The Urey and Miller Story

download (1)This here is Stanley Miller.

When you tell stories in science and make it relevant to students they remember it better. Let’s take this example of the story of Urey and Miller and how their revolutionary experiments have impacted our ideas on the origin of life on Earth.

My Origin of Life on Earth story

So the first thing you should know is that the Earth is really old. Really really old. It’s 4.5 billion years old. But how old is that? I don’t know! So let’s do something else. If we imagine that the whole time that Earth has been around to be 24 hours. Then we can work with a timescale that we’re a little more familiar with. Ready to join me? Okay.

So at 0:00 the Earth just formed.

At 2:35 am prokaryotic life (bacteria + archaea) form

Nothing much else happens till 4pm. Bacteria are just hanging out there. Making the world oxic.

At 4pm eukaryotic life appears. These are organelle bound remember.

Again, nothing much happens until 9:45pm where insects appear.

10:33pm Dinosaurs appear

10:54pm Mammals appear

11:57pm Modern Homo sapiens appear

1 second ago – first Aboriginal cultures appear

All of recorded history lasts only 0.03 of a second.

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Mind = blown. That’s pretty incredible isn’t it?

So then let me introduce you to two men: Oparin and Haldane. These guys both independently hypothesised the conditions of Early Earth. Haldane goes hmmm I wonder if biomolecules began to exist on Earth as a direct result of the conditions of Early Earth. And Oparin goes: oh man! I thought of it first, but I didn’t publish it in English and so no one knew about it! *sad face*

What did they think Early Earth was like?

  • it was HOT
  • it was gaseous
  • there was no oxygen
  • there was a lot of water
  • there was a lot of lightening storms
  • there was a lot of UV radiation as there was no atmosphere

Now introducing another two guys. Harold Urey and his slave graduate student Stanley Miller. Mr. Urey says “Hmmm I wonder if I set up an experiment with all those conditions, would it give rise to those biomolecules? If only I had a grad student to do all this research for me….Oh Stanley!!!!” And Stanley of course says “Yes Boss”.

If you’d like to see a set up of their experiment this site has a fantastic video to explain it.

In my powerpoint I have a whole series of other useful questions to ask of your students regarding the Nature of Science.

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Collaborative Timeline on the Evolution of Life on Earth

timeline

I wanted to do something a bit fun with this. I thought if I made it online, I could make it a whole class collaborative project. I listed the different events in the history of life on Earth and gave my students a brief run down of what the different events were. Then asked them to create a very short summary answering the following questions:

  1. When is this event occurring (provide the best estimates of time period)?
  2. Describe the event that you are researching. Outline key features of the event. Provide references for your research.
  3. What evidence (such as fossils where possible) do scientists use to describe this event? Include images/video.
  4. How does this event contribute to the diversity in the evolution of life on Earth? I.e. what implications does this event have on future life on Earth?

I then asked my students to peer assess another groups summaries against the same above criteria and fix up any suggestions that the other group made on their own summaries. Finally this edited version was to be uploaded onto a class timeline generated on Timeglider. I’m not sure this was the best Web2.0 tool to use for this purpose. It didn’t allow collobration between members so basically we all used the same login and password to create this timeline. In future I would like to look for another tool that allows each pair of students to create an account and then they upload their work from this source. It would aid in me keeping track of who’s submitted their work and who hasn’t. My class’ timeline can be found here.

Modelling the Inheritance of Linked and Unlinked Genes

To model the difference between linked and unlinked genes I used an activity I created that you should view here.

How it works:

By keeping some “alleles” linked and some “unlinked” we observe a difference in the inheritance pattern.

My initial instructions for this worksheet weren’t very clear but I think they are much better now. Ideally it will be printed so that the maternal genes are printed in one colour (let’s say pink, even though it’s a socially constructed convention. Let’s talk about that another time) and the paternal genes are a different colour. If I were to teach this again I would create a class set of laminated linked genes and laminated unlinked genes. The students spent far too long cutting them out themselves and I don’t think the actual process of cutting them adds anything to the learning experience.

Why is linkage important? The linkage of genes has huge implications for the inheritance of alleles. Genes which are on the same chromosome do not randomly segregated in meiosis. They physically cannot because they are on the same chromosome and so are inherited together.

Oh if only biology were so simple. NOT. That would be boooooooring! Evolution is way more sophisticated than that.

In fact, we have a process called crossing over that swaps a little bit of DNA between homologous chromosomes so your maternal and paternal DNA can be rearranged into each of your gametes. So if you can imagine, genes which are closer together are more likely to stay together. It would be very unlikely for a crossing over event to happen right at the exact spot where one gene ends and the other starts and so genes which are closer together tend to stay together.

Difficulties in defining Health and Disease

This is quite a controversial and murky topic when it comes to science (which is something scientists are not always comfortable with let me assure you!). This is because, as you will see for yourself, it is really difficult to define health and disease. I tried to come up with a list of different conditions that might be difficult to classify as “healthy” or “not healthy” if we are to use the World Health Organization definition of health. That is a “complete state of physical, mental and social wellbeing and not merely the absence of disease or infirmity”.

Complete the poll to see what you think. Also, I’d love to make this list even longer, comment with suggestions as to other conditions, which may be difficult to classify. This form of assessment for learning allowed my students to engage critically with the syllabus requirements and is an integral part of my teaching practice (Quality teaching in NSW Public Schools, 2003). Scroll to the bottom if you want to download the lesson in Word format.

