(a) Write the characteristics of 'stem cells'.

(b) From where can one obtain 'stem cells' in humans ?

(c) State any two applications of stem cells in curing human diseases.

The correct answer is:

(a) They have the ability of self-renewal / to divide, and differentiate into any kind of cell/tissue/organ.
(b) Inner cell mass of blastocyst / umbilical cord / Bone marrow.
(c) Diabetes treatment via forming islets of Langerhans, Restoration of vision by injecting stem cells, to treat rheumatoid arthritis, reduces pancreatic cancer, to treat genetic disorder like cystic fibrosis, spinal cord injurie, heart disease, any other correct application.

Here is a detailed, step-by-step educational explanation of the characteristics, sources, and applications of stem cells in humans:

Step 1: Understanding the Characteristics of Stem Cells (Part a)
Stem cells are unique, unspecialized biological cells that possess two defining characteristics:
1. Self-Renewal: The ability to go through numerous cycles of cell division (mitosis) while maintaining the undifferentiated state. This ensures a continuous supply of stem cells in the body.
2. Potency/Differentiation: The capacity to differentiate or mature into specialized cell types (such as nerve cells, muscle cells, or blood cells) that form tissues and organs. Depending on their origin, they can be pluripotent (capable of forming almost any cell type) or multipotent (capable of forming a limited range of cell types).

Step 2: Sources of Stem Cells in Humans (Part b)
Stem cells can be harvested from various stages of human development and different tissues:
1. Inner Cell Mass of the Blastocyst: Embryonic stem cells (ESCs) are obtained from the inner cell mass of a blastocyst (an early-stage embryo, about 3 to 5 days old). These cells are pluripotent.
2. Umbilical Cord: At birth, stem cells can be isolated from the blood of the umbilical cord (cord blood). These cells are rich in hematopoietic stem cells.
3. Bone Marrow: Adult stem cells (specifically hematopoietic and mesenchymal stem cells) are commonly harvested from bone marrow to regenerate blood and immune cells.

Step 3: Medical Applications of Stem Cells (Part c)
Stem cells have revolutionary applications in regenerative medicine and disease treatment. Key examples include:
1. Diabetes Treatment: Generating insulin-producing beta cells in the islets of Langerhans from stem cells to restore glycemic control in diabetic patients.
2. Restoration of Vision: Injecting retinal pigment epithelium (RPE) stem cells to treat macular degeneration and restore lost vision.
3. Neurological and Spinal Injuries: Using stem cells to repair damaged nerve tissues in spinal cord injuries, restoring mobility and sensation.
4. Heart Disease: Regenerating damaged cardiac muscle tissue following a myocardial infarction (heart attack).
5. Genetic and Autoimmune Disorders: Treating disorders like rheumatoid arthritis and cystic fibrosis, as well as helping reduce pancreatic cancer progression.