Biology: CUET Mock Test - 1 - CUET MCQ

Concept:

• Embryo formation takes place after the fertilization of egg cell by the male gamete.
• Flowering plants have the unique characteristic feature of double fertilization.
• Each pollen grain has 2 male gametes and both take part in fertilization.
• Double fertilization involves 2 processes:
  • Syngamy - It is the fusion of one male gamete with the egg cell to produce a zygote that later develops into embryo.
  • Triple fusion - It is the fusion of the 2nd male gamete with the 2 polar nuclei of the embryo sac to produce the endosperm.
• Therefore, double fertilization can be summed up as:

1st Male gamete (n) + Egg (n) → Zygote (2n)
2nd Male gamete (n) + 2 Polar nuclei (n) → Endosperm (3n)

Important Points

• The endosperm develops before the embryo to provide nutrition to the developing embryo.
• The embryo starts developing at the micropylar end of the embryo sac, where the egg cell was positioned.
• Most zygotes start dividing after partial development of endosperm, in order to assure nutrition to the embryo.
• The process of embryo development is known as embryogeny.
• The early stages of embryogeny are similar in dicots and monocots.
• In a dicot plant, the zygote first gives rise to the proembryo.
• The proembryo then subsequently forms the globular embryo, which is round in shape.
• Then the heart-shaped embryo is formed and the rest of the embryo sac starts degenerating.
• Lastly the mature embryo is formed.
• Thus, the correct sequence of embryo development is:

Proembryo → Globular embryo → Heart-shaped embryo→ Mature embryo

Additional Information

• A typical dicot embryo consists of an embryonal axis and two cotyledons.
• The part of the embryonal axis above the cotyledons is called the epicotyl.
• The epicotyl terminates at the plumule, which later gives rise to the stem.
• Plumule is the shoot tip in dicots.
• The portion below the cotyledons is the hypocotyl, which terminates at the radicle.
• Radicle gives rise to the root and is protected by the coleorhiza.

(A) Correct: Fertilization occurs when the sperm cell fuses with the egg cell.
(B) Incorrect: Self-pollination results in less genetic diversity as it involves the same genetic material.
(C) Correct: Cross-pollination requires external agents such as wind, water, or animals to transfer pollen.
(D) Correct: The embryo sac contains the female gamete, the egg cell, located in the ovule.
(E) Incorrect: The seed coat is formed from the integuments of the ovule, not the fertilized ovule itself.

(A) Incorrect: Pollination is not always dependent on external agents. Some plants can self-pollinate without external assistance.
(B) Correct: Cross-pollination can indeed occur through various agents such as wind, water, or animals, promoting genetic diversity.
(C) Incorrect: The ovary is located at the base of the flower's reproductive system, not at the top.
(D) Correct: Insect-pollinated flowers are typically brightly colored and have a strong fragrance to attract pollinators.
(E) Incorrect: Pollen from one species cannot fertilize the flowers of another species.

(A) Incorrect: Fertilization does not occur in the style. It takes place in the ovule, which is located in the ovary.
(B) Correct: The anther produces pollen, which contains the male gametes in plants.
(C) Correct: Double fertilization is a process unique to plants where one sperm fertilizes the egg, and the other sperm fuses with the central cell to form endosperm.
(D) Incorrect: The pollen tube grows through the style and enters the ovule, carrying the sperm cells for fertilization.
(E) Incorrect: The stigma is part of the female reproductive system; it is the sticky structure that receives pollen.

(A) Correct: Pollination is indeed the transfer of pollen from the male anther to the female stigma. This is a key part of sexual reproduction in plants.
(B) Incorrect: Self-pollination does not result in genetic variation because the pollen comes from the same plant, which leads to the same genetic material being passed on.
(C) Correct: Cross-pollination involves the transfer of pollen between two flowers of the same or different plants, leading to genetic diversity.
(D) Incorrect: Fertilization in plants occurs when a male gamete (sperm) from the pollen grain, delivered via the pollen tube, fuses with the female gamete (egg) within the ovule to form a zygote. The pollen grain itself does not fuse with the ovule; rather, it germinates on the stigma, grows a pollen tube through the style, and delivers sperm cells to the ovule’s embryo sac for fertilization. The statement is scientifically inaccurate due to the incorrect description of the fertilization process.
(E) Incorrect: Fertilization is a sexual process, not asexual. Asexual reproduction involves processes like cloning or vegetative propagation.

Immigration is not necessarily equal to emigration in a population.

Topic in NCERT: Population Density Factors

Line in NCERT: "Under normal conditions, births and deaths are the most important factors influencing population density, the other two factors assuming importance only under special conditions."

Solution:

1 - D: Population Density → The number of individuals per unit area or volume in a population.
2 - C: Exponential Growth → The rate of increase in a population's size under ideal conditions.
3 - A: Carrying Capacity → The maximum number of individuals an environment can support sustainably.
4 - B: Immigration → Movement of individuals into a population from another area.

