5. Diffusion & Osmosis - Don't Stop Movin' (Part 2)

  Today we did another lab about the concept of diffusion and osmosis. We put three cubes of "cells" in the solution of NaOH after we measured their surface areas, and as you can see in the picture above, the cube's reaction with the solution involves color change. We took the cubes out after 3 minutes. 

  As you can see, the purple part on the outer layer of the cube was the part involved in the reaction, and the white part in the center of cube wasn't involved. In order to see the difference in color more clearly, we cut all the cubes in half. 

  We calculated the thickness of the purple part in order to find out the amount of reaction involved. Finally, we discovered that the smaller the volume of the cube is, the faster it reacts with the solution. 

- Andy Liu '15

4. Diffusion & Osmosis - Don't Stop Movin' (Part 1)

  DIFFUSION: Molecules are always in constant motion, and tend to move from a place of higher concentration to another with lower concentration. And the net movement of those molecules are called diffusion. The diffusion can occur in gas, liquid, or through solids. One example of diffusion is that when a bottle of perfume is opened, within minutes people in further distance can smell the perfume.

  OSMOSIS: Osmosis is a type of diffusion. However, it is special as well since it involves a selectively permeable membrane in the transport. The membrane allows certain molecules to pass through to the place with lower concentration, while it restricts the movement of others.

  TYPES OF SOLUTION BASED ON SOLUTE CONCENTRATION:
  If the solution in the bag has lower concentration than the solution in the beaker, the solution in the bag is hypotonic to the solution in beaker.
  If the solution in the bag has higher concentration than the solution in the beaker, the solution in the bag is hypertonic to the solution in beaker.
  If the solution in the bag has same concentration as the solution in the beaker, the solution in the bag is isotonic to the solution in beaker.

  WATER POTENTIAL: Water potential is the tendency of water to move from the place of higher concentration to another with lower concentration. It is affected by the pressure and the amount of solute.
 
  According the 1st lab we did today on diffusion and osmosis, we made 6 small packs ("cells") of 7 ml of solutions in different molarities.

  After we dried and massed all the 6 cells, we placed each of them into a labeled cup, which contained 50ml of distilled water.

  We let them stay for 30 minutes. After taking them out of the cups, we re-massed the cells and calculated the percent change in mass to find out the molarities.

  The 2nd lab we did today was based on diffusion and osmosis as well. However, instead of using "cells" of different solutions, we used russet potato. We cut 24 pieces of russet potatoes into roughly same size. We massed every 4 pieces of potatoes before we put them in each labeled cup.

  Later, we put 25ml of each solution into each labeled cup, and after we covered the top of the cups, we let them stay for about 9 hours. Then after we took the potatoes out of each cup, we re-massed them and calculated the percent change in each cup.

-Andy Liu'15

 
 

Answers for Evolution Quiz #1

1. Explain the following picture in terms evidence for evolution.

  This picture demonstrates the evolution of modern whales. The Mesonychid's living condition began switching from terrestrial to aquatic from around 55 million years ago, while its homologous structure changes as well. 3 million years later, the Ambulocetus it evolved to has a more flexible backbone and hind limbs in order to walk on land and swim. 6 million years later,  the Ambulocetus evolved to Rodhocetus, which its limbs could not support it to walk on land, and swam in an up-and-down motion. 4 million years later, Basilosaurus has more reduced limbs than those of Rodhocetus, and its size was bigger than Rodhocetus, which was closer to the sizes of the modern whale today.

2. Which of the following continents did marsupials begin from?

  E, North America

3. Comparing a dragonfly, bird, bats - explain the type of evolution that these organisms show

  Dragonfly, bird and bats have wings for their ability to fly. However, their underlying structures are different since they evolved from different ancestral structures. The bats has fingers on their wings, and the bird only has a single forelimb, while the dragonfly almost has none. This is why they show a type of convergent evolution.

4. Explain how the Common Descent Lab shows DNA evidence and ancestry as evidence for evolution. Include examples of Primates.

  In the Common Descent lab, we were looking for the similarities and differences of the hemoglobin strands in DNA of humans, chimpanzees, gorillas, and their common ancestor. We found out that the human DNA has the least similarity with DNA of the common ancestor, while it share the most similarities with Chimpanzee DNA. comparison of DNA sequences can be a useful tool to find out the similarities between species. Therefore, it can be a strong evidence for evolution.

5. Explain homology using some examples from your readings.

  Homology is the similarities in the structures of organisms of same or different species because of their common ancestor. For example, tiktaalik has same backbone structure as fish, and modern whale has same tail and backbone structure as Basilosaurus.

3. The Water Miracle

  The water has some very important properties, based on its polarity and capacity to create hydrogen bonds to help support Earth's fitness for life, including its ability to moderate temperature, its cohesive behavior, its expansion upon freezing, and its versatility as a solvent.

  One of the "miracles" water performs is that the ice can float on water. This can happen because hydrogen bonds water molecules create between each other can break and re-form through molecular motion. However, the hydrogen bonds will become stable at a certain temperature (0 degree Celsius), and the bonds will form a crystalline structure while the water molecules become farther from each other. Therefore, that's why the ice is less dense than water and, as a result, the ice floats on water.

The Crystalline Structure of Ice

-  Andy Liu '15

2. Covalent + Ionic Bonds

  The covalent bond is usually described as sharing of valence electrons, and this is why the covalent bonds only consist of non-metals. The covalent bonds are strong, and they usually lead to stable compounds. However, the covalent bonds are poor conductors of heat and electricity since they aren't composed of charged ions.

  Examples of covalent bonds: H2, H2O, Cl2, O2, CO2 & CH4

  The ionic bond is made up by a metal element and a non-metal element. To create bonds between each other, the metal donates certain amount of valence electrons to the non-metal. This results with a strong attraction between a positive ion and a negative ion. However, the ionic bonds usually lead to unstable compounds or molecules. 

  Examples of ionic bonds: KCl, MgI2, Na2O, NaCl, CaCl2, AlCl3

-Andy Liu '15