6.5 Flashcards
Differentiation
The process of a cell becoming specialised.
stem cells
What are stem cells?
Undifferentiated cells
Originate from meiosis or mitosis
Have the potential to become any type of specialised cells within the organism.
Undergo cell differentiation
Source of new cells necessary for growth, development and repair.
Once stem cells have become specialised they lose the ability to divide, and enter the G0 phase of the cell cycle.
Why is the activity of stem cells strictly controlled?
If they do not divide fast enough, then tissues are not efficiently replaced, leading to ageing
However, if there is uncontrolled design then they form masses of cells called tumours, which lead to cancer
stem cell potency
What is stem cell potency?
A stem cell’s ability to differentiate into different cell types.
The greater the number of cell types it can differentiate into, the greater its potency.
Types of potency:
Totipotent
Pluripotent
Multipotent
Explain totipotent
These stem cells can differentiate into any type of cell
Embryonic stem cells.
Explain pluripotent
Can form all tissue types but not while organisms
Present in early embryos and are the origin of the different types of tissue within an organism.
Explain multipotent
Can only form a range of cells within a certain type of tissue
Haematpoetic stem cells in bone marrow as they give rise to the various types of blood cells.
replacement of red and white blood cells
Red blood cells
Lifespan of about 120 days
Replaced constantly
The stem cell colonies in the bone marrow produce 3 billion erythrocytes per kg of body mass per day to keep up with demand..
White blood cells
Live for about 6 hours
The colonies of stem cells in bone marrow produce a region of 1.6 billion per kg per hour.
This figure increases during infection
sources of animal stem cellss
Sources of animal stem cells
Embryonic stem cells
Tissue (adult) stem cells
Embryonic stem cells
Totipotent
After about 7 days a mass of cells called a blastocyst, has formed and is now pluripotent.
They remain in this state until the foetus is born.
Tissue (adult) stem cells
Found in bo
sources of plant stem cells
Meristems (meristematic tissues)
Tips of roots and shoots
Located between the phloem and xylem tissues, this is called the vascular cambium.
Cells originating from this region differentiate into different cells present in xylem and phloem tissues.
Vascular tissue grows as the plant grows.
uses of stem cells
Treatment of burns
Drug trials
Developmental biology
potential uses of stem cells
Heart disease
Type 1 diabetes
Parkinson’s disease
Alzheimer’s disease
Macular degeneration
Birth defects
Spinal injuries
ethics
Embryos used originally were donated from those left over after fertility treatment.
The UK changed the law that embryos can be specifically created in the lab as a source of stem cells.
The removal of stem cells from embryos results in the destruction of the embryo.
Although techniques are being developed to remove the stem cells without damaging the embryo.
Religious and moral objections.
The use of umbilical cords overcomes these issues to an extent, however they are only multipotent therefore restricting their usefulness.
Adult tissue stem cells do not divide as well as umbilical cord stem cells and are more likely to have acquired mutations.
difference between multipotent and pluripotent
1 Pluripotent – stem cells that can form all tissue types but not whole organisms (1). Only present in
embryos (1). Multipotent – stem cells that can only form a range of cells within a certain type of tissue
(1). For example, bone marrow is multipotent (or any appropriate answer) (1).
state where you would find meristematic tisse and explain the importance of the position
2 Shoot tips / root tips (1); (meristematic tissue contains) dividing cells (1); (leading to) growth (1); new
cells / stem cells can differentiate (1); (leading to) specialisation (1).
advantages and disadvantgase of using embryonic stemm cells
3 Embryos left over from fertility treatment (1); discarded anyway (1); embryos now created (to supply
stem cells) (1); embryos then destroyed (1); religious objections (1); life begins at conception (1);
embryo has rights (1); ownership of genetic material (1); (incurable) diseases cured (1); improved
quality of life (1).