Difficulties in Defining Heath Word Document

Quality teaching in NSW public schools. (2003). Retrieved from https://www.det.nsw.edu.au/proflearn/docs/pdf/qt_EPSColor.pdf

Using an Encyclopedia analogy to describe DNA organisation

While teaching Year 12 students I noticed from their questions that many of them had not yet grasped the concept of DNA structure and organisation clearly. This was very surprising for me, mostly because (1) they were at a selective school so I naively thought that that must mean they would miraculously grasp concepts (2) we were in our 3rd term in the HSC, they should know it by now! To me, huge red flags started signalling and I approached my supervising teacher asking if she would allow me to deviate from the plan and take a lesson to revise key issues. Thankfully she agreed, although I know a little reluctantly, there is a lot of pressure to “get through” content. I couldn’t have these kids get to their final exams and not understand what a chromosome really is. After all, they were doing the core topic in biology – blueprint of life and they were also doing the genetics option. Effectively they could’ve been tested on this content twice. It was a huge gamble if I didn’t go through it.

So I prepared a series of questions aimed at pinpointing their issues. I projected these on the board and handed out laminated sheets of white paper – that I call mini-whiteboards – to each of the students and some markers and we had a quizzing and intervention session. I’d ask a question they’d respond and if it was clear that a few of them (I think I revised concepts if even 3 of them were unsure) weren’t clear we’d go through it.

From their questions it was clear that the concepts of DNA organisation was completely lost on them. They still weren’t clear on what an allele was, what a gene is and how chromosomes organise DNA or what their functions were.

It’s an abstract concept so I totally understand this confusion. If you’re teaching students about DNA, the following analogy I used might help.

All the DNA that we have in each somatic cell is a complete set called a genome. Let’s pretend this is the Encyclopaedia Britannica. You know how we have A-Z and each book has one section of the Encyclopaedia, well our DNA is organised into a similar mechanism. Each large of DNA is called a chromosome. Our chromosomes are different, just like an Encyclopaedia. The A entries are totally different form the G entries. But we need a complete set of A-Z for a complete encyclopaedia. Similarly, we need a complete set of chromosomes 1-23 for a complete genome. To add a little complexity to it, we don’t just have one set of DNA we have two. One from our mother and one from our father. So if we continue with the Encyclopaedia example this is like if we have a whole set of Britannica and another set of the World Book Encyclopaedia. We find the same entries in there, like you’ll find a definition for apple in each but they might be slightly different.

So let’s take it a step further. Each entry in the encyclopaedia is like a gene – it has a meaning and in cells that meaning is a protein. Each gene is made up of DNA in a combination of a series four bases (ATCG) these letters are what make up DNA. Similarly, definitions are made up of words.

So let’s recap.

 

Encyclopaedia Our cells
Broken up into books, A-Z Broken up into chromosomes 1-23
Come in different brands Come in different alleles. We have one of each of mum’s alleles and one of dad’s.
Each book has different entries Each chromosome has different genes
Entries are made up of words Genes are made up of nucleotides
Words are made up of letters Nucleotides are made of sugar, phosphate and bases. Each base is made of either an A, T, C or G. 

 

What do you think? My kids loved this analogy and their relief was the most satisfying aspect of my first practicum. I want to know if you think it will work for you!

Mitosis Lesson

Your body produces If I had a gun to my head and absolutely HAD to pick a favourite topic in biology, I would probably choose mitosis and meiosis. I can’t imagine that this would ever be the case, but you know, it paints a pretty picture. After 7 years of studying meiosis I still have to think about how to spell it – I don’t know what it is, I just find it so tricky. Anyway, mitosis. I taught this for my very first time on my first teaching practicum and the students absolutely ate it up.

Let me explain why.

So you know how when you’re really excited about something you become very animated about it and you can’t help but infect everyone with your excitement. Yeah that’s pretty much what happened. You can see the powerpoint I used to help in my presentation and you can pretty much feel the excitement leaping out at you.

stole borrowed a lot of ideas from the one and only Hank Green of the VlogBrothers. They have an amazing YouTube series called Crash Course. Here, go watch it and come back.

Oh hai there. Welcome back!

So what I basically did was tell my students (half of whom were on an excursion anyway) put your books away. This is the most exciting story you will ever be told and I don’t want you to write anything I just want you to listen. In retrospect I probably should’ve “Checked for Understanding” but I was a novice. I might do it slightly different in future. I told them about how at a cellular level our bodies are incredible. We make over 300 billion cells per day. Just try to wrap your head around that for a second. There are 7 billion people on the planet. Gosh I love science.

So even on your laziest day where you watch 2 whole seasons of Orphan Black because your student may have told you that it’s a really good show to watch and you totally agree cause it’s about cloning. Even on those days you are freaking incredible. Then I said to them: When do we even need mitosis? What is it?

You cut your finger and your skin needs to repair itself.

BAM MITOSIS.

You’re a newborn and you want to grow bigger and taller.

BAM MITOSIS.

Your immune system wants to fight off disease.

BAM MITOSIS.

Your stomach lining is eaten away by the cells they produce.

BAM MITOSIS.

Are you noticing a pattern here? And half the class said BAM MITOSIS. It was a good moment.

Have I sold you? Wanna see my PowerPoint?

Ask nicely!

Mitosis PowerPoint