CUET UG 2025 Biology Previous Year Solved Paper

The correct answer is Option 2. Filiform apparatus
Explanation:
The filiform apparatus—finger-like wall ingrowths of the synergids at the
micropylar end—serves as the guiding structure that directs the pollen
tube into the embryo sac. The micropyle is only the opening, and antipodals
are at the opposite (chalazal) end.

The correct answer is Option 3. Four peptide chain
Explanation:
A typical antibody (immunoglobulin) consists of four polypeptide chains-
stwo identical heavy chains and two identical light chains-linked by disulfide
bonds to form a Y-shaped molecule.

The correct answer is Option 4. GPP − R = NPP
Explanation:
By definition, Net Primary Productivity is what remains of Gross Primary
Productivity after plants use some energy for respiration (R), so NPP = GPP
− R.

The correct answer is Option 3. (A) – (II), (B) – (I), (C) – (IV), (D) – (III)
Explanation:

• Malaria → (II) Cycles of fever: malarial paroxysms occur periodically
with chills and fever.
• Filariasis → (I) Inflammation of lower limb: Wuchereria causes
lymphatic blockage leading to painful swelling/elephantiasis of legs.
• Ringworms → (IV) Scaly lesions on nails: dermatophytic infection
(tinea) produces scaly, ring-like lesions; can involve nails.
• Amoebiasis → (III) Blood clots and excess mucus in stools: Entamoeba
histolytica causes amoebic dysentery with blood and mucus in stools.

The correct answer is Option 2. (A) – (II), (B) – (III), (C) – (IV), (D) – (I)
Explanation:
• Clostridium butylicum → (II) Butyric acid (butyric fermentation).
• Aspergillus niger → (III) Citric acid (major industrial source).
• Acetobacter aceti → (IV) Acetic acid (oxidizes ethanol → vinegar).
• Lactobacillus → (I) Lactic acid (lactic fermentation of sugars).

The correct answer is Option 2. Chalaza.
Explanation:
• The micropyle is the small opening at one end of the ovule.
• The chalaza is the opposite end of the ovule where the integuments
and nucellus meet.
• Hilum is the seed’s attachment scar to the funicle; funicle is the stalk;
nucellus is the internal nutritive tissue—not an “end.”

The correct answer is Option 2. (A) – (IV), (B) – (III), (C) – (II), (D) – (I)

Explanation:
• Amniocentesis → (IV) Testing of sex: Prenatal sampling of amniotic fluid;
fetal karyotyping reveals chromosomal sex and genetic disorders.
• Maternal mortality rate → (III) Death rate: Number of maternal deaths due
to pregnancy/childbirth-related causes per 100,000 live births.
• Vasectomy → (II) Ligation of vas deferens: Male sterilization by
cutting/sealing the vas deferens to prevent sperm in semen.
• Tubectomy → (I) Ligation of fallopian tube: Female sterilization by
blocking/cutting the fallopian tubes to prevent fertilization.

The correct answer is Option 2. Cytokine barriers.
Explanation:
• Interferons are signaling proteins (cytokines) released by virus-infected
cells.
• They alert nearby uninfected cells and induce an antiviral state (synthesis
of antiviral proteins that inhibit viral replication), thus forming a cytokine
barrier.
• They are not physical barriers (skin/mucus), physiological barriers (pH,
temperature), or cellular barriers (phagocytes, NK cells).

The correct answer is Option 3. Transcription.
Explanation:
• Transcription is the synthesis of RNA using one DNA strand as the
template, carried out by RNA polymerase.
• Replication = DNA → DNA; Translation = mRNA → protein; Regulation =
control of gene expression, not copying.

The correct answer is Option 1. (D) → (C) → (A) → (B)
Explanation:
• (D) Zygote → morula: After fertilization, the zygote undergoes rapid
mitotic cleavages to form an 8–16 cell morula.
• (C) Morula → blastocyst: The embryo develops a cavity; cells segregate
into trophoblast (outer layer) and inner cell mass (ICM).
• (A) Implantation: The blastocyst reaches the uterus and embeds in the
endometrium.
• (B) Chorionic villi: Post-implantation, the trophoblast proliferates to form
finger-like chorionic villi, which participate in placenta formation.

