Evidence for Evolution Quiz

1. Transitional evolution

2. C. Australia

3. They show analogous structures, where there are many similarities, such as similar functions, but the underlying structure is completely different, and they evolved from different ancestral structures. 

4. The Common Descent lab uses DNA evidence to show how species are related, and how closely related they are. For example, in the lab, chimpanzees are proved to be more closely related to humans than gorillas are related to humans. 

5. Homology is the relationship between structures based on the same ancestral structure. One example of homology is the similarities between the arm of a primate and the arm of a bat. 

Starch and Glucose and NaOH and Oh My!

We had two labs in class the other day. The first was a lab where we created a "cell" with glucose and starch in the mixture, then soaked in water (in a beaker) for some time. After soaking it in water, we took out 1 mL of the water in the beaker, put a dropper full of benedict solution in, and put it into a test tube, which we them proceeded to dip into hot water for a few minutes. The water in the test tube turned a murky orange color, like this: 

Then, we put a few drops of iodine into the beaker, and waited for another few minutes. The cell turned into a bluish black color, since the iodine went into the cell because of diffusion. The iodine reacted with the starch and glucose, which is why the cell's contents changed color. It looked like this at the end: 

The second lab was a lab that also had to do with diffusion. We had pieces of NaOH that were cut into cubes and prisms, and we dropped them into beakers filled with phenolphthalein. The solution immediately turned pink, and we left the pieces of NaOH in the solution for around 3 minutes. Afterwards, we took them out and cut them in half. The pink color had soaked through about 1 millimeter all around, and the rest was still white. (It's not very clear in the picture, but that's definitely what happened.)

Water is Pretty Cool

     Water makes up 70% of the world--97% of which is salt water, 3% freshwater--with 2% still underground and 1% in rivers and lakes across the world. The water cycle recycles the water over the years, and the stages include:
1. Evaporation: Water is turned from a liquid form into water vapor in the atmosphere.
2. Condensation: Water vapor collects and turns into droplets of water in the atmosphere
3. Precipitation: Water droplets that are heavy enough fall to the earth as rain, hail, snow, or sleet.

     Water, as a molecule (H2O) is polar, with oxygen as the negatively charged part and the two hydrogens as the positively charged parts. Because they attract each other (opposites attract) it forms a bond between hydrogen and water, called a hydrogen bond. Hydrogen bonds are not as strong as some other bonds, but they are strong enough to hold onto the water molecule, and once broken, can reform again with other water molecules.

     Ice and water are curiously related. Ice has a lesser density than water, because the hydrogen bonds don't efficiently line up the water molecules, which results in the water molecules being more spread out and less dense than water. Water is also used mainly as a solvent because it is polar--therefore, it's called a polar solvent. Polar solvents are usually better at dissolving other polar solutes. However, water and oil do not mix because oil is not polar--therefore, they don't mix well at all.