EmSAT Biology Mock Test - 4 - EmSAT Achieve MCQ

The best stage to count the number and study the morphology of chromosomes is during metaphase. During metaphase, the chromosomes are condensed and highly visible, making it easier to count and study their structure. The chromosomes are also lined up at the equatorial plane of the cell, which makes it easier to observe them under a microscope.

Metaphase is a stage in the process of cell division known as mitosis, during which the cell's nucleus divides into two identical daughter nuclei. At this stage, the chromosomes, which contain the cell's genetic material, are visible under a microscope as thin, elongated structures. They are arranged in pairs, with one chromosome from each pair being inherited by each daughter nucleus.

By counting the number of chromosomes and studying their morphology (shape, size, and structure), scientists can learn more about the genetic makeup of an organism and how it may be affected by various factors, such as environmental conditions or genetic mutations.

Line in NCERT: "This then, is the stage at which morphology of chromosomes is most easily studied."

In late prophase, the nuclear envelope, nucleolus, Golgi complex, and endoplasmic reticulum disappear, allowing the chromosomes to become fully condensed and visible. This marks the transition into metaphase, where the mitotic spindle fully forms.

Line in NCERT: "Cells at the end of prophase, when viewed under the microscope, do not show golgi complexes, endoplasmic reticulum, nucleolus and the nuclear envelope."

• This graph indicates stabilizing selection. As we can see, the peak gets higher and narrower.
• In this selection, most of the individuals acquire mean character value.

Bt cotton is a genetically modified variety of cotton producing an insecticide. The bacterium Bacillus thuringiensis (Bt) naturally produces chemicals harmful to selective insects, most notably the larvae of moths and butterflies, beetles, cotton bollworms and flies, and harmless to other forms of life. The gene coding for Bt toxin i.e., CRY gene has been inserted into the cotton plant with the help of DNA of bacteria, causing cotton to produce this natural insecticide in its tissues. The bacteria that is used as a vector is Agrobacterium tumefacien.

Prokaryotic cell is usually small (0.1-5.1μm) in size whereas eukaryotic cell size is comparatively larger (5-100μm). Prokaryotic cells multiply very rapidly by asecial means like binary fission, sporulation etc.

Line in NCERT: "They are generally smaller and multiply more rapidly than the eukaryotic cells."

Genotypes of different individuals in the given pedigree chart can be illustrated as:

• The nucleus contains the nucleolus which is not a membrane-bound organelle.
• The mitochondria, the endoplasmic reticulum, and lysosomes are present in the cytosol.
• They are membrane-bound organelles of the cell.

The first cell was observed and named by Robert Hooke in 1665. He described that it looked like cellula, small rooms which are inhabited by monks hence derived the name 'cell'. The cell he actually saw was the dead cell walls of the plant (cork) under a microscope. Hooke described the characteristics of a cell he observed in his book 'Micrographia'.

The cellular factory responsible for synthesising proteins is the ribosome. The ribosome consists of structural RNAs and about 80 different proteins. In its inactive state, it exists as 2 subunits, as a large subunit and a small subunit. When the small subunit encounters an mRNA, the process of translation of the mRNA to protein begins.

Enzymes are highly specific in their action on substrates. Each enzyme has a specific substrate or group of substrates with which it interacts and catalyses a particular chemical reaction. This specificity is due to the precise three-dimensional structure of the enzyme's active site, which complements the shape and chemical properties of the substrate.

Insulin is a hormone released by pancreas that control sugar level in blood. Diabetic patients take insulin in form of injection to control blood sugar level.

The cell cycle starts from interphase. Interphase is the phase in the cell cycle that prepares a cell nucleus for division. It has three stages — G₁, S and G₂ G₁, Phase is the longest stage of interphase, also first growth phase or post-mitotic gap phase. Both and its nucleus grow in size. There is synthesis proteins, nucleotides, amino acids for histones an rich compounds. In S-Phase chromosomes along with their DNAs replicate. DNA content doubles during this phase. In G₂-Phase there is increased synthesis of RNA and proteins. Cell organelles or their precursorsmultiply. Cell grows in Size.

Line in NCERT: "G₁ phase corresponds to the interval between mitosis and initiation of DNA replication. During G₁ phase the cell is metabolically active and continuously grows but does not replicate its DNA. S or synthesis phase marks the period during which DNA synthesis or replication takes place. During this time the amount of DNA per cell doubles. If the initial amount of DNA is denoted as 2C then it increases to 4C. However, there is no increase in the chromosome number; if the cell had diploid or 2n number of chromosomes at G₁, even after S phase the number of chromosomes remains the same, i.e., 2n."

