NCERT Class 11-Biology: Exemplar Chapter – 3 Plant Kingdom Part 5 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 3:

Lichen is usually cited as an example of ‘symbiosis’ in plants where an algal and a fungal species live together for their mutual benefit. Which of the following will happen if algal and fungal partners are separated from each other?

a. Both will survive and grow normally and independent from each other.

b. Both will die

c. Algal component will survive while the fungal component will die.

d. Fungal component will survive while algal partner will die.

Based on your answer how you justify this association as symbiosis.


Option ‘b’ is the correct option. i.e.. both will die.

Lichen is usually cited as an example of symbiosis in biology where in a fungal and an algal species live together for mutual benefit. The algal component synthesizes the food through photosynthesis which is utilized by the fungal species for its survival. The fungal component in return provides shelter and waste products that are consumed by algal species. Experiments though have shown that algal component can grow independently when separated from fungal species. But same is not true with the fungal component which dies when separated from algal component. This association is, therefore, a typical case of master-slave relationship where fungus (master) has trapped the algal components (slave) for its own survival while giving nothing in return to it. Some authors consider this association as controlled parasitism or helotism due to the fact that sometimes the fungus sends its haustoria into the algal cells to derive nourishment.

Question 4:

Explain why sexual reproduction in angiosperms is said to take place through double fertilization and triple fusion. Also draw a labelled diagram of embryo sac to explain the phenomena.


An angiospermic plants sexually reproduces by the fromation of male and female gametes. The male is a pollen which contain two male nuclei and female gamete is egg cell produced in ovule (female gametophyte)

The pollen grains germinarte on the stigma of a flower and the resulting pollen tube grow through the tissue of stigma and style and each near the egg apparatus. The two male gametes are discharge within the embryo sac. One of the male gamete fuses with the egg cell to from a diploid zygote

This fusion is known a fetilisiton or Syngamy. The second male gamete fuses with the diploid secondary nucleus and forms the triploid Primary Endosperm Nucleus (PEN) . This fusion is known as triple fusion.

Because of the involvement of two, this event in angiosperms is termed as double fertilization. The zygote then develops into embryo and PEN develops into endosperm which provides nourishment to the developing embryo

An Angiospermic Plants Sexually

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