Percentile charts and stem cells 2.7 - 2.9

How percentile charts are used to monitor growth

- show the overall pattern in development

- a baby is monitored regularly to make sure it is growing normally

What measurements are taken for a baby's growth

- length, mass, head circumference

How to read percentage charts

- the chart shows percentiles

- e.g the 50th percentile shows the mass that 50% of babies will have reached at a certain age

- babies vary in size but doctors are likely to investigate if a baby's size is above the top percentile or below the bottom percentile line, their size increases or decreases by two or more percentile lines over time, or if there's an inconsistent pattern

Stem cells definition

undifferentiated cells

What can stem cells do

- Divide by mitosis to become new cells, which then differentiate.

- they are really important for the growth and development of organisms

Embryonic stem cells

- stem cells found in early human embryos

- these embryonic cells have the potential to divide and produce any kind of cell at all

Adult stem cells

- adults have stem cells found in places such as bone marrow

- these aren't as versatile as embryonic stem cells - they can't produce any cell type at all and only certain ones

Stem cells in animals

Adult stem cells are used to replace damaged cells e.g to make new skin or blood cells

Meristem plant stem cells

- the only cells that divide by mitosis are found in plant tissues called meristems

- meristem tissue is found in the areas of a plant that are growing e.g the tips of the roots and shoots

- meristems produce unspecialised cells that a re able to divide and form any cell type in the plant - they act like embryonic stem cells

- these cells can divide and differentiate to generate any type of cell for as long as the plant lives unlike human stem cells

- the unspecialised cells go on to form specialised tissues like xylem and phloem

Benefits of use of stem cells

- adult stem cells cure some diseases such as sickle cell anaemia can sometimes be cured with a bone marrow transplant

- stem cells from early embryos under certain conditions can be stimulated to differentiate into specialised cells

- stem cells may be used to create specialised cells to replace those which have been damaged by disease and injury e.g new cardiac muscles could be transplanted into someone with heart disease

- this POTENTIAL for new cures is a reason for huge scientific interest in stem cells

Risks of stem cell medically

- tumour development - if scientists are unable to control the rate at which transplanted cells divide in a patient a tumour may develop

- disease transmission - viruses live inside cells. If donor stem cells are infected with a virus and isn't picked up, the virus could be passed on making the patient sicker

- rejection - the body may recognise the cells as foreign and trigger an immune response to try and get rid of them.

The patient can take drugs to suppress this response but this makes them susceptible to diseases

- ethical issues - people thing that human embryos shouldn't be used for experiments because each one is a potential human life, others think curing a human who is suffering is more important than the potential life of the embryos