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