stem cells and differentiation

* specialised cells origionally came from stem cells 

* stem cells are unspecialised- so can develop into any kind of cell 

* all multicellular organisms have some form of stem cell 

* in humans stem cells are found in embryos and in adult bone marrow

* in bone marrow they are not as 'flexible' so can only develop into a limited rtange of cells 

* stem cells divide to become new cells- which them become specialised, when a cell becomes speicalised for its job it is called differentiation 

* in animals stemm cells are used to replace damaged cells 

* in plants stem cells (found in the cambium) are needed to make new shoots and roots. they can also become xylem/phloem tissues. 

* cells in the bone marrow differenciate into blood cells (they replace worn out blood cells- erythrocytes and neutrophils- white blood cells, that help fight infection) 

* cells in the cambium differentiate into xylem and phloem

* once cells differentiate they have a specific function- structure is adapted tpo perfom that function 

animal cells

* neutrophils- white blood cells: defend the body against disease- flexible shape allows them to engulf forign particles or pathogens. the lysosomes in there cytoplasm contain digestive enzymes to break down the engulfed particles 

* erythrocytes- white blood cells: carry oxygen in the blood. the biconcave shape provides a large surface area and no nucleus so there in more room for haemoglobin 

* epithelial cells- cover the surface of organs. the cells are joined by interlinking cell membranes at there base. some epithlia have cilia to move particles away. others have microvilli- folds in the membrane that increase surface area. 

* sperm cells, have a flagellum, so they can swim to the egg. they have lots of mitochondria to provide energy. 

plant cells

* palisade mesophyll cell- in leaves, so most of the photosnyhesi