Biology: CUET Mock Test - 3 - CUET MCQ

Coitus or copulation is the process that leads to the release of semen from the penis into the vagina. The sperms populate the vagina along with other contents of semen. This process is called insemination.

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

Key Points

• Human skin colour is determined by Polygenic inheritance (II).
  • Polygenic inheritance refers to the inheritance of a phenotypic trait that is attributable to two or more genes and can be measured along a continuum.
  • Human skin color is an excellent example of polygenic inheritance, which is influenced by more than one gene and shows a wide range of phenotypes.
• A pair of alleles expressing contrasting traits refers to being Heterozygous (IV).
  • Heterozygous individuals have two different alleles for a given gene.
  • This condition often results in a phenotype that may express a dominant trait over a recessive one, illustrating the concept of dominance and recessivity in genetics.
• The ABO blood group system demonstrates Multiple allelism (I).
  • Multiple allelism occurs when three or more alleles for a gene exist within a population.
  • In the ABO blood group system, the A, B, and O alleles interact to produce the four blood types: A, B, AB, and O, showcasing multiple allelism.
• Antirrhinum flower colour is an example of Incomplete dominance (III).
  • Incomplete dominance occurs when the phenotype of the heterozygote is intermediate between the phenotypes of the two homozygotes.
  • For Antirrhinum (snapdragon) flowers, a cross between a red-flowered plant and a white-flowered plant results in offspring with pink flowers, demonstrating incomplete dominance.

Therefore, the correct pairing is:

A - II: Human skin colour - Polygenic inheritance

B - IV: Pair of alleles expressing contrasting traits - Heterozygous

C - I: ABO blood group - Multiple allelism

D - III: Antirrhinum flower colour - Incomplete dominance

Key Points

• During transcription, the sequence of the template strand of DNA is used to create a complementary mRNA transcript.
• Adenine (A) pairs with Uracil (U) in RNA, and Cytosine (C) pairs with Guanine (G).
• The template DNA strand sequence given is 3'-ATTGAACTG-5'. To find the mRNA sequence, we must use complementary base pairing and remember that RNA uses Uracil (U) instead of Thymine (T).
• The correct mRNA sequence is 5'-UAACUUGAC-3' because it is complementary and antiparallel to the DNA template strand.

Additional Information

• Option 1 (3'-AUUGAACAG-5') is incorrect because it provides the sequence in the wrong direction and does not properly complement the DNA template.
• Option 2 (5'-UAACUUGAC-3') is correct as it accurately reflects the rules of base pairing in RNA and is in the correct 5' to 3' orientation.
• Option 3 (3'-CAGUUCAAU-5') is incorrect because it reverses the direction and does not accurately reflect the complementary base pairing.
• Option 4 (5'-GUUAGUCCA-3') is incorrect because it does not match the base pairing rules for the given DNA template strand.
• The transcription process involves creating an mRNA strand that is complementary to the DNA template strand, ensuring that genetic information can be effectively transferred from DNA to RNA for protein synthesis.

Key Points

• Thymine is not present in RNA; instead, RNA contains Uracil.
• Adenine, Guanine, and Cytosine are present in both RNA and DNA.
• In DNA, Thymine pairs with Adenine, whereas in RNA, Uracil takes the place of Thymine to pair with Adenine.
• The presence of Uracil instead of Thymine is one of the key differences between RNA and DNA.

Key Points

• The correct answer is option 3: (A), (C) and (D) only.
• This means the regions of the transcription unit include the Promoter, Terminator, and the Structural Gene.
• The Promoter is a region of DNA that initiates transcription of a particular gene. It is where the RNA polymerase binds to start transcription.
• The Terminator is a sequence of nucleotides in DNA that marks the end of a gene or operon in genomic DNA during transcription.
• The Structural Gene consists of the DNA sequence that is actually transcribed into RNA, which may then be translated into a protein.

