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B2 Revision:Cell division and Stem cells (Stem cells: (Risks (Rejection:…
B2 Revision:Cell division and Stem cells
Chromosomes
Genetic material, found in the nucleus, is stored in chromosomes
DNA is coiled up to form the arms of chromosomes
Body cells contain 2 copies (diploid)
Mitosis
When a cell reproduces itself by splitting in two to form two genetically identical offspring
Part of cell cycle:
Cell cycle starts when cell produced by cell division and ends when it produces two identical cells
Cell cycle:
Interphase:
Cell grows and increases amount of subcellular structures,e.g. mitochondria and ribosomes
Duplicates DNA so there is a copy of each chromosome for each new cell.
DNA forms X shaped chromosomes which each arm being the same
Mitosis:
Prophase:
Chromosomes condense, getting fatter
Membrane around nucleus breaks down and the chromosomes lie free in the cytoplasm
Metaphase:
Chromosomes line up at the centre of the cell
Anaphase:
Cell fibres pull the chromosomes apart so the two arms of each chromosomes go to opposite ends of the cell
Telophase:
Membranes form around each of the sets of chromosomes (the nuclei of the two new cells are formed)
Cytokinesis:
Before telophase ends, the cytoplasm and cell membrane divide to form 2 separate cells
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eaches
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Uses:
To replace cells that have been damaged
Asexual reproduction
Growth
Number of cells after multiple divisions
2 to the power of n(number of divisions by mitosis
Growth:
Cell division
Mitosis
Cell differentiation:
Cell becomes specialised for its job
Cell elongation(only for plants):
In Animals:
Cell division at fast rate for growth until adult, when just used for repair
Cell differentiation lost at an early stage
In Plants:
Elongation for height
Cell division in meristems (tips of roots and shoots)
Differentiation happens through all the plants' life to develop new parts(leaves, roots)
Cancer:
Rate cells divide(cell division) is controlled by genes in DNA
If there was a change in a gene that controls cell division, cells will divide uncontrollably, causing a mass of abnormal cells(tumour)
If the tumour invades and destroys surrounding tissue, it is called
cancer
Percentile Charts:
Used to assess a child's growth overtime
Measures
length, mass and head circumference
50th percentile means 50% of babies have reached that at that age
Likely for doctors to investigate if:
Inconsistent pattern
Above or below the percentile lines
Size increases or decreases but 2 or more percentile lines overtime
Stem cells:
Undifferentiated cells
Can divide to produce many stem cells which can then make different types of cells depending on instructions given
Found in early embryos
which can divide and differentiate into any kind of cell
Adult stem cells
only found in certain place(e.g.
bone marrow
which is a spongy tissue inside bones)
Aren't as versatile(can only produce certain types of cells
Adult stem cells used to replace damaged cells(e.g.skin or blood cells)
Medicine
Adult stem cells
People with blood diseases(e.g.sickle cell anaemia) can get bone marrow transplants which contain stem cells which can differentiate into new blood cells
Embryonic stem cells
Under certain conditions, these stem cells can be stimulated to differentiate into specialised cells
Risks
Tumour development
If scientists are unable to control the rate of which a transplanted cell divides in a patient, a tumour may develop
Disease transmission
If donor stem cells are infected with a virus and no one realises, the virus could be passes on, making the recipient more sick
Rejection:
If transplanted cells aren't grown using the patient's own stem cells, the body may recognise the cells as foreign and will trigger an immune response to try to get rid of them
The patient can take drugs to suppress the response, but this makes them susceptible to diseases.
Ethical issues
Human embryos shouldn't be used for experiments as it is a potential human life
Curing someone who already exists and who is suffering is more important
Embryos used for experiments are unwanted from fertility clinics which would probably be destroyed if not used for research
In plants
In meristems found in areas the pants are growing(e.g.roots and shoots)
Produce unspecialised cells which can divide and form any cell type in the plant
These cells can divide and differentiate for as long as the plant lives