The correct answer is Option 2. (C) and (D) only
Explanation:
Intrauterine devices (IUDs) are small, T-shaped or loop-shaped devices
inserted into the uterus to prevent pregnancy. Common examples include
the Lippes Loop and LNG-20 (levonorgestrel-releasing IUD).
• Lippes Loop (A): An early type of inert plastic IUD.
• LNG-20 (B): A hormonal IUD that releases levonorgestrel.
• Saheli (C): ❌ Not an IUD; it is an oral non-steroidal contraceptive pill.
• Implants (D): ❌ Not an IUD; these are subdermal contraceptive
implants placed under the skin.
Thus, Saheli and implants are not intrauterine devices.

The correct answer is Option 4. (A)–(IV), (B)–(I), (C)–(II), (D)–(III)

Explanation:
• Flower colour (A) → White (IV) is recessive (purple/violet is dominant).
• Seed colour (B) → Green (I) is recessive (yellow is dominant).
• Pod colour (C) → Yellow (II) is recessive (green is dominant).
• Pod shape (D) → Constricted (III) is recessive (inflated is dominant).
Hence, the correct matching is A–IV, B–I, C–II, D–III.

The correct answer is Option 2. Methyl guanosine triphosphate
Explanation:
• Transcription in bacteria involves synthesizing RNA from a DNA
template. The key components are:
o DNA-dependent RNA polymerase → catalyzes RNA synthesis.
o Sigma factor → guides RNA polymerase to the promoter region.
o Rho factor → involved in termination of transcription in some
bacterial genes.
• Methyl guanosine triphosphate (m⁷GTP) is part of the 5’ cap structure
in eukaryotic mRNA, which stabilizes the transcript and aids in
translation. It is not involved in bacterial transcription, since bacteria
do not cap their mRNAs.

The correct answer is Option 1. (B) and (D) only
Explanation:
Aneuploidy is a chromosomal abnormality where the number of
chromosomes is not an exact multiple of the haploid number, leading to
extra or missing chromosomes.
• Down's Syndrome (B): Caused by trisomy 21 (an extra copy of
chromosome 21).

• Turner's Syndrome (D): Caused by monosomy X (a female has
only one X chromosome).
• Haemophilia (A): ❌ Caused by a mutation in a gene on the X
chromosome, not due to aneuploidy.
• Thalassemia (C): ❌ Caused by mutations in the globin genes, not
due to chromosomal number changes.
Thus, Down's Syndrome and Turner's Syndrome are the disorders resulting
from aneuploidy.

The correct answer is Option 4. aaBbcC
Explanation:
• Skin colour in humans is an example of polygenic inheritance,
controlled by multiple genes (A, B, C, etc.).
• Each dominant allele contributes to darker pigmentation, while
recessive alleles contribute to lighter pigmentation.
• An intermediate skin colour occurs when there is a mix of dominant
and recessive alleles across these genes.
Analysis of options:
1. AABBCC → All dominant alleles → very dark skin
2. aabbcc → All recessive alleles → very light skin
3. AaBDCC → Mostly dominant alleles → dark skin
4. aaBbcC → Mix of dominant and recessive alleles → intermediate skin
colour
Hence, aaBbcC will express intermediate skin colour.

The correct answer is Option 3. (A)–(II), (B)–(IV), (C)–(I), (D)–(III)

Explanation:
• ‘i’ gene (A) → Repressor (II) (regulator gene codes the lac repressor).
• ‘z’ gene (B) → β-galactosidase (IV) (lacZ).
• ‘y’ gene (C) → Permease (I) (lacY).
• ‘a’ gene (D) → Transacetylase (III) (lacA).
Hence, matching is A–II, B–IV, C–I, D–III.

The correct answer is Option 3. Nicotine is a very effective sedative and pain
killer
Explanation:
• Cannabinoids: Affect the cardiovascular system, increasing heart
rate and blood pressure.
• Heroin: Derived from the latex of Papaver somniferum (opium
poppy).
• Nicotine: ❌ Is not a sedative or pain killer; it is a stimulant that
increases alertness, heart rate, and blood pressure.
• Coca alkaloid (cocaine): Excessive dosage can cause
hallucinations, paranoia, and other psychological effects.
Thus, the statement about nicotine being a sedative and pain killer is
incorrect.

