cell | The smallest structural and functional unit of an organism. |
| |
nucleus | A structure that contains genetic material and controls the activities of the cell. |
| |
chromosome | A thread like structure of coiled DNA found in the nucleus of eukaryotic cells. |
| |
DNA | A polymer made up of two strands forming a double helix. |
| |
gene | A section of DNA that codes for a specific protein or characteristic. |
smallest largest
MITOSIS AND THE CELL CYCLE
Cells divide in a series of stages. The genetic material is doubled and then divided into two identical cells.
Stage 1 | Growth | Increase the number of sub-cellular structures e.g. ribosomes and mitochondria. |
Stage 2 | DNA Synthesis | DNA replicates to form two copies of each chromosome. |
Stage 3 | Mitosis | One set of chromosomes is pulled to each end of the cell and the nucleus divides. Then the cytoplasm and cell membranes divide to form two cells that are identical to the parent cell. |
Mitosis occurs during growth, repair, replacement of cells. Asexual reproduction occurs by mitosis in both plants
& simple animals.
STEM CELLS
Undifferentiated cell of an organism
Divides to form more cells of the same type, and can differentiate to form many other cell types.
Human Embryonic stem cells | Can be cloned and made to differentiate into most cell types | Therapeutic cloning uses same genes so the body does not reject the tissue. Can be a risk of infection |
Adult bone marrow stem cells | Can form many types of human cells e.g. blood cells | Tissue is matched to avoid rejection, risk of infection. Only a few types of cells can be formed. |
Meristems (plants) | Can differentiate into any plant cell type throughout the life of the pant. | Used to produce clones quickly and economically, e.g. rare species, crop plants with pest /disease resisitance |
Treatment with stem cells may be able to help conditions such as diabetes and paralysis. Some people object to the use of stem cells on ethical or religious grounds
B02) CELL DIVISION