CBSE Class 12 Biology set 1 Question Paper Pdf - Check Solutions with Answer Key Pdf

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CBSE Class 12 2024 Biology Set 1 Question Paper (Paper Code: 57/5/1) is available for download. The exam was successfully conducted by CBSE on March 19 in the morning session from 10:30 AM to 1:30 PM. As per the student’s initial reactions, the CBSE Class 12 2024 Biology Set 1 Question Paper was reported as Moderate. The Ecology section was reported as Easy to Moderate, the Genetics and Evolution section as Challenging, and the Human Physiology section as Moderate.

Download CBSE Class 12 2024 Question Paper Pdf with Solutions

CBSE Class 12 2024 Biology Set 1 57/5/1 Question Paper with Answer Key PDF

Candidates can download the CBSE Class 12 Biology Question Paper with Solution and Answer Key PDFs for Set 1 Question Paper (Code: 57/5/1) using the link below.

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CBSE Class 12 2024 Biology Questions with Solutions

SECTION - A

Question 1:

A single gene that controls the expression of more than one trait is said to show:

(A) Multiple allelism
(B) Polygenic inheritance
(C) Incomplete dominance
(D) Pleiotropism

Correct Answer: (D) Pleiotropism

View Solution

Pleiotropism refers to the phenomenon where a single gene influences multiple phenotypic traits. For example, the gene responsible for sickle-cell anaemia affects both the shape of red blood cells and oxygen transport efficiency.

Question 2:

A person with trisomy of 21st chromosome shows:

(i) Furrowed tongue
(ii) Characteristic palm crease
(iii) Rudimentary ovaries
(iv) Gynaecomastia

Select the correct option from the choices given below:

(A) (ii) and (iv)
(B) (i), (ii) and (iv)
(C) (ii) and (iii)
(D) (i) and (ii)

Correct Answer: (D) (i) and (ii)

View Solution

Solution: Trisomy of the 21st chromosome, also known as Down syndrome, is characterized by:
- Furrowed tongue (i).
- Characteristic palm crease (ii).

Question 3:

Observe the schematic representation of assisted reproductive technology given below:

Identify the most appropriate technique depicted in the above diagram:

(A) IUT
(B) IUI
(C) ICSI
(D) ZIFT

Correct Answer: (C) ICSI

View Solution

Solution: The diagram shows Intracytoplasmic Sperm Injection (ICSI), where a single sperm is directly injected into the cytoplasm of an egg using a fine needle. This technique is used in cases of severe male infertility.

Question 4:

Interferons are proteins secreted by:

(A) RBC
(B) WBC
(C) Bacteria-infected cell
(D) Virus-infected cell

Correct Answer: (D) Virus-infected cell

View Solution

Solution: Interferons are proteins secreted by virus-infected cells as part of the immune response. They help inhibit viral replication and activate immune cells to fight infection.

Question 5:

During biological treatment of sewage, the masses of bacteria held together by fungal filaments to form mesh-like structures are called:

(A) Primary sludge
(B) Flocs
(C) Activated sludge
(D) Anaerobic sludge

Correct Answer: (B) Flocs

View Solution

Solution: Flocs are masses of bacteria and fungi that aggregate during the secondary treatment of sewage. These flocs help in the breakdown of organic matter in wastewater, significantly reducing BOD (Biochemical Oxygen Demand).

Question 6:

Which one of the following statements is correct in the context of observing DNA separation by agarose gel electrophoresis?

(A) DNA can be seen in visible light.
(B) DNA can be seen without staining in visible light.
(C) Ethidium bromide stained DNA can be seen in visible light.
(D) Ethidium bromide stained DNA can be seen under UV light.

Correct Answer: (D) Ethidium bromide stained DNA can be seen under UV light

View Solution

Solution: Ethidium bromide is a fluorescent dye that binds to DNA. When exposed to UV light, it fluoresces, making the DNA bands visible after separation by agarose gel electrophoresis.

Question 7:

A phenomenon where a male insect mistakenly identifies the patterns of an orchid flower as the female insect partner, and tries to copulate and thereby pollinates the flower, is said to be:

(A) Pseudocopulation
(B) Pseudopollination
(C) Pseudoparthenocarpy
(D) Pseudofertilisation

Correct Answer: (A) Pseudocopulation

View Solution

Solution: Pseudocopulation refers to the process where a male insect is attracted to the flower’s patterns, mistaking them for a female insect. The male attempts to copulate, inadvertently transferring pollen and pollinating the flower.

