Stem cells (AQA GCSE Biology): Revision Notes
Stem cells
What are stem cells?
Stem cells are special cells that haven't developed into a specific type yet. We call them undifferentiated. This means they can grow and change into many different types of specialised cells through a process called differentiation.
Think of stem cells like blank templates that can become any type of cell the body needs - they're like the body's repair kit, waiting to be programmed for specific functions.
Types of stem cells in animals
There are two main types of stem cells found in animals, each with different capabilities and locations.
Embryonic stem cells
These stem cells are found in very early stages of development and have the greatest potential for forming different cell types.
- Found in very early stages of development
- A zygote forms when an egg and sperm join together
- The zygote divides to create a ball of cells called an embryo
- These embryonic cells can turn into any type of cell in the body
- They have the most potential to become different cell types
Adult stem cells
Unlike embryonic stem cells, adult stem cells are more specialised but still maintain important regenerative abilities.
- Found in grown-up animals, including humans
- Bone marrow contains many adult stem cells
- These can form different types of blood cells
- They're more limited than embryonic stem cells
Adult stem cells are more limited in what they can become compared to embryonic stem cells, but they don't raise the same ethical concerns since no embryo is destroyed.
Stem cells in plants
Plants have stem cells too! They're found in areas called meristems. These specialised regions are responsible for continuous growth throughout a plant's life.
Where meristems are located:
- Tips of roots - help roots grow longer
- Tips of shoots - help stems and leaves grow
What they create:
- Root hair cells for absorbing water
- Xylem and phloem for transport
- Mesophyll cells in leaves for photosynthesis
Unlike animal stem cells, plant stem cells in meristems remain active throughout the plant's entire life, which is why plants can continue growing and regenerating lost parts.
Using stem cells for treatment
Stem cells offer exciting possibilities for treating diseases by replacing damaged or non-functioning cells in the human body.
Stem cells could help treat serious illnesses like:
- Diabetes - by replacing damaged pancreas cells
- Paralysis - by replacing damaged nerve cells
The idea is to inject healthy stem cells that can replace the damaged or missing cells.
Treatment Example: Diabetes
Step 1: Extract stem cells from the patient or donor Step 2: Guide the stem cells to differentiate into insulin-producing pancreatic cells Step 3: Inject these specialised cells into the patient's pancreas Step 4: The new cells begin producing insulin, potentially curing diabetes
Advantages and disadvantages
Understanding the benefits and limitations of different stem cell types is crucial for making informed decisions about their use.
Embryonic stem cells
Advantages:
- Easy to collect from embryos
- Can become any type of cell
Disadvantages:
- Embryo is destroyed when cells are removed
- Some people think embryos have a right to life
- May continue dividing and cause cancer
- Risk of viral infections
Adult stem cells
Advantages:
- No embryo is harmed
- Can be taken from the patient themselves
- Lower risk of rejection by the body
Disadvantages:
- Can only make a few types of cells
- Harder to collect enough cells
The choice between embryonic and adult stem cells often involves balancing scientific potential with ethical considerations and practical limitations.
Cloning with stem cells
Clones are living things that are genetically identical to each other. Stem cells play a crucial role in both natural and artificial cloning processes.
Plant cloning
Scientists have successfully used plant stem cells for various beneficial purposes:
- Scientists can use stem cells from plant meristems
- This helps create many identical plants quickly
- Useful for saving rare plant species from extinction
- Farmers can grow crops with good features (like disease resistance)
Therapeutic cloning
This is a way to create an embryo using a patient's own cells, avoiding immune rejection issues.
Therapeutic Cloning Process:
Step 1: Take the nucleus from one of the patient's cells Step 2: Put it into an empty egg cell Step 3: Stimulate the egg to start dividing Step 4: This creates an embryo with the patient's DNA Step 5: Stem cells from this embryo won't be rejected by the patient's body
Key Points to Remember:
- Stem cells are undifferentiated - they haven't become specialised yet
- Animal stem cells are found in embryos and bone marrow
- Plant stem cells are found in meristems at root and shoot tips
- Stem cells can treat diseases by replacing damaged cells
- Different types have different advantages - embryonic cells are more flexible but raise ethical concerns
- Cloning uses stem cells to create genetically identical organisms