Biology: CUET Mock Test - 6 - Class 12 MCQ

Mesic means an area having a moderate or well-balanced supply of moisture. The hydrarch, as well as xerarch succession finally leads to the formation of a mesic community. It is neither to wet nor too dry.

The correct option is 'A - III, B - I, C - IV, D - II'.

Key Points

• Aspergillus niger is known for producing Citric acid.
  • It is a microorganism that is used in the industrial production of citric acid.
  • This fungus is capable of converting sugars into citric acid through fermentation processes.
• Clostridium butylicum is associated with the production of Butyric acid.
  • This bacterium is used in the fermentation industry to produce butyric acid.
  • Butyric acid is known for its importance in the food and flavoring industries.
• Saccharomyces cerevisiae is a yeast used for producing Ethanol.
  • It is one of the most well-known yeasts, widely used in the baking and brewing industries for its ability to ferment sugars into ethanol and carbon dioxide.
• Acetobacter aceti is known for its role in producing Acetic acid.
  • It is a bacterium that oxidizes ethanol to acetic acid, a process central to vinegar production.

Therefore, the correct pairing is:
A - III: Aspergillus niger - Citric acid
B - I: Clostridium butylicum - Butyric acid
C - IV: Saccharomyces cerevisiae - Ethanol
D - II: Acetobacter aceti - Acetic acid

Key Points

• Chitinase is used for the isolation of genetic material from fungal cells because the cell walls of fungi are primarily composed of chitin, and chitinase helps in breaking down this component.

Additional Information

• Lysozyme is incorrect because it is primarily used to break down the cell walls of bacteria, which are rich in peptidoglycan, not chitin.
• Pepsin is incorrect as it is a digestive enzyme that breaks down proteins in the stomach, not a component of fungal cell walls.
• Cellulase is incorrect because it breaks down cellulose, which is a major component of plant cell walls, not fungal cell walls.

Key Points

• The correct sequence for the Polymerase Chain Reaction (PCR) process is Denaturation of DNA, Annealing of primers, Extension of primers, and finally the Amplified DNA.
• This sequence is represented by option 3: (C), (A), (D), (B).

Additional Information

• Denaturation of DNA: This first step involves heating the reaction mixture to separate the DNA strands, providing single-stranded DNA templates for the next step.
• Annealing of primers: In this step, the temperature is lowered to allow primers to bind (anneal) to their complementary sequences on the single-stranded DNA templates.
• Extension of primers: The temperature is adjusted so that the DNA polymerase can synthesize the new DNA strand by adding dNTPs (deoxyribonucleotide triphosphates) to the annealed primers.
• Amplified DNA: The result of repeating these steps (denaturation, annealing, extension) is an exponential increase in the specific DNA segment being amplified.

• Option 1: The sequence (A), (C), (B), (D) is incorrect because it does not follow the standard PCR steps.
• Option 2: The sequence (D), (A), (C), (B) is incorrect as it starts with the extension step, which cannot occur before the DNA is denatured and primers are annealed.
• Option 4: The sequence (C), (B), (D), (A) incorrectly places the amplified DNA step before the extension step, which is not feasible in the PCR process.

The correct option is 'A - III, B - IV, C - I, D - II'.

Key PointsPlasmid of Salmonella - Construction of 1st recombinant DNA

• Plasmids are small, circular, double-stranded DNA molecules distinct from a cell's chromosomal DNA.
• They naturally occur in bacterial cells, including Salmonella.
• Plasmids are used in biotechnology as vectors to insert foreign DNA into host cells.
• The construction of the first recombinant DNA involved the use of a plasmid to introduce foreign DNA into a host cell, creating a genetically modified organism.

Restriction enzymes - Molecular scissors

• Restriction enzymes are enzymes that cut DNA at specific recognition nucleotide sequences known as restriction sites.
• They are often referred to as "molecular scissors" because they can cut DNA strands at precise locations, allowing for the manipulation of DNA for cloning, analysis, and other genetic engineering purposes.

Ligases - Join foreign DNA to plasmid

• DNA ligases are enzymes that facilitate the joining of DNA strands together by catalyzing the formation of a phosphodiester bond.
• They are crucial in genetic engineering for ligating foreign DNA into plasmid vectors, a process essential in the construction of recombinant DNA molecules.

β-galactosidase - Insertional inactivation

• β-galactosidase is an enzyme involved in the hydrolysis of β-galactosides into monosaccharides.
• Insertional inactivation is a method used in molecular cloning to detect the insertion of a DNA fragment into a plasmid vector.
• When a gene for β-galactosidase in a plasmid is disrupted by the insertion of foreign DNA, the enzyme's activity is lost, indicating successful cloning.