Question 8:

Identify the correct labellings in the figure of a fertilized embryo sac of an angiosperm given below:

(A) A – zygote, B – degenerating synergids, C – degenerating antipodals, D – PEN
(B) A – degenerating synergids, B – zygote, C – PEN, D – degenerating antipodals
(C) A – degenerating antipodals, B – PEN, C – degenerating synergids, D – zygote
(D) A – degenerating synergids, B – zygote, C – degenerating antipodals, D – PEN

Correct Answer: (B) A – degenerating synergids, B – zygote, C – PEN, D – degenerating antipodals

View Solution

Solution:
- A: Degenerating synergids – Synergids disintegrate after fertilization.
- B: Zygote – Formed by the fusion of the male gamete and the egg cell.
- C: Primary Endosperm Nucleus (PEN) – Formed by the fusion of the second male gamete with two polar nuclei.
- D: Degenerating antipodals – Antipodals disintegrate after fertilization.

Question 9:

Study the pedigree chart of a family showing the inheritance pattern of a certain disorder. Select the option that correctly identifies the nature of the trait depicted in the pedigree chart:

(A) Dominant X-linked
(B) Recessive X-linked
(C) Autosomal dominant
(D) Autosomal recessive

Correct Answer: (D) Autosomal recessive

View Solution

Solution: The pedigree shows characteristics of an autosomal recessive inheritance:
- The disorder skips generations, indicating it is recessive.
- Both males and females are equally affected, suggesting it is autosomal.
- Affected individuals inherit two recessive alleles (one from each parent).

Question 10:

Match the following genes of the lac operon listed in column ‘A’ with their respective products listed in column ‘B’:

Column A (Gene)	Column B (Product)
a. ‘i’ gene	(iii) Repressor
b. ‘z’ gene	(i) β-galactosidase
c. ‘a’ gene	(iv) Transacetylase
d. ‘y’ gene	(ii) Lac permease

Select the correct option:

(A) a–(i), b–(iii), c–(ii), d–(iv)
(B) a–(iii), b–(i), c–(iv), d–(ii)
(C) a–(iii), b–(i), c–(ii), d–(iv)
(D) a–(iii), b–(ii), c–(iv), d–(i)

Correct Answer: (B) a–(iii), b–(i), c–(iv), d–(ii)

View Solution

‘i’ gene: Codes for the repressor protein, which inhibits transcription of the operon in the absence of lactose.
‘z’ gene: Codes for β-galactosidase, an enzyme that hydrolyses lactose into glucose and galactose.
‘a’ gene: Codes for transacetylase, which transfers an acetyl group to β-galactosides.
‘y’ gene: Codes for lac permease, which facilitates lactose transport into the cell.

Question 11:

If both the parents are carriers for thalassaemia, the chances of an afflicted child to be born to them is:

(A) 25%
(B) 50%
(C) 75%
(D) 100%

Correct Answer: (A) 25%

View Solution

Thalassaemia is an autosomal recessive disorder. If both parents are carriers (T t):

Punnett Square:

	T	t
T	TT	Tt
t	Tt	tt

The possible genotypes are:

TT: Normal (25%)
Tt: Carrier (50%)
tt: Afflicted (25%)

Question 12:

If the sequence of nitrogen bases of the coding strand in a transcription unit is 5′–ATGAATG–3′, the sequence of bases in its RNA transcript would be:

(A) 5′–AUGAAUG–3′
(B) 5′–UACUUAC–3′
(C) 5′–CAUUCAU–3′
(D) 5′–GUAAGUA–3′

Correct Answer: (A) 5′–AUGAAUG–3′

View Solution

The RNA transcript is complementary to the template strand of DNA and identical to the coding strand (except uracil replaces thymine).

Coding strand: 5′–ATGAATG–3′
RNA transcript: 5′–AUGAAUG–3′

Question 13:

Assertion (A): AIDS is a syndrome caused by HIV.
Reason (R): HIV is a virus that damages the immune system with DNA as its genetic material.

(A) Both (A) and (R) are true and (R) is the correct explanation of (A).
(B) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(C) (A) is true, but (R) is false.
(D) (A) is false, but (R) is true.

Correct Answer: (C) (A) is true, but (R) is false.

