Biology Test 339

Retroviruses contain RNA as genetic material and this RNA is converted to DNA using enzyme reverse transcriptase.

• During mid- 1960s, three independent researches reported the purification and chemical characterization of three different kinds of inhibiters : inhibitor - B, abscission II and dormin.
• Later all the three were proven to be chemically identical. It was named abscisic acid (ABA).
• ABA plays an important role in seed development, maturation & dormancy.

Taxonomy play no role in protection of biodiversity

The dominant stage in the bryophyte life cycle is the haploid stage, in which a multicellular haploid gametophyte develops from a spore and produces haploid gametes. Both male and female gametes are produced by the mature gametophyte, that joins to form a diploid zygote. The dominant phase of bryophyte-gametophyte bears multi-cellular jacketed sex organs. The male and female sex organs are multicellular called antheridium and archegonium, respectively.

Bryophytes are called amphibian plants. There are two classes, Hepaticopsida or Liverworts, and Bryopsida or Mosses.

The predominant phase of the plant body is gametophytic and haploid. Gametic fusion causes the formation of a diploid zygote. The zygote develops into a partially-parasitic phase called the sporophyte which is partially dependent on the gametophyte. There are three main parts of the sporophyte. The capsule is the sac that bears the spores, which undergo meiosis to form protonema and eventually the gametophyte again. The capsule is held by a long seta and there is the foot that attaches the sporophyte to the gametophyte.

The sporophyte has the power to synthesise its food but is dependent on the gametophyte for water and minerals.

Over the period of time, there are major changes in the different divisions of the kingdom Plantae. Some major evolutionary changes in the major divisions are:

• Thallophyta and Bryophyta members are predominant gametophytes. The sporophytic phase is partially parasitic in Bryophytes.

• Pteridophyta, Gymnosperms, and Angiosperms are with predominant sporophytic phase.

• In Pteridophyta, the gametophytes are still with independent existence. In the other two sub-divisions, the gametophyte is represented as cells.

• Thallophyta shows the presence of non-jacketed sex organs. A layer of sterile jacket appeared in Bryophyta and Pteridophyta.

• Presence of archaegonia in Bryophyta, Pteridophyta, and primitive Gymnosperms. Angiosperms are devoid of such structure.

• Pteridophyta members (few) evolved the heterospory and this gave rise to seed habit in Gymnosperms and Angiosperms.

When the pollination takes place in between the two different flowers of two different plants of the same species then it is called xenogamy. This is real or true cross-pollination. Genetically, as well as ecologically, it is cross-pollination.

The Kingdom Monera includes all prokaryotes. They are basically unicellular but can be mycelial, colonial and filamentous. They contain peptidogycan in cell wall. Naked circular DNA coiled to form nucleoid without association with histones, ribosomes 70S, thylakoids present photoautotrophs but other membrane bound organelles are absent. Nutrition is of various types- parasitic, chemoautotrophic, photoautotrophic and saprobic.

Some monerans have the ability to fix nitrogen. Due to presence of these characters in archaea and nitrogen-fixing organisms they are placed undermonera.

All others fungi, plantae, protists and animalia are eukaryotic.

Male reproductive organ is called androecium and their unit is called stamen. Stamen is also known as microsporophyll. A typical stamen differentiates into three parts- filament, anther and connective tissue. The anther is bilobed and the lobe encloses 4 pollen sacs or microsporangia. The integumented nucellus or megasporangium is called ovule. The correct mismatched pair is 'Megasporophyll - Filament.' A megasporophyll is associated with female reproductive structures and not the filament. The microsporangium is indeed the pollen sac where pollen is produced, and the megasporangium is the ovule. Therefore, the correct mismatched pair is option 3.

Normally bacteria cannot survive in antibiotic containing medium but if it does so it must have acquired resistance against that antibiotic. These are well adapted to grow in streptomycin containing medium and thus are more evolved. So due to natural selection only the more evolved and better adapted species is able to survive.