Monarch butterflies (a) have cryptic coloration to avoid being preyed upon, making them (iii) prey with cryptic coloration.
Cactus-feeding moths (b) are predators of the prickly pear cactus, making them (i) predator.
Starfish Pisaster (c) is a predator that regulates prey populations, so it's (iv) a predator.
Herbivorous insects (d) are prey species in an ecosystem, making them (ii) prey.

In an open ocean, the large numbers of phytoplankton quickly complete their life cycles and sets of new population or crops of phytoplankton are formed every few hours or days. Thus, the cumulative energy contents that these generation after generation of phytoplankton trap in course of a year is certainly much more than trapped by only a few generations of herbivorous fishes in the corresponding time and space. The energy content trapped by the carnivores living on the herbivorous fishes is the leat.

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)

- Statement i is correct as the introduction of the Nile perch into Lake Victoria led to the extinction of over 200 species of cichlid fish.

- Statement ii is incorrect because invasive weed species like Lantana and water hyacinth are known to threaten native species and ecosystems.

- Statement iii is correct as co-extinctions occur when the extinction of one species, such as a host fish, leads to the extinction of its obligate parasites or mutualistic partners.

- Statement iv is incorrect because the introduction of Clarias gariepinus has been illegal and poses a threat to indigenous catfish populations.

Thus, the correct statements are i and iii, making option A the correct answer.

RNAi or RNA interference takes place in all eukaryotic organisms as a method of cellular defense. This method involves silencing of a specific mRNA. Using Agrobacterium vectors, nematode specific genes are introduced into the host plant (tobacco plant). The introduction of DNA was such that it produced both sense and anti-sense RNA in the host cells. These two RNAs being complementary to each other formed a dsRNA (double stranded RNA) that initiated RNAi.

Human insulin is made up of 51 amino acids arranged in two polypeptide chains: A, having 21 amino acids and B, with 30 amino acids. The two polypeptide chains are interconnected by two disulphide bridges.

Topic in NCERT: Genetically engineered insulin

Line in NCERT: "insulin consists of two short polypeptide chains: chain a and chain b, that are linked together by disulphide bridges."

In a dihybrid cross, tightly linked genes on the same chromosome show very few recombinations because they are so close together that they tend to be inherited as a unit. This is consistent with Option D, which accurately describes the nature of tightly linked genes. Options A, B, and C do not correctly describe the behavior of linked genes.

NCERT Topic: Linkage and recombination

NCERT Line: "Tightly linked genes on the same chromosome showed very low recombination."

Heterogeneous nuclear RNA or hnRNA is a term that encompasses various types and sizes of RNAs found in the eukaryotic cell nucleus. When this undergoes modifications and processing it will give rise to the mature mRNA that has the inherent code for the protein synthesis (amino acid code). The mRNA in eukaryotes is synthesized in the nucleus and hence should be transported to the cytoplasm and into the ribosome for protein synthesis by the process of translation. 

NCERT Topic: The fully processed hnRNA is called mRNA and is transported out of the nucleus into the cytoplasm for translation.

NCERT Line: "It is the fully processed hnRNA, now called mRNA, that is transported out of the nucleus for translation."

DNA Replication: DNA replication is the process by which a cell makes an identical copy of its DNA. It occurs during the cell cycle to ensure that each daughter cell receives a complete set of genetic instructions. DNA replication is a highly accurate process in which the DNA double helix is unwound, and each strand serves as a template for the synthesis of a complementary strand. 

Transcription: Transcription is the process by which a segment of DNA is used as a template to synthesize a complementary RNA molecule. It is the first step in the central dogma of molecular biology, which describes how genetic information is used to produce proteins. In transcription, an enzyme called RNA polymerase reads the DNA template and assembles a single-stranded RNA molecule, known as messenger RNA (mRNA), by matching RNA nucleotides to the DNA template. 

Translation: Translation is the process in which the information contained in an mRNA molecule is used to synthesize a protein. This process occurs at ribosomes, cellular structures that serve as the protein-manufacturing factories. During translation, the mRNA is read in sets of three nucleotides called codons. Each codon corresponds to a specific amino acid, the building blocks of proteins. 

• Two mya, Australopithecines probably lived in East African grasslands.
• Fossils discovered in Java in 1891 revealed the next stage, i.e., Homo erectus about 1.5 mya.
• The Neanderthal man with a brain size of 1400cc lived in near east and central Asia between 1,00,000 - 40,000 years back.
• During ice age between 75,000 - 10,000 years ago modern Homo sapiens arose.

