As you read in the answer to question 2, biofilms can build up on boat bottoms and create friction that reduces the boats' speed. The microbes that make up biofilms also may produce acidic chemicals as by-products of their daily metabolic (basically, eating and breathing) processes. These chemicals could corrode the boat surfaces. The same is true of biofilms that form on your teeth. The acidic chemicals the microbes make gradually corrode tooth enamel, causing cavities. Biofilms can also build up in pipes, clogging drains.
Some substances can hinder the formation of biofilms. By using these substances, we can slow or prevent biofilm growth on those objects. This is important in many industries. For example, biofilms quickly form on the bottoms of boats sitting in the water. By using paints made with special chemicals or more environmentally friendly hot pepper sauce, boat owners can protect their boats from microbial colonies that cause boats to drag and that could damage the hull. We use chlorine in swimming pools to prevent colonies of algae and bacteria from forming on the pool sides and bottom.
Different sweeteners will have similar or lesser effects on dough rising as sugar. You could try this experiment with as many different types of sweetening agents as you want to compare the results. Then you could do some research on the types of sugars in these different sweeteners to determine which ones work best as food for yeast.
You probably saw some rising happen in the straws containing Control dough. This is because flour is a starch. Starches contain glucose, a form of sugar (this is why a saltine cracker tastes a little sweet if you let it sit on your tongue for a while; the enzymes in your saliva break the cracker starch down into glucose and other simpler molecules). So even though you didn't add any sugar to the Control dough, it already contained some for the yeast to munch on. However, because the amount of sugar in this dough was much less than in the others, less carbon dioxide could be made by the yeast in this batch and the dough couldn't rise as much in comparison.
You will notice that the dough from the other bowls also rose some in their straws, the height connected to how much sugar was in the flour. The more sugar, the higher the dough rose. What can you figure out from this? Well, you've already read that yeast makes bread rise and become puffy instead of flat and this has something to do with yeast activity. What makes living things active? Food energy. The sugar is food for the yeast cells. The more sugar there is, the more active the yeast cells are.
Depending on what objects you tested, you may have seen a difference in the amount of bacterial growth. Objects that are kept in moist and/or dark places or that come into frequent contact with food, dirt, vegetation or bodies of living creatures often contain more microbes than other objects such as walls, ceiling light fixtures, door frames, etc. that are generally dry.
Did your petri plate grow bacterial colonies after you wiped the object with just water? Probably. This shows you that while plain water can help get rid of some microbes, it doesn't necessarily get rid of all of them. But you didn't grow too many microbes in the dish you swabbed after wiping the object down with your chosen disinfectant. Disinfectants are chemicals that kill microbes or at least lift them up off a surface so they can then be washed or wiped away. Disinfectants are one of the ways we can control microbial growth. Heat and cold are other means--you can sterilize water by boiling it and you can keep food from going bad by refrigerating or freezing it. Irradiation and antibiotics are other control methods.