Cell Specialisation (IB Topic B2.3)

Essential Idea(s): Stem cells have intricate roles and by differentiating to perform specialized functions. Gene expression controls the progression of stem cells differentiation.

 Unit Length: 3 Lessons (AHL content in B2.3 is covered in other units)

  Guiding Questions

◊ What are the roles of stem cells in multicellular organisms?

◊ How are differentiated cells adapted to their specialized functions?

Materials:

Self-Teaching Slides   Quizlet Vocab Set
Teaching Slides   Notes Template
IB Statement(s) and Objective(s)

B2.3.1: Production of unspecialized cells following fertilization and their development into specialized cells by differentiation

  • Define cellular differentiation
  • Explain the concept of differential gene expression
  • Define morphogen gradient  
  • Explain the role of morphogen gradients in gene expression of early stage embryos

B2.3.2: Properties of stem cells

  • Define stem cell

B2.3.3: Location and function of stem cell niches in adult humans

  • Define stem cell niche
  • Give 2 examples of stem cell niches

B2.3.4: Differences between totipotent, pluripotent and multipotent stem cells

  • Define totipotent, pluripotent, and multipotent stem cells
  • Explain why stem cells are most prevalent in the early embryonic development of a multicellular organism

 

B2.3.5: Cell size as an aspect of specialization

  • Outline the range of cell size in humans

 

B2.3.6: Surface area-to-volume ratios and constraints on cell size

  • Explain why cells are often limited in size by the ratio of surface area to volume
  • NOS Concept: Modeling as a tool in science 
  • Give examples of models used in science
  • Outline limitations of models in science
  • Explain the benefits and limitations of using cubes to model the surface area and volume of a cell.
  • NOS Concept: Reliability of quantitative data is increased by repeating measurements
  • Explain the need for repeated measurements (multiple trials) in an experiment
  • Explain why standard deviation is used to summarize the spread of values
  • State that error bars are a graphical representation of the variability of data
  • Explain the need for controlled variables in experimental design

 

B2.3.7: Adaptations to increase surface area-to-volume ratios of cells (*is actually AHL, but included in SL content)

  • Explain three adaptations of cells that maximize SA: volume ratio
Activities: ⓟ = podcast / ⍰ = inquiry 5 / ⓦ = Write it /  Ӕ = The academy  / Ⓡ = Read it

ⓦ (required) – Design a Lab: Modeling cell membranes with agar & acid: Why Cells are Limited to Small Sizes? (💁)

There’s a simple problem with big cells: as a cell grows, the volume increases faster than the surface area. This is true of any 3D object – be it spheres, rocks, cubes, or cells. Because of this, the cell membrane cannot keep up with the resource supply demands of a large cell. Your task for this lab: use agar cubes to design an experiment that shows how increasing cell size limits the ability of a cell to carry out its basic functions. 

Use this writing guide to help you complete this task. A data table template is available here – this should help give you an idea of what you need to do. Here’s what you should aim to submit:

  • A research question – with clearly written variables within it. 
  • Clear variables, including: an independent variable, a dependent variable, and all relevant control variables. 
  • An introduction/background section – summarize the relevant background science (e.g. diffusion, metabolism, etc), and outline what the purpose and benefit of this lab is. (1-2 paragraphs)
  • A hypothesis – Consider the background science to predict what will happen to your DV as you manipulate your IV (no more than 1 paragraph)
  • A methodology – What specific steps will you take in the lab to ensure it is accurate and reliable? (Roughly 7-10 steps is ideal).
  • A properly formatted data table of your results
  • A graph to display your end results (error bars are NOT required for this)

Use the following resources if you need help with this task:

  • Want to know how you’re going to be graded? 

Here’s the rubric

  • Need help with experimental design vocab?

Practice this Quizlet review set

 

Debate It! (recommended): Science, Politics, & Religion – The Bioethics of Stem Cells ([+NOS, +TOK], 👬min 5, max whole class)

Key moments of the stem cell debate

Arguments FOR

Arguments AGAINST

Simple debate rules for the classroom

Ethics is that center of the realms of politics, science, and religion. Since the discovery of stem cells, ethics has been at the forefront. Some people consider the use of stem cells for research akin to murder; others say we should be able to freely experiment with as many as possible. Review the attached files, then, then together with your group, defend and critique the ethical stances behind the harvesting, use, and destruction of stem cells for purposes of science. Use specific examples of diseases that are currently treated with stem cell use, and give an overview of stem cell regulations by country. 

 

ⓟ: What are Stem Cells, and Why Are They So Controversial? (👬 max 3)

Watch this video to learn about stem cells, then watch this video and this video  to learn about why they are so controversial. With your fellow podcasters, discuss: 1) What stem cells are, 2) What regenerative medicine is, and how stem cells are used in regenerative medicine, and 3) Why they are so controversial. What do you think about the controversy? Where do you stand on it?  

 

Ӕ: Dolly the Sheep (💁)

Create a Khan Academy-style video (go here for inspiration) to tell the story of Dolly the Sheep. Make sure you describe the process of cloning by SCNT, and use visuals to explain how Dolly was cloned in the lab.

 

ⓡ: Playing God? The Future of Human Cloning  (💁)

Could human embryos one day be used to grow new organs in the lab? Though often accused of “playing God”, scientists are closer and closer to being able to grow human parts – and possibly even a human – inside the lab. Read this article and discuss: 1) How cloning works, 2) How SCNT works, and 3) What you think governments should / should not do about the future of cloning. (You can also read this Wikipedia article for more info on the current state of human cloning).  

 

ⓟ: The Primitive Streak (💁 / 👬 max 3)

Last May, two research groups announced a breakthrough: they each grew human embryos, in the lab, longer than ever before. In doing so, they witnessed a period of human development no one had ever seen. But in the process, they crashed up against something called the ’14-day rule,’ a guideline set over 30 years ago that dictates what we do, and possibly how we feel, about human embryos in the lab. Listen to this Radiolab podcast (30 minutes) entitled “The Primitive Streak.” Then respond by discussing the key ideas, highlighting: 1) The different levels of organization in living things; 2) How gene expression “awakens” in an embryo, and 3) How you feel about the idea of humans placing limits on how long an embryo is permitted to grow in a petri dish. 

 

ⓟ: The Flatworm Key to Regeneration (💁 / 👬Max 3)

Researchers around the world are hard at work trying to understand how most of a group of flatworms called planarians can use powerful stem cells to regenerate their entire bodies, an ability humans can only dream of. Read this article / watch the video and respond, discussing: 1) What stems cells are; 2) What the different types of stem cells are, and 3) How flatworms might hold the key to regeneration in humans.

 

Extras for helping you study: 

Review of stem cells

Quiz Yourself! 50 Questions on stem cells & differentiation