Page 79 - Biology - XII

2. Cuscuta on Host
(i) Cuscuta commonly called dodder or amerbel and lives
as stem ectoparasite on other plants. Cuscuta Branch of host plant
(ii) Cuscuta has no fully expanded form of leaves (scale like
leaves are present) and has no chlorophyll.
(iii) Stem of Cuscuta is thin and slender shaped and it winds
around the stem of host plant. Stem of Cuscuta fi xes
itself to the stem of host plant with special structures
called haustoria.
(iv) Haustoria forms direct connection to the vascular
bundles of the host and withdraws water, carbohydrates, Fig. 14.2: Cuscuta on host plant
and other solutes.
(v) Roots of Cuscuta are temporary and die as soon as it makes connection with the host plant.
(vi) Cuscuta can weaken or kill plant and reduce crop yield.

3. Lichens
(i) Lichens are composite organisms representing a symbiotic association (mutualism) between
fungus and algae.
(ii) The algal component is known as phycobiont and fungal component is known as mycobiont.
(iii) Algae prepare food for fungi and fungi provide shelter and absorb mineral, nutrients, and water
for its partner.
(iv) They grow on lands, rocks, true trunks, and walls of houses like dry vegetation.

(a) (b)
Fig. 14.3: Diff erent types of Lichens

VIVA VOCE

Q1. Mention the role of Haustoria.
Ans. It fi xes the plant on the host and also helps to absorb nutrients from the host.

Q2. What is the colour of Cuscuta living on the host plant?
Ans. It is golden yellow coloured.

Q3. How does the nitrogen fi xation help the leguminous plant?
Ans. It helps in growth and development.

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