Section 1 of 8What meristems are
Location
- Location Found at the growing tips of shoots and roots, and in the cambium of stems, where the plant increases in length and width.
Stem cells
- Stem cells Meristem cells are unspecialised stem cells that keep dividing by mitosis, so they stay genetically identical to each other.
Lifetime growth
- Lifetime growth Unlike most animals, plants can produce new cells and differentiate them throughout their lives, which is why trees keep growing.
Section 2 of 8From meristem to specialised cell
1Division
- Division Meristem cells divide by mitosis, producing identical daughter cells.
2Elongation
- Elongation The new cells absorb water and enlarge, making the shoot or root longer.
3Differentiation
- Differentiation Cells develop special structures for particular jobs, controlled by which genes are switched on.
4Mature tissue
- Mature tissue Examples include xylem, phloem, palisade cells and root hair cells.
Section 3 of 8Uses of meristem tissue
| Use | How it works | Benefit |
|---|---|---|
| Cloning rare plants | Cells from the tip are grown on agar with nutrients and hormones | Many identical copies, saving a species |
| Disease-free crops | Meristem tissue is usually free from viruses | Healthy plants for growers |
| Commercial production | Large numbers of plants with desirable features made quickly | Uniform crops and faster supply |
Section 4 of 8Tissue culture steps
1
Cut a small piece of meristem from the parent plant using sterile tools, working in clean conditions to prevent contamination.
2
Place it on sterile agar jelly containing nutrients and plant hormones.
3
Seal the container and keep it under controlled warmth and light so cells divide.
4
Move small plantlets to compost when roots and shoots appear, and grow them on in a greenhouse.
Section 5 of 8Advantages and limits of cloning plants
| Point | Explanation |
|---|---|
| Advantage: speed | Thousands of plants can be produced from one parent in a short time, in any season |
| Advantage: uniform quality | Every clone keeps the useful features of the parent, such as yield or flower colour |
| Disadvantage: no variation | All clones are genetically identical, so one disease can wipe out the whole crop |
| Disadvantage: cost | It needs sterile equipment, skilled workers and expensive growth media |
Section 6 of 8Comparison with animal stem cells
Plants
- Plants Meristem cells stay active, so many plant cells can differentiate throughout life.
- Whole new plants can be grown from a small piece.
Animals
- Animals Most animal cells differentiate early and then lose the ability to become other types.
- Stem cells are found in the embryo and in places such as bone marrow.
Section 7 of 8Key terms
| Term | Meaning |
|---|---|
| Meristem | Plant tissue in which cells can divide and differentiate. |
| Stem cell | An unspecialised cell that can become different cell types. |
| Differentiation | Development of a cell into a specialised type. |
| Clone | A genetically identical copy of an organism. |
| Mitosis | Cell division that produces two identical daughter cells. |
Section 8 of 8Exam technique
1
Saying meristems are found in all parts of the plant; they are at specific growth regions.
2
Describing clones from meristems as genetically different; they are identical.
3
Forgetting aseptic technique, so cultures become contaminated with microbes.