Biology: CUET Mock Test - 4 - Class 12 MCQ

Connective also known as sterile parenchyma tissue possesses a vascular strand. This is the tissue that attaches 2 anther lobes together. Since monothecous anthers are made of only 1 anther lobe, it does not have connective.

Key Points

• Wings of a butterfly and wings of a bird are not an example of homology but rather an example of analogy. This is because, while both serve the same function of flight, they do not share a common evolutionary origin. The butterfly's wings are made of chitin and develop from the exoskeleton, whereas bird wings are made of feathers that develop from the skin.

Additional Information

• Forelimbs of a whale and forelimbs of a cheetah are examples of homology, indicating a common evolutionary ancestor, despite their different current functions.
• Forelimbs of humans and forelimbs of whales also share a common evolutionary origin, highlighting structural similarities despite different functions, making them homologous.
• The thorn of Bougainvillia and tendril of Cucurbita, despite serving different functions, are considered homologous structures as they both originate from the same part of the plant.

Key Points

• The correct combination is (A) and (B) only, which means that statements about invertebrates forming around 500 million years ago and jawless fish evolving around 350 million years ago are correct.

Additional Information

• Statement (C) about sea weeds existing around 400 mya is not specifically incorrect, but it is misleading as algae and primitive sea plants existed far earlier than 400 million years ago.
• Statement (D) regarding dinosaurs suddenly disappearing about 100 mya is incorrect because the most accepted theory suggests that dinosaurs went extinct around 65 million years ago at the end of the Cretaceous period.
• Options involving (C) and (D) are thus not accurate in the context of the evolution timeline provided.

The primary lymphoid organ is the Thymus.

Key Points

• The Thymus is a primary lymphoid organ where T lymphocytes (T cells) mature. T cells are essential for adaptive immunity.
• Primary lymphoid organs are where lymphocytes are formed and mature. This includes the bone marrow and the thymus.

Additional Information

• The Spleen is a secondary lymphoid organ, involved in filtering blood and responding to systemic infections.
• Tonsils are part of the mucosa-associated lymphoid tissue (MALT) and play a role in protecting the body from pathogens entering through the mouth or nose.
• The Appendix, like tonsils, is part of the gut-associated lymphoid tissue (GALT) and contributes to immunity.
• Secondary lymphoid organs, such as the spleen, tonsils, and appendix, are where mature lymphocytes interact with antigens and initiate adaptive immune responses.

Vaccination is not used as a direct treatment for cancer. While vaccines like the HPV vaccine can prevent certain types of cancer by targeting the viruses that cause them, vaccination itself is not a treatment method for existing cancer.

Key Points

• Radiation therapy uses high doses of radiation to kill cancer cells and shrink tumors. It's a common treatment for various types of cancer.
• Immunotherapy is a type of cancer treatment that helps your immune system fight cancer. It has become a crucial part of treating some types of cancer.
• Surgery is often used to remove cancerous tumors or tissues. It's one of the oldest forms of cancer treatment and can be effective in many cases.

Additional Information

While vaccines can play a role in preventing certain cancers, they are not used to treat cancer that has already developed. Instead, treatments like radiation therapy, immunotherapy, and surgery are utilized to directly target and treat cancer.

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

Key Points

• Entamoeba histolytica is associated with Amoebiasis.
  • Entamoeba histolytica is a parasitic amoeba that causes amoebiasis, also known as amoebic dysentery.
  • It primarily affects the intestines and sometimes the liver, leading to symptoms such as diarrhea, stomach pain, and fever.
• Wuchereria bancrofti causes Filariasis.
  • Wuchereria bancrofti is a filarial nematode worm that causes lymphatic filariasis, also known as elephantiasis.
  • It is transmitted to humans through the bite of an infected mosquito and leads to severe swelling of the limbs and genitals.
• Microsporum is responsible for Ringworm.
  • Microsporum species are a group of fungi that cause ringworm, a contagious skin infection.
  • It affects the skin, hair, and nails, leading to circular rashes, scaling, and sometimes hair loss.
• Plasmodium falciparum leads to Malaria.
  • Plasmodium falciparum is one of the species of Plasmodium parasites that causes malaria in humans.
  • It is transmitted through the bite of an infected Anopheles mosquito and causes symptoms like fever, chills, and anemia.