Additional Information

• Sigma factor is not part of the DNA sequence of the transcription unit but rather a protein needed for the initiation of transcription in bacteria. It helps the RNA polymerase to bind to the promoter.
• Options 1, 2, and 4 are incorrect because they include the Sigma factor, which is not a region of the transcription unit but rather a transcription initiation factor.

Lichens are the correct indicator of industrial pollution.

Key Points

• Lichens are sensitive to air pollution, especially sulfur dioxide. Their presence or absence can indicate the level of air quality and the extent of pollution in an area.
• Lichens are symbiotic organisms made up of fungi and algae living together. They do not have roots and absorb water and nutrients directly from the atmosphere, making them highly susceptible to airborne pollutants.

Additional Information

• Mosses, Ferns, and Pines are not as sensitive to air pollution as lichens and therefore are not reliable indicators of industrial pollution.
• Mosses can tolerate a wider range of pollution levels and still thrive in moderately polluted areas.
• Ferns and Pines are more robust plants that have adaptations to deal with environmental stressors but do not specifically indicate air pollution levels.

Key Points

• Microbes play an important role for the production of industrial products.
• They are used for fermented beverages, antibiotics, bioactive molecules as well as food products like cheese.
• Microbes may include bacteria as well as fungi.
• Monascus pupureus is a type of yeast that is used to produce statins.
• Statins are blood cholesterol-lowering agents.
• It can induce competitive inhibition of the enzyme responsible for synthesis of cholesterol.

Additional Information

• Cyclosporin A -
  • ​It is produced from the fungus Trichoderma polysporum.
  • It is used as an immunosuppressive agent in organ transplant patients.
• Streptokinase -
  • ​It is produced from the bacterium Streptococcus.
  • It is used as a 'clot-buster' to remove unwanted blood clots in the blood vessels.
  • It is particularly useful in patients who have undergone myocardial infarction leading to heart attack.
• Acetic acid -
  • ​It is industrially produced from the bacterium Acetobacter aceti.

The correct answer is halophiles.

Key Points

• A living organism can live in the air, water, and soil and are cosmopolitan.
• The organisms that prefer high salt concentration habitats refer to as halophiles.
• It belongs to the domain of archaea, bacteria, and eukaryotes.
• It is found in lakes and the dead sea.
• Brine shrimp is one of its examples.

Additional InformationAlkaliphiles:

• These organisms can tolerate high alkaline pH.
• It survives at a pH above 9.
• It includes prokaryotes, eukaryotes, and archaea.
• Bacillus and streptomyces are examples.
• It is used to produce antibiotics.

Calcifuges:

• These are the plants that live at low pH.
• It is grown in low-calcium soil.
• Tea is an example of a calcifuge plant.
• Tea boost our immune system.

Nitrophiles:

• These are the plants that live in soil that is rich in nitrate.
• Cannabis sativa is an example of nitrophiles.
• It is used to treat asthma and depression.

• Pollination is the transfer of pollen grains from the anther to the stigma of a flower.
• Pollination can be divided into 3 types:

1. Autogamy -
   • It is the transfer of pollen grains from the anther to the stigma of the same flower.
   • It requires the pollen release and stigma receptivity to be synchronous, to prevent cross-pollination.
   • The anthers and stigma lie close to each other to assure self-pollination.
   • The autogamous flowers can be of 2 types:
   1. Chasmogamous flowers have normal flowers with exposed anther and stigma.
   2. Cleistogamous flowers do not open at all, thus assuring self-pollination and seed set.
   • Some plants like Oxalis, Viola and Commelina produce both chasmogamous and cleistogamuos flowers.
2. Geitonogamy -
   • It is the transfer of pollen grains from the anther to the stigma of a different flower of the same plant.
   • It is functionally cross-pollination as pollinating agents are involved.
   • It is genetically self-pollination as both male and female gametes come from the same plant.
   • Example - Maize, Castor.
3. Xenogamy -
   • It is the transfer of pollen grains to the stigma of different plant.
   • It causes genetic variation and is a type of cross-pollination.
   • It is always found in unisexual plants where male and female flowers are borne on different plants.
   • Example - Papaya.

