1. Unit 1 – Human Cells

2.  Differentiation – an unspecialised cell developing to perform a specialised function  In adult cells, many genes are switched off – cells already specialised  In early embryo’s – all the genes are active  During embryo development, the cells differentiate and specialise  E.g. a motor neuron will develop an axon  This is due to certain genes switching off  - only 3-5% of genes are expressed in specialised cells

3.  Unspecialised cells that can:…  Embryonic:  In an early embryo (blastocyst) all the genes have the potential to be switched on  - cell can differentiate into any cell type  Tissue (adult):  Narrow differentiation potential  Many genes already switched off  Used to replenish certain types of differentiated cells  E.g. bone marrow cells can produce various blood cells

4.  Epithelium :  Layers of cells to form membranes  - form the skin  - also lines the body cavities, oesophagus, blood vessels  - blood vessels have a thin lining  Connective tissue :  - have large quantity of extracellular material between cells  BONE  - layers of calcified material surrounding blood vessels  - live bone cells lie within calcified material  CARTILAGE  - extracellular material can be solid and smooth  E.g. bone endings  - or can be dense and slightly flexible  E.g. knee joints  BLOOD  - extracellular space is plasma

5.  Muscle Tissue:  SKELETAL:  - cells are in striped fibres  SMOOTH:  - arranged in sheets  - control involuntary movements  - e.g. blood vessels, alimentary canal  CARDIAC:  - branched structure  Nervous Tissue:  - made up of neurons  - to receive and transmit impulses  - and glial cells  - to support the neurons

6.  Produce gametes following meiosis  - germline cells start with 46 chromosomes  - are DIPLOID  - end up producing 4 cells  - each are HAPLOID  If mutations occur, they will be inherited by offspring  - e.g. cystic fibrosis (chromosome 7 mutation)  Mutations in somatic cells are not inherited by offspring  - e.g. mole from skin cells

7.  Research:  - human stem cells can be grown in culture  - growth factors required  - increase understanding of differentiation  - mice often used as a model organism  - investigate disease development  - responses of cells to drugs  Therapeutics:  - used for bone marrow transplants, skin grafts, cornea repair  Ethics & Regulation:  - stem cells raise ethical issues  - especially surrounding embryo’s  High levels of regulation  - e.g. Human Fertilisation & Embryology Act

8.  Cancer – an uncontrolled growth of cells  Cell division normally controlled by cycle regulators and chemical signals  - cancer cells don’t respond to these regulatory signals  Tumours:  - a mass of abnormal cells  BENIGN  - group of abnormal cells within a normal tissue  - usually easily removed  E.g. warts  MALIGNANT  - abnormal cell group that enters circulation  - can invade other tissues & create tumours  Genetic Errors:  - cancers start from cells undergoing successive mutations  - often to genes controlling cell division  - cells can divide excessively, outwith normal control  - increased risk with age  - and with causative agents  E.g. smoking, pollution, UV radiation  - common in tissues with high division  E.g. skin, lung, bowel