we wouldn't survive. 
 

Micro-organisms are small

A micro-organism is a living organism that is so tiny it can only be seen with the aid of a microscope.

Consider that the largest human cells are about the diameter of a human hair. Bacteria cells are one-hundredth the size of a human cell and viruses are much, much smaller again. If you imagine that a single virus was the size of an adult human, a bacterium (single cell) would be over 10 storeys high by comparison. A bacterium next to a human cell is like a tiny boat next to a big ship. Hundreds of thousands of bacteria could fit onto a pinhead.

Friend and foe

The main micro-organisms in and on our bodies are protozoa, algae, fungi, bacteria and viruses. Most micro-organisms are beneficial, for example, there are micro-organisms in our large intestine that synthesise vitamins and allow them to be absorbed into the bloodstream. However, a tiny minority are pathogens (disease-causing agents). These pathogens, often called germs or bugs, are a threat to all life forms.

Let’s take a closer look at bacteria, viruses and parasites.

Bacteria

You cannot escape bacteria. They are everywhere! The good thing is that they are mostly harmless, but the pathogenic bacteria can make you sick. They thrive in unhygienic conditions and can grow very quickly by dividing in half and then the two halves grow and then divide again and so on.

Bacteria

A bacterium is a very simple form of life – just a single cell. They have different shapes – some look like balls, rods or spirals. They have a tough cell wall that protects them. They are like all living organisms and need to ‘eat’ (ingest) for energy and growth. They ingest starches and sugars that are found on all organic matter.

Viruses

Viruses are micro-organisms that are so basic (and tiny) that they are not even cells and are not classified as living. Viruses are just genetic material (DNA or RNA) wrapped up inside a strong ‘coat’ made of protein. They cannot survive by themselves, so they need a host that will enable them to multiply. A virus will hijack a cell in your body and change the instructions of the cell so that, instead of doing what it was designed to do, the cell begins to produce copies of the virus.

Viruses

Eventually, it makes so many that the cell bursts open and releases all the viruses, which then hijack many, many more cells. Some viruses hibernate (become dormant) while they wait for the right conditions to come along.

Viruses have different shapes – rods, spheres or many-sided spheres. Some are even shaped like a spaceship! Pathogenic viruses can be very dangerous, but there are a few good viruses that are not harmful. Researchers and scientists are trying to find ways of using these viruses to fight bacterial infections.

Parasites

A parasite lives on or inside its host organism in a very unequal relationship – it takes all its food from its host and doesn't give anything back. Parasites can live on our bodies (like lice) or in our bodies and cause lots of different diseases. Parasitic worms (including hookworms – see Professor Le Gros’s research) can live in our bodies and make us sick. Some parasites are micro-organisms like protozoa – a single-celled parasite. Diseases like malaria and Guardia are protozoa.

Cell a Basic Structural and Functional unit of life.

The cell  is the basic structural, functional and biological unit of all known living organisms. Cells are the smallest unit of life that can replicate independently, and are often called the "building blocks of life". The study of cells is called cell biology.

Cells consist of a protoplasm enclosed within a membrane, which contains many biomolecules such as proteins and nucleic acids. Organisms can be classified asunicellular (consisting of a single cell; including most bacteria) or multicellular (including plants and animals). While the number of cells in plants and animals varies from species to species, humans contain about 100 trillion cells. Most plant and animal cells are visible only under the microscope, with dimensions between 1 and 100 micrometres.

The cell was discovered by Robert Hooke in 1665. The cell theory, first developed in 1839 by Matthias Jakob Schleiden and Theodor Schwann, states that all organisms are composed of one or more cells, that all cells come from preexisting cells, that vital functions of an organism occur within cells, and that all cells contain the hereditary information necessary for regulating cell functions and for transmitting information to the next generation of cells.^[5] Cells emerged on Earth at least 3.5 billion years ago.

What distinguishes a living organism from an inanimate object? A living organism conducts self-sustaining biological processes. A cell is the smallest and most basic form of life. Robert Hooke, one of the first scientists to use a light microscope, discovered the cell in 1665. In all life forms, including bacteria, plants, animals, and humans, the cell was defined as the most basic structural and functional unit. Based on scientific observations over the next 150 years, scientists formulated the cell theory, which is used for all living organisms no matter how simple or complex. The cell theory incorporates three principles:

• Cells are the most basic building units of life.
• All living things are composed of cells.
• New cells are made from preexisting cells, which divide into two.

Who you are has been determined because of two cells that came together inside your mother’s womb. The two cells containing all of your genetic information (DNA) united to begin making new life. Cells divided and differentiated into other cells with specific roles that led to the formation of the body’s numerous body organs, systems, blood, blood vessels, bone, tissue, and skin. As an adult, you are comprised of trillions of cells. Each of your individual cells is a compact and efficient form of life—self-sufficient, yet interdependent upon the other cells within your body to supply its needs.

Independent single-celled organisms must conduct all the basic processes of life: it must take in nutrients (energy capture), excrete wastes, detect and respond to its environment, move, breathe, grow, and reproduce. Even a one-celled organism must be organized to perform these essential processes. All cells are organized from the atomic level to all its larger forms. Oxygen and hydrogen atoms combine to make the molecule water (H₂O). Molecules bond together to make bigger macromolecules. The carbon atom is often referred to as the backbone of life because it can readily bond with four other elements to form long chains and more complex macromolecules. Four macromolecules—carbohydrates, lipids, proteins, and nucleic acids—make up all of the structural and functional units of cells.

Although we defined the cell as the “most basic” unit of life, it is structurally and functionally complex (see Figure 3.1). A cell can be thought of as a mini-organism consisting of tiny organs called organelles. The organelles are structural and functional units constructed from several macromolecules bonded together. A typical animal cell contains the following organelles: the nucleus (which houses the genetic material DNA), mitochondria (which generate energy), ribosomes (which produce protein), the endoplasmic reticulum (which is a packaging and transport facility), and the golgi apparatus (which distributes macromolecules). In addition, animal cells contain little digestive pouches, called lysosomes and peroxisomes, which break down macromolecules and destroy foreign invaders. All of the organelles are anchored in the cell’s cytoplasm via a cytoskeleton. The cell’s organelles are isolated from the surrounding environment by a plasma membrane.

Figure 3.1

The cell is structurally and functionally complex.