Therefore, cleistogamous flowers do not need any agent of pollination as they are self-pollinated.

Additional Information

• Birds, insects and bats are biotic agents of pollination.
• The flowers pollinated by them are usually large, colourful, fragrant and produce nectar.
• These flowers provide nectar and pollen as floral rewards to the agents of pollnation.
• They may also provide a safe place for them to lay eggs.

The correct answer is The energy and biomass relationship between the organisms at different tropic levels

• Ecological pyramids can determine the energy and biomass relationship between organisms at different trophic levels.
• These pyramids depict the flow of energy or biomass through the various levels of a food chain or food web.
• As you move up the pyramid, typically from producers (plants) to primary consumers (herbivores) to secondary consumers (carnivores), the energy or biomass available decreases, representing the loss of energy as it is transferred between trophic levels.

Additional Information An ecological pyramid is a pictorial representation of the relationship between different organisms in an ecosystem.

Pyramid of numbers:

• It depicts the numbers of individual organisms at different trophic levels of the food chain.
• It is helpful to calculate the changes observed in the number of organisms in each trophic level.
• We can identify which level is in the endangered zone and need to be saved. But its limitation is we cannot count a number of all organisms accurately.

Pyramid of Biomass:

• Biomass is the dry weight of the organism.
• Pyramid of biomass indicates a decrease of biomass in each tropical level from base to apex.
• With higher tropical level biomass decreases for ecosystem on land and its inverse for an aquatic ecosystem where biomass increases with higher trophic level.

Pyramid of Energy:
An energy pyramid shows how much energy is needed as it flows upwards to support the next trophic level. Here the pyramid is always upward.

Therefore, "The energy and biomass relationship between the organisms at different tropic levels" is the correct answer.

The correct answer is Option 4 i.e. Law of independent assortment.

• Mendel's law of independent assortment states that the alleles for separate traits are passed independently of one another from parents to offspring. Therefore, according to Mendel, the inheritance of an allele for one trait does not affect the inheritance of an allele for another trait.
• However, when genes are located close to each other on the same chromosome, they tend not to assort independently and usually stay together during cell division due to linkage. This means that the inherited characteristics controlled by those genes tend to be inherited together, violating the law of independent assortment.
• Crossing over, or recombination, during meiosis can break this linkage. In this process, homologous chromosomes pair up and exchange sections of DNA, effectively shuffling the genes. However, occurrence of crossing over between two genes depends on the distance between them on the chromosome. If two genes are very close together, they are likely to be inherited together, again violating the law of independent assortment.

Additional Information Gregor Mendel, a 19th-century monk and scientist, conducted a series of experiments on pea plants which led to the formation of the fundamental principles of genetics. His works are pivotal in understanding heredity and genetics. The principles are mainly broken down into three laws:

• The Law of Dominance: This states that when two different alleles (variations of a gene) are present in a living being, it's the dominant gene that gets expressed while the recessive gene is masked. An allele is considered dominant if it's possible to express its trait in the progeny even when the individual only has one copy from one parent.
• The Law of Segregation : Mendel's First Law states that during the formation of gametes (sperm or egg), the two alleles for a trait separate (segregate) from each other. Each gamete carries only one allele for each trait because gametes are haploid (containing half the total genetic content). During fertilization, the gametes unite, and the resulting genes for a trait in the offspring (zygotes) will have a pair of alleles, one from each parent.
• The Law of Independent Assortment : This law states that genes for different traits are sorted independently and distributed into gametes separately during the formation of gametes. The transmission of an allele for one trait into a gamete does not influence the transmission of an allele for another trait.
• The Purity of gametes refers to the outcome of Mendel's first law, the law of segregation. As the pairs of alleles segregate independently during the formation of gametes, each gamete carries only one kind of allele for each characteristic, meaning that gametes are pure for each gene.

