NCERT Class 11-Biology: Exemplar Chapter –3 Plant Kingdom Part 3

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Question 4:

How far does Selaginella one of the few living members of lycopodiales (pteridophytes) fall short of seed habit.

Answer:

Selaginella produce two kinds of spores, macro (large) and micro (small) spores. The megaspores and microspores germinate and give rise to female and male gametophytes, respectively. But Selaginella falls short of seed habit due to lack of integument around the Megasporangium.

Question 5:

Each plant or group of plants has some phylogenetic significance in relation to evolution: Cycas, one of the few living members of gymnosperms is called as the ‘relic of past’. Can you establish a phylogenetic relationship of Cycas with any other group of plants that justifies the above statement?

Answer:

Cycas is considered as a living fossil as it is the only living species of the family Cycadaceae. It is often known as the Relic of the past. It shares some common features with the Pteridophytes like: i. The seeds are shed while the embryo is still maturing.

ii. The megasporophyll appears like a leaf.

iii. In spite of the presence of the pollen tubes the male gametes are flagellated. Just as in the pteridophytes.

iv. Leaf base is persistent.

Question 6:

The heterosporous pteridophytes show certain characteristics, which are precursor to the seed habit in gymnosperms. Explain.

Answer:

In majority of the pteridophytes all the spores are of similar kinds, such plants are called homosporous. Genera like Selaginella, Salvinia, Marsilea and Azolla which produce two kinds of spores, macro (large) and micro (small) spores, are known as heterosporous. The megaspores and microspores germinate and give rise to female and male gametophytes, respectively. The female gametophytes in these plants are retained on the parent sporophytes for variable periods. The development of the zygotes into young embryos take place within the female gametophytes. This event is a precursor to the seed habit considered an important step in evolution.

Question 7:

Comment on the lifecycle and nature of a fern Prothallus.

Answer:

The life cycle of tern (Dryopteris) clearly shwos the alternation of generation. The gametophytic stage (n) alternates with the sporophytic stage (2n) figure given shows its complete life cycle

Che-3-Question 7- Image of Topographical Representation of L …

Topographical Representation of Life Cycle of Fern

Prothallus the prothalus of the fern is multicelluar, free living. Thallodi, haploid and autotrophic structure. It develops form the spores produced by sporophyll after reduction division.These spore germinate with a germtube with an apical cell and forms a filament of 3-6 cells and one or two rhizoids at the base which later develops into gametophytic plant.

Che-3-Question 7- 1-Image of different stages in the germina …

Germination of a Spore and Development of Prothallus

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