Comparing Amounts

Yesterday we were introduced to the concept that 6.02 x 10^23 particles of something is equivalent to a unit called the mole.  For more about how this number, called Avagadro’s number.  Student’s wishing to learn more about how that number was calculated are encouraged to read the Scientific American article How was Avagadro’s Number Determined?  The mole is one of the basic units of measurement in science – part of the International System of Units (SI units).  To learn more about SI units, including an update on how the kilogram as about to be redefined, check out the Nature article titled New Definitions of Scientific Units are on the Horizon.  As a brief refresher of the mole (and explicitly connecting the value of the mole to Avagadro’s number), we watched the Crash Course video below (at 0.75 speed) from about time stamps 5:30 to 8:00.

After the video, we worked through some example problems from yesterday’s molar conversion worksheet and also from the Chapter 13/14 study guide.  The remaining 15 minutes of class were used to work through the Lesson 79 PowerPoint in which we ultimately compared the toxicities of regular and diet soda, containing fructose and aspartame, respectively.  We will work through the Lesson 79 Worksheet tomorrow as part of our review of Chapters 13 and 14.

Mutation and Selection Gizmo

After an abbreviated end to last week during which a late-start (snow) and two all-school activities conspired to limit our classroom time, we decided to start the class period with Jack Horner’s entertaining TED Talk in which he describes his research connecting dinosaurs and chickens.

After the video, we briefly discussed how scientists study embryology, the fossil record, atavisms, and behavior to add to our understanding of evolution.  Students were then released to work with a partner on the Mutation and Selection Gizmo.  Students were instructed to work at least through Activity A of the handout today in preparation for our work tomorrow.

Counting by Weighing

Our work today involved a Counting By Weighing activity.  Students recorded the mass of a small number of objects to then estimate the mass of a much larger number of objects.  The activity was designed to help students begin to make sense of the mole, a unit of chemistry that represents 6.02 x 10^23 of any given object.  In chemistry, we use the mole as a way to measure the number of atoms or molecules.  Students also received a copy of the Chapter 13/14 Study Guide as a tool to begin preparing for the quiz next Thursday.

Writing to Explain

What a week!  With 12 minute class periods yesterday and only 35 minutes today, we made the most of our time by completing and discussing the Cosmos video and then students were tasked with a “writing to explain” assignment where they compared and contrasted artificial and natural selection.  Most importantly, the assignment asked students to explain using evidence from the video.  The assignment is due Monday.

As we continue in our study of biology this school year, students will continue to practice the skill of explaining using evidence, with the expectation that students will draw on a variety of sources and learn to differentiate between credible and less-than-credible scientific resources.


In the first lesson of Chapter 14, students were introduced to the concept of LD50 (the dose of a compound that is lethal to 50% of the population).  As our entry task, students considered the following:

Which substance do you think is most toxic to you –

  1. Alcohol (ethanol, C2H6O)
  2. Aspirin (salicylic acid, C7H8O3)
  3. Arsenic (III) oxide (As2O3)

Explain your thinking

We then identified the LD50 values for all three substances using the Lethal Doses Handout.  We discussed the meaning of LD50 (the lethal dose at which 50% of rats die after exposure to a given amount of a substance, often expressed in mg/kg) and students were shown a Material Safety Data Sheet (MSDS) for water (toxic at >90 mL/kg), providing students with evidence that all substances are toxic at high enough levels.

Students then received the Lesson 74 Worksheet to work on during class time and they were assigned Lesson 74 textbook questions 1-5.

Introduction to Evolution / Cosmos Video

We began Unit 6 with a brief class discussion about what students know (or think they know) about evolution.  All student ideas were recorded and served as an entry point into the second episode of Cosmos from the 2014 series hosted by Dr. Neil deGrasse Tyson.  Student initial ideas are shared below.  We watched the first 30 minutes of the video today, pausing periodically to answer questions on the handout students received and which will be turned in after we complete the video tomorrow.  Students learned today during the episode (titled “Some of the Things That Molecules Do”):

  • dogs and wolves share a common ancestor (artificial selection);
  • polar bears and brown bears share a common ancestor (natural selection);
  • how random DNA mutations can occasionally produce desirable traits depending on the environment in which the organism with the mutation lives;
  • how all life on Earth is connected via DNA to a common ancestor (using the Tree of Life analogy);
  • how the evolution of sight can be traced all the way back to bacteria
1st period initial ideas
4th period initial ideas
6th period initial ideas

Unit Conversion

As we transition from Chapter 13 to Chapter 14, we took a brief detour to review dimensional analysis and the metric system.  To prepare for “the mole” – a unit new to most chemistry students, we began class with the worksheet “How Many Whoozles?” Students were challenged to complete the first two problems, with a few students completing all of them.  The answer key for problems 1-5 is shown below:

Next, we transitioned to a review of the metric system, focusing on the base units of meters, liters, and grams.  We followed that up with the classic video aptly titled, “Meters, Liters, and Grams.”

For the remainder of class, students solved Dimensional Analysis practice problems on a worksheet.  Students may turn in one completed page (one page = front and back) for homework credit.  Turning in both completed pages will earn the student a bonus point for homework.  We worked through the first six problems together as a class:

Types of Reactions

For the final lesson of chapter 13, students learned to classify the types of reactions as combination, decomposition, single exchange, or double exchange reactions.

  • Combination: A + B -> C
  • Decomposition: A -> B + C
  • Single Exchange: AB + C -> A + BC
  • Double Exchange: AB + CD -> AD + CD

We focused primarily slide 8 of the Lesson 73 PowerPoint.  Students are encouraged to review the full slide deck, including the vocabulary defined on slides 9-12.  Students then received the Lesson 73 Worksheet and Toxic Reaction Cards to work on for the remainder of class.  For homework, students were assigned Lesson 73 textbook problems 3-7.