Lesson 7 of 7 / Cells and stem cells
Build a body, then renew its tissues
Why are stem cells still needed in adults?
I can explain normal embryonic and blood stem-cell functions.
I can explain normal embryonic and blood stem-cell functions.Syllabus
Syllabus 8876, Core 1(q). Explain normal embryonic and blood stem-cell functions.
About 4 min
Make a guess. You are not marked.
When a stem cell becomes a specialised muscle cell, does it lose the genes it no longer needs?
Show the answer
It keeps them but switches many off.
Differentiation changes which genes are expressed. Most specialised cells keep essentially the full genome.
The key idea
Embryonic stem cells supply diverse cell lineages during development. Blood stem cells continually replace short-lived specialised blood cells.
Explore the idea
Keep the source while supplying cells
The source persists while descendants supply cells for tissue function. This is a simplified lineage model, not a claim that every division has exactly these two fates.
Original schematic. Structures, cell numbers and distances are illustrative, not to scale.
Explanation
During development, cell division increases cell number while differentiation produces specialised cells. Embryonic stem cells provide a broad source of these lineages. Cells receive signals that change which genes are expressed, leading to different protein products and functions.
In an adult, many specialised cells have limited lifespans. Blood stem cells in bone marrow self-renew and generate cells that develop into red blood cells, white blood cells and platelet-producing cells. This supports oxygen transport, defence and clotting over time.
Maintenance requires a balance: enough divisions must preserve the stem-cell pool, while other descendants differentiate to replace cells that are lost. Producing only specialised cells would eventually deplete the source; producing only stem cells would fail to replace the working tissue.
Step by step
- 1
State the tissue need
Development requires new cell types; adult renewal replaces cells lost over time.
- 2
Connect both stem-cell properties
Self-renewal preserves the source and differentiation supplies functional cells.
Worked example
A depleted blood stem-cell pool
Explain why losing blood stem cells can affect several blood functions, rather than only one cell type.
One way to explain it
Blood stem cells supply several related lineages. Loss of their self-renewing source can reduce production of red cells, defence cells and platelet-producing cells, affecting oxygen transport, defence and clotting.
Why this answer works
- Start with a common precursor.
- Trace the consequences to multiple descendants.
Watch out for this
A student says: "An adult stem cell normally has to lose most of its genes to become specialised." What is wrong with this?
Show the answer
Differentiation primarily changes gene expression. Most specialised nucleated cells retain essentially the same genome, although particular cell types such as mature mammalian red cells later lose their nucleus.
Check your understanding
Why must a tissue retain some stem cells during renewal?
Show the answer
A continuing source is needed for future replacement cells.
Self-renewal preserves that source while differentiation supplies cells now.
Quick recall
Why are stem cells still needed in adults?