National 4 & 5 Biology – multicellular organisms Section 2a – Stem Cells Recap • How do we get all these different cells from 1 original cell? • How have they become so different to each other? Learning Outcomes • Today we will learn: • - the site of production of specialised cells in animals • - the role of stem cells in growth & repair • - potential uses of stem cells & ethical issues related to these How did you get like this? By the time you finish growing, you will have an estimated 50 trillion cells. That’s 50,000,000,000,000! You started out as a single cell. How did one cell turn into 50 trillion? A slow start For the first week the fertilized egg cell (zygote) splits in two every day to make a bundle of smaller cells. cell division (mitosis) After about 1 week, the zygote is called an embryo. Exponential growth What are stem cells? The first cells are stem cells. These are unspecialized cells capable of developing into many different types of cell. Stem cells found in embryos are called embryonic stem cells and develop into all the different types of cell in the body. Embryonic Stem Cells • - found in newly formed embryo’s • - they can become placenta cells or more embryo cells • - after 4-5 days a ball of embryo cells is formed – blastocyst • - these cells can become any type of human cell • - they are pluripotent • - after about a week, they will start specialising Pluripotent Blastocyst Changing cells When the embryo contains about 500 cells, the cells stop being the same and they stop getting smaller with each division. They start to differentiate into different types of cell. At this point, stem cells no longer form two new stem cells when they divide. Instead, one of the two daughter cells becomes a tissue cell. stem cell stem cell tissue cell What is a stem cell? Stem cell SELF-RENEWAL (copying) Identical stem cells Stem cell DIFFERENTIATION (specializing) Specialized cells Becoming specialized Tissue cells continue to divide and differentiate, each time becoming more and more specialized. stem cell tissue cells Some will become nerve cells, others will become blood cells, muscle cells, bone cells, etc. nerve cells red blood cells cardiac muscle cells Embryonic & Foetal Stem Cells • Cells in a blastocyst will initially specialise into one of three layers • - Endoderm (“endo” = inner) • - forms many internal organs – e.g. stomach, intestines, liver • - Mesoderm (”meso” = middle) • - forms the muscles • - e.g. heart , skeleton, connective tissue, deep layers of skin • - Ectoderm (“ecto” = outer) • - forms the central nervous system, and body surface layers • Once part of these layers, cells will have started to specialise Task • • • • • • You will each be assigned a cell type Around the room there will be three stations: - ectoderm - endoderm - mesoderm You must decide which of the three stations you belong in (others in the group can help) • Your group must then decide which body systems are within your layer Adult Stem Cells • - in adults, stem cells are found within many tissues of the body • - can form specialised cells of a particular tissue • - e.g. Hematopoietic cells can form any type of blood cell • - adult stem cells can only form cells of a certain type • Stem Cells Video • Stem Cell therapies video Re-Cap task Produce a summary of stem cell research:• What are the main types of stem cell and where do they come from? • What are scientists using stem cells for? • What breakthroughs could be possible thanks to stem cell research?