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Secular Science Resources for Homeschoolers

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January 2019

High School Biology 17 – History of Life

Students read Holt Biology Chapter 12 or Chapter 17 in Biology: Life on Earth, both chapters are titled History of Life. I also sent the students links to the following videos to watch before class.

For the lab activity I pulled out my skull collection, which includes a few racoons, a beaver, a rodent, a bird and an impala skull. I purchased most of them from a local store which specialized in bones and skulls, unfortunately its no longer in business, but you can purchase them online from places like Skulls Unlimited or I even found a few on Amazon.  If you don’t have access to real or replica skulls you can do this lab with print outs. The activity is called “Lost World”, and it can be found in Biology Inquiries: Standards-Based Labs, Assessments, and Discussion Lessons by Martin Shields.

IMG_1637.jpegEach pair of students were given a skull to study.  They were to sketch and measure the skull and write down any observations that might be clues about what kind of animal it was, what it ate, where it lived, body size, body shape, etc.  The point of the exercise is not to guess correctly that it was a mouse, but that it had teeth for gnawing and chewing vegetation and that it was a small animal.  By looking at the foramen magnum of the skull (small opening at the bottom/back of the skull where spinal cord attaches/enters), students could infer whether the animal had a horizontal body plan, or a vertically oriented neck.

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Students also drew what the animal might have  looked like when it was alive and the kind of habitat it might have lived in.img_1651

We had about 25 minutes left and many of the students in my high school class have younger siblings in my middle school class, so they asked to do the radioactive decay lab with the candies in the time remaining.  I also showed them the horn coral mentioned on the previous post as well.

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Middle School Biology 17 – Time

We started class with “A Brief History of Geologic Time” by PBS Eons and :Great Minds: Mary Anning, The Greatest Fossilist in the World” by SciShow.

I also brought out some fossils of horn coral, heliophyllum halli, that we have and explained how they have growth ridges, kind of like tree rings. Scientists count the growth ridges and find 400 ridges per year (roughly a centimeter of growth) and since they produce one growth ridge per day that tells us that a year on earth used to consist of roughly 400 days, not the 365 days we have now.  This is because the earth’s rotation is slowing down so the Earth goes through fewer rotations in a one trip around the sun.

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Horn coral fossils showing growth ridges.

We then talked about the different ways to determine the age of a fossil, relative dating, img_1629index fossils, and radioactive dating.  The students did an activity from Real Science Odyssey Biology 2 where they cut out strips of paper that had different animals/plants on them and put them in order the way they would expect to find the fossils in the layers of earth – oldest fossils (simplest organisms) at the bottom and animals resembling what we see living on earth now, at the top.  They glued these into their notebooks after confirming they were correct.

The second activity was about radioactive decay and carbon-14 dating.  Students were each given a cup of chocolate candies, M&Ms, and dumped them on a paper plate.  All img_1628the candies that landed with the M facing up were ‘decayed’ and disposed of (eaten or placed in a separate bowl).  Students counted the remaining candies and recorded it in their data table.  They put the candies back in their cup and tossed them again and again until they were out of candies. We put everyone’s data on the white board and added all the results together and made a bar graph of the results.  The graphing part of this activity was the hardest part. Just about everyone had trouble making the axes of the graphs, not sure how many squares to use, not being consistent in the number of squares, ie just randomly putting numbers on the side of the paper.  Its really good to make the students graph by hand and learn how to do this and to check their axes before they start plotting the data.  You can find lots of different versions of this activity on the web, I used the one here on the AAAS website, Radioactive Decay: A Sweet Simulation of Half-Life.img_1630

Here’s a video explaining carbon dating.

Middle School & High School Biology 16 – Fossils

I had students from both classes come to class today for a guest speaker.  A friend  I know through the Livermore Lithophiles, brought his fossil collection to my home for show and tell.  A large number of the fossils are ones he collected as a boy and some he has purchased over the years.  Here are some photos from his collection.

For the lab activity I purchased a Prehistoric Amber Kit (25 count) from Nature-Watch.  I had purchased this before, years ago, for another class and was pleasantly surprised by the number of insects found in the amber, so decided to buy it again.  The pieces are roughly an inch across, so easy for students to handle.  The amber is rough and you can’t tell if there are any inclusions (insects, pollen, etc stuck in the amber) until you polish them. img_1522 The kit comes with amber, sandpaper, denim pieces (for polishing), plastic bags, a few toothbrushes and toothpaste. Each student polished their piece of amber by dunking it in water and then rubbing it on the sandpaper.  I had some fine grit and some rougher grit for those who needed it, as well as some magnifying lens to help look for tiny critters.  Finally the amber is polished with the scraps of denim.   We had one piece that I suspect might have a chrysalis in it, or maybe a small pine cone, but it really had the shape of a chrysalis.  By putting a flashlight up against the amber you can see inside it a bit better.  IMG_1514.jpeg

I also brought out my son’s amber collection and put one of the smaller pieces under the microscope.  I used the Celestron NexYZ  3-Axis Universal smart phone adapter to get this photo of the spider in amber through the microscope at 40X.  The spider was one of 6 pieces of amber my son got from an Amber of the Month Club for his birthday.  Every piece he received had at least one insect, some had 4 (small gnats).  It was a fun birthday present that lasted 6 months (you can do 6 months or 12 months).

spider in amber

There’s a nice documentary by David Attenborough called The Amber Time Machine (BBC) and it can be found on youtube.

