Biology

• All living organisms are composed of cells, cells are the basic unit structure in all organisms
• Cells are the smallest unit of life
• Cells come from pre-existing cells and connot be created from non-living material

When scientists began investigating the structures if organisms under the microscope, they discovered that all organisms were made up of small units called cells. When these cells were removed frimm the tissues, they were able to survive for some period of time. Nothing smaller than the cell has been proven to able to live independantly, thus deeming the cell the smallest unit of life.

Organisms exist in the form of unicellular and multicellular and all organisms carry out the main functions of life.

• metabolism
• growth
• reproduction
• response
• homeostasis
• nutrition

Mutlicellular organisms show emergent properties. For example; cells form tissues, tissues form organs, organs form organ systems and organ systems form multicellular organisms. Whole is greater than the composition of its parts.

Adults have stem cells in the tissues of their bodies that need to be frequently replaced such as skin. Stem cells have the ability to produce a wide range of cells which makes them pluripotent. They retain the ability to provide and produce many different cells by cell division.

• Recently, the most promising research has been directed towards growing large numbers of embryonic stem cells, so that they can be used to replace differentiated cells lost due to injury and disease, involving therapeautic cloning. 
• Parkinsons and alzheimers disease are caused by loss of brain cells, and it is proposed that implanted stem cells could replace many of these and thus relieve the disease symptoms