NEET Practice Questions (MCQs) with Answers & Solutions

In Ulothrix sexual reproduction is of isogamous type. Two isogametes of + and − strain come together and fuse, as a result a quadriflagellate zygospore is formed which floats on water. After sometime it rests on the bottom of the pond. At this time its four flagella disintegrate and a wall is formed surrounding it from all sides. After taking rest for a long period this zygote divides meiotically and gives rise to 16 zoospores. These zoospores come out of sac and give rise to the new plants of Ulothrix.

During fertilization ventral canal cell and the neck canal cell, along with tip of the neck disintegrate and the neck forms a canal like passage full of mucilage and some chemicals like malic acids. These chemicals attract antherozoids (chemotactic movement of antherozoids) and one of the male gametes fuses with the oospore forming a diploid oospore. Water is essential for this process.

The system of classification of seed plants presented by Bentham and Hooker, represented the most well developed classification of natural system. The classification was published in 3 volumes of 'Genera plantarum'. The system divided phanerogams or seed plants into 3 classes - dicotyledons, gymnospermae and monocotyledons. Dicotyledons were further subdivided into 3 subclasses - polypetalae, gamopetalae and monochlamydae based on the presence or absence of petals and their fusion. They were further divided into series, orders and families. No orders were recognised within monochlamydae and monocotyledons, the series being directly divided into families. But the system had a lot of demerits within it. He did not know the affinities of the families placed under 'Ordines anomate' and the families were tentatively grouped together. So, a few orders were not placed satisfactorily in the classification. Monochlamydae is an unnatural assemblage of taxa, which belongs elsewhere. The creation of this group has resulted in the separation of many closely related families.

Stele is a column containin vascular tissues which is surrounded by pericycle and separated from ground tissue by endodermis.

Siphonostele is medullated protostele or protostele with a central non-vascular pith. Leaf gaps are absent. Siphonostele is of two types:

In Ectophloic siphonostele, central pith is surrounded successively by xylem, phloem, pericycle and endodermis. In amphiphloic siphonostele there is a central pith and xylem is surrounded on either side by phloem, pericycle and endodermis. It is found in Osmunda and Equisetum.

Chlorenchyma or assimilatory parenchyma are parenchymatous cells that posses abundant chloroplasts in them. They are capable of photosynthesis. A spore capsule of moss can perform photosynthesis because of the presence of chlorenchyma cells in them.

Sexual reproduction in Spirogyra takes place by the process of conjugation. In Spirogyra, the process of conjugation may be of two types - scalariform conjugation and lateral conjugation. Scalariform conjugation occurs in heterothallic species. Lateral conjugation occurs between the adjacent cells of the same filament of homothallic species of Spirogyra. Lateral conjugation are of two types. They are indirect lateral conjugation (chain type) and direct lateral conjugation.

In mosses the sporophytes (i.e., the diploid body) are short-lived and dependent on the gametophyte. In the presence of water, sperms from the antheridia swim to the archegonia and fertilization occurs, leading to the production of a diploid sporophyte. The sperm of mosses is biflagllate, i.e., they have two flagella that aid in propulsion. Since the sperms must swim to the archegonium, fertilization cannot occur without water.

Endosperm is the food laden tissue which is meant for nourishing the embryo in seed plants. In gymnosperms, it represents the female gametophyte and thus is haploid (n). In angiosperms, the endosperm is a special tissue which is formed as a result of fusion of a male gamete with diploid secondary nucleus of the central cell (vegetative fertilization or triple fusion). The fusion product is primary endosperm cell having a triploid (3n) endosperm nucleus.

In pteridophytes, majority of plants are homosporous (producing similar kind of spores) e.g., Lycopodium. However, plants of genera like Selaginella and Salvinia are heterosporous (producing macro and micro spores). Pinus and Cycas, which are gymnosperms, are also heterosporous.