The correct answer is Option 2. (B), (A), (D), (C)
Explanation:
The correct sequence of steps in gel electrophoresis for DNA separation is:
1. Staining with ethidium bromide (B): DNA is first treated with
ethidium bromide, which intercalates between base pairs and allows
visualization.

2. Exposure to UV light (A): The gel is observed under UV light to
visualize DNA fragments.
3. Elution (D): Desired DNA fragments can be extracted (eluted) from
the gel for further use.
4. Moving of DNA fragments towards anode (C): DNA fragments migrate
through the gel matrix towards the positively charged anode due to
their negative phosphate backbone.
Thus, the correct order is staining → UV visualization → elution → migration
towards anode.

The correct answer is Option 1. (A)–(IV), (B)–(III), (C)–(II), (D)–(I)
Explanation:
• Citric acid (A) → Aspergillus niger (IV): industrial production of citric acid
by this fungus.
• Ethanol (B) → Saccharomyces cerevisiae (III): yeast fermentation yields
ethanol.
• Statins (C) → Monascus purpureus (II): produces cholesterol-lowering
statins.
• Cyclosporin A (D) → Trichoderma polysporum (I): immunosuppressant
from this fungus.

The correct answer is Option 3. Enzyme
Explanation:
• EcoRI is a restriction endonuclease enzyme isolated from Escherichia
coli bacteria.
• It is widely used in recombinant DNA (rDNA) technology to cut DNA at
specific recognition sites, producing sticky ends that facilitate the
insertion of genes into vectors.

• It is not a bacterium, plasmid, or purine, but a biochemical tool
(enzyme) essential for molecular cloning.

The correct answer is Option 4. (C), (D), (A), (B)
Explanation:
The correct chronological order of the given geological periods from latest
to oldest is:
• Tertiary (C): Latest, part of the Cenozoic Era (~66–2.6 million years
ago)
• Jurassic (D): Middle, part of the Mesozoic Era (~201–145 million
years ago)
• Triassic (A): Earlier, part of the Mesozoic Era (~252–201 million
years ago)
• Carboniferous (B): Oldest, part of the Paleozoic Era (~359–299
million years ago)
Hence, the correct sequence is: Tertiary → Jurassic → Triassic →
Carboniferous.

The correct answer is Option 1. (A), (B) and (D) only
Explanation:
Polymerase Chain Reaction (PCR) is a technique used to amplify DNA and
involves three main steps in each cycle:
1. Denaturation (D): The double-stranded DNA is heated to separate it
into two single strands.
2. Annealing (B): The temperature is lowered to allow primers to bind
(anneal) to the complementary sequences on the single-stranded
DNA.
3. Extension (A): DNA polymerase synthesizes the new DNA strand by
adding nucleotides complementary to the template.

Propagation (C) is not a standard PCR step; it refers generally to
multiplication of organisms, not the molecular steps of PCR.
Thus, the correct steps are Extension, Annealing, and Denaturation.

The correct answer is Option 1. Insects
Explanation:
• Baculoviruses are a family of viruses that specifically infect insects,
particularly Lepidoptera (moths and butterflies), Hymenoptera
(wasps and bees), and Diptera (flies).
• They are used in biological pest control because of their specificity
and safety to plants, humans, and other animals.
• Baculoviruses do not infect roundworms, molluscs, or birds, making
them ideal for environmentally friendly insect management.

The correct answer is Option 1. Expanding
Explanation:
• An age pyramid shows the distribution of a population across
different age groups.
• If the reproductive age group (15–44 years) is larger than the
prereproductive age group (0–14 years), it indicates that more
individuals are capable of reproducing, leading to a high potential for
population growth.
• Such a population exhibits expanding growth, typically represented
by a broad middle section in the age pyramid, sometimes even wider
at the base if birth rates remain high.
Hence, the growth status of the population would be expanding.

