Stem Cells

Stem Cells & Differentiation
Multicellular organisms are made up of many different cell types which are Adapted for their Function. i.e. blood cells, muscle cells e.t.c. All of these originated from Stem Cells. Stem cells are Unspecialised, but can develop into different types of cell. All multicellular organisms have stem cells in some form. In Humans, they are found in early Embryos and in a few places in adults. Stem cells in embryos can develop into Any Type of cell. However, Adult stem cells can only develop into a Limited Range of cells

The process where stem cells become specialised for their function is called Differentiation. In adults, stem cells can be used to Replace Damaged Cells, i.e. skin cells or blood cells. Plants are always growing, so stem cells are needed to Produce New Shoots and Roots. Stem cells in plants can also differentiate into Xylem and Phloem Cells.
Stem cells can also divide to produce more Unspecialised Stem Cells.

BONE MARROW
Bones are living organs. They contain Nerves and Blood Vessels. The main bones of the body have Bone Marrow in the Centre. It is here that adult stem cells can differentiate to Replace Worn Out Blood Cells - Erythrocytes (Red) and Neutrophils (White).

MERISTEMS
Meristems are the part of the plant where Growth takes place. In the Root and the Stem of the plant, stem cells of the Vascular Cambium Divide and Differentiate into Xylem Vessels and Phloem Sieve Tubes.

STEM CELL TREATMENT
As stem cells can differentiate into different types of cell, Scientists think we can Replace Damaged Tissue Cells to cure diseases, mostly neurological disorders like Alzheimer's and Parkinson's.

Alzheimer's	Parkinson's
Alzheimer's is where Nerve Cells in the Brain Die in increasing numbers.	People with Parkinson's suffer from Uncontrollable Tremors
This results in Severe Memory Loss.	The disease causes the loss of a particular type of nerve cell located in the brain.
In this case, researchers want to Replace Damaged Nerve Cells with re-grown nerve cells that have been differentiated from stem cells.	These cells release a chemical called Dopamine, which is needed to Control Movement
	It is thought that transplanted stem cells will help to Regenerate the dopamine-producing cells.

Stem cells are also used for Developmental Biology (studying how cells grow and develop). This can help us understand developmental disorders and cancer.

DIFFERENTIATION

Once cells differentiate, they have a Specific Function. Their structure is then adapted to perform that function.

Below is a table of cell types that are specialised for their specific function.

Cell Type	Function	Adaptations
Neutrophil	Defends the body against disease	Flexible shape to engulf foreign particles or pathogens More lysosomes contain digestive enzymes to break down engulfed particles
Erythrocytes	Carry oxygen in the blood	Biconcave shape provides large surface area for gas exchange No Nucleus to allow more haemoglobin
Epithelial Cells	Cover the surfaces of organs	Ciliated epithelia have cilia that beat to move particles away Squamous epithelia are very thin to allow  efficient diffusion of gases
Sperm Cells	Fertilisation of ovum cells	Flagellum so they can swim to the ovum Lots of mitochondria to provide energy to swim The acrosome contains digestive enzymes to enable the sperm to penetrate the surface of the egg.
Palisade Cells	Photosynthesis	Lots of chloroplasts to absorb more sunlight Thin walls so CO2 can easily diffuse into the cell.
Guard Cells	Open and close the stomata	Thin outer walls and thickened inner walls force them to bend outwards opening the stomata, allowing the leaf to exchange gases for photosynthesis
Root Hair Cells	Absorb water and mineral ions from the soil	Large surface area for absorption Thin permeable cell wall for entry of water and mineral ions More mitochondria to provide energy needed for active  transport