KCET 2025 Biology Question Paper with Answer and Solution

(B) According to the rules of Binomial Nomenclature:
$1$. Biological names are generally in Latin or derived from Latin,irrespective of their origin.
$2$. The first word in a biological name represents the genus,while the second component denotes the specific epithet.
$3$. Both the words in a biological name,when handwritten,are separately underlined,or printed in italics to indicate their Latin origin.
$4$. Therefore,the statement that biological names are printed in italics to indicate their non-Latin origin is incorrect,as italics are used to indicate their Latin origin.

(B) The correct matching is as follows:
$A$. Leptotene: During this stage, chromosomes become visible under a light microscope.
$B$. Zygotene: During this stage, homologous chromosomes start pairing together, a process called synapsis.
$C$. Pachytene: During this stage, crossing over occurs, which is the exchange of genetic material between non-sister chromatids of homologous chromosomes.
$D$. Diplotene: During this stage, the synaptonemal complex dissolves, and homologous chromosomes begin to separate except at the sites of crossovers (chiasmata).
$E$. Diakinesis: This is the final stage of prophase $I$, characterized by the terminalisation of chiasmata.
Therefore, the correct sequence is $A-i, B-ii, C-iii, D-iv, E-v$.

(D) In mitosis,the $Anaphase$ stage is characterized by the splitting of the centromere of each chromosome,allowing the sister chromatids to separate. These separated chromatids,now referred to as daughter chromosomes,are pulled towards the opposite poles of the cell by the spindle fibers. Therefore,observing chromosomes at the opposite poles indicates that the cell is in the $Anaphase$ stage.

(B) Both Statement $I$ and Statement $II$ are false.
In the Calvin cycle ($C_3$ cycle),the primary carboxylation reaction is catalysed by the enzyme $RuBisCO$ (ribulose$-1,5-$bisphosphate carboxylase/oxygenase).
In the Hatch-Slack pathway ($C_4$ cycle),the primary carboxylation reaction is catalysed by the enzyme $PEP$ carboxylase $(PEPCase)$.

(C) The correct answer is $C$.
The $TCA$ cycle (also known as the Krebs cycle or Citric acid cycle) begins with the condensation of an acetyl group $(2C)$ with Oxaloacetic acid $(4C)$ in the presence of water to form Citric acid $(6C)$.
This reaction is catalyzed by the enzyme Citrate synthase.

$(A)$ The chemical nature of plant growth regulators is as follows:
$1$. Abscisic acid $(ABA)$ is a derivative of carotenoids $(A-iii)$.
$2$. Gibberellins $(GA)$ are chemically terpenes $(B-iv)$.
$3$. Kinetin is a modified form of adenine, which is a purine derivative $(C-i)$.
$4$. Auxin, specifically Indole$-3-$acetic acid $(IAA)$, is an indole derivative $(D-ii)$.
Therefore, the correct matching is $A-iii, B-iv, C-i, D-ii$.

(C) The respiratory rhythm center is primarily located in the medulla oblongata region of the brain.
However,a specialized center called the Pneumotaxic center is present in the pons region of the brain.
This center can moderate the functions of the respiratory rhythm center by reducing the duration of inspiration and thereby altering the respiratory rate.
Therefore,the correct option is $C$.

(C) The wall of blood vessels consists of three layers: $Tunica \text{ intima}$ (innermost), $Tunica \text{ media}$ (middle), and $Tunica \text{ externa}$ (outermost).
In arteries, the $Tunica \text{ media}$ is thick and muscular to withstand high blood pressure.
In veins, the $Tunica \text{ media}$ is comparatively much thinner than in arteries because the blood pressure in the venous system is significantly lower.
Therefore, the $Tunica \text{ media}$ is the layer that is characteristically thin in veins.

(C) The correct answer is $C$.
In the nephron, the counter-current mechanism is a specialized arrangement that maintains the concentration gradient in the medullary interstitium.
This mechanism is primarily facilitated by the close proximity and opposite flow of filtrate in the $Henle's$ loop and blood in the $vasa \text{ } recta$.
This system helps in concentrating the urine by allowing the reabsorption of water and solutes.

