Looking to earn some bonus credit and boost your grade? You’ve come to the right place! Each week, you will have the opportunity to earn bonus credit for completing extra learning about science…or maybe just for sharing a smile.
This week’s bonus credit opportunity is called…Some Good News. If you haven’t had the opportunity to watch John Krasinski’s YouTube Channel, you are in for a treat! This week’s bonus credit opportunity is pretty simple. Sit back, watch an episode (or 4), smile as much as you can, and then share a piece of good news about your own life by clicking here and filling out the Google Form. That’s it! +10 bonus in the Assignment category.
Welcome to Week 32! For this week, we will be extending our study of evolution to include the process of constructing phylogenetic trees from physical observations of species, as well as DNA analysis. Please work through the list of links below. Each section contains important information and ends with a portion of the weekly assignment. You can complete it all in one sitting or break it up as needed. Ready, set, go!
You did it! Just to make sure, here’s a checklist of items you must complete this week by Sunday, May 3 at 11:59pm:
Weekly Attendance Check-In (school district requirement)
Natural Selection Video Recap section of Google Doc (worth 10 assignment points)
Beak of the Finch section of Google Doc (worth 20 assignment points)
Sorting Finch Species section of Google Doc (worth 20 assignment points)
Creating Phylogenetic Trees from DNA section of Google Doc (worth 40 assignment points)
Remember, you can email me any time. Office hours for Science are Tuesdays from 11am-12pm and Thursdays from 1pm-2pm. Check your student Gmail for Zoom instructions.
For our final piece of work for this week’s lesson, you will engage in the process of constructing a phylogenetic tree using DNA sequences. Darwin constructed a phylogenetic tree of the various finch species he encountered in the Galapagos Islands by comparing various physical traits shared by the different species, scientists today construct phylogenetic trees by comparing DNA sequences. The more similar the DNA sequences, the closer together two species would be on a phlyogenetic tree. With the move to using DNA sequence-based phylogenetic trees, scientists have a new tool to understand evolution and this has resulted in a number of changes to the what we previously though in terms of the evolutionary relationships between species.
Visit the HHMI Creating Phylogenetic Trees from DNA Sequences (available in both English and Spanish)
Work through the Click and Learn activity (available in both English and Spanish), adding a new section to your Week 32 Google Doc (section title: Creating Phylogenetic Trees from DNA Sequences).
Bonus Activity (not required, but awesome): Watch the video below and see if you can construct a phylogenetic tree using real DNA sequences!
For our final section of this week’s lesson, we need to connect back with the theme of toxicity. Simply stated, too much of anything can be toxic. For example, caffeine is toxic (LD50 = 150 mg/kg). One cup of strong coffee has about 150 mg of caffeine. Two cups of strong coffee would have about 300 mg of caffeine. Therefore, two cups of coffee (300 mg of caffeine) is more toxic than 1 cup of coffee (1 cup of caffeine). Thankfully, for most people, it takes a whole lot more than a couple of cups of coffee to be lethal. For this example, since the LD50 for caffeine is the same as the amount of caffeine per cup of coffee, you can figure out how many cups of coffee it would take to reach the LD50 for you by converting your weight in pounds to mass in kg (weight in pounds divided by 2.2 = mass in kg). A 180 pound person has a mass of about 82 kg, so drinking 82 cups of coffee would result in a 50% chance of death.
Fun fact: A cup of coffee is nearly 8 ounces of water, and there are about 30 mL per ounce. Therefore, drinking a cup of coffee means drinking about 240 mL of water. The LD50 for water is 90 mL/kg. For that 82 kg person in the coffee example, drinking 7380 mL of water (90 mL/kg x 82 kg) would result in a 50% chance of death. How many cups of water are in 7380 mL? Divide 7380 mL by 240 mL / cup and that comes out to 30.75 cups of water. So for all you coffee haters out there…go easy on your delicious water! Turns out water is more toxic than coffee. Sorry.
When comparing substances to determine which is more toxic, the key point is you must convert LD50 values to mol/kg. When you convert from mass to moles, you remove the impact of molecule size and instead normalize the data on a per molecule basis. When we ask whether one substance is more toxic than another, we want to be able to compare the toxicity of the molecules, irrespective of the mass of those molecules. In Lesson 79 of the textbook, there is a table comparing the sweeteners fructose (fruit sugar) and aspartame (artificial sweetener). Fructose is commonly found in regular soda, while aspartame is found in some diet sodas. The molecules have different molecular formulas, which means they have different molar masses. Converting the LD50 values to mol/kg shows that aspartame is more toxic than fructose. That’s an important finding, but doesn’t address the real-world question: how much of each sweetener is added to regular (fructose) or diet (aspartame) soda? How many cans of regular or diet soda does it take to reach the LD50 for fructose and aspartame? Read through Lesson 79 in the textbook and find out – the answer might surprise you!
For your final piece of chemistry work this week, complete the Week 32 Exit Task.
On the macro scale, if you have 10 small glass marbles and 10 large clay bricks, what is similar and what is different? Well, clearly you have 10 of each (similar) but the materials have different masses (difference), with large clay bricks having more mass than small glass marbles. Thinking about everyday items and quantities isn’t too bad. However, in chemistry, we have to think about atoms and molecules (things that are incredibly small). When we work with visible amounts of substances composed of atoms or molecules, we have to work with enormous numbers of those substances. This brings us back to everyone’s favorite topic: The Mole.
In Unit 3, you learned that 1 mole is equal to 6.02 x 1023 “things” – such as atoms, molecules, or literally anything you want to count. If you had one mole of glass marbles, you would have 6.02 x 1023 glass marbles. If you had one mole of clay bricks, you would have 6.02 x 1023 clay bricks.
