cell differention, stem cells, mitosis and some chromosomes

• pholem and xylem are tubes that transport substances such as food and water around the plant
• guard cells control the size of stomata by changing shape
• stomata is an opening on the surface of a leaf through which gases can enter or leave the leaf
• stomata allow gases to enter and exit the leaf, but also allows water vapour to escape which can cause dehydration
• the epidermis is made up of one layer of cells called guard cells
• the guard cells surround the stoma
• xylem transports water from roots to leaves
• when the guard cells become turgid, they pull apart to open the stoma
• the guard cells regulate the size of the stoma by changing their shape
• when the guard cells lose water, they shrink and push together to close the stoma
• when it's light outside, the guard cells become turgid (swollen) so they pull apart allowing CO2 into the leaf
• in the evening when there isn't much sunlight, the guard cells lose water and shrink causing them to close up preventing water loss from the leaf
• when the guard cells become turgid they pull apart allowing gas exchange
• the epidermis has tiny openings called stomata
• if there isn't enough carbon dioxide then the guard cells will lose their turgidity causing them to close
• phloem transports sugars from leaves to other parts of plant
• guard cells are sensitive to light levels and CO2 concentration
• in the dark, the guard cells lose water and shrink pushing back together closing the stomata
• stem cells are undifferentiated cells that can divide to produce more undifferentiated cells
• stem cells are found in early human embryos and can differentiate into any type of cell
• in adults stem cells can be found in bone marrow
• embryonic stem cells have been used to treat leukaemia by replacing damaged blood-forming cells with healthy ones
• adult stem cells cant turn into any cell, only certain ones such as blood cells
• stem cell from embryos and bone marrow are lab grown to produce clones (genetically identical) and made to differentiate into specialised cells to use in medicane or research
• mediciane can use adult stem cells to cure dieases i.e strem cells from bone marrow can replace faulty blood cells in a paitenet who recives them
• embryonic stem cells can be used to replace insulin-producing cells for diabetics, nerve cells e.c.t
• therapeutic cloning - cloning of an embryo to produce an embryonic stem cell. this means that the embryo can be genetically modified to produce a specific type of cell and wont be rejected by the patients body
• chromosomes contain genetic material in the form of DNA molecules that have been coiled up
• each chromosome carries a large number of genes. genes control the development of different characteristics such as eye colour
• a gene is a section of dna which codes for a particular protein
• mitosis produces two identical daughter cells
• mitosis- the chromosones line up at the centre of the cell and the chromosones are pulled to opposite ends of the cell due to the cell fibres
• 2)mitosis- memebranes form around each of these chromosones. these become the nuclei of two new cells, the nucleus has been divided
• 3)lastley, the cell membrane and the cytoplasm divide

  now have two daughter cells
• the first round of mitosis results in two haploid cells called daughter cells