*OCR 21st CenturyB5 Growth and Development

http://www.youtube.com/watch?v=I-vbE-k3uo0 *

*B5.1 How do organisms develop?

*Cell specialisationDuring the development of a multi-celled organism cells differentiate to form specialised cells:

*Cells, tissues, organs and systemsBasically, all living things are made up of cellsA group of CELLS makes up a TISSUEA group of TISSUES makes up an ORGANA group of ORGANS makes up a SYSTEMA group of SYSTEMS make up an ORGANISM

*Another exampleHeres another example in humans:

*FertilisationThe human egg and sperm cell (GAMETES) contain 23 chromosomes each and are created by meiosis.When fertilisation happens the gametes fuse together to make a single cell called a ZYGOTE. The zygote has 46 chromosomes (23 pairs) and continues to grow through mitosis.

*Embryos When the zygote grows all of the initial cells are identical (up to the 8-cell stage). These are called embryonic stem cells. From this stage on the cells grow through mitosis and start to specialise.

*Adult Stem CellsIt is also possible to have adult stem cells these are unspecialised cells that can become specialised later (but they cant form ALL types of cell)Adult stem cells can be found in places like bone marrow.

*Plant Growth IntroductionPlants grow due to their cells dividing through mitosis. The cells then specialise into root hair cells, palisade cells etc. Unlike animals, plants continue to grow for the rest of their lives.

*Plant Growth - MeristemsPlant growth occurs in areas called meristems. These meristems are mitotically active:Cells from the meristem behave like stem cells they can develop into any kind of cell. Cloned plants can be produced from these cells.

*Cloning Plants by tissue culture1) Scrape of a few cells from the desired plant2) Place the scrapings in hormones (auxin) and nutrients3) 2 weeks later you should have lots of genetically identical plants

*Plant HormonesThe growth of roots and shoots is controlled by hormones:

*Some DefinitionsShoots grow towards light (positive phototropism) and against gravity (negative geotropism).

Roots grow away from light (negative phototropism) and in the direction of gravity (positive geotropism).

*B5.2 How does an organism produce new cells?

*Cell growth 1 - Mitosis

*Cell growth 2 - Meiosis

*Mitosis vs. MeiosisMitosis:Used for growth and repair of cellsUsed in asexual reproductionCells with identical number of chromosomes and genetic information are produced (clones)Meiosis:Used to produce haploid gametes for sexual reproductionEach daughter cell has half the number of chromosomes of the parent

*Fertilisation RevisionThe human egg and sperm cell (GAMETES) contain 23 chromosomes each and are created by meiosis.When fertilisation happens the gametes fuse together to make a single cell called a ZYGOTE. The zygote has 46 chromosomes (23 pairs) and continues to grow through mitosis.

*B5.3 How do Genes control growth?

*Genes, Chromosomes and DNA

*Some facts: - DNA has a double ______ structure - This contains instructions on what a cell does, how the organism should work etc - The instructions are in the form of a ______ - The code is made up from the four ____ that hold the strands together with hydrogen bonds; A always pairs with T and C with G - The bases represent the order in which _____ acids are assembled to make specific ________How genes work - DNAWords helix, amino, code, bases, proteins

*Making proteins1) DNA unravels and a copy of one strand is made2) The strand copy is made to produce RNA3) The copy (with its code) then moves towards the ribosome 4) The ribosome decodes the code which tells the ribosome how to make the proteinIn other words, genes do NOT leave the nucleus but a copy of the gene (the mRNA) carries the genetic code to the cytoplasm.

*Adult Stem CellsCells inside an organism contain the same genes. So how can cells specialise if they have the same genes and make the same proteins?The reason is that many of the genes in the nucleus are switched off so that the cell only produces the proteins it needs.It is possible to switch on different genes to make the cell produce different proteins this is the basis of stem cell research.

*Stem cell researchAs well as adult stem cells from bone marrow, stem cells can also come from...Egg and spermEmbryoCloned embryosThese stem cells have the potential to develop into any kind of cell. The rest of the embryo is destroyed. Most of these embryos come from unused IVF treatments.The ethical issue:Should these embryos be treated as humans?

Dolly..\..\..\..\..\Clips\Reproduction\cloning_animals__hello_dolly.mpg*

*Cloning AnimalsHeres how Dolly the sheep was cloned:It is possible to switch on inactive genes in the nucleus of a body cell to form cells of all tissue types. Are cloning and stem cell research the way forward???