Nvq3 Hsc - Ic02

ICO2 – Causes and Spread of Infection

Understand the cause of infection

1.1 – Identify the differences between bacteria, viruses, fungi and parasites

Bacteria are singly-celled organisms that measure just a few micrometres in length. The rigid cell wall of bacteria is made of peptidoglycan and contains a closed circle of double-stranded DNX. As bacteria do not possess a membrane-enclosed nucleus or other cell structures such as mitochondria or chloroplasts, they are prokaryotes. Bacteria may respire either aerobically or anaerobically depending on the presence of oxygen. Bacteria move through the environment by the use of a flagellum and reproduce asexually through a process known as binary fission i.e. they divide into two identical daughter cells. Bacteria are intercellular organisms i.e. they live among other cells, and may be beneficial or pathogenic.

Fungi are eukaryotic cells as they possess a membrane-enclosed nucleus and their rigid cell walls are made of chitin, a modified polysaccharide, making them distinct from bacteria and animal cells. Fungi are non-motile and reproduce both sexually and asexually through budding or producing spores. Fungi may be unicellular or multi-cellular structures and most are beneficial.

Viruses are very small organisms, much smaller than bacteria and other cells. They comprise of a small piece of genetic material – either RNA or DNA – surrounded by a thin protein coating. Viruses are obligate parasites as they need a living host in order to survive and replicate. Viruses seize cellular materials for energy and hereditary genetic material present in the virus takes over the nucleus of the host cell, enabling the virus to copy large numbers of itself before the host cell ruptures, releasing more virus cells into the surrounding environment which then attack new cells.

Parasites are organisms that benefit at the expense of another, known as the host. Some are large multicellular organisms that live outside of...