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
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?
How did you get like this?
A slow startFor 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
BlastocystPluripotent
Changing cellsWhen 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
tissue cellstem cell
What is a stem cell?
Identical stem cells
Stem cell
SELF-RENEWAL(copying)
Stem cell
Specialized cells
DIFFERENTIATION(specializing)
Becoming specializedTissue cells continue to divide and differentiate, each time becoming more and more specialized.
Some will become nerve cells, others will become blood cells, muscle cells, bone cells, etc.
nerve cellsred blood
cells
stem cell
tissue cells
cardiac musclecells
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?