(D) According to the sliding filament theory of muscle contraction,the thin filaments slide over the thick filaments.
During this process,the $I$ bands (isotropic bands) get reduced in length as the actin filaments move deeper into the $A$ bands.
Conversely,the $A$ bands (anisotropic bands) retain their original length because the myosin filaments do not change in size.
Therefore,the correct answer is $I$ bands,$A$ bands.

(C) When an action potential reaches the axon terminal,it triggers the following sequence of events:
$1$. The depolarization of the axon terminal membrane causes the opening of voltage-gated calcium channels.
$2$. Calcium ions enter the terminal,which stimulates the synaptic vesicles to move towards and fuse with the pre-synaptic membrane.
$3$. The neurotransmitters are released into the synaptic cleft via exocytosis.
$4$. These neurotransmitters diffuse across the synaptic cleft and bind to specific receptors on the post-synaptic membrane.
$5$. This binding leads to the generation of a new action potential in the post-synaptic neuron.
Therefore,the correct sequence is: Axon terminal $\rightarrow$ Synaptic vesicles $\rightarrow$ Synaptic cleft $\rightarrow$ Post-synaptic membrane $\rightarrow$ Post-synaptic neuron.

(A) $Cortisol$ is a glucocorticoid primarily involved in carbohydrate metabolism,anti-inflammatory reactions,and immune suppression.
Statement $(i)$ is correct as $Cortisol$ supports cardiovascular and kidney functions.
Statement $(ii)$ is correct as it produces anti-inflammatory reactions.
Statement $(iii)$ is incorrect because the maintenance of electrolyte balance,body fluid volume,osmotic pressure,and blood pressure is primarily the function of $Aldosterone$ (a mineralocorticoid),not $Cortisol$.
Statement $(iv)$ is correct as it suppresses the immune response.
Statement $(v)$ is correct as it stimulates $RBC$ production.
Therefore,only statement $(iii)$ does not correspond to the functions of $Cortisol$.

(D) The shapes of bacteria are classified based on their morphology:
$1$. $A$. Coccus: These are spherical or oval-shaped bacteria.
$2$. $B$. Bacillus: These are rod-shaped bacteria.
$3$. $C$. Vibrio: These are comma-shaped bacteria.
$4$. $D$. Spirillum: These are spiral-shaped bacteria.
Therefore,the correct matching is $A-iii, B-i, C-iv, D-ii$.

(B) $Mycoplasma$ is the correct answer.
$Mycoplasma$ are the smallest living cells known and are unique because they completely lack a cell wall,which makes them naturally resistant to antibiotics like penicillin that target cell wall synthesis.

(D) Inclusion bodies.
In prokaryotic cells,reserve materials are stored in the cytoplasm in the form of inclusion bodies. These are not bound by any membrane system and lie free in the cytoplasm. Examples include phosphate granules,cyanophycean granules,and glycogen granules.

(A) Statement $I$ is false because gemmae are green,multicellular,asexual buds,not sexual buds.
Statement $II$ is true because in mosses,the spore germinates to form a filamentous,creeping,green,branched,and frequently filamentous stage called the protonema.
Therefore,Statement $I$ is false and Statement $II$ is true.

(C) . $Balanoglossus$.
During a field trip,a student observed a marine organism with a worm-like body. The cylindrical body of $Balanoglossus$ (a hemichordate) is distinctly divided into three parts: a proboscis,a collar,and a long trunk. Therefore,the organism is $Balanoglossus$.

(A) The mode of arrangement of sepals or petals in a floral bud with respect to the other members of the same whorl is known as aestivation.
- $A$ represents Vexillary aestivation,where the largest petal (standard) overlaps the two lateral petals (wings),which in turn overlap the two smallest anterior petals (keel).
- $B$ represents Imbricate aestivation,where the margins of sepals or petals overlap one another but not in any particular direction.
- $C$ represents Twisted aestivation,where one margin of the appendage overlaps that of the next one and so on in a regular pattern.
- $D$ represents Valvate aestivation,where the sepals or petals in a whorl just touch one another at the margin,without overlapping.
Thus,the correct sequence is $A$-Vexillary,$B$-Imbricate,$C$-Twisted,$D$-Valvate.

