Chapter 3: Plant Kingdom

Ans. By analysing characteristics such as pigmentation, food storage products, and flagellation, we can classify algae into different groups from which the most common classification system divides algae into three main classes-

Ans. In liverwort, moss, and fern, during sexual reproduction, the sporophytic phase of the plant produces haploid spores after meiosis which happens in the spore mother cells. While in gymnosperm and angiosperm, meiosis takes place in the anthers and ovary during the formation of pollen grains and ovules.

Ans. Bryophytes, Pteridophytes, and Gymnosperms are the three groups of plants that bear archegonia. The life cycle of  gymnosperms involves:

• Reproduction: The gymnosperms are heterosporous and produce haploid microspores and megaspores. 

• The micro and megaspores are produced within sporangia that are borne on sporophylls. 

• The spores are arranged spirally along an axis to form lax or compact strobili or cones.  

• Male Gamete: The microsporangia or male strobili are strobili bearing microsporophylls and microsporangia. 

• The microspores develop into a male gametophytic generation which is highly reduced and is confined to a limited number of cells. 

• This reduced gametophyte is called a pollen grain which develops within the microsporangia. 

• Female Gamete: The microsporangia or female strobili are the cones bearing megasporophylls with ovules or megasporangia. 

• The male or female cones or strobili can be borne on the same tree as in Pinus or, needle-like on the different trees as in Cycas. From one of the cells of the nucellus, the megaspore mother cell is differentiated. 

• The nucellus is protected by envelopes and the composite structure that is called an ovule. The ovules are borne on megasporophylls which may get clustered to form the female cones. 

• To form four megaspores the megaspore mother cell divides meiotically. Within the megasporangium or nucellus, one of the megaspores is enclosed and develops into a multicellular female gametophyte that bears two or more archegonia or female sex organs. Within the megasporangium, the multicellular female gametophyte is also retained.

• Fertilisation: The pollen grain is released from the microsporangium, and is carried through air currents, and comes in contact with the opening of the ovules developed on megasporophylls. 

• In the ovules, the pollen tube carrying the male gametes grows towards archegonia, and near the mouth of the archegonia, they discharge their contents.

• The zygote develops into an embryo and the ovules into seeds after completing fertilisation.

Ans. The related ploidy is as follows:

Ans. The note is as follows: 

• Economic Importance of Algae: In a variety of ways the algae is useful to mankind. They perform half of the total carbon dioxide fixation on earth by photosynthesis, acting as the primary producers in aquatic habitats.

• Chlorella and Spirulina are rich in proteins. They are used as food supplements as many species of marine algae such as Porphyra, Sargassum, and Laminaria are edible. 

• In the preparation of jellies and ice cream agar is used. It is obtained from Gelidium and Gracilaria. 

• In chocolates, paints, and toothpaste the carrageenan is used as an emulsifier. It is obtained from the red algae. Many red algae are used in treating worm infections eg. Corallina.

• Economic Importance of Gymnosperms:

• Gymnospermous plants are widely used as ornamentals.

• Many conifers such as pine, cedar, etc., are sources of softwood used in construction and packing.

• It has medicinal uses also as an anticancer drug Taxol is obtained from Taxus.

• For the treatment of asthma and bronchitis, many species of Ephedra are used which produce ephedrine.

• The seeds of Pinus gerardiana are edible. For manufacturing sealing waxes and water-proof paints, the resins are used commercially.

• Turpentine, a type of resin, is obtained from various species of Pinus.

Ans. Both gymnosperms and angiosperms bear seeds, but they are classified separately because the seeds of gymnosperms are naked i.e., they lack any kind of covering around them, while angiosperms are covered mostly by fruits. The presence or lack of coverage leads to very different methods of dispersion and fertilization process.

Ans. A phenomenon in which two kinds of spores are produced by the same plant is known as heterospory. These spores also differ in size. The smaller ones are called microspores and the bigger ones are called megaspores. The male gametophytes are produced by microspores and female gametophytes are produced by megaspores. Thus, it is considered a crucial step in evolution as it is a precursor to the seed habit. In gymnosperms and angiosperms, this ultimately led to the development of seeds.

Ans. A brief explanation of the given terms is as follows:

(i) Protonema: It is the first stage in the life cycle of moss and is developing directly from the spore. This stage consists of creeping, green, branched, and often filamentous structures.

(ii) Antheridium: In bryophytes and pteridophytes these are the male sex organ which is surrounded by a jacket of sterile cells. The sperm mother cells are enclosed by antheridium, which gives rise to the male gametes.

(iii) Archegonium: Archegonium is the female sex organ present in bryophytes, pteridophytes, and  gymnosperms. Generally,  in bryophytes and pteridophytes, a swollen venter and a tubular neck contain the female gamete called the egg.

(iv) Diplontic:  For the life cycles of seed-bearing plants in gymnosperms and angiosperms the term diplontic is used The diploid sporophyte is dominant, photosynthetic, and independent in seed-bearing plants. A single-celled (or a few celled) structures represent the gametophyte.

(v) Sporophyll: The sporophytic plant body bears sporangia in pteridophytes. These sporangia are subtended by sporophylls which are leaf-like appendages. Microsporophylls and megasporophylls are found in gymnosperms, which bear microspores and megaspores respectively.

(vi) Isogamy: A type of sexual reproduction which involves the fusion of morphologically similar gametes is known as isogamy. This indicates that the gametes are of the same size, but perform different functions.  In Spirogyra this type of reproduction is commonly observed.

Ans. The differences are given below:

(i) red algae and brown algae

(ii) liverworts and moss

(iii) homosporous and heterosporous pteridophyte 

(iv) syngamy and triple fusion 

Ans. The correct match of column I is represented in column II.