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what do most cells in your body have

a nucleus that contains your genetic material in the form of chromosomes


what are chromosomes

coiled up lengths of DNA molecules


what happens when a cell divides by mitosis

it makes two diploid genetically identical daughter cells and the nucleus of each contains the same amount as the original cell


body cells in what organisms divide by mitosis



what do multicellular organisms use mitosis for

to grow or replace cells that have been damaged
reproduce (asexual reproduction)


what is interphase

- In a cell that's not dividing the DNA is all spread out into long strings
- before it divides the cell has to grow and to increase the amount of subcellular structures
- It then duplicates its DNA so there's one copy for each new cell
- the DNA is copied and forms X shaped chromosomes and each arm of the chromosome is an exact duplicate of the each other


what happens in prophase

- the chromosomes condense getting shorter and fatter
- the membrane around the nucleus breaks down and the chromosomes lie free in the cytoplasm


what happens in metaphase

- the chromosomes line up in the middle of the cell


what happens in anaphase

cell fibres pull the chromosomes apart and the two arms of each chromosome go to opposite ends of the cell


what happens in telophase

- membranes form around each of the sets of chromosomes. These become the nuclei of the two new cells
- the nucleus has divided


what happens in cytokinesis

- the cytoplasm and cell membrane divide to form two separate cells


how can you calculate the number of cells a certain amount of cell divisions

2 the power of n
for example after 5 cell divisions there will be 32 cells because 2 to the power of 5 is 32


how do plants grow

differentiation, division , elongation


what is cell differentiation

the process by which a cell changes to become specialised for its job
having specialised cells allows multicellular organisms to work more efficiently


what is cell division



what is cell elongation

where a plant cell expands making the cell bigger and so the plant grow


discuss growth in animals

- happens by cell division
- animals tend to grow while they're young and then they reach full growth and stop growing
- so when you are young cells divide at a fast rate but once your an adult most cell division is for repair
- the cells divide to replace old or damaged cells
- this also means in animals cell differentiation is lost at an early stage


discuss growth in plants

- growth in height mainly due to cell elongation
- cell division usually just happens in the tips of the roots and shoots in areas called meristems
- but plants often grow continuously (even really old trees will keep putting out new branches)
- so plants continue to differentiate to develop new parts like leaves and roots


discuss cancer in relation to cell division and growth

- the rate at which cells divide by mitosis is controlled by the chemical instructions (genes) in an organisms DNA
- If there's a change in one of the genes that controls cell division, the cell may start dividing uncontrollably
- This can result in a mass of abnormal cells called a tumour
- if the tumour invades and destroys surrounding tissue it is called cancer


why do we use percentile charts

to assess a child's growth over time so that an overall pattern in development can be seen and any problems highlighted (e.g obesity, malnutrition, dwarfism)
for example a baby growth is regularly monitored after birth to make sure its growing normally
- length
- mass
- head circumference


what are undifferentiated cells

stem cells


where are adult stem cells found

bone marrow


why do embryonic stem cells need to be able to differentiate into any type of cell

because all the body's cells develop from the one embryo


what is the problem with adult stem cells

only found in certain places like bone marrow
they only make certain types of cell


discuss meristems

- in plants the only cells that divide by mitosis are found in plant tissues called meristems
- meristem tissue is found in the areas of a plant that are growing e.g the tips of roots and shoots
- meristems produce unspecialised cells that are able to divide and from any cell type in the plant (they act like embryonic stem cells)
- unlike human stem cells these cells can divide and differentiate to generate any type of cell for as long as the plant lives
- these unspecialised cells go on to form specialised tissues like xylem and phloem


how can stem cells be used in medicine

- doctors use adult stem cells to cure some diseases like sickle cell anaemia can sometimes be cured with a bone marrow transplant (contain adult stem cells which produce new blood cells)
- Scientists have experimented with extracting stem cells from very early human embryos and growing them. Under certain conditions the stem cells can be stimulated to differentiate into specialised cells
- It might be possible to use stem cells to create specialised cells to replace those which have been damaged by disease and injury
e.g new cardiac muscle cells could be transplanted into someone with heart disease


why is there a large scientific interest in stem cells

the potential for new cures


what potential risk are associated with the use of stem cells

tumour development - stem cells divide very quickly. If Scientists are unable to control the rate at which the transplanted cells divide inside a patient a tumour may develop

disease transmission - viruses live inside cells and if donor cells are infected with a virus and this isn't picked up the virus could be passed onto the recipient and make them sicker

rejection - if the transplanted cells aren't grown using the patients own stem cells the patients body may recognise the cells as foreign and trigger an immune response to try and get rid of them. The patient can take drugs to supress this response but this makes them susceptible to disease.


what is the problem with using embryonic stem cells

it raises ethical issues because some people argue that they shouldn't be used because they are a potential human life


what is the CNS

brain and spinal cord