$(A)$. Radial,tetrarch,cambial ring between xylem and phloem at later stages corresponds to $T.S$ of dicot root $(A-ii)$.
$B$. Conjoint,open and endarch vascular bundles are characteristic of dicot stem $(B-iv)$.
$C$. Radial,polyarch,large pith without cambial ring is characteristic of monocot root $(C-iii)$.
$D$. Conjoint,closed with sclerenchymatous bundle sheath is characteristic of monocot stem $(D-i)$.
Therefore,the correct matching is $A-ii, B-iv, C-iii, D-i$.

(D) The vascular bundles are described as conjoint,collateral,and open.
$1$. Conjoint: Xylem and phloem are present on the same radius.
$2$. Collateral: Phloem is located towards the outer side and xylem towards the inner side.
$3$. Open: The presence of cambium between xylem and phloem allows for secondary growth.
These characteristics are diagnostic features of a Dicot Stem.
In contrast,Monocot stems have closed vascular bundles (no cambium),and roots have radial vascular bundles (xylem and phloem on different radii).

(A) The correct statements are $A$ and $C$.
$1$. $Bidder's$ canals are present in the kidneys of male $Frogs$ and are involved in the transport of spermatozoa.
$2$. Copulatory pads (nuptial pads) are present on the first digit of the forelimbs in male $Frogs$ to assist in amplexus during mating.
$3$. Vocal sacs are present in male $Frogs$ to produce sound for attracting females.
$4$. The $Cloaca$ is a common chamber for the urinary,reproductive,and digestive tracts,and it is present in both male and female $Frogs$.

(C) The graph represents the potential energy changes during a chemical reaction.
$M$ represents the activation energy required for the reaction to proceed in the absence of an enzyme,which is higher.
$N$ represents the activation energy required for the reaction to proceed in the presence of an enzyme,which is lower because enzymes lower the activation energy barrier.
Therefore,$M$ is the activation energy without an enzyme and $N$ is the activation energy with an enzyme.
The correct option is $C$.

(B) The correct answer is $B$.
According to the rules of Binomial Nomenclature,biological names are printed in italics to indicate their Latin origin,not their non-Latin origin.
Option $A$ is correct because hand-written scientific names must be underlined separately to indicate their Latin origin.
Option $C$ is correct because the first word in a biological name represents the genus and the second component denotes the specific epithet.
Option $D$ is correct because biological names are derived from Latin or are Latinised,regardless of their actual origin.

(A) The death rate is calculated as the number of deaths divided by the initial population size over a specific time interval.
Death rate = $\frac{\text{Number of deaths}}{\text{Initial population size}}$
Death rate = $\frac{8}{80} = 0.1$ individual per individual per time interval.
Therefore, the death rate is $0.1$ individual/time interval.

(C) The correct pathway of sperm transport from the testes to the outside is as follows:
$1$. Sperm are produced in the $\text{Seminiferous tubules}$.
$2$. They move into the $\text{rete testis}$.
$3$. From the $\text{rete testis}$,they pass through the $\text{vasa efferentia}$.
$4$. They then enter the $\text{epididymis}$ for maturation and storage.
$5$. From the $\text{epididymis}$,they travel through the $\text{vas deferens}$.
$6$. Finally,they reach the $\text{ejaculatory duct}$ before being expelled through the urethra.
Therefore,the correct sequence is: $\text{Seminiferous tubules} \rightarrow \text{rete testis} \rightarrow \text{vasa efferentia} \rightarrow \text{epididymis} \rightarrow \text{vas deferens} \rightarrow \text{ejaculatory duct}$.

(C) The correct matches are as follows:
$1$. $hCG$ (human Chorionic Gonadotropin) and $hPL$ (human Placental Lactogen) are produced by the placenta during pregnancy.
$2$. Progesterone is primarily secreted by the corpus luteum in the ovary after ovulation.
$3$. Androgens (mainly testosterone) are synthesized and secreted by the Leydig cells (interstitial cells) of the testes.
$4$. Relaxin is produced by the ovary (specifically the corpus luteum) during the later stages of pregnancy.
Therefore,the correct matching is $A-ii, B-iii, C-iv, D-i$.