High School Biology 15 – Evolution of Populations

Over winter break students were told to read Chapter 11 in Holt Biology textbook or Chapters 15 & 16 in the Biology: Life on Earth text.  I started class with a slideshow on some of the early scientists like Linneaus, Comte de Buffon, William Smith (geologist), Lamark (gave us the word biology) and Darwin and then moved on to the evidence for evolution:  natural selection, comparative anatomy,  embryo similarities, and molecular evidence (similarities in DNA).  We also discussed genetic flow, the founders effect, bottleneck events and other selection effects.

IMG_1378.jpegWe did two labs, both found in the Holt Biology online teacher resources.  For Lab 11.6 Microevolution and Antibiotic-Resistant Bacteria, students used light colored (white & yellow) cubes to represent bacteria and dark colored (brown and black) cubes to represent antibiotic resistant bacteria.  They started out with 20 light colored cubes in a bowl and then rolled two dice which determined the next event for their bacteria population.  A roll of 4, 5, 6 means nutrients are plentiful and the population doubles, but a roll of 3 means one bacterium mutates and becomes resistant to antibiotic A (students replaced one light colored cube with a dark one).  Other events included low nutrients (two thirds of the bacteria die),  cleaning products are used killing 90% of the bacteria, Antibiotic A is introduced killing all but the antibiotic-resistant bacteria.  The lab handout has a table of dice rolls matched with events.  Students kept track of their population until it was wiped out (which can happen in just a few rolls of the dice), or they continued until they reached 20 rolls of the dice.  If their population died out quickly they just started over.  We had one population that evolved to  consist entirely of antibiotic-resistant bacteria that just kept growing since there was no way to wipe it out – cleaning products kills 90% and low nutrients cut down the population but since they are resistant to antibiotics, there were no events that killed them all.

IMG_1375.jpegThe second lab, 11.3 Modeling Alleles, investigated the bottleneck effect on cheetahs.  Before class I prepared two bottles (for 2 groups), each containing 100 beads total – 10 beads of 10 different colors.  Each color represents one trait (allele), such as fast legs, good night vision, weak immune system, etc.  Students randomly assigned one color to each trait in the handout.  The 100 beads in the bottle represents the gene pool of the original population of cheetahs.  A disaster occurs and only 20-30 cheetahs survive – students simulate this by slowing pouring out beads into a bowl until they have roughly 20-30 beads.  They record the color of beads and traits that survived (were poured into the bowl).  Some students actually still had all 10 colors in this first generation after the bottleneck effect, while others only had 6 colors, or 60% of the genetic diversity of the original population (100 beads).  For the second generation of cheetahs, students blindly grabbed a bead from the bowl, recorded the color and then placed it back in the bowl. They did this 10 times and usually lost a few more traits in the process.  Before doing the third generation they removed all the color beads that hadn’t been passed on to the second generation and then repeated the drawing of beads from the bowls.  The lab handout asked a number of questions about their remaining cheetahs and problems that might arise with the decreased genetic diversity.

IMG_1382.jpegWe actually finished with 30 minutes to spare, so I handed out the timeline cards from the middle school class and asked students to try to put them in order.  The cards had major events, such as first fish, first land animals, first flowering plants,  largest mass extinction, etc.

Middle School Biology 15 – Geologic Time

There are a lot of different timeline activities to be found on the web.  I used the Geological Timeline Activity found here, and searched the web for photos to put with many of the major events. I printed out the photos (22 of them) with captions (first fish, etc) and had the students try to put them in order from the oldest to the most recent.  I had them do this before giving them the timeline activity with the events and times so they could try to puzzle it out themselves.  I did not expect them to get them all right but wanted them to spend some time thinking about what came first… winged insects?  flowering plants?  dinosaurs?  After they had the cards laid out,  I flipped through my set that were in order and we discussed why the ones they had in the wrong place were earlier or later.

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This photo is from the high school class doing the card sorting activity.

For the timeline activity, students measured out 5 meters of adding machine tape (basically just a roll of paper that you can find at office stores pretty cheap).  1 meter stands for 1 billion years, 1 cm = 10 million years and 1 mm = 1 million years.  They put a line on the left side of the paper and marked it TODAY and only 0.1 mm from the TODAY line, they were supposed to draw another line showing the beginning of Homo Sapiens.  This is pretty much impossible to draw accurately so I told them to draw the second line as close as possible to the TODAY line.  The handout has a table with major events, when they occured and the distance the students should mark on their timeline.  It really helps to have a meter stick so you can at least mark off meters.  This would not be fun if you only had a short ruler.  When they had their timelines done we discussed how most of the complex life appeared relatively recently and humans had only been around for a very short time.

Most of the students made their own timelines but some worked in pairs.  They either rolled up their timelines and secured them with a rubber band or folded them and put them in their notebooks.

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