CUET 2025 Biology Question Paper with Answers & Solutions

Correct answer: B

The filiform apparatus is a special cellular thickening at the micropylar tip of the synergids. It guides the entry of the pollen tube into the synergid (and thus into the embryo sac) by producing chemical guidance cues.

Correct answer: C

An antibody (immunoglobulin) has the structure H2L2: two identical heavy (H) chains and two identical light (L) chains, i.e., four peptide chains in total.

Correct answer: D

NPP = GPP - R, which rearranges to $GPP - R = NPP$. NPP is the biomass available after subtracting respiratory losses from gross primary productivity.

Correct answer: C

Malaria - cycles of fever (II); Filariasis - inflammation/swelling of lower limbs (I); Ringworm - scaly lesions on skin/nails (IV); Amoebiasis - blood clots and mucus in stools (III). Matches option C.

Correct answer: B

Clostridium butylicum - butyric acid (II); Aspergillus niger - citric acid (III); Acetobacter aceti - acetic acid (IV); Lactobacillus - lactic acid (I). Matches option B.

Correct answer: B

The chalaza is the basal part of the ovule located opposite the micropylar end, where the integuments and nucellus join the funicle.

Correct answer: B

Amniocentesis - testing of sex/foetal disorders (IV); Maternal mortality rate - death rate (III); Vasectomy - ligation of vas deferens (II); Tubectomy - ligation of fallopian tube (I). Matches option B.

Correct answer: B

Interferons are cytokines secreted by virus-infected cells that protect surrounding non-infected cells; this represents the cytokine barrier of innate immunity (NCERT).

Correct answer: C

Transcription is the process of copying genetic information from the template strand of DNA into RNA.

Correct answer: A

Order: morula forms (D), then blastomeres arrange into trophoblast and inner cell mass forming blastocyst (C), blastocyst implants in endometrium (A), then chorionic villi appear (B). Sequence D, C, A, B = option A.

Correct answer: B

IUDs include Lippes Loop and hormone-releasing LNG-20. Saheli is an oral contraceptive pill and Implants are subdermal hormone implants, so (C) and (D) are NOT IUDs. Option B.

Correct answer: D

Recessive traits in Mendel's pea: Flower colour - white (IV); Seed colour - green (I); Pod colour - yellow (II); Pod shape - constricted (III). Matches option D.

Correct answer: B

Methyl guanosine triphosphate is the 5' cap added during eukaryotic mRNA processing, not bacterial transcription. Rho factor (termination), sigma factor (initiation), and DNA-dependent RNA polymerase are all part of bacterial transcription.

Correct answer: A

Aneuploidy is gain/loss of chromosomes. Down's syndrome (trisomy 21) and Turner's syndrome (XO, monosomy) are aneuploidies. Haemophilia and thalassemia are gene mutations, not aneuploidies. Option A.

Correct answer: C

Skin colour is polygenic. AaBbCc has three dominant (dark) alleles out of six, giving an intermediate skin colour. AABBCC is darkest, aabbcc is lightest.

Correct answer: C

In the lac operon: i gene - repressor (II); z gene - beta-galactosidase (IV); y gene - permease (I); a gene - transacetylase (III). Matches option C.

Correct answer: C

Nicotine stimulates the adrenal gland to release adrenaline and noradrenaline; it is a stimulant, not a sedative/pain killer (those are opioids like morphine). So statement C is incorrect.

Correct answer: D

DNA fragments move towards anode (C), gel is stained with ethidium bromide (B), exposed to UV light to visualise bands (A), and the desired fragments are cut out and eluted (D). Sequence C, B, A, D = option D.

Correct answer: A

Citric acid - Aspergillus niger (IV); Ethanol - Saccharomyces cerevisiae (III); Statins - Monascus purpureus (II); Cyclosporin A - Trichoderma polysporum (I). Matches option A.

Correct answer: C

EcoRI is a restriction endonuclease, i.e., an enzyme used to cut DNA at specific recognition sequences in recombinant DNA technology.

Correct answer: D

From latest (most recent) to oldest: Tertiary (most recent), Jurassic, Triassic, Carboniferous (oldest). Sequence C, D, A, B = option D.

Correct answer: A

The three steps of PCR are denaturation, annealing (primer binding), and extension. Propagation is not a PCR step. So (A), (B) and (D) only = option A.

Correct answer: A

Baculoviruses (genus Nucleopolyhedrovirus) are pathogens that attack insects and other arthropods, used as biocontrol agents.

Correct answer: C

When reproductive age individuals exceed pre-reproductive individuals (narrow base), the population has fewer young to replace, indicating a declining population age pyramid.