(B) The correct answer is $B$. The pair "Second month of pregnancy - Movement of foetus" is mismatched.
According to human development milestones:
$1$. During the first month, the heart is formed.
$2$. During the second month, the foetus develops limbs and digits.
$3$. By the end of the third month (first trimester), most major organ systems are formed.
$4$. During the fifth month, the first movements of the foetus and appearance of hair on the head are observed.
$5$. By the end of the sixth month (second trimester), the body is covered with fine hair, eye-lids separate, and eye-lashes are formed.

(C) $MTP$ stands for Medical Termination of Pregnancy.
Statement-$I$ is correct because $MTP$ is primarily used to terminate unwanted pregnancies resulting from unprotected intercourse, contraceptive failure, or rape.
Statement-$II$ is also correct because $MTP$ is a legal procedure that must be performed by qualified medical practitioners under specific medical or social justifications to ensure safety and legality.

(D) The correct answer is $D$.
Natural methods of contraception work on the principle of avoiding chances of ovum and sperm meeting.
$A$,$B$,and $C$ are natural methods.
$D$ (Implants) are hormonal preparations that are inserted under the skin,which are considered a chemical or barrier-based artificial method of contraception,not a natural one.

(C) The population density of an area increases due to two main factors:
$1$. Natality $(B)$: It refers to the number of births during a given period in the population that are added to the initial density.
$2$. Immigration $(I)$: It refers to the number of individuals of the same species that have come into the habitat from elsewhere during the time period under consideration.
Therefore,both Natality and Immigration contribute to an increase in population density.

(A) The correct answer is $A$.
In the assisted reproductive technology known as Zygote Intrafallopian Transfer $(ZIFT)$,the zygote or early embryo containing up to $8$ blastomeres is collected from the laboratory and transferred into the fallopian tube of the female.
If the embryo has developed beyond the $8$-blastomere stage (e.g.,$16$ or $32$ blastomeres),it is instead transferred into the uterus,a procedure known as Intrauterine Transfer $(IUT)$.

(D) In prokaryotes:
$A$. Prokaryotic structural genes are typically polycistronic,not monocistronic. Thus,statement $A$ is incorrect.
$B$. Prokaryotic genes do not contain introns (non-coding sequences). Thus,statement $B$ is correct.
$C$. Since there is no nuclear membrane,transcription and translation occur in the same compartment and are coupled. Thus,statement $C$ is correct.
$D$. Splicing is a process required to remove introns from eukaryotic pre-mRNA. Since prokaryotes lack introns,they do not undergo splicing. Thus,statement $D$ is incorrect.
$E$. Prokaryotes possess only a single type of $RNA$ polymerase that transcribes all types of $RNA$ $(mRNA, tRNA, rRNA)$. Thus,statement $E$ is correct.
Therefore,statements $B, C$,and $E$ are correct.

(D) In the $lac$ operon of $E. coli$, three structural genes are involved: $lacZ$, $lacY$, and $lacA$.
$1$. $lacZ$ encodes $\beta$-galactosidase, which hydrolyzes lactose into glucose and galactose.
$2$. $lacY$ encodes Permease, which increases the permeability of the cell membrane to $\beta$-galactosides like lactose, allowing it to enter the cell.
$3$. $lacA$ encodes Transacetylase, which transfers an acetyl group from acetyl-CoA to $\beta$-galactosides.
Therefore, the enzyme responsible for increasing the permeability of the bacterial cell to lactose is Permease.

(A) The correct answer is $A$ (hnRNA).
In eukaryotes,there are three types of $RNA$ polymerases in the nucleus.
$1$. $RNA$ polymerase $I$ transcribes $rRNA$ ($28S, 18S,$ and $5.8S$).
$2$. $RNA$ polymerase $II$ transcribes the precursor of $mRNA$,which is known as heterogeneous nuclear $RNA$ $(hnRNA)$.
$3$. $RNA$ polymerase $III$ is responsible for the transcription of $tRNA$,$5S$ $rRNA$,and $snRNA$ (small nuclear $RNA$).