The correct answer is Option 1. (A), (B) and (D) only
Explanation:
• (A) Homology indicates common ancestry: Correct. Homologous
organs have a similar structural origin even if their functions differ.
• (B) Whale and Cheetah share similarities in forelimb bones:
Correct. The forelimbs of vertebrates like whales and cheetahs show
similar bone patterns, indicating homology.
• (C) Vertebrate heart as homologous organs: ❌ Incorrect. The heart is
considered analogous across vertebrates, as it performs the same
function but may vary in structure; homology is based on structural
similarity.
• (D) Thorn of Bougainvillea and tendrils of Cucurbita: Correct. Both
are modified shoots, showing homology despite functional
differences.
Hence, statements (A), (B), and (D) are true.

The correct answer is Option 1. (C), (D), (B), (A)
Explanation:
The appearance of plants on Earth followed an evolutionary timeline:
• Rhynia type plants (C): Early vascular plants appeared during the
Silurian-Devonian period.
• Psilophyton (D): Primitive vascular plants evolved slightly later in
the Devonian period.
• Seed ferns (B): These gymnosperm-like plants appeared in the late
Devonian to Carboniferous period.
• Angiosperms (A): Flowering plants evolved much later, during the
Cretaceous period.

Hence, the chronological order of appearance is: Rhynia → Psilophyton →
Seed ferns → Angiosperms.

The correct answer is Option 3. Third
Explanation:
• In a food chain:
1. Producers (plants, phytoplankton) occupy the first trophic level.
2. Primary consumers (herbivores that eat producers) occupy the
second trophic level.
3. Secondary consumers (carnivores or omnivores that eat
herbivores or primary consumers) occupy the third trophic
level.
• If a man eats fish, the fish are typically primary or secondary
consumers feeding on smaller aquatic organisms (like plankton or
smaller fish). Therefore, the man becomes a secondary consumer,
placing him at the third trophic level in the food chain.

The correct answer is Option 1. Homologous structures
Explanation:
• Thorn of Bougainvillea and tendril of Cucurbita are both modified
shoots, meaning they share a common origin in the plant’s anatomy,
even though their functions are different (protection vs. climbing).
• Homologous structures are organs that have the same structural
origin but may perform different functions.
• Analogous structures, in contrast, have different origins but similar
functions.
• Therefore, these structures are homologous.

The correct answer is Option 2. Inverted pyramid of biomass
Explanation:
In aquatic ecosystems, a small standing crop of phytoplankton (producers)
can support a large biomass of zooplankton (primary consumers) because
phytoplankton reproduce and grow rapidly.
• Pyramid of biomass: Shows the total mass of organisms at each
trophic level at a given time.
• In this case, the biomass of producers (phytoplankton) is less than
that of consumers (zooplankton), resulting in an inverted pyramid of
biomass.
• Pyramid of energy: Always upright, because energy transfer between
trophic levels is never 100% efficient.
Hence, the scenario is best represented by an inverted pyramid of biomass.

The correct answer is Option 1. Hind II
Explanation:
• The first restriction endonuclease to be isolated was HindII,
discovered in 1970 by Hamilton Smith and his coworkers from
Haemophilus influenzae Rd strain II.
• HindII cuts DNA at specific internal recognition sequences, a property
that became essential for molecular biology and genetic engineering.
• Other enzymes like EcoRI, BamHI, and PvuII were discovered later
and are also widely used in recombinant DNA technology.

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

Explanation:
During sewage treatment, the sequence of products formed is as follows:
1. Primary sludge (D): Formed during primary sedimentation, where
heavier solids settle down.
2. Flocs (C): In the secondary treatment, microorganisms aggregate to
form flocs that help in removing organic matter.
3. Activated sludge (B): Flocs that are rich in microbial biomass are
termed activated sludge, which is used to further degrade pollutants.
4. Biogas (A): In the anaerobic digestion of primary or secondary sludge,
microorganisms produce biogas (methane + CO₂) as a byproduct.
Hence, the correct sequence is: Primary sludge → Flocs → Activated sludge
→ Biogas.

