B2.3 Stem Cells

A free GCSE Combined Science: Trilogy lesson for AQA (8464) from OBA School: what stem cells are, where they come from in animals and plants, and how they can be used. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• Describe what a stem cell is
• Describe the differences between embryonic stem cells, adult stem cells and plant meristem cells
• Describe how stem cells could be used to treat conditions such as diabetes and paralysis
• Explain how meristem tissue is used to clone plants quickly and cheaply

Key words

• Stem cell: An undifferentiated cell that can divide to make many more cells of the same type, and that can differentiate into certain other types of cell.
• Undifferentiated: Not yet specialised for a particular job.
• Embryonic stem cell: A stem cell from an early embryo. It can differentiate into most types of human cell.
• Adult stem cell: A stem cell found in adult tissues such as bone marrow. It can form only a few types of cell.
• Clone: An organism or cell that is genetically identical to its parent.

What makes a cell a stem cell?

A stem cell can do two things: it can divide by mitosis to make more stem cells, and it can differentiate into specialised cells. Most specialised cells have lost both abilities.

Sources of stem cells

• Embryonic stem cells; Where from early human embryos, a few days old (often spare embryos from fertility treatment); What it can become most types of human cell
• Adult stem cells; Where from bone marrow and some other tissues; What it can become a limited range, e.g. bone marrow cells form red and white blood cells and platelets
• Plant stem cells; Where from meristems at root and shoot tips; What it can become any type of plant cell, throughout the life of the plant

Key fact: Embryonic stem cells are the most flexible because, in an early embryo, no cells have differentiated yet.

Using stem cells in medicine

Scientists can grow stem cells in the lab and give them chemical signals that make them differentiate into a chosen cell type. Stem cells may be able to help conditions where cells are damaged or missing.

• Leukaemia (a blood cancer); How stem cells could help already used: bone marrow transplants give the patient healthy adult stem cells that make new blood cells
• Type 1 diabetes; How stem cells could help make new insulin-producing cells for the pancreas
• Paralysis (spinal cord damage); How stem cells could help make new nerve cells to repair the damaged nerves
• Damaged heart muscle; How stem cells could help replace cells killed in a heart attack

Exam tip: Most stem cell treatments are still being researched. Only a few, such as bone marrow transplants, are used routinely.

Stem cells in plants: cloning

Meristem cells can be taken from a plant and grown on a sterile jelly containing nutrients and plant hormones (tissue culture). Each tiny piece grows into a whole new plant: a clone of the parent.

• Produces large numbers of identical plants quickly and cheaply.
• Rare species can be cloned to protect them from extinction.
• Crop plants with useful features, such as disease resistance, can be cloned to give farmers lots of identical plants.

Worked example: counting clones

A grower cuts 4 meristem pieces from a rare fern. Each piece produces 30 plantlets in 6 weeks.
After 6 weeks: 4 × 30 = 120 plantlets.
If each plantlet is then used to make 30 more: 120 × 30 = 3600 plants after 12 weeks.

Answer: 3600 genetically identical ferns

Common mistakes

• Saying adult stem cells can become “any cell”. They form only a limited range.
• Saying stem cells are “specialised”. They are undifferentiated.
• Forgetting that plant meristem cells can differentiate into any plant cell for the whole of the plant’s life.
• Saying clones are “similar” to the parent. They are genetically identical.

Revision questions

Try these, then check your answers below each one.

Question 1. What is a stem cell? (Choose from: A cell found only in plant stems, An undifferentiated cell that can divide and differentiate into other types of cell, A specialised cell that carries water, A cell with no nucleus.)

Answer: An undifferentiated cell that can divide and differentiate into other types of cell

Working: A stem cell is undifferentiated. It can divide to make more stem cells and differentiate into other cell types.

Question 2. True or false? Adult stem cells can differentiate into any type of cell in the body.

Answer: False

Working: False. Adult stem cells, such as those in bone marrow, form only a limited range of cell types.

Question 3. The diagram shows two stem cells, P and Q, and some of the cells each can form. Which statement is correct? (Choose from: P is from an embryo, because it forms blood cells, Q is from an embryo, because it forms many different types of cell, P and Q are both from bone marrow, Q is a plant meristem cell.)

Answer: Q is from an embryo, because it forms many different types of cell

Working: Q forms nerve, muscle and liver cells, a wide range, so it is embryonic. P forms only blood cells, so it is an adult stem cell from bone marrow.

Related lessons

• Previous lesson: B2.2 Growth and Differentiation
• Next lesson: B2.4 Stem Cell Dilemmas
• In this chapter: B2.1 Cell Division

Continue in the full course

This lesson is section B2.3 (AGCSC0203) of our free GCSE Combined Science course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Combined Science course.