Plant Kingdom Test - 26

In Vaucheria, the multiflagellate compound zoospores also known as synzoospores or coenozoospores are developed in these genus usually in aquatic forms. A single compound zoospore develops in a single zoosporangium. Any distal branch of the thallus may convert into a zoosporangium. Much of the food reserves, chloroplasts and nuclei accumulate in the distal end of the branch of the thallus. It is multi flagellate. From each peripheral nucleus, a pair of flagella is given out. The zoospore swims for about 15 to 20 minutes and then settles down to some substratum, withdraws its flagella and secretes a wall around it. Very soon, it germinates giving rise to 2 or 3 tubular outgrowths and a new branched thallus develops. Thus, the correct answer is option C.

Agar, alginic acid and carragheen obtained from Gracilaria and Chondrus respctively are chemically phycocolloids. The cell walls of many seaweeds contain phycocolloids also called as algal colloids, that can be extracted by hot water. The three major phycocolloids are alginates, agars, and carrageenans. Alginates are extracted primarily from brown seaweeds, and agar and carrageenan are extracted from red seaweeds. These phycocolloids are polymers of chemically modified sugar molecules.

Chlamydomonas is a genus of green algae consisting of unicellular flagellates, found in stagnant water and on damp soil, in freshwater, seawater, and even in snow as snow algae.

Macrocystis is the largest algal form. Macrocystis is a genus of kelp or large brown algae. This genus contains the largest of all the phaeophyceae or brown algae. Macrocystis has pneumatocysts at the base of its blades. Sporophytes are perennial, and individual stipes may persist for many years. It is common along the coast of the eastern Pacific Ocean.

Acetabularia is the largest unicellular organism. Acetabularia is a genus of green algae, specifically of the Polyphysaceae family. It is typically found in subtropical waters. Acetabularia is a single-celled organism, but gigantic in size and complex in form, making it an excellent model organism for studying cell biology. Thus, the correct answer is option E.

Red algae represent triphasic lifecycle. They display alternation of generations; in addition to gametophyte generation, many have two sporophyte generations, the carposporophyte-producing carpospores, which germinate into a tetrasporophyte this produces spore tetrads, which dissociate and germinate into gametophytes. The gametophyte is typically (but not always) identical to the tetrasporophyte. Carpospores may also germinate directly into thalloid gametophytes, or the carposporophytes may produce a tetraspore without going through a (free-living) tetrasporophyte phase. Tetrasporangia may be arranged in a row (zonate), in a cross (cruciate), or in a tetrad. In its diploid phase, a carpospore can germinate to form a filamentous "conchocelis stage", which can also self-replicate using monospores. The conchocelis stage eventually produces conchosporangia. The resulting conchospore germinates to form a tiny prothallus with rhizoids, which develops to a cm-scale leafy thallus. This too can reproduce via monospores, which are produced inside the thallus itself. They can also reproduce via spermatia, produced internally, which are released to meet a prospective carpogonium in its conceptacle. Hence, it undergoes a complex triphasic lifecycle.

The algae that forms motile colonies is Volvox. Volvox is the most developed in a series of genera, that form spherical colonies. 

Each mature Volvox colony is composed of numerous flagellate cells similar to Chlamydomonas, up to 50,000 in total, and embedded in the surface of a hollow sphere or coenobium containing an extracellular matrix made of a gelatinous glycoprotein. Except, during the formation of daughter colonies, vegetative cells comprise a single layer with the flagella facing outward. The cells swim in a coordinated fashion, with distinct anterior and posterior poles. Hence, form a motile colonies. Thus, the correct answer is option A.

Cephaleuros is a genus of parasitic thalloid algae and its common name is red rust. Dichotomous branches are formed in these algae. The alga is parasitic on some important economic plants of the tropics and subtropics such as tea, coffee, mango and guava causing damage limited to the area of algal growth on leaves or killing new shoots, or may be disfiguring fruit. Members of the genera may also grow with a fungus to form lichen, that does not damage the plants. Thus, the correct answer is option A.

Coenocytic cells are present in diverse and unrelated groups of algae, including Xanthophyceae, e.g., Vaucheria and red algae, Griffithsia and green algae. A coenocyte is a multinucleate cell, which can result from multiple nuclear divisions without their accompanying cytokinesis. Thus, the correct answer is option A.

Diatom cells are contains a unique silica cell wall, comprising two separate valves or shells. The biogenic silica that the cell wall is composed of is synthesised intracellularly by the polymerisation of silicic acid monomers. This material is then extruded to the cell exterior and added to the wall. Diatom cell walls are also called as frustules. The silica of the diatom cell wall is resistant to decay, although it will begin to dissolve once its organic coating has been stripped off. Once incorporated into silica-rich sediments, however, frustules may survive for hundreds to millions of years and can be used to monitor changes in freshwater or marine environments.