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Viruses cause diseases such as the common cold, COVID-19, mumps, measles, HIV and Polio to name but a few. It is common at A Level to be asked why viruses are classed as 'non-living' or why antibiotics are not used when someone is infected by them. In this post, we will discuss the answers to these two important questions and explain what a virus is.
A Virus has a protein coat (a Capsid) surrounding a piece of DNA or RNA (Nucleic Acid. In some viruses there is an additional lipid layer on the outside of the capsid. The proteins can stick out from the surface (sometimes projecting through the lipid layer) and these are referred to as 'spike proteins.'
A virus attaches to living cells and either enters the cell whole or injects its Nucleic Acid into the host cell. The host cell then copies the nucleic acid and uses it to produce more virus capsids. The virus particles are assembled in the cell and then leave it to infect more cells. In this way they are using the host cell's organelles to make virus copies. They can be transferred from one host to another via blood or mucus.
Viruses are non living. They are not like animals, plants, fungi, protists and bacteria. These are all living and are made up of one or more cells. Viruses are not made of cells and are instead referred to as 'particles.'
Viruses are not classed as living organisms because they do not possess all the characteristics of living things. See "The features of all living organisms" to find out which characteristics viruses do not possess.
Antibiotics are chemicals used to kill bacterial cells or stop them from multiplying inside animals. They work against bacteria in one of three main ways:
Since they target bacterial enzymes only and viruses have no enzymes anyway, antibiotics are useless against a viral infection. In fact, using antibiotics when they are not needed increases the chances of bacteria becoming resistant to them. So they should only be taken as prescribed for a bacterial infection.
The features of all living organisms are listed below . Test yourself by considering each feature in turn . Think about what the statement means then click on the box to see if you are correct.
Living organisms can move independently. Even plants move by phototropism changing their direction of movement towards a light source. Many bacteria have a flagellum to allow them to move in a liquid. Viruses don't move independently, they require a medium like mucus or blood in order to be moved.
Living organisms can produce offspring or copies of their cells by replicating their DNA and cells independently. Although viruses contain genetic material they can not make copies of themselves without a host cell. It is the host cell that makes copies of them.
Living organisms can respond to stimuli in their environment and alter their behaviour as a result. Perhaps by moving or increasing the production of a substance. Viruses are not sensitive and do not change their behaviour.
All living organisms can change their size. If they are unicellular like bacteria their cytoplasm can change in volume response to changes in the concentration of their surroundings. If they are multicellular like humans they can change in size due to their nutrition or genetics.
All living organisms require an organic molecule like sugars and fats in order to survive. They can digest these and release the energy from the bonds in the molecule. With that energy they make a molecule called ATP. ATP is used to fuel the chemical reactions that take place in their cells. This process of breaking down organic molecules and releasing the energy in them is called respiration. Viruses do not respire. They do not require energy as no chemical reactions take place in them.
All organisms produce waste substances from chemical reactions that take place in them. These are removed from the organism in a process called excretion. Chemical reactions do not take place inside viruses so they do not excrete.
All living organisms require nutrients for energy and to obtain the chemicals needed to build their cells. Viruses do not require energy nor do they copy themselves independently. Nutrients from host cells are used to build new virus particles.
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