stem cells

what are stem cells

undifferentiated cell of an organism which is capable of dividing to many more genetically identical cells. From these cells, other cells can arise from the process of differentiation

how are embryos made

when a sperm cell fertilises an egg cell it forms a single cell called a zygote which divides by mitosis and forms a ball of cells called an embryo. The cells in embryos are called embryonic stem cells which can differentiate into any type of cell. So overtime the embryo differentiates into all the other cells we need and we end up with a baby.

what are the two types of stem cells found in animals

adult stem cell, embryonic stem cell

where are adult stem cells found

in the bone marrow

what can adult stem cells differentiate into

platelets, white blood cells, red blood cells

can adult stem cells divide by mitosis?

yes, as much as they like. only difference is they can’t differentiate into any cell, only different types of blood cells

what are plant stem cells called

meristems

where are meristems found

in the tips of roots and the tips of shoots (areas that are continually growing)

what cells do plant stem cells differentiate into

all the cells the plant needs, eg palisade cells, phloem or xylem cells, root hair cells

difference between plant stem cells and embryonic stem cells

plant stem cells persist for the plants entire life, embryonic stem cells disappear by the time we are fully developed

what is the use of stem cells in medicine?

lots of conditions are due to faulty cells (damaged/no longer working) so stem cells can be used to replace the faulty cells with working ones and treat the condition

cause of type 1 diabetes

damage to the pancreas cells that normally produce insulin

cause of paralysis

(sometimes) caused by damaged nerve cells

cause of sickle cell anaemia

misshapen red blood cells

technique for using stem cells in medicine

scientists extract embryonic stem cells from early embryos, grow them in a laboratory, stimulate them to differentiate into whichever type of specialised cell they need, transplant them to the patient to replace their faulty cells

what are the drawbacks of using stem cells in medicine

1) requires embryonic stem cells (as they’re the only ones that can differentiate into any type of cell)

• limited supply

• some ethical issues

2) because the embryo and the patient have different genomes the patients immune system may reject the stem cells so their body tries to destroy them because it identifies the, as foreign. Patient can be given rejection medication to suppress their immune system however it doesn’t always work and has side effects

how can scientists overcome the drawbacks of using stem cells in medicine

they can use adult stem cells

• easier to get ahold of (taken from patient)

• won’t cause rejection

problems of using adult stem cells in medicine

can only differentiate into different types of blood cells (however there is new research exploring how we could use adult stem cells to produce any type of cell)

risks of using stem cells in medicine

• virus transmission, if the donor stem cells are infected with a virus (either before taken by scientists or while in the lab) so when transplanted into patient they will get infected with the virus and cause more problems

• tumour development, because stem cells can divide so quickly there’s a chance they could get out of control once transplanted into patient, could go on to develop a tumour/cancer.

ethical objection to using embryonic stem cells

because embryos have a potential for human life some people object to their use in research (embryos used are usually unwanted ones from fertility clinics)

on the other hand some think the benefits of curing existing people who are suffering is more important than the rights of embryos