View Solution

HIV is a virus that causes AIDS by destroying helper T-cells, leading to immune system failure. However, HIV is an RNA virus, not a DNA virus.

Question 14:

Assertion (A): In molecular diagnosis, single-stranded DNA or RNA tagged with a radioactive molecule is called a probe.
Reason (R): A probe always searches and hybridises with its complementary DNA in a clone of cells.

(A) Both (A) and (R) are true and (R) is the correct explanation of (A).
(B) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(C) (A) is true, but (R) is false.
(D) (A) is false, but (R) is true.

Correct Answer: (A) Both (A) and (R) are true and (R) is the correct explanation of (A).

View Solution

Solution: Probes are single-stranded DNA or RNA molecules tagged with a radioactive or fluorescent label. They hybridise with complementary sequences in target DNA during molecular diagnosis, making them highly specific for detecting genetic abnormalities.

Question 15:

Assertion (A): In birds, the sex of the offspring is determined by males.
Reason (R): Males are homogametic while females are heterogametic.

(A) Both (A) and (R) are true and (R) is the correct explanation of (A).
(B) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(C) (A) is true, but (R) is false.
(D) (A) is false, but (R) is true.

Correct Answer: (D) (A) is false, but (R) is true.

View Solution

Solution: In birds, females are the heterogametic sex (ZW), and males are homogametic (ZZ). Therefore, the sex of the offspring is determined by the female, not the male.

Question 16:

Assertion (A): Communities that comprise more species tend to be more stable.
Reason (R): A higher number of species results in less year-to-year variation in total biomass.

(A) Both (A) and (R) are true and (R) is the correct explanation of (A).
(B) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(C) (A) is true, but (R) is false.
(D) (A) is false, but (R) is true.

Correct Answer: (A) Both (A) and (R) are true and (R) is the correct explanation of (A).

View Solution

Solution: Communities with higher species diversity are more resilient to environmental changes, ensuring greater stability in total biomass over time.

SECTION – B

Question 17:

(a) “Farmers prefer apomictic seeds to hybrid seeds.” Justify giving two reasons:

View Solution

Correct Answer:
• Apomictic seeds do not require repeated hybridization every year, saving costs.
• They maintain genetic uniformity, ensuring stable yields.

Explanation: Apomixis is an asexual reproduction process that produces seeds without fertilization, retaining the parent’s genetic traits.

(b) Mention one advantage and one disadvantage of amniocentesis:

Correct Answer:
• Advantage: Helps detect genetic disorders like Down syndrome and other chromosomal abnormalities in the fetus.
• Disadvantage: It carries a small risk of miscarriage or harm to the fetus.

View Solution

Explanation: Amniocentesis is a prenatal diagnostic procedure that analyzes amniotic fluid for genetic testing.

Question 18:

5′–G↓AATTC–3′
3′–CTTAA↑G–5′

(a) Name the restriction enzyme that recognizes the given specific sequence of bases. What are such sequences of bases referred to as?

View Solution

Correct Answer:
• Restriction enzyme: EcoRI.
• The sequences are referred to as palindromic sequences.

Explanation: Palindromic sequences are unique DNA sequences that read the same in both directions, enabling precise enzymatic cuts.

(b) What are the arrows in the given figure indicating? Write the result obtained thereafter:

Correct Answer:
• The arrows indicate the site where the restriction enzyme EcoRI cuts the DNA.
• Result: The DNA is cleaved into fragments with sticky ends, enabling the insertion of foreign DNA during genetic engineering.

View Solution

Explanation: Sticky ends generated by EcoRI facilitate the joining of DNA fragments for creating recombinant DNA molecules.

Question 19:

Observe the population growth curve and answer the questions given below:

(a) State the conditions under which growth curve ‘A’ and growth curve ‘B’ plotted in the graph are possible:

View Solution

Correct Answer:
• Growth curve ‘A’ (Exponential growth): Possible when resources are unlimited and there are no environmental constraints.
• Growth curve ‘B’ (Logistic growth): Possible when resources are limited, and environmental resistance impacts population growth.

Explanation: Exponential growth occurs under ideal conditions, while logistic growth reflects real-world scenarios with environmental limitations and carrying capacity.

(b) Mention what does ‘K’ in the graph represent:

Correct Answer:
‘K’ represents the carrying capacity of the environment, which is the maximum population size that the environment can sustain with the available resources.

