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?