- Created by: msahay
- Created on: 31-07-17 12:43
B2.1 Cell division
Chromosomes carry genes. Gene= small packet of DNA. Genes control characteristics.
46 chromosomes in human body cell in 23 pairs. One inherited from father, one from mother. Sex cells (gametes) have only 23 chromosomes.
Stage 1: Cells grow bigger, mass increased, DNA replicated to form two copies of each chromosome and sub-cellular structures e.g. mitochondria increased.
Stage 2: Mitosis occurs. Chromosomes pulled to each end of cell and nucleus divides.
Stage 3: Cytoplasm and cell membranes divide to form two identical daughter cells.
Important in growth, repair and development of multi-cellular organisms.
B2.2 Growth and differentiation
Differentiation in animal cells
- Cell specialisation happens early in life
- Nerve cells, muscle cells, skin cells
- Specialised cells have different sub-cellular structures to carry out specific functions
- Specialised cells able to divide by mitosis to make more of the same cell
- Adult stem cell replace dead or damaged cells
- Mature animal = no growth, only repair and replacement of cells
Differentiation in plant cells
- Plant cells able to differentiate all through life
- Undifferentiated cells formed in meristems - shoots and roots. Mitosis takes place, cells elongate, then divide.
B2.3 Stem cells
Embryonic stem cells - undifferentiated (stem) cells from an early embryo that can differentiate to form all specialised cells in the body.
Adult stem cells - undifferentiated (stem) cells that are found in adults that can differentiate and form a limited number of cells.
Embryonic stem cells (from human embryos) and adult stem cells (from adult bone marrow) can be cloned and differentiated into many different types of cell.
Treatment using stem cells = paralysis (nerve cells) and diabetes
Stem cells in plants
Plant meristems contain stem cells.
Clones can be made quickly and economically
Research, horticulture and agriculture.
B2.4 Stem cell dilemmas
Problems with stem cells
- Stem cells come from aborted and spare embryos. Violation of human rights.
- Religious believers cannot interfere with human reproduction.
- Slow, difficult, expensive
Problems with adult stem cells
- Risk of infection from viruses
- Cells may be rejected by patient's body.
Using embryonic stem cells from umbilical cord instead of aborted embryos = more ethical
Therapeutic cloning - embryo produced that is genetically identical to patient so can be used in treatment with no rejection from cells.
Stem cells can be used to make special insulin producing cell for diabetics.