Topic in NCERT: Origin and evolution of man

Line in NCERT: "a rough sketch of the evolution of life forms, their times on a geological scale are indicated in (figures 6.9 and 6.10). homo erectus probably ate meat. the neanderthal man with a brain size of 1400cc lived in near east and central asia between 1,00,000-40,000 years back. homo sapiens arose in africa and moved across continents and developed into distinct races."

This principle says that allele frequencies in a population are stable and is constant from generation to generation.

Given figures represent the forelimbs of different vertebrates, which possess the same basic structural plan, i.e., in each case, the forelimb consists of humerus, radio-ulna, carpals, metacarpals and digits. Thus, the skeletal parts of these forelimbs are similar in structure and arrangement, but have different shapes and functions. It depicts the example of homologous structures.

A- Lactobacillus B- Trichoderma polysporum C-Yeast D-Penicillin

The cloning vector requires the presence of a selectable marker, which helps in identifying and eliminating non-transformants and selectively permitting the growth of the transformants. Normally, the genes encoding resistance to antibiotics such as ampicillin, chloramphenicol, tetracycline or kanamycin, etc. are considered useful selectable markers for E. coli. The normal E.coli cells do not carry resistance against any of these antibiotics.

Lines in NCERT: 1. Restriction enzymes belong to a larger class of enzymes called nucleases.
2. The cutting of DNA at specific locations became possible with the discovery of the so-called  ‘molecular scissors’– restriction enzymes.
3. Downstream processing is the last process in recombinant DNA technology(6th). After completion of the biosynthetic stage, the product has to be subjected through a series of processes before it is ready for marketing as a finished product.
4. And the last method uses ‘disarmed pathogen’ vectors, which when allowed to infect the cell, transfer the recombinant DNA into the host.

Stirred-tank bioreactor is used for processing large volumes of culture. It is a cylindrical tank with a curved base to facilitate the mixing of the reactor contents. The stirrer facilitates even mixing and oxygen availability throughout the bioreactor.

• Statement 1: The tumour-inducing plasmid (Ti plasmid) acts as a cloning vector in recombinant DNA technology.
  The Ti plasmid, derived from Agrobacterium tumefaciens, is widely used in recombinant DNA technology as a cloning vector to deliver genes into plant cells. The T-DNA (transfer DNA) region of the Ti plasmid is modified to carry the desired gene, which is then transferred into the plant genome. This statement is correct.
• Statement 2: The Ti plasmid, which is used in the mechanisms of delivering genes to a cell, remains pathogenic.
  In its natural form, the Ti plasmid is pathogenic because it causes crown gall disease in plants by transferring T-DNA, which includes genes that induce tumor formation. However, in recombinant DNA technology, the Ti plasmid is modified by removing the tumor-inducing genes (oncogenes) from the T-DNA region, replacing them with the gene of interest. This modified Ti plasmid is no longer pathogenic; it is disarmed to prevent tumor formation while retaining its ability to transfer DNA. Therefore, this statement is incorrect.

Correct Answer:

b) Statement 1 is correct but statement 2 is incorrect

MCQ Solution:

• a) Incorrect: Statement 2 is incorrect, so both cannot be correct.
• b) Correct: Statement 1 is true (Ti plasmid is used as a cloning vector), but Statement 2 is false (the modified Ti plasmid is not pathogenic).
• c) Incorrect: Statement 1 is correct, not incorrect.
• d) Incorrect: Statement 1 is correct, so both are not incorrect.

Thus, the correct answer is b).

Soil bacterium, Bacillus thuringiensis (Bt) produces proteins that kill certain insects like lepidopterans (tobacco budworm, armyworm), coleopterans (beetles) and dipterans (flies, mosquitoes). Bacillus thuringiensis forms some intracellular protein crystals. These crystals contain a toxic insecticidal protein. The Bt toxin protein exists as inactive toxin and is converted into an active form due to the alkaline pH of the alimentary canal that solubilises the crystals. The activated toxin binds to the surface of midgut epithelial cells and create pores which cause cell swelling and lysis and finally cause death of the insect.

Decomposition is the process that involves the breakdown of complex organic matter or biomass from the body of dead plants and animals with the help of decomposers into inorganic raw materials such as carbon dioxide, water, and other nutrients.

The various processes involved in decomposition are as follows:
➢ Fragmentation 

• It is the first step in the process of decomposition.
• It involves the breakdown of detritus into smaller pieces by the action of detritivores such as earthworms.

➢ Leaching

• It is a process where the water soluble nutrients go down into the soil layers and get locked as unavailable salts.

➢ Catabolism

• It is a process in which bacteria and fungi degrade detritus through various enzymes into smaller pieces.

➢ Humification

• The next step is humification which leads to the formation of a dark-coloured colloidal substance called humus, which acts as reservoir of nutrients for plants.

➢ Mineralization

• The humus is further degraded by the action of microbes, which finally leads to the release of inorganic nutrients into the soil.
• This process of releasing inorganic nutrients from the humus is known as mineralization.