View Solution

Explanation: Carrying capacity is determined by factors like food availability, habitat space, and environmental conditions.

Question 20:

Explain how are plants benefitted by their association with “Glomus species”:

View Solution

Correct Answer:
• Glomus species form mycorrhizal associations with plant roots.
• These fungi enhance the absorption of nutrients, particularly phosphorus, and improve water uptake.
• They also provide resistance to root pathogens and increase the plant’s tolerance to drought and salinity.

Explanation: Mycorrhizal fungi establish a symbiotic relationship with plants, offering nutrient exchange and protection in return for carbohydrates.

Question 21:

If the base adenine constitutes 31% of an isolated DNA fragment, then write what will be the expected percentage of the base cytosine in it. Explain how did you arrive at the answer given:

View Solution

Correct Answer:
• Adenine (A) pairs with Thymine (T), so A + T = 31% + 31% = 62%.
• Cytosine (C) pairs with Guanine (G), and since C + G = 100% − (A + T) = 38%, the percentage of cytosine is C = 19%.

Explanation: DNA follows Chargaff's rule, where A pairs with T and C pairs with G in a 1:1 ratio, ensuring the total percentage sums up to 100%.

SECTION – C

Question 22:

Identify a, b, c, d, e, and f in the table given below:

Sl. No.	Organism	Bioactive Molecule	Use
1	Monascus purpureus	Statins	Lowers cholesterol
2	Streptomyces	Streptomycin	Antibiotic
3	Trichoderma polysporum	Cyclosporin A	Immunosuppressant

View Solution

Quick Tip: Bioactive molecules derived from microorganisms play a crucial role in medicine, such as antibiotics, cholesterol-lowering agents, and immunosuppressants.

Question 23:

(a) Tropical regions harbour more species than the temperate regions. How have biologists tried to explain this in their own ways? Explain:

View Solution

Correct Answer: Biologists explain the higher species richness in tropical regions due to:

Favourable climate: The warm and stable climate supports year-round plant growth and species survival.
Longer evolutionary time: Tropical regions remained undisturbed during glaciation periods, providing longer periods for species diversification.
Higher productivity: Abundant sunlight and rainfall result in high primary productivity, supporting diverse food webs.

Quick Tip: The stability and resource availability in tropical regions make them biodiversity hotspots with numerous endemic species.

(b)(i) What does an ecological pyramid represent?

Correct Answer: An ecological pyramid represents the trophic structure and functional levels in an ecosystem, such as energy, biomass, or the number of organisms at each trophic level.

(ii) The ecological pyramids may have an ‘upright’ or an ‘inverted’ shape. Justify with the help of suitable examples:

Correct Answer:

Upright pyramid: Found in most ecosystems, such as grasslands, where producers have the highest energy or biomass, followed by primary and secondary consumers.
Inverted pyramid: Found in aquatic ecosystems, where phytoplankton (producers) have a smaller biomass than zooplankton and higher trophic levels.

View Solution

Quick Tip: The shape of the pyramid depends on the ecosystem type and the parameter being measured (energy, biomass, or numbers).

Question 24:

(a) What are transgenic animals?

View Solution

Correct Answer: Transgenic animals are organisms that have had foreign genes inserted into their genome using recombinant DNA technology.

Quick Tip: Transgenic animals are valuable in research, agriculture, and medicine, helping to study diseases, improve productivity, and develop therapeutic proteins.

(b) Name the transgenic animal having the largest number amongst all the existing transgenic animals:

Correct Answer: Mice.

View Solution

Quick Tip: Transgenic mice are extensively used in research to study human diseases, drug development, and gene functions due to their genetic similarity to humans.

(c) State any 3 reasons for which these types of animals are being produced:

Correct Answer:

Studying the effects of genes and their role in development and disease.
Producing biologically important proteins like insulin and vaccines.
Testing the safety of drugs and chemicals before human use.

View Solution

Quick Tip: Transgenic animals are valuable tools in medical research, biotechnology, and drug development.

Question 25:

If the cells in the leaves of a maize plant contain 10 chromosomes each, write the number of chromosomes in its endosperm and zygote. Name and explain the process by which an endosperm and a zygote are formed in maize:

View Solution

Correct Answer:

Chromosomes in zygote: 10 (diploid).
Chromosomes in endosperm: 15 (triploid).