Therefore, the correct pairing is:
A - III: Entamoeba histolytica - Amoebiasis
B - I: Wuchereria bancrofti - Filariasis
C - IV: Microsporum - Ringworm
D - II: Plasmodium falciparum - Malaria

Key Points

• The 'cry' gene produces the cry protein, which is also known as the Bt-toxin.
• It is present in the bacterium Bacillus thuringiensis.
• This toxin is effective in killing insects like -
  • Lepidopterans - Tobacco budworm, armyworm.
  • Coleopterans - Beetles.
  • Dipterans - Flies, mosquitoes

Mechanism of Action of Cry protein -

• The bacteria produce crystals containing insecticidal Cry proteins during a particular growth phase.
• The protein exists in the inactive protoxin form in the bacteria.
• It gets activated in the alkaline gut of insects, where the crystals get solubilized.
• This releases the active toxin, which binds to the midgut epithelial cells of insects.
• This creates pores causing cell swelling and lysis, that leads to the death of the insect.

Explanation:

• The cry genes produce insect-group specific toxins and thus can be introduced into crop plant genomes to make them pest-resistant.
• There are different forms of cry genes that are effective only against a specific insect pest.
• Example -
  • cryIAb - effective against corn borers.
  • cryIAc, cryIIAb - effective against cotton bollworms.

Hence, the correct answer is option 1.

Concept:

• Growth models help us understand if the growth of any population over time follows a particular pattern or not.
• This also helps us to understand several other attributes of the population.
• Growth models explain 2 types of growth curves:
  • Exponential - This takes place when the resources are unlimited and the population keeps growing.
  • Logistic - This is a growth model that takes the limitations of resources into account.

Important PointsExponential Growth -

• Growth of a population depends on the resources available.
• Therefore, ideally if the resources in a habitat are unlimited, the growth in also unlimited.
• Such cases where the population keeps growing exponentially is known as exponential growth.
• As observed by Darwin, with unlimited resources the species are able to realize their full growth potential.
• This results in an increased reproductive ability leading to exponential growth of the population.

It can be denoted by the equation:

where, N = Population Density,

= Rate of change of population density.

• Here, 'r' represents the intrinsic rate of natural increase, which is the difference between the per capita birth and death (b-d).
• The 'r' value varies from population to population:
  • Norway rat - 0.015
  • Flour beetle - 0.12
  • Human population in India (1981) - 0.0205
• When the population density (N) is plotted against time (t), it produces a J-shaped curve for exponential or geometric growth.

Additional InformationThe integral form of the above equation is:
N_t = N₀e^rt  
where, N_t = Population density after time 't'
N₀ = Population density at time 0 (zero)
e = Base of natural log (2.71828)
r = Intrinsic rate of natural increase

Concept-

• Restriction enzymes belong to a larger class of enzymes called nucleases.
• Restriction enzymes are used to break DNA molecules.
• Restriction enzymes are of three types- Exonuclease, endonuclease, and restriction endonuclease.
  • Exonuclease- They cut off nucleotides from 5' or 3' ends of DNA molecule.
  • Endonuclease- They break DNA duplex at any point except the end.
  • Restriction endonuclease- They cleave DNA duplex at specific points.

Explanation-

• Restriction endonuclease was found by Arber.
• They act as "molecular scissors".
• They recognize the base sequence at palindrome sites in the DNA duplex and cut its strands.
• Hind II, whose functioning depended on a specific DNA nucleotide sequence was isolated.
• It was found that Hind II always cut DNA molecules at a particular point by recognizing a specific sequence of six base pairs.
• This specific base sequence is known as the recognition sequence for Hind II.

The first restriction endonuclease-Hind II.

Additional Information

The correct answer is Mast cells

• The cells that release histamine and other vasoactive substances in response to allergens are mast cells.
• Mast cells are a type of white blood cell that is found in connective tissue and mucous membranes.
• When allergens bind to IgE antibodies attached to the surface of mast cells, it triggers the release of histamine, leukotrienes, prostaglandins, and other vasoactive substances.
• These substances cause inflammation, vasodilation, bronchoconstriction, and other symptoms associated with allergic reactions.

Additional Information

• Neutrophils: Neutrophils are a type of white blood cell that plays a key role in the body's immune response to infections. They are primarily involved in phagocytosis, which is the process of engulfing and destroying pathogens like bacteria and fungi. While neutrophils are important in fighting infections, they are not typically involved in allergic reactions or the release of histamine.
• Macrophages: Macrophages are another type of white blood cell that is involved in the immune response. They function by engulfing and digesting cellular debris, pathogens, and other foreign substances. Macrophages also play a role in presenting antigens to other immune cells to initiate an immune response.
• NK cells: NK cells, or natural killer cells, are a type of lymphocyte that plays a role in the innate immune response against infected or abnormal cells, such as cancer cells. NK cells recognize and destroy these abnormal cells through a process called cytotoxicity.

Conclusion:
Cells that release histamine and other vasoactive substances in response to allergens are Mast cells.

