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B1 pages 14-15 (cells differentiate to become specialised (differentiation…
B1 pages 14-15
cells differentiate to become specialised
differentiation is the process by which a cell changes to become specialised for its job
as cells change, they develop different subcellular structures and turn into different types of cells. this allows them to carry out specific functions
most differentiation occurs as an organism develops. in most animal cells, the ability to differentiate is then lost at an early stage, after they become specialised. however, lots of plants cells don't ever lose this ability
the cells that differentiate in mature animals are mainly used for repairing and replacing cells such as skin or blood cells
some cells are undifferentiated cells called stem cells
examples of specialised cells
root hair cells
specialised for absorbing water and minerals
root hair cells are cells on the surface of plant roots, which grow into long 'hairs' that stick out into the soil. this gives the plant a big surface area for absorbing water and mineral ions from the soil
phloem and xylem cells
specialised for transporting substances
phloem and xylem cells form phloem and xylem tubes, which transport substances such as food and water around plants. to form the tubes, the cells are long and joined together end to end. xylem cells are hollow in the centre and phloem cells have very few subcellular structures, so that stuff can flow through them
sperm cells
specialised for reproduction
the function of a sperm is basically to get the male DNA to the female DNA. it has a long tail and a streamlined head to help it swim to the egg. there are lots of mitochondria in the cells to provide the energy needed. it also carries enzymes in its head to digest through the egg cell membrane
nerve cells
specialised for rapid signalling
the function of nerve cells is to carry electrical signals from one part of the body to another. these cells are long (to cover more distance) and have branched connections at there ends to connect to other nerve cells and form a network throughout the body
muscle cells
specialised for contraction
the function of a muscle cell is to contract quickly. these cells are long (so that they have space to contact) and contain lots of mitochondria to generate the energy needed for contraction
the cell cycle (makes new cells for growth development and repair)
body cells in multicellular organisms divide to produce new cells as part of a series of stages in the cell cycle
the stage of the cell cycle when the cell divides is called mitosis
multicellular organisms use mitosis to grow or replace cells that have been damaged
the end of the cycle results in two new cells identical to the original cell, with the same number of chromosomes
the two main stages in the cell cycle
growth and DNA replication
1) in a cell that's not dividing, the DNA is spread out in long strings
2) before it divides the cell has to grow and increase the amount of subcellular structures such as mitochondria and ribosomes
3) it then duplicates its DNA do that there is one copy for each new cell. the DNA is copied and forms x shaped chromosomes. each 'arm' of the chromosome is an exact duplicate of the other
mitosis
5) membranes form around each of the sets of chromosomes. these become the nuclei of the two new cells - the nucleus has divided
6) lastly the cytoplasm and cell membrane divide
4) the chromosomes line up at the centre of the cell and cell fibres pull them apart. the two arms of each chromosome go to opposite ends of the cell
the cell has now produced two new daughter cells. the daughter cells contain the exact same DNA meaning they are identical. their DNA is also identical to the parent cell.
chromosomes (contain genetic material)
most cells in your body have a nucleus. the nucleus contains your genetic material in the form of chromosomes
chromosomes are coiled up lengths of DNA molecules
each chromosome carries a large number of genes. different genes control the development of different characteristics e.g. hair colour
body cells normally have two copies of each chromosome. one from the organisms 'mother' and one from its 'father'. so humans have two copies of chromosome 1, two copies of chromosome 2, etc
cells don't all look the same. they have different structures to suit there different functions
in order to survive and grow our cells have to be able to divide (that means our DNA as well)