Test: Economic Botany (Old NCERT) - Grade 12 MCQ

A large number of different herbicide classes inhibit photosynthesis by binding to the quinone-binding protein, D-1, to prevent photosynthetic electron transfer. Mostly they interfere with photolysis of water. Herbicides does not interfere with water absorption, translocation of sugar and CO₂​ absorption. 

Some very special sources of genetic diversity have been identified during germplasm evaluation. For example, a thorough evaluation of O. sativa germplasm failed to find resistance to the grassy stunt virus. It was found, however, in just one accession of the closely related wild species, O. nivara (IRGC 101508) from India. IRRI breeders exploited this resistance and subsequently released IR 36, which was at one time the most widely cultivated variety of any cereal (Swaminathan, 1982). Few examples of germplasm have had a similar impact; however, a cursory analysis of rice pedigrees (e.g. IR 36) shows how wide the search has been for new germplasm capable of increasing productivity in rice cultivation.

Coffee was not native to the Americas and had to be planted in the country. The first coffee was grown by Native Americans. The first coffee bush in Brazil was planted by Francisco de Melo Palheta.Coffee production in Brazil is responsible for about a third of all coffee, making Brazil by far the world's largest producer, a position the country has held for the last 150 years.

Organochlorine compounds are highly lipophilic and can accumulate in fat-rich food such as meat and milk (Hernandez et al., 1994). Pesticides are introduced into cattle mainly through fodder or contaminated water used for household and public purposes (Sabbah and Bouguerra 1997).

2, 4-D is a weedicide. 2,4-Dichlorophenoxyacetic acid  is a common systemic herbicide used in the control of broadleaf weeds. It is a synthetic auxin (plant hormone) and one of the most widely used herbicides in the world. 2,4-D is a possible carcinogen as  per WHO.2,4-D was one of the ingredients in Agent Orange, a herbicide widely used during the Vietnam War. 2,4-D is primarily used as a selective herbicide which kills many terrestrial and aquatic broadleaf weeds, but not grasses. It acts by mimicking the action of the plant growth hormone auxin, which results in uncontrolled growth and eventually death in susceptible plants.Weed is a wild plant growing where it is not wanted and in competition with cultivated plants. Weedicide is the chemical which kills weeds.

Jojoba (Simmondsia chinensis) is a shrub. It is the sole species of the family Simmondsiaceae, placed in the order Caryophyllales. It is grown commercially for its oil, a liquid wax ester extracted from the seed.

Organophosphate (OP) compounds are the most widely used group of insecticides in the world. Their acute toxicity causes a hazard both to professional and amateur users. OPs were first recognised in 1854, but their general toxicity was not established until the 1930s. Tetraethyl pyrophosphate (TEPP) was the first OP insecticide, which was developed in Germany during World War Two as a by-product of nerve gas development. OPs are all derived from phosphoric acid. They are generally among the most acutely toxic of all pesticides to vertebrate animals. They are also unstable and therefore break down relatively quickly in the environment. So, organo phosphates are more toxic to vertebrates compared to organo chlorine, carbamates and parathion. Thus, option A is correct and other options are wrong.

Triticale is an intergeneric hybrid of wheat and rye. The first one was bred in laboratories during the late 19th century in Scotland and Germany.

Most of organochlorine pesticides are highly soluble in fat of animals. Further, these chemicals are resistant to be metabolized, so they start accumulating in the bodies of animals. 

In India due to prolonged use of DDT, 13-31 ppm of DDT can be detected in the body fat of people, which is highest in the world. Thus, the correct answer is option C.

Genetic erosion is a process whereby an already limited gene pool of an endangered species of plant or animal diminishes even more when individuals from the surviving population die off without getting a chance to meet and breed with others in their endangered low population. Low genetic diversity in a population of wild animals and plants leads to a further diminishing gene pool, inbreeding and a weakening immune system and fast tracks that species towards eventual extinction.

Late blight caused by the oomycete, Phytophthora infestans is the most destructive disease in potato cultivation worldwide. New, more virulent P. infestans strains have evolved which overcome the genetic resistance that has been introgressed by conventional breeding from wild potato species into commercial varieties. R genes (for single-gene resistance) and genes for quantitative resistance to late blight are present in the germplasm of wild and cultivated potato. The species Solanum demissum proved to be an important source of resistance, and by conventional plant breeding (crossing and back-crossing) in the 1940s and 1950s this resistance was bred into commercial potato cultivars. Four major resistant genes (termed R genes) were discovered and were introduced successively into commercial cultivars. Thus, the correct answer is option A.

Herbicides, also commonly known as weed killers, are pesticides used to kill unwanted plants. Selective herbicides kill specific targets, while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic mimics of natural plant hormones. Herbicides interfere with photolysis of water, inhibits O2 evolution and also inhibits translocation of organic solutes. Thus, option D is correct.

A biofertilizer is a suspension of the living organism which remains in close association with the soil and increases the fertility of the soil. It is applied to plant surfaces, or soil colonizes the rhizosphere or the interior of the plant and promotes growth by increasing the supply or availability of primary nutrients to the host plant. Blue-green algae is a free living nitrogen fixing bacteria. So, BGA has been recommended as a biofertilizer. VAM plays a great role in inducing plant growth. VAM are symbiotic entophytic soil fungi, which colonize the roots of approximately 80% plants. VAM also is used as biofertilizer. 

So, the correct answer is option C.

Bacillus thuringiensis (Bt) is a bacteria that can infect and kill insects and thus, it is used as an insecticide. Alfalfa webworms killed by Bacillus thuringiensis. The insecticidal activity of Bt was first discovered in 1911. However, it was not commercially available until the 1950s. In recent years, there has been tremendous renewed interest in Bt.

Anabaena-Azollae is a small filamentous phototrophic cyanobacteria generally seen as a multicellular organism with two distinct, interdependent cell types. It is a small, circular, photoautotrophic vegetative cell that performs oxygenic photosynthesis and is typically blue green in color. Since it is a phototrophic cyanobacteria, it derives energy for N2 fixation by performing photosynthesis. Thus, option A is correct.

A pyrethroid is an organic compound similar to the natural pyrethrins produced by the flowers of pyrethrums (Chrysanthemum cinerariaefolium and C. coccineum). Pyrethroids now constitute the majority of commercial household insecticides. In the concentrations used in such products, they may also have insect repellent properties and are generally harmless to human beings in low doses but can harm sensitive individuals. Pyrethroids are axonic excitoxins, the toxic effects of which are mediated through preventing the closure of the voltage-gated sodium channels in the axonal membranes. The sodium channel is a membrane protein with a hydrophilic interior. This interior is a tiny hole which is shaped precisely to strip away the partially charged water molecules from a sodium ion and create a favorable way for sodium ions to pass through the membrane, enter the axon, and propagate an action potential. When the toxin keeps the channels in their open state, the nerves cannot repolarize, leaving the axonal membrane permanently depolarized, thereby paralyzing the organism. So, pyrethroids are largest group of insecticides of plant origin. Thus, option C is correct.