Correct answer: C

All four are correct: homology indicates common ancestry; whale and cheetah forelimb bones share the same pattern; vertebrate heart/brain are homologous; Bougainvillea thorn and Cucurbita tendril are homologous (both stem modifications). Option C.

Correct answer: A

Order of appearance (earliest to latest): Rhynia type plants (early vascular), Psilophyton, Seed ferns, then Angiosperms (most recent). Sequence C, D, B, A = option A.

Correct answer: D

Food chain: phytoplankton/plants (T1) -> zooplankton/herbivore (T2) -> small fish/carnivore (T3) -> man eating fish (T4). Man occupies the fourth trophic level.

Correct answer: A

Both the thorn of Bougainvillea and the tendril of Cucurbita are modifications of the stem (axillary bud), having a common origin but different functions; hence they are homologous structures.

Correct answer: B

In aquatic ecosystems, a small biomass of phytoplankton supports a larger biomass of zooplankton, giving an inverted pyramid of biomass. The pyramid of energy is always upright.

Correct answer: A

Hind II was the first restriction endonuclease to be isolated and characterised; it always cuts DNA at a specific point within a particular sequence of six base pairs.

Correct answer: B

Sequence: primary treatment yields primary sludge (D); secondary treatment forms flocs (C) which settle as activated sludge (B); anaerobic digestion of sludge produces biogas (A). Sequence D, C, B, A = option B.

Correct answer: A

Wildlife safari parks, like zoos and botanical gardens, conserve organisms outside their natural habitat, so they are examples of ex situ conservation.

Correct answer: C

Humification is the process during decomposition that leads to the formation and accumulation of humus, a dark amorphous substance resistant to microbial action.

Correct answer: C

By Chargaff's rule, $A=T$ and $G=C$. If $A=15\%$ then $T=15\%$, so $A+T=30\%$. Remaining $G+C=70\%$, hence $C=70/2=35\%$.

Correct answer: C

NCERT: transgenic animals are used as models to study how genes contribute to diseases such as cancer, cystic fibrosis, rheumatoid arthritis and Alzheimer's.

Correct answer: C

GM plants are useful in making crops more tolerant to abiotic stresses (cold, drought, salt, heat), reducing post-harvest losses, increasing yield and improving mineral use efficiency. Correct option is making crops tolerant to stresses.

Correct answer: C

The ovaries are the primary female sex organs, producing the female gametes (ova) and hormones (estrogen, progesterone). The rest are accessory/secondary organs.

Correct answer: A

Secondary spermatocytes are formed after meiosis I and are haploid (n). Primary spermatocytes, Leydig cells and Sertoli cells are all diploid (2n).

Correct answer: B

NCERT: of the incident solar radiation, less than 50% is photosynthetically active radiation (PAR); plants capture only 2-10% of PAR.

Correct answer: A

ELISA (Enzyme-Linked Immuno-Sorbent Assay) is based on the principle of antigen-antibody interaction, used to detect infections such as HIV.

Correct answer: A

National parks, wildlife sanctuaries and biosphere reserves are in situ conservation. A zoological park (zoo) conserves organisms outside their natural habitat, so it is ex situ, not in situ.

Correct answer: B

Narrowly utilitarian arguments are direct economic benefits like food, medicines, construction materials and industrial products. Pollination is an ecosystem service - a broadly utilitarian argument, not narrowly utilitarian.

Correct answer: A

Tropics had no frequent glaciations; they remained relatively undisturbed for millions of years, had more solar energy and constant climate. 'Frequent glaciations in the past' does NOT account for tropical diversity.

Correct answer: C

NCERT states there have been five episodes of mass extinction of species in Earth's history (the sixth, current one being human-driven).

Correct answer: B

India's biodiversity hotspots are Western Ghats-Sri Lanka, Indo-Burma and Himalaya. The Amazon forests of South America are not an Indian hotspot.

Correct answer: A

The ovule (not the endosperm) develops into the seed; endosperm only provides nourishment. So statement A is incorrect. B, C and D are correct.

Correct answer: D

Dicot embryo stages are proembryo, globular, heart-shaped and mature embryo. Epiblast is a vestigial structure in monocot (grass) embryos, not a stage of dicot embryo development.

Correct answer: A

Coconut water is the free-nuclear endosperm (liquid syncytial endosperm), while the surrounding white kernel is the cellular endosperm.

Correct answer: C

Syngamy is the fusion of one male gamete with the egg cell to form the diploid (2n) zygote. Triple fusion forms the triploid PEN.

Correct answer: C

Zygote is diploid (2n) = 38, so $n = 38/2 = 19$. The haploid egg cell has 19 chromosomes.