Process:

Zygote formation: One male gamete fuses with the egg cell (syngamy) to form the zygote.
Endosperm formation: The second male gamete fuses with two polar nuclei in the central cell (triple fusion), forming the triploid endosperm.

Quick Tip: Double fertilisation is a characteristic feature of angiosperms, resulting in the formation of both zygote and endosperm.

Question 26:

(a) Why does DNA replication occur within a replication fork and not in its entire length simultaneously?

View Solution

Correct Answer:

DNA replication occurs within a replication fork because:
The fork structure allows helicase to unwind the DNA strand gradually.
Polymerases can synthesise the new strand step by step in the 5′ to 3′ direction.

Quick Tip: The replication fork ensures accurate DNA synthesis by coordinating unwinding, priming, and elongation processes step by step.

(b) “DNA replication is continuous and discontinuous on the two strands within the replication fork.” Explain with the help of a schematic representation:

View Solution

Correct Answer:

Leading strand: Synthesised continuously in the 5′ to 3′ direction.
Lagging strand: Synthesised discontinuously in short fragments (Okazaki fragments) and later joined by DNA ligase.

Schematic Representation:

Quick Tip: The antiparallel nature of DNA strands necessitates continuous and discontinuous replication in the fork structure.

Question 27:

Explain the processing of heterogeneous nuclear RNA (hnRNA) into a fully functional mRNA in eukaryotes. Where does this processing occur in the cell?

View Solution

Correct Answer:

Steps of Processing:

Capping: Addition of a 5′ methyl guanosine cap.
Splicing: Removal of introns and joining of exons.
Polyadenylation: Addition of a poly-A tail at the 3′ end.

Location: The processing occurs in the nucleus of eukaryotic cells.

Quick Tip: RNA processing ensures the stability and translatability of mRNA before it moves to the cytoplasm for translation.

Question 28:

The world is facing accelerated rates of species extinction largely due to human activities. Explain any three human activities responsible for accelerated rates of species extinction:

View Solution

Correct Answer:

Habitat destruction: Clearing forests for agriculture, urbanisation, and infrastructure development destroys natural habitats, leading to the loss of biodiversity.
Overexploitation: Overhunting, overfishing, and overharvesting of natural resources deplete populations of species beyond recovery.
Pollution: Release of pollutants into the air, water, and soil disrupts ecosystems, making them uninhabitable for many species.

Quick Tip: Conservation efforts and sustainable practices are essential to mitigate the impact of human activities on biodiversity.

Question 29:

In a human female, the reproductive phase starts on the onset of puberty and ceases around middle age of the female. Study the graph given below regarding the menstrual cycle and answer the questions that follow:

reproductive phase starts on the onset of puberty

(a) Name the hormones and their source organ, which are responsible for the menstrual cycle at puberty:

View Solution

Correct Answer:
• Hormones: Follicle Stimulating Hormone (FSH) and Luteinising Hormone (LH).
• Source organ: Anterior pituitary gland.

Explanation: FSH and LH are vital pituitary hormones that regulate follicle maturation and ovulation during the menstrual cycle.

(b) For successful pregnancy, at what phase of the menstrual cycle can an early embryo (up to 3 blastomeres) be implanted in the uterus (IUT) of a human female who has opted for Assisted Reproductive Technology (ART)? Support your answer with a reason:

View Solution

Correct Answer:
• Implantation should occur during the luteal phase (days 15–28) of the menstrual cycle.
• Reason: The uterine lining (endometrium) is thick and vascularised during the luteal phase, providing optimal conditions for embryo implantation and development.

Explanation: The luteal phase provides a supportive environment for implantation due to high progesterone levels.

(c) Name the hormone and its source organ responsible for the events occurring during the proliferative phase of the menstrual cycle. Explain the event:

Correct Answer:
• Hormone: Oestrogen.
• Source organ: Ovaries (developing follicles).
• Event: Oestrogen stimulates the proliferation of the endometrial lining of the uterus, preparing it for possible implantation of a fertilized egg.

View Solution

Explanation: Oestrogen plays a crucial role in regenerating the uterine lining during the proliferative phase of the menstrual cycle.

(c) In a normal human female, why does menstruation only occur if the released ovum is not fertilised? Explain:

View Solution

Correct Answer:
• If the ovum is not fertilised, the corpus luteum degenerates, leading to a decline in progesterone levels.
• Low progesterone levels cause the breakdown of the endometrial lining, resulting in menstruation.

