Gram's staining is a method used to differentiate bacterial species based on differences in their cell walls. It involves staining bacteria with crystal violet dye and rinsing with iodine solution or alcohol to reveal whether the bacteria takes a red or purple stain. Gram-positive bacteria retain the purple crystal violet dye after rinsing, while Gram-negative bacteria do not and appear red. The difference is due to the thicker peptidoglycan layer in Gram-positive cell walls.

1. Gram’s StainingName:_________<br />Bacterial cell wall<br />Determine …………………. of bacteria<br />Strength prevents ………………….………………….<br />………………….of bacteria<br />Unique to ………………….<br />Some antibiotics effect directly e.g. ………………….<br />………………….…………………. polymer <br />-amino acids + sugar<br />Amino acids cross link sugars <br />What is Gram’s staining?<br />The characteristic compound found in all true bacterial cell walls is peptidoglycan. <br />The ………………….of ………………….…………………. is among one of the differences between the ………………….………………….and ………………….………………….cell walls. <br />Gram Positive Cell WallsGram Negative Cell Walls<br />Salmonella ToxinsEnterotoxin: released by microorganism in the lower ………………….………………….alters ………………….…………………. of intestinal wall water leaks into intestinal tract causing ………………….………………….Endotoxin:Salmonella enters intestinal cells through ………………….………………….………………….…………………. damage the cells from the inside cause fever and ………………….…………………. in large amounts <br />lefttopMaking YoghurtPractical Investigation<br />Background<br />Yoghurt is produced by curdling milk. The milk is curdled by the addition of lactic acid. Lactic acid can be produced by special strains of bacteria which are added to the milk for this purpose. These bacteria produce lactic acid through fermentation.<br />The bacteria used in yoghurt making are Streptococcus thermophilus and Lactobacillus bulgaris. S. thermophilus is added first to lower the pH for the acid-loving L. bulgaris to grow. Together the bacteria produce enough acid to curdle the milk. <br />Method<br />Take a clean pot and label with your name and the date<br />Fill 2/3 of the pot with UHT<br />Dissolve 1 teaspoon of milk powder into the milk<br />Add 1 teaspoon of yoghurt to the milk<br />Test the pH and make a note of it<br />Put the lid on and place in the water bath at 35 degrees C <br />Results<br />pH of the milk + starter culture:______________<br />pH of the yoghurt: ______________<br />Conclusion:<br />Using the information above, explain why the pH is different at the beginning of the experiment to the pH at the end of the experiment?<br />