Bacteria and viruses differ in their structure. Bacteria have cell walls, lack organelles, and divide through binary fission. They can be gram-positive or gram-negative. Viruses are much smaller, lack cells, and contain genetic material surrounded by a protein coat. They invade host cells and use the cell's machinery to replicate. Microorganisms play important roles in decomposing organic matter and recycling carbon through the environment.

1. Bacteria and VirusesDistinguish between the structure of bacteria and viruses

2. Describe the role of microorganisms in the decomposition of organic matter and recycling of carbonBacteria

3. Main features of prokaryotes

4. Key featuresNo nucleusDNA in simple ring structure free in cytoplasmCell wall present, not made of cellulose but peptidoglycans ( polymer of sugar and amino acids)Cell membrane controlling passage of substances into and out of the cellLack of membrane bound organellesInfolding of the cell membrane called mesosome is the site of respirationRibosomes (18nm diameter) free in cytoplasm are the sites of protein synthesisCell size – 0.5 and 5 µmCells divide by binary fission with no spindle formation

5. Gram positive and gram negative bacteriaOne of the major differences between types of bacteria is the ability to stain their cell walls using a procedure called Gram staining.Bacteria which have cells walls which take up the stain = Gram positiveThose that do not = gram negativeUseful as both types of bacteria respond differently to antibiotics.

6. Gram Negative bacteriaE.g. E-CoilThinner layer of peptidoglycan and no teichoic acid between two layers of membrane, then outer layer of lipopolysaccharidesStain does not stick

7. VirusesSmallest microorganism0.02-0.3µm across50x smaller than average bacteriumNot cellsArrangement of protein and genetic materialInvade other cells take over biochemistry to make more copies.

8. Viruses

9. Viruses

10. Features of virusesHave a protein coat (capsid) around a core containing nucleic acid and virus enzymesLack of internal membranes, cytoplasm and ribosomesSome have an outer envelope taken from the host’s cell surface membrane – it contains lipids and proteinsViral envelopes have glycoproteins which are recognised by the host immune system – helps virus attach to cell and penetrate the membrane