The bone marrow contains multipotent stem cells that are responsible for the constant replacement of blood cells. Two major cell types derived from these stem cells are erythrocytes (red blood cells) and neutrophils (a type of white blood cell).
During the differentiation of an erythrocyte, the cell undergoes dramatic changes to maximize its oxygen-carrying capacity. This includes the synthesis of large amounts of haemoglobin, the loss of the nucleus and other organelles, and a shape change into a biconcave disc to increase surface area.
Neutrophils differentiate by developing a lobed nucleus and a high density of lysosomes. These adaptations allow the cell to be flexible enough to squeeze through capillary walls and effectively digest pathogens through phagocytosis.
In plants, stem cells are located in specialized growth regions called meristems. The most common study areas are the root and shoot tips, where rapid cell division occurs to facilitate primary growth.
The vascular cambium is a specific type of meristematic tissue located between the xylem and phloem. Stem cells in the cambium divide and differentiate to produce new vascular tissue, allowing the plant to grow in girth (secondary growth).
When cambium cells differentiate into xylem, they undergo lignification, lose their living contents, and break down their end walls to form hollow tubes. Conversely, differentiation into phloem involves the formation of sieve plates and the maintenance of living cytoplasm supported by companion cells.
Understanding the differences between potency levels is critical for distinguishing between developmental stages and medical potential.
| Feature | Totipotent | Pluripotent | Multipotent |
|---|---|---|---|
| Source | Zygote / Early Embryo | Blastocyst (Inner Mass) | Adult Tissues (e.g., Bone Marrow) |
| Differentiation Range | All body cells + Placenta | All body cells only | Limited range of related cells |
| Medical Use | High (but ethical issues) | High (but ethical issues) | Moderate (lower ethical concern) |
Another key distinction is between animal and plant stem cells. Animal stem cells often lose potency permanently as they differentiate, whereas many plant cells retain a higher degree of flexibility, though the primary source remains the meristem.
Potency Definitions: Always be precise with the definitions of totipotent, pluripotent, and multipotent. A common mistake is confusing pluripotent with totipotent; remember that pluripotent cells cannot form the placenta.
Cell Adaptations: When asked about differentiation, link the structural change directly to the function. For example, 'Erythrocytes lose their nucleus to provide more space for haemoglobin.'
Plant Tissues: Ensure you can identify the cambium as the source of both xylem and phloem. Note that xylem cells are dead at maturity while phloem cells remain living.
Indefinite Division: Remember that the defining feature of a stem cell is its ability to divide an unlimited number of times. Most specialized cells have a finite number of divisions before they stop.
