If you could point out the differences, props to you. If you couldn't point them out or if you sensed something different but you couldn't put your finger on it, then don't worry because you're a part of the majority of people who couldn't! (Sorry, not all of us are special).

What this video proves is the unreliability of eyewitness testimonies in court and in life. We overestimate the accuracy of eyewitness testimonies, often disregarding  the factors which influence a witness's ability to accurately identify a suspect, including how much stress a witness is under, whether a weapon is present, the amount of time a witness had to look at the person, the lighting present at the time, how long it's been since someone first witnessed the crime or suggestions of guilt by police, etc. This point, fortunately, has been brought to the attention of the court and now measures are being taken to prevent false accusations based solely on eyewitness testimonies. Thankfully, we have Forensics Biology to help us identify the true verdict through hard evidence. This is exactly what we covered in Jerrel's missing iPod case. 

While attempting to pin point the iPod thief, we attempted to investigate what exactly were the substances this criminal left on the crime scene (careless, rookie mistake). However, before attempting to see what substances made up this compound, we first had to figure out how to identify whether or not a substance contained protein, glucose, lipids or carbohydrates.

(Left to right): Lipid, Water, Protein, Glucose, Starch

• You can test whether or not a substance has Glucose present by mixing 10 drops of Benedict Reagent with it and then heat it in a water bath. The colour will change to a fiery orange if it does (see right) Alternatively, you could use a Glucose Strip. 
• You can test whether or not a substance has Starch present by dripping 3 drops of Iodine into a sample of the substance. The colour will change to a dark blue colour if it has starch present. 
• You can test whether or not a substance has Protein present by dripping 10 drops of Biuret into a sample of the substance. The colour will turn from pale blue to a lavender purple.

  Iodine and Biuret Tests

• Finally, you can test a substance for Lipids by doing the Paper bag test. Lipids will leave a greasy, shiny stain on unglazed brown paper bags.
  
  

  Paper bag test (still in the process of drying)

After testing the sample of evidence for glucose, starch, protein or lipids, we came to the conclusion that Bruce was the criminal in this case because he ate Toast with butter and jelly for lunch, which corresponds to the crumbs that were left on the crime scene. The crumbs only had glucose present, which means that it had to be Bruce because no other employee had only glucose present in their lunch meal. Case closed.

What is osmosis? Osmosis is the diffusion of water molecules from a region of  higher concentration (dilute solution) to a region of lower concentration (concentrated solution) through a partially permeable membrane. Note that a partially permeable membrane allows small molecules such as water to pass through but not large solute molecules.

Each cell is surrounded by a cell membrane. It separates the contents f the cell from the outside. The cell membrane has tiny holes in it which allows small molecules to pass through but not large ones. Te cell membrane is described as being partially permeable.

Osmosis is a special kind of diffusion involving water molecules. It occurs when two solutions are separated by a partially permeable membrane.

Osmosis is the diffusion of water from a dilute solution into a more concentrated solution through a partially permeable membrane.

The tiny holes in the membrane allow small water molecules to pass through, but the large solute molecules are too big to pass through the partially permeable membrane. Water is diffusing from a place where there is a dilute solution with a high concentration of water to a place where there is a concentrated solution with a low concentration of water.

Water potential is a way of thinking about the ability of water to move by osmosis. This is influenced by how much water is available, but also by other factors such as the pressure exerted on water in plant cells by the cell wall. It is more accurate to say that a dilute solution (containing a lot of water molecules) has high water potential. A concentrated solution (containing fewer water molecules) has a low water potential.


Back in 9th grade, I did an experiment which explored diffusion. Below is link to a copy of my (embarrassing, yet simultaneously informative) lab report from 2 years ago.


A cute Apparatus/Materials picture:

You're probably wondering why the post title consists of letters from the alphabet. I hope this answers your question:

DONALD : H I J K L M N O!!

TEACHER : What are you talking about?

DONALD : Yesterday you said it was H to O!

If you recall,  cohesion is the ability of water molecules to be able to bond to each other. When I say "bond," I mean hydrogen bonds--the weak bond between two or more water molecules which are caused by water's polar covalent ability to take a positive side hydrogen and a negative side oxygen. Cohesion is what allows molecules of water to "stick" to each other, ultimately creating surface tension.

On the video above, we explored the effect of dishsoap on water tension. Previously, we hypothesized that dishsoap weakens the chemical bonds that hold the fats and proteins together in milk, and that this "weakening" is what caused the motion in milk. Here we prove that it was not the fats that made the milk "dance," but in fact the water. Dishsoap affects the surface tension in water by weakening their hydrogen bonds, causing surface tension to break as demonstrated in the video above.

Rachel Putri Utomo
Block F, Honors Biology
Mr. Kevin Quick
Academic Year 2013-2014