Biology: CUET Mock Test - 2 - CUET MCQ

Key Points

• The correct sequence of human embryo development starts with (D) Cleavage in zygote, which is the first step following fertilization. This process involves the division of the zygote into smaller, multicellular stages without the zygote increasing in size.
• Following cleavage, the zygote develops into (C) the morula, a solid ball of cells.
• As development continues, the morula transforms into (A) the blastocyst, a hollow ball of cells with an inner cell mass that eventually forms the embryo.
• The final step in the sequence is (B) implantation, where the blastocyst attaches itself to the wall of the uterus.

The correct answer is option 2: (D), (C), (A), (B).

Additional Information

• Option 1: (C), (D), (B), (A) is incorrect because it suggests that the morula forms before cleavage, which is not the correct order of development.
• Option 3: (D), (B), (C), (A) incorrectly places implantation before the formation of the morula and blastocyst, which is not possible as implantation is the final step in this sequence.
• Option 4: (A), (C), (D), (B) is incorrect as it suggests the blastocyst forms before cleavage and morula formation, which contradicts the actual developmental sequence.

Amniocentesis is a medical procedure used for prenatal diagnosis of chromosomal abnormalities and fetal infections. It involves extracting a small amount of amniotic fluid, which contains fetal tissues, for analysis.

Key Points

• Amniocentesis is primarily used to detect the presence of certain genetic disorders. This includes conditions such as Down syndrome, cystic fibrosis, and spina bifida.

Additional Information

• Sexually transmitted diseases: Amniocentesis is not typically used to detect sexually transmitted diseases. Such conditions are usually diagnosed through blood tests, urine tests, or swabs of the affected area.
• Causes of infertility: Amniocentesis cannot be used to determine the causes of infertility. Infertility assessments usually involve a different set of tests for both men and women.
• Presence of pneumonia germs: Although amniocentesis can detect some infections, it is not specifically used for diagnosing pneumonia in the fetus. Pneumonia diagnosis would typically involve chest X-rays or sputum tests in the suspected individual.

Key Points

• In a cross between RRyy (round, yellow seeds) and rrYY (wrinkled, green seeds), the F1 generation will all be RrYy, exhibiting the dominant traits (round and green seeds).
• The F2 generation, obtained by self-pollinating the F1 generation, will show a variety of genotypes due to the independent assortment and segregation of alleles during gamete formation.
• When considering two traits controlled by two genes, each with two alleles (Rr and Yy), the Punnett square method predicts that 16 different genotypes can be formed in the F2 generation.
• However, these 16 genotypes will only result in 4 different phenotypes because the traits are independently inherited and express complete dominance (round yellow, round green, wrinkled yellow, wrinkled green).
• Therefore, the number of genotypes is 9 and the number of phenotypes is 4, which aligns with option 3.

Additional Information

• Option 1 (16 genotypes and 4 phenotypes) incorrectly suggests a reversal in the number of genotypes and phenotypes.
• Option 2 (4 genotypes and 16 phenotypes) also incorrectly reverses the numbers, and it is not possible to have more phenotypes than genotypes in this scenario.
• Options 4 and 5 are not applicable as they either present incorrect combinations or are left blank.
• The correct understanding of Mendelian genetics and the principles of dominance, segregation, and independent assortment is crucial for predicting the outcomes of genetic crosses.

The correct answer is An ecosystem which can be easily damaged but can recover after some time if damaging effect stops

• Low Stability: Stability in an ecosystem refers to its ability to resist change or disturbance. In this case, the ecosystem described can be easily damaged, indicating low stability. This means that even minor disturbances or stresses can disrupt its structure and function.
• High Resilience: Resilience is the ability of an ecosystem to recover and return to its original state after being disturbed. The ecosystem described in option 1 can recover after some time if the damaging effect stops. This demonstrates high resilience because despite being easily damaged, it has the capacity to bounce back and restore itself.

In summary, option 1 represents an ecosystem that is prone to damage (low stability) but has the ability to recover effectively (high resilience). This combination of characteristics is typical of ecosystems that are subject to frequent disturbances but can adapt and regenerate over time.

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.

