OCR A Level Biology

Revision Notes

6.4.1 Natural Clones in Plants

Natural Clones in Plants

  • Many plants can reproduce asexually using meristem cells, in a process called vegetative reproduction
  • Vegetative organs of plants include:
    • Root and shoot tips
    • Axillary buds (where leaves and the stem meet)
    • Vascular cambium (between xylem and phloem)
  • Naturally, over time a young, miniature plant (a plantlet) forms at these locations and remains attached to its parent plant
  • These plantlets are clones of their parent (as no other DNA has been introduced)
  • At maturity, the plantlet becomes detached from its parent and can live independently, when it is capable of photosynthesizing by itself
  • The new plants all have the same phenotype, so are uniform, making growing and harvesting easier
    • Plants that are hard to grow from seeds can be propagated, eg. orchids for the horticulture industry
  • Some plants have horizontal stems or runners that form over the soil surface, pointing sufficiently far away so that a new plant at that location will not be overshadowed by its parent, or in competition for water or soil nutrients
    • Roots form under the nodes of runners, called adventitious roots
    • The runner dies when the plantlet is self-sustaining
    • Strawberries, peppermint and spider plants reproduce in this way

Runners and adventitious roots, downloadable AS Level & A Level Biology revision notes
An example of asexual reproduction in plants with runners that form adventitious roots

Propagation techniques using vegetative reproduction

  • Many methods of propagation do not require seeds as it is not sexual reproduction that is occurring, it is asexual reproduction
  • A well as runners, plants can propagate asexually using tubers, rhizomesbulbs, suckers, and offsets
  • All modes of vegetative propagation contain modified stems that can generate meristematic tissue
  • Potato tubers are swollen modified roots that form eyes on their surface
    • Eyes can sprout new growth (called ‘chitting’)
    • The starch stored in the tuber fuels the early growth of the new plant
  • Ginger forms rhizomes, a modified stem that grows horizontally underground
    • New growth stems from nodes in the rhizome, forming new stems and adventitious roots
    • The section used in cookery is the rhizome
  • Onions and garlic form bulbs that can grow adventitious roots underground and leafy shoots above ground
  • Suckers are growths that appear from the root systems of many trees and shrubs, which can provide meristematic tissue for vegetative propagation
    • Examples are poplars, cherries and plums
  • Offsets are small, virtually complete daughter plants that have been asexually produced on the mother plant
    • Examples are tulips and lilies
  • Gardeners and horticulturalists can use these techniques to propagate desirable species asexually, effectively and at less cost than utilising sexual reproduction techniques
    • This is done by taking cuttings and dividing up plants into different clumps or sections
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