Conclusion:

Therefore, the correct pairing is

• A - III: Plasmid of Salmonella - Construction of 1st recombinant DNA
• B - IV: Restriction enzymes - Molecular scissors
• C - I: Ligases - Join foreign DNA to plasmid
• D - II: β-galactosidase - Insertional inactivation

Key Points

• Transgenic animals are those that have had their genomes altered through genetic engineering techniques. These animals carry genes from other species, which can give them new traits or characteristics.
• The incorrect statement is that transgenic animals are used "To make better quality seeds." This is because transgenic animals are primarily used in medical and scientific research, not in the production of plant seeds.
• Transgenic animals are indeed used "To study disease" by introducing or modifying genes related to specific human diseases, allowing researchers to study the progression and treatment of these diseases in a living organism.
• They are also used "To test vaccine safety" by carrying genes that make them susceptible to diseases for which vaccines are being developed, thus serving as models for testing the efficacy and safety of these vaccines.
• "To test chemical safety" is another correct use of transgenic animals. They can be engineered to be more sensitive to toxic substances, allowing scientists to study the effects of chemicals and drugs on living organisms.

Additional Information

• The use of transgenic animals is a powerful tool in genetics research, allowing scientists to understand gene functions and their effects on health and disease more clearly.
• While transgenic technology has great potential in various fields, it also raises ethical and environmental concerns that need to be carefully considered.

Concept:

• There are different Modes of reproduction in organisms and they can be classified into two types-
  • Sexual mode of reproduction
  • Asexual mode of reproduction

Asexual reproduction -

• It is the type or mode of reproduction in which a new offspring is produced by a single parent.
• Here the offspring produced are genetically and physically identical to their parents.
• Different types of Asexual reproduction are- Fission, Fragmentation, Regeneration, Budding, Vegetative propagation, Spore formation

​Sexual reproduction -

• It is a mode of reproduction in which both the sexes, male and female, are involved in reproduction of an offspring.
• The male and female gametes fuse to form a fertilized zygote.
• This zygote divides to form an embryo and later forms an individual organism.
• Sexual reproduction produces genetic variability and hence the organisms are not identical to the parents.

Important Points

Apomixis -

• Apomixis is the type of asexual production in which seeds are formed without fertilization.
• The plants which grow from these seeds are identical to the mother plant.
• Apomixis in flowering plants is considered as the asexual formation of a seed from the maternal tissues of the ovule.

Vegetative Reproduction -

• Vegetative propagation is a type of asexual reproduction in which fragments or parts of plant develop into a new plant.​
• Roots and stem both can be used for the vegetative propagation.
• As the new plants develop without any fertilization between the gametes produced from two different parents, therefore there is no variation in the offspring.
• The new offspring is identical to the parents.
• New plants arise from the root and stem structures like buds, tubers, rhizomes, bulbs suckers, offsets etc. naturally.
• These structures which give rise to new plants are known as vegetative propagules.
• Artificially, vegetative propagation can be carried out through cutting, layering, grafting and tissue culture.

Antibiotics produced by microbes are regarded as one of the most significant discoveries of the twentieth century and have greatly contributed towards the welfare of the human society. Anti is a Greek word that means ‘against’, and bio means ‘life’, together they mean ‘against life’ (in the context of disease-causing organisms); whereas with reference to human beings, they are ‘pro-life’ and not against. Antibiotics are chemical substances, which are produced by some microbes and can kill or retard the growth of other (disease-causing) microbes.

• Sir Alexander Fleming, a Scottish researcher discovered penicillin in 1928.
• Antibiotics like penicillins produced by useful microbes are used to kill disease-causing harmful microbes.
• Antibiotics have played a major role in controlling infectious diseases like diphtheria, whooping cough and pneumonia.
• For more than a hundred years, microbes are being used to treat sewage (waste-water) by the process of activated sludge formation and this helps in recycling of water in nature.

Hence, we conclude that Penicillin was discovered by Alexander Flemming.

Note

• Edward Jenner discovered the Small Pox Vaccine.
• Robert Koch discovered the causative agents of Cholera, Tuberculosis, Anthrax.
• Robert Hooke discovered cell.

The correct answer is Typhus.

• Typhus, also known as typhus fever, is a group of infectious diseases that include epidemic typhus, scrub typhus, and murine typhus.
• Common symptoms include fever, headache, and a rash.
• The diseases are caused by specific types of bacterial infection.
• Chlamydia is a sexually transmitted infection (STI) caused by a bacteria called chlamydia trachomatis.
• Gonorrhoea is an infection caused by a sexually transmitted bacterium that infects both males and females.
• Hepatitis B is spread when blood, semen, or other body fluids from a person infected with the virus enters the body of someone who is not infected.

Additional Information

• Some common sexually transmitted diseases are - Pelvic Inflammatory Disease (PID), Genital Warts and Human Papillomavirus (HPV), Genital Herpes (HSV-1, HSV-2),
  Syphilis, etc.

The correct answer is Only 2

RNA polymerase is an enzyme responsible for catalyzing the synthesis of RNA from a DNA template during transcription. Transcription involves three main stages: initiation, elongation, and termination.