Key Points

• DNA was discovered by Friedrich Meischer (1869) as an acidic substance present in the nucleus.
• By 1926, the search for genetic material was already narrowed down to the chromosomes present in the nucleus.
• But the molecule acting as the genetic material was yet to be determined.
• Frederick Griffith (1928) conducted a series of experiments with Streptococcus pneumoniae in search for the genetic material.
• He found that S. pneumoniae produced 2 types of strains when grown in culture medium:
  • S strain- produced smooth shiny colonies because of a mucous polysaccharide coating.
  • R strain- produced rough colonies that lacked the mucous coating.

Experiment:

Observations:

• Mice injected with S-strain died of pneumonia infection, while mice injected with R-strain did not.
• Therefore, S-strain was the virulent (infectious) form.
• Heat-killed S-strain bacteria did not cause any infection, so the mice lived.
• When heat-killed S-strain bacteria were injected along with R-strain, the mice died and live S-strain bacteria were recovered from the dead mice.

Conclusions:

• From the above observations, Griffith concluded that R-strain had somehow been "transformed" by the heat-killed S-strain to become virulent.
• Some substance was transferred from the heat-killed S-strain to the R-strain that enabled the R-strain bacteria to produce the mucous coating and become virulent.
• This substance was named as the 'transforming principle'.

Drawback:

• The biochemical nature of the genetic material could not be defined.

A genetic material must be both chemically and structurally stable. It must be able to replicate. It should provide scope for the evolutionary changes. But it should also be able to express itself in the form of “Mendelian characters” and not “Bohr’s characters”. These Mendelian characters refer to the three laws that were proposed by Gregor Mendel.

There are three different types of RNA. They are mRNA (messenger RNA), rRNA (ribosomal RNA) and tRNA (transfer RNA). sRNA is a small ribosomal RNA. They are produced by the bacterium. The three different types of RNA are required for the synthesis of protein.

Pollen sacs or microsporangia are present within the anther lobes. Each anther lobe has 2 microsporangia. It’s very rare to see a single microsporangium in an anther lobe. Example-Wolffia.

Recombination frequency is a simple measure that can be obtained by analyzing the progeny of the cross. It can then be used to determine the linkage, genetic maps, and gene density.

The hydrogen atom which is attached to the hydroxyl group on the 2’- C atom of the RNA can be easily deprotonated. The presence of larger grooves in RNA is also a reason for it not being stable under alkaline conditions. But under the same condition, the DNA molecule will be stable for it has smaller grooves which cannot be easily attacked or penetrated.

The role of mRNA is to provide the template strand. The role of tRNA is to bring the amino acids and read the genetic code. rRNA plays the structural and catalytic role during the process of translation.

Amino acids do not have any structural specialties to read a code. Francis Crick came up with an ideology that an adapter molecule will be present. This adapter molecule will be capable of both reading the code and also on binding itself to the specific amino acid.

Recombination frequencies provide an inside on the location of genes on the chromosome. It does not provide any information about the possible functions and hence associated phenotypes of a gene.

Proteins form polypeptide chains by the peptide bond formation between amino acids. Their different folding statures results in the formation of non-covalent bonds as well as the different forms of proteins. Despite these capabilities, proteins lack the ability to generate their replica.

The RNA polymerase binds to the promoter region of the DNA molecule. After the attachment of the RNA polymerase enzyme to the promoter, the process of transcription is being initiated.

The tRNA was known by the name sRNA in its early days. sRNA stands for soluble RNA. This was even before the postulation of the genetic code. But, the role of tRNA as an adapter was assigned much later.

Gynoecium represents the female part of the flower. It consists of a stigma, style and ovaries. The gynoecium is non motile. It’s the pollens that are motile. They fall on the stigma which starts the fertilization process.

Pistil is the free unit of a gynoecium. A pistil has three parts-style, stigma and ovaries. Stigma acts as a landing platform for the pollens. Style is the long tube-like structure that carries the male gamete to the ovaries.

During the termination stage of transcription process, the nascent RNA falls off. This is observed when the polymerase enzyme reaches the terminator region. Following this, the RNA polymerase enzyme also falls off.

The stop codons are UAA, UAG and UGA. These codons are absent in the tRNA molecules. tRNA possesses an amino acid acceptor end which is the site for binding the amino acids. Finally, the anticodon loop of the tRNA contains bases that are complementary to the codes.

If the genes are farther away on a chromosome, their linkage decreases. This allows them to recombine more frequently.

Stigma acts as a landing place for the pollen grains from where the style carries it to the ovaries for the fertilization. Stigma also checks the pollen grain for compatibility or incompatibility.

There are three stages in the transcription process. They are initiation, elongation and termination. Among these three, the stage of elongation is catalyzed by the RNA polymerase enzyme.

The actual structure of the tRNA is actually a compact molecule which appears to be like an inverted L shaped molecule. But, the secondary structure of the tRNA appears to look like a clover leaf shaped structure.