Find the CBSE Class 11 Biology NCERT Solution for the Chapter- 3, Plant Kingdom. It has been framed keeping the Students' perspective in mind. This will help the Students with easy and simple understanding of the concept and technique employed in solving as per the CBSE Marking Scheme.
Few Sample Question from this Chapter are given below:
Q. What is the basis of classification of algae?
Ans. Algae are classified on the basis of type of the pigments present in them. They are divided into three main classes – Chlorophyceae, Phaeophyceae, and Rhodophyceae.
- Chlorophyceae: They are usually green in colour due to the presence of pigments chlorophyll a and b. Chlorophyceae are also called ‘green algae’. Some commonly found green algae are: Chlamydomonas, Volvox, Spirogyra, etc.
- Phaeophyceae: Chlorophyll a and c and fucoxanthin are present in them. Fucoxanthin imparts brown colour to Phaeophyceae. Phaeophyceae are also called ‘brown algae’. Some common examples of brown algae are Ectocarpus, Dictyota, Laminaria, Sargassum and Fucus.
- Rhodophyceae: Chlorophyll a and d and phycoerythrin are present. Phycoerythrin imparts red colour to Rhodophyceae. Rhodophyceae are also called ‘red algae’. Some common examples of red algae are Polysiphonia, Porphyra, Gracilaria and Gelidium.
Q. When and where does reduction division take place in the life cycle of a liverwort, a moss, a fern, a gymnosperm and an angiosperm?
Ans. Reduction division in the life cycle of a liverwort, moss, fern and a gymnosperm take place during the production of spores from the spore mother cell. In case of angiosperm, the reduction division takes place during the pollen grain formation from anthers and during production of embryo sac from ovule.
Q. Name three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them.
Ans. Three groups of plants that bear archegonia are bryophytes, pteridophytes and gymnosperms.
Life cycle of gymnosperms:
- Reproduction: The gymnosperms are heterosporous; they produce haploid microspores and megaspores. The two kinds of spores are produced within sporangia that are borne on sporophylls which are arranged spirally along an axis to form lax or compact strobili or cones.
- Male gamete: The strobili bearing microsporophylls and microsporangia are called microsporangiate or male strobili. The microspores develop into a male gametophytic generation which is highly reduced and is confined to only a limited number of cells. This reduced gametophyte is called a pollen grain. The development of pollen grains takes place within the microsporangia.
- Female gamete: The cones bearing megasporophylls with ovules or megasporangia are called macrosporangiate or female strobili. The male or female cones or strobili may be borne on the same tree (Pinus) or on different trees (Cycas). The megaspore mother cell is differentiated from one of the cells of the nucellus. The nucellus is protected by envelopes and the composite structure is called an ovule. The ovules are borne on megasporophylls which may be clustered to form the female cones. The megaspore mother cell divides meiotically to form four megaspores. One of the megaspores enclosed within the megasporangium (nucellus) develops into a multicellular female gametophyte that bears two or more archegonia or female sex organs. The multicellular female gametophyte is also retained within megasporangium.
- Fertilization: The pollen grain is released from the microsporangium. They are carried in air currents and come in contact with the opening of the ovules borne on megasporophylls. The pollen tube carrying the male gametes grows towards archegonia in the ovules and discharge their contents near the mouth of the archegonia. Following fertilisation, zygote develops into an embryo and the ovules into seeds.
Q. Both gymnosperms and angiosperms bear seeds, then why are they classified separately?
Ans. Both gymnosperms and angiosperms bear seeds, but they are yet classified separately because in case of gymnosperms the seeds are naked, i.e., the seeds are not produced inside the fruit whereas in case of angiosperms the sedds are enclosed inside the fruit.
Q. What is heterospory? Briefly comment on its significance. Give two examples.
Ans. Heterospory is the phenomenon of formation of two kinds of spores that differ in size. Smaller one is known as microspore and larger one as megaspore. The microspore germinates to form the male gametophyte that releases the male gametes. Similarly, megaspore germinates to form the female gametophyte that releases the male gametes (eggs). The male gametes reach the female gametophyte to fuse with the egg and form a zygote. This retention and germination of the megaspore within the megasporangium ensures proper development of the zygote which finally becomes a seed.