All Free Biology MCQs with Answers

• A. Bt protein exists as active toxin in the Bacillus
• B. The activated toxin enters the ovaries of the pest to sterilise it and thus prevent its multiplication
• C. The concerned Bacillus has antitoxins
• D. The inactive protoxin gets converted into active form in the insect gut

Explanation: Soil bacterium Bacillus thuringiensis produces proteins that kill certain insects like lepidopterans (tobacco budworm, armyworm), coleopterans (beetles), and dipterans (flies, mosquitoes). B. thuringiensis forms some protein crystals which contain a toxic insecticidal protein. This toxin does not kill the Bacillus (bacterium) because it exists as inactive protoxins in them. But, once an insect ingests it, it is converted into an active form of toxin due to the alkaline pH of the alimentary canal. The activated toxin binds to the surface of midgut epithelial cells and creates pores that cause swelling and lysis and finally cause the death of the insect.

• A. Generated by introducing foreign DNA into a cell and regenerating a plant from that cell
• B. Produced after protoplast fusion in artificial medium
• C. Grown in artificial medium after hybridization in the field
• D. Produced by a somatic embryo in artificial medium

Explanation: The plants produced through genetic engineering contain genes, usually from an unrelated organism. Such genes are called transgenes and the plants having transgenes are called transgenic plants. Recombinant DNA techniques are being used to improve crop plants by increasing their productivity, making them more nutritious, and by developing disease resistance. Transgenic plants have a natural resistance to herbicides and pests. In the future, plants may have an ability to fix atmospheric nitrogen and an increased ability to grow in arid and salty soils.

• A. Insecticide
• B. Agent for production of dairy products
• C. Source of industrial enzyme
• D. Indicator of water pollution

Explanation: Soil bacterium Bacillus thuringiensis produces proteins that kill certain insects like lepidopterans (tobacco budworm, armyworm), coleopterans (beetles), and dipterans (flies, mosquitoes). B. thuringiensis forms some protein crystals which contain a toxic insecticidal protein. This toxin does not kill the Bacillus (bacterium) because it exists as inactive protoxins in them. But, once an insect ingests it, it is converted into an active form of toxin due to the alkaline pH of the alimentary canal. The activated toxin binds to the surface of midgut epithelial cells and creates pores that cause swelling and lysis and finally cause the death of the insect.

• A. Encourage eco­friendly herbicides
• B. Reduce herbicide accumulation in food articles for health safety
• C. Eliminate weeds from the field without the use of manual labour
• D. Eliminate weeds from the field without the use of herbicides.

Explanation: Genetic engineering has helped to develop such transgenic crop plants which are resistant to herbicides so that they are not damaged when farmers spray herbicides in the fields. Herbicide resistant plants have been developed in such a way that they continue to produce normal crop yield and at the same time remain unaffected by the activity of herbicides. These plants also reduces the use of weeding labour, farmer's cost and increases yield.

• A. Rhizobium
• B. Saccharomyces
• C. Escherichia
• D. Mycobacterium

Explanation: Insulin is now being commercially produced by genetic engineering. Insulin consists of two short polypeptide chains: chain A and chain B, that are linked together by disulphide bonds. Insulin in mammals is synthesized as a prohormone which contains an extra stretch called the C-­peptide. During maturation, this C­-peptide is removed. The production of insulin could only have been commercially possible if somehow the maturation process of C­-peptide could've been skipped.This problem was solved in 1988 by Eli Lilly, an American company that prepared functional insulin from two DNA sequences corresponding to A and B chains of human insulin and introduced them in plasmids of E.coli to produce insulin chains. In this way, chains A and B were produced separately, extracted and combined by creating disulfide bonds to get human insulin.

• A. Trichoderma
• B. Xanthomonas
• C. Bacillus
• D. Pseudomonas.

Explanation: Bioremediation is the process of using living micro­organisms to clean up a contaminated site. Micro­organisms do this by removing toxins from materials. They decompose these compounds by using enzymes, specific proteins that control reactions in living cells. Organisms that produce enzymes capable of degrading petroleum are useful in cleaning up oil spills. Some common ones that break down oil are genetically engineered species of Pseudomonas and Azotobacter. Bioremediation accounts for 5 to 10 percent of all pollution treatment and has been used successfully in cleaning up leaking underground gasoline storage tanks. Bioremediation has many applications, from ordinary garden compost to the removal of selenium and other toxic metals from waste. The best agents for bioremediation are the ones that can break down contaminants without becoming contaminated or harmful themselves.

• A. Biofertilizers
• B. Bio­-metallurgical techniques
• C. Bio­-mineralization processes
• D. Bioinsecticidal plants.

Explanation: Bacillus thuringiensis strains have been used for designing bioinsecticidal plants. A gene from this bacteria has insecticidal property which is transferred to cotton plants to produce Bt cotton which is resistant to bollworm insect which is a major pest of cotton. Similarly, insects affecting maize; cabbage, sunflower etc., are also controlled by mutant strains of Bacillus thuringiensis bacteria.

• A. The human chromosome can replicate in bacterial cell
• B. The mechanism of gene regulation is identical in humans and bacteria
• C. Bacterial cell can carry out the RNA splicing reactions
• D. The genetic code is universal.

Explanation: Genetic code may be defined as the sequence of nucleotides in polynucleotide chain which determines the sequence of amino acids in a polypeptide chain. Thus the genetic code is universal. There is no ambiguity regarding the genetic code. It means that each codon codes for the same amino acid in all organisms including bacteria, plants and animals.

• A. Insect resistance
• B. High lysine (essential amino acid) content
• C. High protein content
• D. High vitamin­-A content

Explanation: Golden rice is a transgenic crop rice with high vitamin A content. It has been developed by transferring beta carotene synthesizing gene into the transgenic rice. Beta carotene is the precursor of vitamin A. This transgenic rice has been crossed with the already adapted varieties of rice to make them grow well in a particular area. It is very useful for people suffering from vision impairment due to vitamin A deficiency.

• A. Molecular analysis of profiles of DNA samples
• B. Analysis of DNA samples using imprinting devices
• C. Techniques used for molecular analysis of different specimens of DNA
• D. Techniques used for identification of fingerprints of individuals

Explanation: DNA fingerprinting is a technique of determining nucleotide sequences of certain areas of DNA which are unique to each individual. The difference of about 0.1% or 3 × 10 6 base pairs (out of 3 × 10 9 bp) provides individuality to each human being. The human genome possesses numerous small noncoding but inheritable sequences of bases that are repeated many times. These sequences occur near telomere, centromeres, Y chromosome and heterochromatic area. The area with the same sequence of bases repeated several times is called repetitive DNA. It is separated as satellite from the bulk DNA during density gradient centrifugation and hence called satellite DNA where repetition of bases is in tandem. Satellite DNAs show polymorphism (the occurrence of mutations in a population at high frequency), which is the basis of genetic mapping of the human genome as well as DNA fingerprinting. While mutations in genes produce alleles with different expressions, mutations in noncoding repetitive DNA have no immediate impact. These mutations which have piled up with time form the basis of polymorphism.