The correct answer is Option 2. In situ conservation
Explanation:
Wildlife safari parks are examples of in situ conservation, where plants and
animals are protected in their natural habitats or semi-natural
environments. In such areas, species are conserved within ecosystems that
maintain ecological processes, allowing natural interactions to continue.
Other options:
• Ex situ conservation: involves conserving species outside their natural
habitats, such as in zoos, botanical gardens, or seed banks.
• Biodiversity hotspots: regions with high species richness and
endemism, not necessarily a conservation method.
• Sacred groves: traditional protected areas, also an example of in situ
conservation but culturally specific.
Hence, wildlife safari parks fall under in situ conservation.

The correct answer is Option 3. Accumulation of humus
Explanation:
Humification is the process by which dead plant and animal matter is
decomposed by microorganisms and converted into humus, a dark, organic
component of soil. Humus improves soil fertility by:
• Increasing water retention
• Enhancing nutrient availability
• Improving soil structure
Other options:
• Soil erosion: ❌ Humification does not cause soil loss.
• Soil conservation: ❌ While humus helps soil quality, humification
itself is a natural decomposition process, not a direct conservation
method.
• Accumulation of salts: ❌ Humification does not lead to salt
accumulation.
Therefore, humification primarily results in the accumulation of humus in
soil.

The correct answer is Option 3. 35%
Explanation:
According to Chargaff's rules for double-stranded DNA:
• The amount of adenine (A) = thymine (T)
• The amount of guanine (G) = cytosine (C)
• The total percentage of all bases = 100%
Given: A = 15%
• Therefore, T = 15%

• Total A + T = 15% + 15% = 30%
The remaining percentage is for G + C:
100% − 30% = 70%
Since G = C, each contributes half of 70%:

Hence, the percent of cytosine in the DNA is 35%.

The correct answer is Option 3. Cancer and cystic fibrosis
Explanation:
Transgenic animals are genetically modified to carry foreign genes, allowing
researchers to study the effects of specific genes on biological processes
and disease development. They are particularly valuable in modeling
genetic and chronic diseases, such as cancer and cystic fibrosis, where gene
function and mutation contribute to disease progression. These models
help in understanding disease mechanisms and testing potential therapies.
Diseases like cholera, typhoid, pneumonia, elephantiasis, ringworm, and
kala-azar are infectious or parasitic and are typically studied using
microbial or pathogen models rather than transgenic animals.

The correct answer is Option 3. Making crops tolerant to stresses
Explanation:
Genetically modified (GM) plants are engineered to enhance desirable traits.
One of the key applications is improving stress tolerance, which includes
resistance to:
• Biotic stresses: pests, diseases
• Abiotic stresses: drought, salinity, extreme temperatures

This modification helps increase crop productivity and stability. GM plants
do not increase post-harvest losses, decrease crop yield, or reduce mineral
usage efficiency; in fact, they are designed to improve overall crop
performance and resource utilization.

The correct answer is Option 3. Ovaries
Explanation:
The primary female sex organs, also called gonads, are the ovaries. They are
responsible for:
• Producing female gametes (ova or eggs)
• Secreting sex hormones such as estrogen and progesterone, which
regulate the menstrual cycle and secondary sexual characteristics.
Other options:
• Mammary glands: secondary sexual characteristic, involved in
lactation.
• Uterus: site of implantation and fetal development, not a primary sex
organ.
• Cervix: lower part of the uterus, also not a primary sex organ.

The correct answer is Option 1. Secondary spermatocytes
Explanation:
In the male reproductive system, spermatogenesis occurs in the
seminiferous tubules of the testes:
• Primary spermatocytes → diploid (2n), formed from spermatogonia;
undergo meiosis I.
• Secondary spermatocytes → haploid (n), result from meiosis I of
primary spermatocytes; each contains half the chromosome number.
• Leydig cells → diploid somatic cells; secrete testosterone.

• Sertoli cells → diploid somatic cells; support and nourish developing
sperm.
Thus, the haploid cells in the male reproductive system are the secondary
spermatocytes, which further divide by meiosis II to form spermatids.