(A) . Charles Darwin travelled around the world in a ship called $HMS$ Beagle. This is a correct statement.
$B$. Evolution is a gradual process where life forms change over time. This is a correct statement.
$C$. According to Darwin,fitness refers to reproductive fitness (the ability to survive and produce offspring),not just physical fitness. This is an incorrect statement.
$D$. Fossils are the preserved remains or traces of organisms (often hard parts like bones or shells) found in sedimentary rocks. This is a correct statement.
$E$. Alfred Russel Wallace,not Hugo De Vries,worked in the Malay Archipelago. Hugo De Vries is known for his work on mutation theory in evening primrose. This is an incorrect statement.
Therefore,statements $A, B$,and $D$ are correct.

(D) Darwin's finches are a classic example of $Adaptive \text{ } radiation$.
During his voyage to the Galapagos Islands, Charles Darwin observed a variety of small birds, now known as Darwin's finches.
He noted that these birds had evolved from a single ancestral species into various forms with different beak shapes, adapted to different feeding habits (such as eating seeds, insects, or nectar).
This process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (habitats) is called $Adaptive \text{ } radiation$.

(B) Genetic drift is defined as the change in the frequency of an existing gene variant (allele) in a population due to random sampling of organisms.
It occurs by chance and is more pronounced in small populations.
Unlike natural selection,which is a non-random process,genetic drift is a stochastic (random) process.
Therefore,the correct answer is Genetic drift.

(C) After entering the human body,the $HIV$ virus enters into macrophages where the $RNA$ genome of the virus replicates to form viral $DNA$ with the help of the enzyme reverse transcriptase.
This viral $DNA$ gets incorporated into the host cell's $DNA$ and directs the infected cells to produce virus particles.
The macrophages continue to produce virus particles and in this way,they act like an $HIV$ factory.
Simultaneously,$HIV$ enters into $Helper$ $T$-lymphocytes ($T_H$ cells),replicates,and produces progeny viruses.
The progeny viruses released in the blood attack other $Helper$ $T$-lymphocytes.
This leads to a progressive decrease in the number of $Helper$ $T$-lymphocytes in the body of the infected person.

(A) The correct answer is $A$.
$Cyclosporin-A$ is an immunosuppressive agent used in patients who have undergone organ transplantation to prevent organ rejection.
It is produced by the fungus $Trichoderma polysporum$.

(C) The correct matches are as follows:
$1$. $Streptococcus$ is used as a 'clot buster' because it produces streptokinase,which is used to remove clots from the blood vessels of patients who have undergone myocardial infarction $(A-ii)$.
$2$. $Penicillium$ is a fungus that serves as the source of the first antibiotic,penicillin $(B-iii)$.
$3$. $Methanogens$ are bacteria that grow anaerobically on cellulosic material and produce large amounts of methane,which is used in biogas production $(C-iv)$.
$4$. $Anabaena$ is a cyanobacterium that acts as a free-living nitrogen-fixing bacterium in the soil $(D-i)$.
Therefore,the correct sequence is $A-ii, B-iii, C-iv, D-i$.

(A) To isolate $DNA$ from cells,the cell wall must be broken down to release the genetic material.
$1$. Fungal cells have a cell wall made of chitin,which is broken down by the enzyme $Chitinase$.
$2$. Bacterial cells have a cell wall made of peptidoglycan,which is broken down by the enzyme $Lysozyme$.
$3$. Plant cells have a cell wall made of cellulose,which is broken down by the enzyme $Cellulase$.
Therefore,the correct sequence of enzymes is $Chitinase$,$Lysozyme$,and $Cellulase$.

(C) . Bioreactors are vessels in which raw materials are biologically converted into specific products using microbial,plant,or animal cells.
$B$. Downstream processing refers to the processes of separation and purification of the product after the biosynthetic stage.
$C$. Recombinant protein refers to the protein encoded by the recombinant $DNA$,such as insulin produced by rDNA technology.
$D$. $PCR$ (Polymerase Chain Reaction) is a technique used to amplify $DNA$ segments and can be used to detect mutated genes in suspected cancer patients.
Therefore,the correct match is $A-ii, B-iv, C-i, D-iii$.

(A) The correct answer is $A$.
In the $pBR322$ plasmid,the $rop$ gene codes for proteins involved in the replication of the plasmid.
$rop$ stands for 'repressor of primer'.
It regulates the copy number of the plasmid.