GCSE · Biology · Edexcel · Spec 1BI0

Stem cells and meristems

A root tip, bone marrow and an eight-cell embryo all hide cells that haven't picked a job yet. Why can some become anything, but others only a few things?

Sort it out

Three kinds of stem cell, one big overlap

Each statement below is true for at least one kind of stem cell. Tick every set it belongs to, then check.

  • A Embryonic stem cells
  • B Adult stem cells
  • C Meristem cells
  1. Unspecialised
  2. Divide by mitosis
  3. Can differentiate into any type of cell in their own organism
  4. Found in animals
  5. Only make a limited number of related cells
  6. In bone marrow, making blood cells
  7. Make up all eight cells of an early embryo
  8. At the tips of roots and shoots, and in the stem
  9. Used to clone plants from cuttings

Be honest

What can a bone marrow stem cell become?

A stem cell sits in the bone marrow of an adult human.

Which idea is closest to what you think right now?
How sure are you?

Predict, then check

Think about what a stem cell is doing when it differentiates.

Imagine the stem cells in bone marrow only ever differentiated into blood cells and never divided. What would happen to the supply of stem cells?

Plant · Meristems

Where a plant keeps its meristem cells
soil level

Showing 2 layers: The plant, Meristem zones

Layers

Explore

tap a glowing region

The glowing zones mark where meristem cells are: at the tips of the shoot and the roots, and in the stem.

Switch the meristem layer on, then tap a region to see what it makes.

Cloning a plant from a cutting

Look for the one step the whole method depends on.

  1. Pick the parentChoose a parent plant that has the wanted characteristics (phenotypes). Whatever you want in the new plants, it has to be in the parent.
  2. Take a cuttingCut off a piece of the parent that contains meristem tissue. This is the step everything else depends on.
  3. Cells divide and differentiateThe meristem cells in the cutting divide and differentiate into other kinds of cell.
  4. The cutting rerootsMeristem cells at work let the cutting reroot, so it can live as a plant of its own.
  5. A clone growsThe new plant is a clone: genetically identical to the parent. Meristem tissue lets clones be grown quickly and economically, for crops or to protect endangered species.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

Cells that haven't picked a job yet, and what each kind can still become

What you need to know

  • Most cells in multicellular organisms are specialised: their structures are adapted for their jobs.
  • Differentiation turns unspecialised cells into specialised ones. Particular genes are switched on or off, so only the proteins the job needs are made.
  • A zygote divides by mitosis to form an embryo. At the eight-cell stage, every cell is an unspecialised embryonic stem cell.
  • Have a goYour friend says an eight-cell embryo is 'one boss cell and seven helpers'. How many of the eight are embryonic stem cells?

    All eight.

    At the eight-cell stage every cell is still unspecialised, so there are no helpers with special jobs yet.

  • Embryonic stem cells can become any type of cell in the animal's body. Once specialised and in tissues, they can't become other types.
  • As an animal grows up, some cells stay unspecialised. These are adult stem cells, and they become most but not all types of cell.
  • Adult stem cells also divide by mitosis to renew themselves. If they only differentiated, they would run out.
  • In humans, bone marrow stem cells make blood cells, and stem cells in the brain make different types of neuron.
  • Have a goA stem cell in an adult's brain differentiates. What does it most likely become: a red blood cell or a neuron?

    A neuron (one of the different types of neuron).

    Adult stem cells make a limited number of related cells. In the brain that means neurons, while blood cells come from bone marrow.

  • Plants have unspecialised meristem cells in the stem and the tips of roots and shoots. They divide by mitosis and can become any plant cell.
  • Meristem cells make roots and shoots grow, and they make leaves, flowers, xylem and phloem.
  • A cutting must contain meristem tissue to divide, differentiate and reroot. The new plant is a clone, genetically identical to its parent.
  • Have a goTwo cuttings come from the same parent plant. One contains meristem tissue and one doesn't. Which can divide, differentiate and reroot?

    The one with meristem tissue.

    Meristem cells are the unspecialised cells that can divide and differentiate, so a cutting without them can't reroot.

The big picture

Stem cells are unspecialised cells that can divide and differentiate. Embryonic stem cells and plant meristem cells can become any type of cell in their organism, while adult stem cells can become only a limited number of related cells. Meristem tissue in a cutting lets a plant be cloned.

Key points

1Specialised cells are adapted for a job. Unspecialised cells become specialised by differentiation, when particular genes are switched on or off.
2Embryonic stem cells and meristem cells can become any type of cell in their organism. Adult stem cells can become only a limited number of related cells.
3Adult stem cells divide by mitosis as well as differentiate, so they renew themselves and don't run out.
4Meristem cells are in the stem and at the tips of roots and shoots. They divide and differentiate to make growth, leaves, flowers, xylem and phloem.
5A cutting that contains meristem tissue can grow into a clone: a genetically identical plant.

Worked example

Problem

Three unspecialised cells are found. Cell X is in the tip of a pea plant's root. Cell Y is in an adult human's bone marrow. Cell Z is one of the eight cells of a human embryo. Name each kind of cell and say what it can differentiate into.

⚠ Watch out

Saying that all stem cells can become any type of cell. Only embryonic stem cells and meristem cells can. Adult stem cells can become most but not all types: a limited number of related cells.

🧠

Memory hook

Embryo and meristem: 'any cell, any job'. Adult: 'a limited family of cells'. Cut a stem with meristem in it and you get a clone.

✓

Check yourself

Without looking back: name the three kinds of stem cell in this lesson, say where each one is found, and say what each can become.

Flashcards

(13)
What is a specialised cell?
A cell with structures adapted for its job. Most cells in multicellular organisms are specialised.
What is differentiation?
The process by which unspecialised cells become specialised. Particular genes are switched on or off, so only the proteins needed for the job are made.
Which stem cells can differentiate into any type of cell in an animal's body?
Embryonic stem cells, the unspecialised cells that make up an early animal embryo.
What is an adult stem cell?
An unspecialised cell that remains as an animal develops into an adult. It can become most but not all types of cell, a limited number of related cells.
What is a meristem cell?
An unspecialised plant cell found in the stem and the tips of roots and shoots. It divides by mitosis and can differentiate into any type of plant cell.
What is a clone?
An organism that is genetically identical to another organism.
How many cells in an eight-cell embryo are embryonic stem cells?
All of them. At that stage every cell is unspecialised.
Why do adult stem cells divide by mitosis as well as differentiate?
To renew themselves. If they only differentiated, they would run out.
Give a human example of adult stem cells and what they make.
Bone marrow makes blood cells: red blood cells, platelets and different white blood cells. Stem cells in the brain make different types of neuron.
Once embryonic stem cells have specialised and formed tissues, what can they become?
They cannot become other types of cell.
Where in a plant are meristem cells found?
In the stem and at the tips of the roots and shoots.
What do meristem cells make?
Roots and shoots that grow longer and wider, leaves and flowers from shoots, and xylem and phloem from the stem and roots.
What must a cutting contain to be grown into a new plant?
Meristem tissue, so its cells can divide, differentiate and reroot.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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