Let’s figure out the mass of one mole of marbles. One marble has a mass of 1.80 g.
1 marble x 1.80 g/marble = 1.80 g/marble
1.80 g/marble x 6.02 x 1023 marbles/mole = 10.8 x 1023 g/mole
10.8 x 1023 g/mole = 1.08 x 1024 g/mole
Your turn! The Entry Task will guide you through another macroscale calculation (the mass of clay bricks) and then we will transition to the microscale (atoms and molecules).
Need a refresher on the Mole? Watch the video below, then head back to the mole lesson in Unit 3 and review as needed.
We often think of evolution as a process requiring many thousands, even millions, of years. First, random DNA mutations must happen in a gamete which is passed along to an offspring. If the DNA mutation affects the coding region of a gene, and the gene product (the protein) is altered, more often then not, the mutation has a negative effect on the viability of the offspring. However, occasionally a mutation will be beneficial, providing the offspring with an increased chance of surviving and having offspring of their own (passing along the new mutation). Again, mutations occur randomly and it takes time for mutations to spread through a population, something that only happens if the mutation is either beneficial, or at least is not harmful.
Sometimes evolution appears to happen quickly. This occurs when a genetically diverse population (one with several different alleles, or versions, of a given gene) undergoes selective environmental pressure. For example, imagine a new virus appears on the scene. The virus enters cells by binding to a specific cell surface receptor and then injecting its nucleic acid into the cell which can then be copied by the cell to make more virus. The human population has multiple different alleles of the cell surface receptor. This is important: each individual person in the population has cells with one version of the receptor (one allele), while there are several alleles of the receptor within the entire human population.The alleles for the receptor were present before the virus. Individuals with properly functioning receptors went about their daily life, growing up, having kids, working, working, working, and taking the occasional vacation.
Suddenly, with the arrival of the new virus, the environment changed. The virus represents a selective pressure. Because the virus binds to a particular cell surface receptor allele expressed by some (not all!) humans in the population, those humans are vulnerable to infection by the virus. Sadly, infection by the virus results in the death of anyone infected. Imagine what will happen to the human population. If there were five different cell surface receptor alleles before the virus, how many alleles would remain in the population after the virus? With only four remaining alleles, the population has evolved. But remember…so has the virus. Viruses accumulate mutations as well, often at a very fast rate, and given enough time, a mutated virus may be able to bind to one of the remaining four cell surface receptor alleles. Hopefully scientists will develop a vaccine before that happens! Note: this is a hypothetical example virus – not the current coronavirus!
Well that was intense! Let’s lighten the mood with another example of evolution in action: antibiotic resistance. After watching the Amoeba Sisters video below, complete the Natural Selection Video Recap assignment. To complete the assignment:
Create a Google Doc titled “Week 32 – Your Name” (example: Week 32 – Pickles Swart).
Share the document with david.swart@g.highlineschools.org.
Create a section in the document titled “Natural Selection Video Recap”
Answer questions 1-9 from the worksheet in your doc.
Now that you have been introduced to toxins, it’s time to bring it all together:
Begin by reading Lesson 74 (Toxicity) in our online chemistry textbook. Chemistry textbook login instructions are provided at the bottom of this post.
Complete textbook exercises 1-5 on page 384 of the book (the last page of Lesson 74). (Worth 20 assignment points)
Create a Google Doc titled “Week 31 – Student Name” (example: Week 31 – Carter Swart), share the Google Doc with Mr. Swart, and type in your answers to the Doc.
Or, answer on paper, take a picture of your work, and email it to Mr. Swart
Need help? You have options!
Click here for more help on understanding toxins.
Reach out to a friend a create an online study group.
Email Mr. Swart with specific questions.
Attend Mr. Swart’s office hours on Tuesday (11am-12pm) and/or Thursday (1pm-2pm) via Zoom.
Check out this helpful video tutorial on how to calculate LD50:
Work through the practice problems at the end of Lesson 74.
Please ask questions about anything from Lesson 74 you do not yet fully understand.
Extend Your Learning!
Wondering about how scientists define the kilogram? Turns out the way we define the kilogram just changed late in 2018. Read about it at PBS.org or watch the video below:
Looking to earn some bonus credit and boost your grade? You’ve come to the right place! Each week, you will have the opportunity to earn bonus credit for completing extra learning about science.
This week’s bonus credit opportunity is called…What’s in that graph? With the current COVID-19 outbreak dominating the news right now, science articles are making headlines daily. To earn +10 bonus credit in the lab report category:
Browse the article to be sure it contains at least one graph. If yes, continue to step 3. If no, go back to step 1 and try again!
If your article contains at least one graph: Read the article carefully. Look up words you aren’t sure about. Decide which one graph you want to analyze.
Link to the article (copy the web address and paste it into the field)
Title of the graph you selected
Type of graph
Description of the x-axis
Description of the y-axis
Explain the general trend of the graph. What is the graph trying to tell you?
Anticipated FAQs
Question: What kind of article should I be looking for? Answer: You may select any scientifically credible article that is interesting to you.
Question: Where is a good place to start looking for science articles? Answer: There are lots of great websites out there. National Geographic, Discover Magazine, and Smithsonian Magazine all have some great articles, many of which are free.
Question: My article doesn’t have a graph in it. What should I do? Answer: Find an article that has a graph in it.
Question: How many bonus credit submissions can I make each week? Answer: You can submit one of each type of bonus credit assignment per week. Some weeks will have a single bonus credit opportunity. Other weeks may have more than one.
Question: I still have questions. What should I do? Answer: Email Mr. Swart!
Science with Swart 
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