• F1 pink flowered plants are heterozygous. When selfing is done the genotype and phenotype develops as 1:2:1 as 40 red, 80 pink and 40 white flowering plants.  It is called Incomplete dominance.
• The appearance of a new phenotype in the progeny but not either of the parents is called Incomplete dominance.

Fig: Cross showing incomplete dominance in Mirabilis jalapa

Hence, the correct option is C.
NCERT Reference: Topic-  Incomplete Dominance” of chapter "Principles of Inheritance and Variation" of NCERT.

Line in NCERT: "When the F, was self-pollinated the F2 resulted in the following ratio 1 (RR) Red: 2 (Rr) Pink: 1 (rr) White."

Nucleic acids carry hereditary information and are passed on from parental generation to progeny.

• Co-dominance is the phenomenon that deviates from Mendel’s law of inheritance.
• Both the alleles appear in offspring instead of one as in Mendel’s experiment.
• ABO blood grouping in human beings is an example of co-dominance in which both I^A and I^B appear simultaneously to form AB blood type.

Hence, the correct option is D.

Topic in NCERT: Co-dominance

Line in NCERT: "A good example is different types of red blood cells that determine ABO blood grouping in human beings."

• In humans, the males are heterogametic as they have XY sex chromosomes, so they make 50% sperms with X chromosome and 50% sperms with Y chromosome. Females are homogametic. All gametes made by them have X chromosomes. So, humans show XX-XY type of sex determination.

Hence, the correct option is A.
NCERT Reference: Topic SEX DETERMINATION of chapter "Principles of Inheritance and Variation" OF NCERT.

Line in NCERT: "It has already been mentioned that the sex determining mechanism in case of humans is XY type."

The Hardy-Weinberg principle states that allelic and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences. There are five factors which are known to affect the equilibrium. These are gene flow, genetic drift, mutation, genetic recombination and natural selection. In population genetics, gene flow (also known as gene migration) is the transfer of alleles or genes from one population to another. Migration into or out of a population may be responsible for a marked change in allele frequencies (the proportion of members carrying a particular variant of a gene). Genetic drift (also known as allelic drift) is the change in the frequency of a gene variant (allele) in a population due to chance events. Genetic recombination is the production of offspring with combinations of traits that differ from those found in either parent. Mutation causes variations in the species, which influences the gene pool. Natural selection favours certain variations over others, resulting in an increase in allelic frequency of the favourable variations in the gene pool. Reproduction is a natural process in all organisms, which as such, does not affect Hardy-Weinberg equilibrium; it would be the genetic recombinations that arise from sexual reproduction, that affect it.

In ecological succession, the individual transitional communities to inhibit an area are commonly called seral stage or seral communities that leads to climax communities.

The chromatin material which takes darker stain in interphase is called Heterochromatin. Heterochromatin is a tightly packed form of DNA, which comes in different varieties. These varieties lie on a continuum between the two extremes of constitutive and facultative heterochromatin.

The cell wall of fungi is made of chitin,complex sugar molecules. The cell wall of plants are made up of cellulose.

- 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.

The given molecule is adenylic acid. It is a nucleotide found in RNA. It is an ester of phosphoric acid with the nucleoside adenosine. It consists of a phosphate group, a pentose sugar ribose, and the nucleobase adenine.

A single species may occupy more than one trophic level. Sparrow being omnivorous can be a primary consumer if it feeds on seeds, fruits and peas or a secondary consumer if it feeds on insects and worms.

In a self-cross of heterozygous violet-flowered pea plants (Vv), the Punnett square for the flower color gene would yield the following genotypic and phenotypic ratios:

Genotypic Ratio: 25% VV (violet), 50% Vv (violet, but carrying the white allele), 25% vv (white)
Phenotypic Ratio: 75% violet and 25% white

This means that 75% of the offspring would have violet flowers, and 25% would have white flowers. Therefore, the correct answer is option D, "75% violet and 25% white.

The species facing completion might evolve mechanisms that that promote co-existence rather than exclusion. This mechanism is called resource partitioning.

There are many evidences that favor the organic evolution of life. According to this concept life originate from pre-existing organisms by evolution in cousr of time. Homologous and vestigial organs hit the uses of different organs in different organism for different purpose.

The tropical Amazonian rain forest situated in South America has maximum biodiversity on Earth. Situated in the tropical region, it is home for 378 of reptiles, 427 of amphibians and mammals, 1,300 birds, 3,000 of fishes, 40,000 plants and 1,25,000 invertebrates species.

The mRNA produced by transcription of DNA consists of exons and introns. The removal of introns and joining of exons to obtain mature mRNA is called splicing. It is followed by capping and tailing.

Bt toxin is coded by a gene named Cry. There are a number of them, the protein encoded by these cryIAc and cryIIAb control the cotton bollworms.