A Level Biology OCR Notes: Stem Cells Overview

The Basics of Stem Cells

Think of stem cells as cellular blank slates that haven't decided what they want to be when they grow up. These cells can divide repeatedly through mitosis, making them perfect for growth, development, and fixing damaged tissues. Once they specialise into specific cell types, they enter the G0 phase and lose their ability to divide.

The power of stem cells lies in their potency - basically how many different cell types they can become. Totipotent cells (like fertilised eggs) are the ultimate overachievers, capable of creating an entire organism. Pluripotent cells from early embryos can form all tissue types but can't create a whole organism. Multipotent cells are more limited, forming only certain types of cells within specific tissues.

Your body constantly replaces worn-out cells using stem cells. Red blood cells only last about 120 days because they've ditched their nucleus and organelles to carry more oxygen. Neutrophils, your infection-fighting white blood cells, barely survive 6 hours in the battlefield of your immune system.

Quick Fact: All your blood cells come from stem cells in your bone marrow - it's like a cellular factory running 24/7!

Sources and Applications of Stem Cells

Embryonic stem cells are found in early-stage embryos and are totipotent powerhouses. Tissue stem cells hang out in specific areas like bone marrow and are multipotent. Plants have their own version in meristematic tissue at root and shoot tips, plus the vascular cambium that helps them grow throughout their lives.

Medical applications are genuinely exciting. Stem cells could revolutionise treatment for heart disease, Type 1 diabetes, Parkinson's, Alzheimer's, and spinal injuries by replacing damaged cells. They're already being used to grow new skin for burn victims and in drug testing to avoid animal experiments.

However, ethical controversies surround embryonic stem cell research. Religious and moral objections centre on whether removing stem cells constitutes destroying human life, since some believe life begins at conception. Questions about embryo rights and ownership of genetic material remain hotly debated.

The controversy has slowed potentially life-saving research, though alternatives like umbilical cord stem cells sidestep some ethical issues. Adult stem cells avoid controversy entirely but don't divide as effectively and can develop mutations over time.

Think About It: Plant stem cells don't raise the same ethical concerns as animal cells - could they hold answers for future medical breakthroughs?