Special modes of nutrition in plants

  • Plants are autotrophic as they have chlorophyll and can carry out photosynthesis.
  • The most important aspect of photosynthesis is the conversion of light energy into chemical energy.
  • Plants use carbon dioxide and water in the presence of chlorophyll and sunlight to produce glucose and oxygen.
  • Some plants have special devices to obtain their food material and fulfill their nutritional requirement which are categorized as follows:
  1. Insectivorous plants:
  • These are autotrophic plants which grow in nitrogen deficient soil, i.e. bog swamp etc.
  • They depend on small insects and hence kill them for their nitrogen requirement.
  • The leaves of such plants are modified in various ways for capturing insects such as:
    • Nepenthes (Pitcher plant):
      • It is a climber with a modified pitcher.
      • The pitcher contains number of nectiferous glands which secrete acidic fluid.
      • The insects slip down the pitcher in search of nectar where they are finally digested by the digesting enzymes.
    • Utricularia (Bladdderwort):
      • It is an aquatic plant.
      • The leaflets are modified into small bladders which are provided with a trap door entrance.
      • The trap door acts as a sort of valve opening only inwards when pushed from outside.
      • Very small aquatic animals enter by pushing the trap door.
      • The inner surface of the bladder is dotted all over with numerous digestive glands which produce digestive enzymes to digest the dead animals.
    • Drosera (Sundew):
      • It is a small herb whose upper surface of leaf is covered with numerous tentacles which are sensitive to touch.
      • Each gland secretes a sticky fluid which glitters in the sun like dew-drops and hence named ‘sundew’.
      • As soon as the insect is trapped, tentacles bend inward and entangle the insect.
      • The acidic secretion finally digests the protein and converts into soluble form.
    • Dionaea (Venus fly trap):
      • This plant consists of leaves with broad teethed lamina having sensory spicules inside them.
      • The upper surface of the lamina is thickly covered with reddish digestive glands.
      • When the insect is caught, the leaves close suddenly and the glands begin to secrete digestive enzymes.
                                               Insectivorous plants
  1. Root parasites:

Total root parasites: They live parasitically on the roots of other plants.

  1. Rafflesia: It is a parasite on the roots of figs.
  2. Orobanche: it is a leafless parasite growing on the roots of mustard, turnip, brinjal (eggplant) etc.
  3. Balanophora: It is parasitic on the roots of trees.
  4. Striga: It is parasitic in sugarcane.

Partial root parasites: They grow as partial parasites on the roots of other plants.

Santalum (Sandal wood):

  • This plant develops haustoria that enter the roots of the neighboring trees of Dalbergia sisoo (sisau).
  • It only absorbs water and minerals from the host.

Thesium: It grows as a partial root parasite on grasses.

3. Stem parasites:

Total stem parasites:

  • Cuscuta (Dodder plant) grows as total stem parasite on Citrus, Duranta, Zizyphus
  • It has haustorial roots, which derive required materials from the stem of host.

Partial stem parasites:

  • They are chlorophyll containing autotrophic plants.
  • They depend on the host plant to take water and minerals.
  • Loranthus (parasite on mango, Acacia and Dalbergia trees) and Viscum (parasitic on walnut and oak plant)

Special modes of nutrition in plants