The correct answer is Option 2. Less than 50%
Explanation:
Photosynthetically Active Radiation (PAR) is the portion of sunlight that
plants can use for photosynthesis, spanning the wavelength range of 400–
700 nm (violet to red light). While the sun emits a broad spectrum of
radiation—including ultraviolet (<400 nm) and infrared (>700 nm)—only
the visible portion is effectively usable by plants. Of the total solar radiation
incident on Earth, less than 50% falls within this PAR range, as a significant
fraction is in the ultraviolet or infrared regions, which plants cannot use for
photosynthesis.

The correct answer is Option 1. Antigen–antibody interaction.
Explanation:
• ELISA (Enzyme-Linked Immunosorbent Assay) detects or measures
antigens or antibodies using their specific binding to each other.
• An enzyme-linked antibody produces a color change; the intensity reflects
the amount of target present.
• Not PCR (nucleic acid amplification), not radioactive molecules (that’s
RIA), and not measuring DNA amount.

The correct answer is Option 1. Zoological park.
Explanation:

• In-situ = conservation in natural habitats (e.g., national parks, wildlife
sanctuaries, biosphere reserves).
• Zoological parks are ex-situ (off-site) conservation facilities.

The correct answer is Option 2. Pollination.
Explanation:
• Narrowly utilitarian = direct consumptive uses like medicines,
construction materials, industrial products.
• Pollination is an ecosystem service (broadly utilitarian), not a direct
product.

The correct answer is Option 1. Frequent glaciations in the past.
Explanation:
• High tropical diversity is linked to greater solar energy, stable/less
seasonal climate, and being undisturbed for millions of years.
• Frequent glaciations cause extinctions and do not explain tropical
richness.

The correct answer is Option 3. Five.
Explanation: Earth has witnessed five major mass extinction events since
life diversified (e.g., end-Ordovician, Devonian, Permian, Triassic, and
Cretaceous).

The correct answer is Option 2. Amazon forests.
Explanation:

• India’s biodiversity hotspots include Western Ghats–Sri Lanka, Indo-
Burma, and Himalaya (also Nicobar within Sundaland).
• Amazon forests are in South America and do not cover India.

The correct answer is Option 1. Endosperm develops into seed
Explanation:
This statement is incorrect. After fertilization, the ovule develops into the
seed, and the ovary develops into the fruit. The passage clearly states that
the "primary endosperm cell forms the endosperm tissue," which serves as
nutrition for the developing embryo inside the seed.

The correct answer is Option 4. Epiblast
Explanation:
The development of a dicot embryo progresses through the proembryo,
globular, and heart-shaped stages before maturing. The epiblast is a small,
flap-like, undifferentiated structure considered to be a vestigial
(undeveloped) second cotyledon in the embryos of some monocots, like
grasses. It is not part of dicot embryogenesis.

The correct answer is Option 1. Free-nuclear endosperm
Explanation:
The passage states that the primary endosperm cell forms the endosperm.
In coconuts, the primary endosperm nucleus undergoes thousands of
mitotic divisions without immediate cell wall formation. This creates a
liquid multinucleate cytoplasm called the free-nuclear endosperm, which is
the nutritious coconut water. The white kernel that forms later is the
cellular endosperm.

The correct answer is Option 3. Syngamy
Explanation:
The passage mentions two key fusion events: syngamy and triple fusion.
Syngamy is the specific process where one of the male gametes (haploid, n)
fuses with the female gamete (the egg cell, also haploid, n) to form the
diploid (2n) zygote. Triple fusion, on the other hand, results in the triploid
endosperm.

The correct answer is Option 3. 19
Explanation:
A zygote is formed by the fusion of a haploid male gamete (𝑛) and a haploid
egg cell (𝑛), making the zygote diploid (2𝑛).
• Given: Number of chromosomes in the diploid zygote (2𝑛) = 38.
• To find the number of chromosomes in the haploid egg cell (𝑛), we
simply divide the zygote's chromosome number by 2.
• Therefore, to find the number of chromosomes in the haploid egg cell,
you must divide the number of chromosomes in the diploid zygote by
2.
𝑛 = 2𝑛/2
𝑛 = 38/2
𝑛 = 19