Explanation: Menstruation occurs due to the absence of fertilisation, leading to hormonal changes and shedding of the uterine lining.

Question 30:

Read the following passage and answer the questions that follow:
“Mosquitoes are drastically affecting the human health in almost all the developing tropical countries. Different species of mosquitoes cause very fatal diseases so much so that many humans lose their life and if they survive, are unable to put in productive hours to sustain their life. With the result, the health index of the country goes down.”

(a) Name the form in which Plasmodium gains entry into (i) human body (ii) the female Anopheles body:

View Solution

Correct Answer:
• (i) Plasmodium enters the human body as sporozoites through the bite of an infected female Anopheles mosquito.
• (ii) It enters the female Anopheles body as gametocytes from the blood of an infected human host.

Explanation: Sporozoites are the infective stage of Plasmodium, while gametocytes are responsible for transmission back to the mosquito.

(b) Why do the symptoms of malaria not appear in a person immediately after being bitten by an infected female Anopheles? Give one reason. Explain when and how the symptoms of the disease would appear:

View Solution

Correct Answer:
• The symptoms of malaria do not appear immediately because the parasite undergoes an incubation period within the human liver and red blood cells before multiplying.
• Symptoms appear after 10–14 days, once the merozoites are released into the bloodstream, causing fever, chills, and other symptoms.

Explanation: The incubation period allows the parasite to multiply in the liver and red blood cells, causing a delay in the onset of symptoms.

(b) Explain the events which occur within a female Anopheles mosquito after it has sucked blood from a malaria patient:

View Solution

Correct Answer:
• The gametocytes of Plasmodium ingested with human blood develop into gametes in the mosquito’s gut.
• Fertilisation occurs, forming a zygote which develops into an ookinete and then into an oocyst.
• The oocyst releases sporozoites which migrate to the mosquito’s salivary glands, ready to infect another human.

Explanation: The life cycle of Plasmodium involves complex stages within the mosquito’s gut, leading to the formation of infectious sporozoites.

(c) Name a species of mosquito other than female Anopheles and the disease, for which it carries the pathogen:

View Solution

Correct Answer:
• Species: Aedes aegypti.
• Disease: Dengue fever.

Explanation: Aedes aegypti is a vector for several diseases, including dengue fever, chikungunya, and Zika virus.

SECTION – E

Question 31:

(a) (i) Draw a schematic diagram of the cloning vector pBR 322 and label (1) Bam HI site (2) gene for ampicillin resistance (3) ‘ori’ (4) ‘rop’ gene:

Correct Answer:

A schematic diagram of pBR 322 must include:

The origin of replication (‘ori’).
Ampicillin resistance gene.
Restriction site for Bam HI.
‘rop’ gene regulating plasmid copy number.

cloning vector pBR 322

View Solution

Explanation: The pBR 322 vector is a widely used cloning vector in genetic engineering due to its multiple cloning sites and selectable markers.

(ii) State the role of ‘rop’ gene:

View Solution

Correct Answer: The ‘rop’ gene regulates the plasmid copy number by controlling the replication of the plasmid within the host cell.

Explanation: The ‘rop’ gene ensures stable replication of plasmids, maintaining a controlled number of plasmids per host cell.

(iii) A cloning vector does not have a selectable marker. How will it affect the process of cloning?

Correct Answer: Without a selectable marker, it becomes difficult to identify and isolate transformed cells, as there is no way to distinguish between transformed and non-transformed cells.

View Solution

Explanation: Selectable markers, such as antibiotic resistance genes, help in identifying and isolating transformed cells in genetic engineering.

(iv) Why is insertional inactivation preferred over the use of selectable markers in cloning vectors?

Correct Answer: Insertional inactivation ensures that the cloned DNA disrupts the marker gene, providing a visual or functional confirmation of successful transformation (e.g., loss of antibiotic resistance or colour change).

View Solution

Explanation: Insertional inactivation reduces dependency on antibiotics and provides a safer alternative for identifying recombinant colonies.

(b) (i) Name the nematode (scientific name) that infects the roots of tobacco plants and reduces its yield:

View Solution

Correct Answer: Meloidogyne incognita.

Explanation: Root-knot nematodes like Meloidogyne incognita cause significant agricultural losses by affecting crop yields.

(ii) Name the vector that is used to introduce nematode-specific genes into the host plant (tobacco):

Correct Answer: Agrobacterium tumefaciens.