• Initiation: In this stage, RNA polymerase binds to the promoter region of the DNA, forming a transcription initiation complex. In prokaryotes, this process often involves the transient association of a sigma factor (σ) with the RNA polymerase core enzyme, which helps in recognizing and binding to the promoter sequence.
• Elongation: Once the initiation complex is formed, RNA polymerase begins moving along the DNA template, synthesizing RNA in the 5' to 3' direction. During elongation, RNA polymerase does not require the transient association of initiation or termination factors. It simply catalyzes the addition of ribonucleotides to the growing RNA chain based on the complementary base pairing with the DNA template.
• Termination: In the termination stage, RNA polymerase recognizes specific sequences in the DNA template that signal the end of the gene or transcription unit. In prokaryotes, termination often involves the transient association of a termination factor (ρ) with the RNA polymerase complex, leading to the release of the newly synthesized RNA molecule and dissociation of RNA polymerase from the DNA template.

Conclusion-
RNA polymerase can perform elongation on its own without the need for additional factors such as the initiation factor (σ) or termination factor (ρ).
During elongation, RNA polymerase moves along the DNA template, catalyzing the addition of ribonucleotides to the growing RNA chain based on the complementary base pairing with the DNA template

The correct answer is Option 3.

Key Points

• Pleiotropy is the phenomenon of a single gene influencing two or more distinct phenotypic traits. Hence Statement 1 is correct.
• An example of a Pleiotropy is phenylketonuria which is a genetic disorder caused by the low metabolism of the amino acid phenylalanine in the body cells.
• Phenylketonuria (PKU) is a rare genetic condition that causes an amino acid called phenylalanine to build up in the body.
  • It is caused by a mutation of the gene responsible for the production of an enzyme called phenylalanine hydroxylase. Hence statement 2 is correct.
  • This enzyme breaks down the amino acid phenylalanine that we get from protein digestion.
  • Without this enzyme, levels of the amino acid phenylalanine increase in the blood and damage the nervous system in infants.
  • This disorder may result in several conditions in infants including intellectual disabilities, seizures, heart problems, and developmental delays.

The habitat having an excess of hydration is known as a hydric habitat. They have wet soils and are characterized by an abundance of moisture. Wetland area is an example of a hydric habitat.

The first biotic community to invade a bare land or area is known as the pioneer community. In a xerarch succession, lichens in the temperate region act as pioneering species. Some examples of lichens are Rinodina, Lecanora, Parmelia, etc.

The sequence of successional stages occurring on bare rocks is known as xerarch succession. In a xerarch succession, the pioneering species lichens release acids to dissolve rocks. This helps in weathering and soil formation.

The sequence of successional stages occurring on bare rocks is known as xerarch succession. The mosses are replaced by the herbaceous plants in a xerarch succession. Some examples of xeric grasses are Aristida, Solidage, Poa, etc.

The sequence of successional stages occurring on bare rocks is known as xerarch succession. The shrub stage is replaced by a forest in a xerarch succession. The trees found in the forest are Acacia, Prosopis, Boswellia, etc.

The sequence of successional stages occurring on bare rocks is known as xerarch succession. It occurs in an area where there is less amount of moisture. It is mostly observed in the desert area.

Ecological succession is the gradual change in the species composition of a given area which can be predicted. Biomass is the total organic material required for energy production.

The sequence of successional stages occurring on bare rocks is known as xerarch succession. It mostly starts with the invasion of lichens and ends with the formation of the forest. The pioneering species grow with time leading to a formation of a climax community called a forest.

The changes in the community are constant, orderly and sequential. These changes lead to the formation of a stable, self-perpetuating and final biotic community that developed during the end of biotic succession known as a climax community.

The first biotic community to invade a bare land or area is known as the pioneer community. These are the organisms of the first seral stage. They further grow and expand to form a climax community.

The sequence of successional stages occurring on bare rocks is known as xerarch succession. The herbaceous plants are replaced by the shrubs in a xerarch succession. Some examples of shrubs are Phytocarpus, Rhus, etc.

The sequence of successional stages occurring on bare rocks is known as xerarch succession. In a xerarch succession, the pioneering species lichens release acids to dissolve rocks. This helps in weathering and soil formation.

The sequence of successional stages occurring on bare rocks is known as xerarch succession. The pioneering species lichens are replaced by mosses in a xerosere. Some examples of mosses are Tortula, Grimmima, Polyerichum, etc.

The sequence of successional stages occurring on bare rocks is known as xerarch succession. It is also known as xerosere and starts in a newly formed rocky area.

The habitat having too much dryness is known as a xeric habitat. It is deficient in moisture and is characterized by limited water availability. Desert region is an example of a xeric habitat.

Recombinant therapeutics is the type of medicines obtained from recombinant organisms. These are mostly protein in nature. Till date, 30 recombinant therapeutics have been approved for human use which includes insulin, human factor IX, etc.

In early days the insulin was obtained from the pancreas of cattle and pigs. Insulin obtained this way had many disadvantages. Nowadays insulin is obtained using recombinant DNA technology. For this microorganisms are used.

The polypeptide chains present in insulin is connected by disulphide bonds. These disulphide bonds are formed between two cysteine residues. In total insulin consists of 3 disulphide bonds.

Insulin is a pro-hormone secreted in mammals by the pancreas. This pro-hormone need to be processed to become a fully mature and functional hormone. Insulin allows the absorption of glucose I blood.