Conclusion
Crossing over and Linkage are an exception to Mendelian Law of Independent Assortment.

The heart is the first organ to form in the developing fetus. It is formed after one month of pregnancy. The brain takes more time to develop.

The F2 generation in a dihybrid cross produces all possible phenotypes. The ratio obtained for it is 9:3:3:1.

Syngamy is the process of fertilization that produces a diploid cell on the fusion of two haploid cells. It is also often called internal fertilization since the process takes place on the inside. However, there are few species of organisms where syngamy occurs outside their bodies, in an external medium. Example, algae, fishes, amphibians, etc. This is also called as external fertilization.

Sperms are released into the vagina. From here, they travel through the cervix and uterus before reaching oviduct or fallopian tube, where they can encounter an egg.

Limbs and digits, along with external genitalia, are formed during the first trimester. This is a period of 12 weeks after pregnancy.

The F2 progeny of a dihybrid Mendelian cross has a phenotypic ratio of 9:3:3:1. Thus of the 1600 plants sampled, 900 will be round yellow, 300 round green, 300 wrinkled yellow and 100 wrinkled green.

The pair of chromosomes that line up during meiosis has two copies of each homologous chromosome. Hence it is called a bivalent.

Androecium is a collection of stamens. Stamens consists of anthers and filaments. Anthers are fused to the top of the filament that acts like a stalk. Pollen sacs are present on the anthers, within which are the pollen grains.

Trimesters are periods of three months’ post-pregnancy. Fetal movements can be observed starting five months’ post-pregnancy i.e., during the second trimester.

The first two laws of Mendel were based on his studies on monohybrid crosses. These were the law of dominance and the law of segregation. The dihybrid cross studies supported them, but also led to the formulation of a third law: the law of independent assortment.

Sutton and Boveri had studied the segregation of chromosomes very closely by staining the cells and then developing a differential staining approach to visualize the pairs of chromosomes. To their surprise, this was very similar to the expectation of Mendel’s factors. Hence they made the conclusion that independent separation of chromosomes should lead to independent segregation of factors.

The egg is released and awaits in ampulla for the sperm. The sperms cross the reproductive tract barriers before reaching the ampulla to fertilize the egg.

The maternal increase in the hormones is responsible for the development and growth of the fetus, maintenance of pregnancy, and the changes in metabolism in mother essential for the proper nourishment of fetus. Lactation is not a part of pregnancy. It occurs after the baby has been delivered.

The Law of Independent Assortment states the independent segregation of traits that are unrelated. Mendel drew this conclusion based on his studies on garden pea plants.

Sutton and Boveri were the key players in the world of biology during the decade of 1900-1910. They observed chromosome movements and studied Mendel’s experiments. Based on these, they devised the chromosomal theory of inheritance.

The correct answer is C: Menstrual phase.

During the menstrual phase, which occurs at the beginning of the menstrual cycle, the lining of the uterus is shedding. This phase is typically characterized by low fertility because ovulation has not yet occurred and the egg is not available for fertilization. The menstrual flow makes the conditions less conducive to conception at this time.

In comparison:

• The onset of the follicular phase (B) is when the body starts preparing for ovulation, and there's potential for fertilization in the upcoming days.
• The end of the follicular phase (A) and end of the ovulation phase (D) are closer to ovulation, the time when fertility is highest.

The process of implantation is followed by the rapid differentiation of the inner mass of cells of the blastocyst. These cells differentiate into the outer layer of ectoderm and the inner layer of endoderm. Mesoderm arises later.

The law of independent assortment was the third law of Mendel. It states that when multiple traits are under consideration, each trait segregates independently of the other.

Sutton and Boveri were inspired by Mendel’s studies. With the advent of microscopy, they could observe the chromosomal movements during meiosis. Both of these led them to devise the chromosomal theory of inheritance.