View Solution

Explanation: Agrobacterium tumefaciens is a natural genetic engineer widely used for transferring foreign genes into plants.

(iii) How does an anti-sense RNA function?

View Solution

Correct Answer: Anti-sense RNA binds to the complementary mRNA sequence, blocking its translation and silencing the expression of the target gene.

Explanation: Anti-sense RNA technology is an effective tool in gene silencing, used for studying gene functions and controlling diseases.

Question 32:

(a) (i) Draw a diagram of a human sperm. Label any four parts and write their functions:

View Solution

Correct Answer:

Head: Contains the nucleus with genetic material and is covered by the acrosome, which has enzymes to penetrate the egg.
Midpiece: Contains mitochondria to provide energy for motility.
Tail: Propels the sperm towards the egg.
Acrosome: Helps in breaking the egg membrane during fertilisation.

human sperm.

Explanation: A diagram of a human sperm cell should include the head, midpiece, tail, and acrosome, along with their respective functions.

(ii) In a human female, the probability of an ovum to get fertilised by more than one sperm is impossible. Give reason:

View Solution

Correct Answer: After the entry of one sperm into the egg, a fertilisation membrane develops around the egg, preventing the entry of additional sperms. This ensures monospermy.

Explanation: The fertilisation membrane acts as a protective barrier, ensuring only one sperm fertilises the ovum, maintaining genetic stability.

(b) (i) With the help of a labelled diagram only, show the different stages of embryo development in a dicot plant:

View Solution

Correct Answer:

Zygote.
Globular stage.
Heart-shaped stage.
Mature embryo.

different stages of embryo development in a dicot plant.

Explanation: The development of the embryo after syngamy involves multiple stages, culminating in the mature dicot embryo.

(ii) Endosperm development precedes embryo development. Justify:

View Solution

Correct Answer: Endosperm development provides the necessary nutrients for the developing embryo, ensuring its proper growth and maturation.

Explanation: The endosperm acts as a nutritional reserve for the embryo, facilitating its development and viability.

Question 33:

(a) Natural selection operates in different ways in nature.

Phenotype distribution of White Winged and Dark Winged Moths.

(i) Identify the type of natural selection depicted in the graph above:

View Solution

Correct Answer: The graph depicts directional selection, where one phenotype is favoured over another, shifting the population mean.

Explanation: Directional selection leads to a gradual shift in the population’s traits due to environmental pressures favouring one extreme.

(ii) In England after industrialisation, the population of dark-winged moths were more favoured than white-winged moths. Explain:

View Solution

Correct Answer: During industrialisation, trees were covered in soot, making dark-winged moths less visible to predators compared to white-winged moths. This gave dark-winged moths a survival advantage, increasing their population.

Explanation: Camouflage is an important evolutionary trait that enhances survival in changing environments.

(iii) Anthropogenic action can enhance the rate of evolution. Explain with the help of an example:

View Solution

Correct Answer: Anthropogenic actions like pesticide use have led to the evolution of pesticide-resistant insect populations. For example, mosquitoes have developed resistance to DDT due to its widespread use.

Explanation: Human activities like pollution and overuse of chemicals create selection pressures, driving rapid evolutionary changes.

(b)

(i) Why did Hershey and Chase use ³⁵S and ³²P in their experiment? Explain:

View Solution

Correct Answer:

³⁵S: Used to label proteins as sulphur is present in proteins but not in DNA.
³²P: Used to label DNA as phosphorus is present in DNA but not in proteins.

This helped to determine whether DNA or proteins are the genetic material.

Explanation: Radioactive isotopes are valuable tools for tracing molecules in biological experiments.

(ii) State the importance of (1) blending and (2) centrifugation in their experiment:

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Correct Answer:

Blending: Separated the phage protein coats from the bacterial cells.
Centrifugation: Allowed the heavier bacterial cells to settle, separating them from the lighter phage protein coats.

Explanation: Blending and centrifugation techniques are essential for separating biological components during experiments.

(iii) Write the conclusion they arrived at the end of their experiment:

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Correct Answer: Hershey and Chase concluded that DNA is the genetic material as only ³²P-labelled DNA was found inside the bacterial cells, while ³⁵S-labelled protein remained outside.

Explanation: Their experiment demonstrated that DNA, not protein, is responsible for heredity, revolutionizing our understanding of molecular biology.