Totipotent, pluripotent and multipotent stem cells (Edexcel A-level Biology B)

This lesson describes the meaning of the term stem cell and the differences between totipotent, pluripotent and multipotent stem cells. The PowerPoint and accompanying worksheets have been designed to cover points 7.3 (i) and (ii) of the Edexcel A-level Biology B specification meaning that this lesson also contains discussion periods about the potential opportunities to use stem cells from embryos in medicine.

The lesson begins with a knowledge recall of the structure of eukaryotic cells and the students have to use the first letters of each of the four answers to reveal the key term, stem cell. Time is then taken to consider the meaning of cellular differentiation, and this leads into the key idea that not all stem cells are equal when it comes to the number of cell types that they have the potential to differentiate into. A quick quiz round introduces the five degrees of potency, and then the students are challenged to use their understanding of terminology to place totipotency, pluripotency, multipotency, oligopotency and unipotency in the correct places on the potency continuum. Although the latter two do not have to be specifically known based on the content of specification point 7.3 (i), an understanding of their meaning was deemed helpful when planning the lesson as it should assist with the retention of knowledge about totipotency, pluripotency and multipotency. These three highest degrees of potency are the main focus of the lesson, and key details are emphasised such as the ability of totipotent cells to differentiate into any extra-embroyonic cell, which the pluripotent cells are unable to do. The morula, and inner cell mass and trophoblast of the blastocyst are used to demonstrate these differences in potency. The final part of the lesson discusses the decisions that the scientific community have to make about the use of pluripotent embryonic stem cells, adult stem cells and also multipotent foetal stem cells

As there is a heavy mathematical content in the current A-level Biology exams, a Maths in a Biology context question is included in the lesson (when introducing the morula) to ensure that students continue to be prepared for the numerous calculations that they will have to tackle in the terminal exams. This resource has been differentiated two ways to allow students of differing abilities to access the work