Define differentiation
Process where cells become differentiated, this involves cells selectively expressing genes of its genome.
Define stem cells
Undifferentiated cells capable of differentiating into any variety of specialised cell type within an organism for the growth & repair of tissue
What happens to stem cells once they differentiate (in terms of the cell cycle)?
They enter G0. They no longer divide
Why must stem cell activity be controlled?
- If they don’t divide fast enough, the tissues may age (called ageing), as the cells are not replaced efficiently
- If the cells divide too fast - this is uncontrolled division, causing a build up of cells (a tumour), which could lead to cancer.
Define totipotent.
Define pluripotent.
Define multipotent.
Totipotent: Can differentiate into any type of cell and form a whole organism
Pluripotent: Can differentiate into any cell type - but not a whole organism
Multipotent: Can only differentiate into a range of cell types of a certain tissue
Explain blood cell replacement of erythrocytes.
Erythrocytes have a role in transporting oxygen around the body
- Lack of nucleus and organelles maximises their function
- Have a 120 day lifespan - must be constantly replaced
- Body produces 3bn erythrocytes per kg of body mass per day
Explain blood cell replacement of neutrophils.
Neutrophils have a role in the immune system - most common phagocyte
- Lifespan of 6 hours
- Stem cells in bone marrow produce 1.6bn neutrophils per kg of body mass per day (more during infection)
Explain how embryonic stem cells are a source of stem cells.
Embryonic Stem Cells…
- Totipotent, present during early embryo development
- After 7 days, blastocyst (mass of cells) form pluripotent cells and remain in this state in fetus until birth
What are the different sources of stem cells?
- Embryonic stem cells, present in young embryo
- Blood from umbilical cord (has multipotent adult stem cells)
- Adult stem cells in developed tissue such as bone marrow
- no invasive surgery is needed to get the stem cells
- can be stored, cultured tissues of these stem cells will not be rejected by body
- Tissue cells can be induced to become stem cells
- known as iPS (induced pluripotent cells)
How do stem cells repair damaged tissues and treat neurological conditions?
- Bone marrow stem cells used to treat blood diseases - e.g. leukaemia
- Stem cells repair spinal cord of rats
- Stem cells treated type 1 diabetes of a mice
- Retinal stem cells produce new light-sensitive cells
- Treat arthritis, stroke, burns, blindness, deafness, heart disease
Neurological Disease
- Stem cells become nerve tissue to treate Alzheimer’s and Parkinson’s
How are stem cells used in developmental biology?
Develpomental biology: Study of how organisms develop, grow and mature
Stem cells are used to …
- Study how differentiation occurs - how cells specialise
- Study what occurs when cell specialisation goes wrong
- Trying to see if they can re-enable differentiation in adult cells to repair tissue, or re-grow organs/limbs
How are xylem and phloem vessels produced?
By mitosis in meristematic tissue
Xylem:
- Lignin deposited in cell wall to strengthen and waterproof
- Cells die and contents removed as ed walls break
- Form continuous hollow column
- In some areas, lignification is incomplete, bordered pits form
Phloem:
- Sieve tube elements lose nuclei and organelles, end walls develop sieve pores forming sieve plates between elements
- Companion cells retain organelles and nuclei, they carry out metabolism to obtain and use ATP to actively load sugar
