Problem: Mark decides he want a cold drink and puts a bottle of warm water in his freezer. By doing this he makes the water colder and as water cools its density increases eventually freezing and becoming a solid, Ice. After a while mark forgets that he put the bottle of water in the freezer. He eventually remembers and comes back to check and the bottle of water is frozen solid. Because of this he leaves the bottle out on his kitchen counter for a few hours and returns to a nice cold bottle of water. Which is denser, warm water or ice? Hint: Liquid water is a fluid. The hydrogen bonds in liquid water constantly break and reform as the water molecules tumble past one another. As water cools, its molecular motion slows and the molecules move gradually closer to one another. The density of any liquid increases as its temperature decreases. For most liquids, this continues as the liquid freezes and the solid state is denser than the liquid state. However, water behaves differently. It actually reaches its highest density at about 4C.

A: ice

Problem: Two groups of athletes started new training routines this year. Group A started weight lifting for three months, while Group B, did running exercises. Which group's hearts will pump less blood? Hint: In exercises such as weight lifting, skeletal muscle contracts against a resisting force (see Figure below ). Using skeletal muscle in this way increases its size and strength. In exercises such as running, the cardiac muscle contracts faster and the heart pumps more blood. Using cardiac muscle in this way increases its strength and efficiency. Continued exercise is necessary to maintain bigger, stronger muscles. If you don't use a muscle, it will get smaller and weakerso use it or lose it.

A: Group A

Problem: Justin and Thomas are two college students conducting an experiment in their chemistry laboratory course. They are mixing together acids and bases to produce sodium based compounds. Justin conducts his reactions at a high temperature, while Thomas conducts his reactions at a lower temperature. In which person's reactions will the acid and base particles be less likely to collide with each other? Hint: When the temperature of reactants is higher, the rate of the reaction is faster. At higher temperatures, particles of reactants have more energy, so they move faster. As a result, they are more likely to bump into one another and to collide with greater force. For example, food spoils because of chemical reactions, and these reactions occur faster at higher temperatures (see the bread on the left in the Figure below ). This is why we store foods in the refrigerator or freezer (like the bread on the right in the Figure below ). The lower temperature slows the rate of spoilage.

A: Thomas

Problem: Two researches studied living organisms, Joe studied eukaryotes, while Bill studied prokaryotes. They were fascinated by genetic variation. Which researcher observed less bacterial conjugation taking place? Hint: Prokaryotes have a different way to increase genetic variation. It's called genetic transfer or bacterial conjugation . It can occur in two ways. One way is when cells "grab" stray pieces of DNA from their environment. The other way is when cells directly exchange DNA (usually plasmids) with other cells. For example, as shown in Figure below , the donor cell makes a structure called an F pilus , or sex pilus. The F pilus attaches one cell to another cell. The membranes of the two cells merge and genetic material, usually a plasmid , moves into the recipient cell. Genetic transfer makes bacteria very useful in biotechnology. It can be used to create bacterial cells that carry new genes.

A:
Joe