Key Points

• A 'J-shaped' curve represents an exponential growth curve.
• Such cases where the population keeps growing exponentially is known as exponential growth.
• Exponential growth takes place when the environmental conditions are favorable and the resources available are unlimited.
• Under such ideal conditions, the species are able to realize their full growth potential.
• This results in an increased reproductive ability leading to exponential growth of the population.
• When the population density (N) is plotted against time (t), it produces a J-shaped curve for exponential or geometric growth.

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).

(A) Incorrect: The male gamete (pollen) is produced in the anther, not the ovary.
(B) Correct: Pollination can occur through wind, water, or animals (like bees).
(C) Correct: The style is the tube that connects the stigma to the ovary.
(D) Incorrect: Self-pollination involves pollen from the same plant, not cross-breeding.
(E) Correct: Fertilization results in a diploid zygote, which develops into the embryo.

(A) Incorrect: Human reproduction is sexual, not asexual. It involves the fusion of male and female gametes.
(B) Correct: The male reproductive system produces sperm and transfers them into the female reproductive system during ejaculation.
(C) Correct: The scrotum keeps the testes outside the body to maintain a temperature lower than body temperature, essential for sperm production.
(D) Correct: The female reproductive system produces eggs (ova), and fertilization occurs in the fallopian tubes, while the uterus provides a site for fetal development.
(E) Correct: Hormonal regulation by the hypothalamus, pituitary gland, and gonads controls human reproduction.

Fertilization occurs inside the ovary, where the sperm cell from the pollen fertilizes the ovule, resulting in the formation of a zygote.

The pollen tube forms after pollination and grows down through the style, allowing the sperm cell to reach and fertilize the ovule in the ovary.

The fusion of male (sperm) and female (egg) gametes forms the zygote, which later develops into the seed.

Exons are the coding sequences in eukaryotic genes that contain the genetic information necessary for protein synthesis.

NCERT Topic: Exons in eukaryotes

NCERT Line: "In eukaryotes, the gene is split. The coding sequences, exons, are interrupted by non-coding sequences, introns."

UAA is a nonsense codon. It signals for polypeptide chain termination. Hence, only 24 amino acids chain will be formed.

The accessibility of promoter regions of prokaryotic DNA is regulated by interaction of proteins with sequences called as operators. Repressor molecules that repress gene expression bind to the operator sits and as a result the promoter cannot initiate gene transcription. Promoter is the site for the binding of the RNA polymerase to initiate the process of transcription. It refers to a conserved sequence that is specific for the binding of the RNA polymerase that can bring the expression genes for various functions. Regulator gene is the gene of an operon that codes for a repressor molecule that can bind to the operator sequence and stop gene expression. Structural gene codes for proteins or enzymes that are essential for the cell growth and survival 
So, the correct option is 'A - (ii), B - (i), C - (iv), D - (iii)'.

The anticodon loop is crucial for the accurate translation of mRNA into protein, as it ensures that the correct amino acid is added to the growing polypeptide chain.

• All the varieties, he conjectured, evolved on the island itself.
• From the original seed eating features, many other forms with altered beaks arose, enabling them to become insectivorous and vegetarian finches

Gene migration or gene flow (1) involves the movement of genes between populations, affecting gene frequencies.
Genetic drift (2) refers to random changes in gene frequencies due to chance events, especially in small populations.
Mutation (3) introduces new genetic variations that can alter gene frequencies.
Genetic recombination (4) during gametogenesis creates new combinations of alleles, influencing genetic diversity.
Natural selection (5) acts on heritable traits, enhancing reproductive success and influencing the frequency of advantageous alleles in future generations.
All these factors contribute to changes in allele frequencies and can lead to speciation over time.

A thorn of Bougainvillea and a tendrill of Curcurbita, both are stem modifications and thus represent homologous structures. The modifications indicate the evolution of the organ to suit different functions which is also known as divergent evolution.

DPT vaccine is for diphtheria, pertussis and tetanus. The patient suffering from typhoid is required to be treated with antibiotics as it is a bacterial disease.

Statement i is incorrect because there is no complete cure for HIV/AIDS, but the disease can be managed with treatment.
Statement ii is correct as anti-retroviral drugs help control the replication of HIV and can prolong life.
Statement iii is correct because safe sex practices and other preventive measures can reduce the transmission of HIV, and there is no current vaccine.
Statement iv is incorrect as HIV treatment can be effective throughout the course of the disease, not just in the early stages.
Thus, the correct answer is Option B: ii and iii.

Topic in NCERT: Treatment of aids with anti-retroviral drugs

Line in NCERT: "treatment of aids with anti-retroviral drugs is only partially effective. they can only prolong the life of the patient but cannot prevent death, which is inevitable."

    A: A−(iv), B−(i), C−(v), D−(iii), E−(ii)

B: A−(ii), B−(i), C−(v), D−(iii), E−(iv)

C: A−(iv), B−(v), C−(iii), D−(ii), E−(i)

D: A−(ii), B−(v), C−(iii), D−(i), E−(iv)

Allergy: Linked to IgE, which is responsible for allergic reactions.

Helper T-cells: Linked to activation of B-cells, crucial for immune response.

AIDS virus: HIV is a single-stranded RNA virus.

X-rays: Known carcinogens that can cause cancer.

Treatment of cancer: Often involves immunotherapy.

The correct option is: A: A−(iv), B−(i), C−(v), D−(iii), E−(ii)

• Option (1) is the correct answer as the body is able to differentiate between ‘self’ and ‘non-self’ and the cell-mediated immune response is responsible for the graft rejection.
• Option (2) is incorrect as body of higher vertebrates have the ability to differentiate foreign organisms from self cells.
• Option (4) is incorrect as the autoimmune response occur when the body’s immune system fails to recognize ‘self’ from ‘non-self’ and starts destroying the body’s own cells.

Strains are produced by Monascus purpureus. Dung is used to producing Biogas. Saccharomyces cerevisiae is used in the production of ethanol.  Cyclosporin A is obtained from Trichoderma polysporum.

Baculoviruses are pathogens that attack insects and other arthropods. The majority of them used as a biological control agents are in the genus Nucleopolyhedrovirus.These viruses are excellent candidates for species-specific, narrow spectrum insecticidal applications. Infection with baculoviruses occurs when susceptible hosts eat virus particle present on foliage and dies. These are important in organic farming because of their specific action on harmful insects without causing any damage to beneficial insects as well as to the environment.

HindII was the first discovered restriction endonuclease. It was isolated from Haemophilus influenzae. It produces blunt ends.

The final step of PCR is extension, wherein TaqDNA polymerase (isolated from a thermophilic bacterium Thermus aquaticus) synthesies the DNA region between the primers, using DNTPs (denoxynucleoside triphosphates) and Mg2⁺. The primers are extened towards each other so that the DNA segment lying between the two primers is copied. The optimum temperature for this polymerisation step is 72^∘C. Taq polymerase remains active during high temperature induced denaturation of double stranded DNA.

Two cry genes, crylAc and cryllAb have been incorporated in cotton. The genetically modified crop is called Bt cotton as it contains Bt toxin genes. The genes crylAc and cryllAb control cotton bollworms.

NPP at first trophic level would be the GPP for second trophic level. NPP at second trophic level would be GPP for third trophic level. Therefore, 100x(kcal/m²/yr) would be GPP at second trophic level and 100x * 10% (kcal/m²/yr) i.e 10x(kcal/m²/yr) energy would be GPP at third trophic level.

Topic in NCERT: Productivity

Line in NCERT: The rate of biomass production is called productivity. It is expressed in terms of gm–2 yr –1 or (kcal m–2 ) yr –1 to compare the productivity of different ecosystems. It can be divided into gross primary productivity (GPP) and net primary productivity (NPP)

The correct statements are i, ii, and iii.

1. Statement i is correct because the tropics have been relatively undisturbed for millions of years, allowing for more time for species diversification compared to temperate regions that have faced frequent glaciations.

2. Statement ii is also correct since the less seasonal and more stable environments in the tropics allow for niche specialization, thus enhancing species diversity.

3. Statement iii is correct as well; the greater solar energy availability in tropical regions contributes to higher productivity, which supports a wider range of species.

4. Statement iv is incorrect because polar regions have been significantly affected by glaciation events, leading to lower species diversity compared to tropical regions.

Therefore, the accurate answer is Option A: i, ii, and iii.