This includes questions from Class 12 Biology chapters.
Q 1: Assertion (A): Entomophilous flowers are large, colourful, fragrant and rich in nectar.
Reason (R): It helps in attracting the pollinating agent.
Reason (R): It helps in attracting the pollinating agent.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is NOT the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
✅ (1) Both A and R are true and R is the correct explanation of A
Pollination by insects is called Entomophily.
Features of insect-pollinated flowers:
▶️ Large, colourful, fragrant and rich in nectar. Nectar & pollen grains are the floral rewards for pollination.
▶️ Small flowers form inflorescence to make them visible.
▶️ The flowers pollinated by flies and beetles secrete foul odours to attract these animals.
▶️ The pollen grains are generally sticky.
Q 2: Assertion (A): In angiosperms, fertilization is unique and is called double fertilization.
Reason (R): A male gamete fuses with two polar nuclei located in the central cell to produce a triploid primary endosperm nucleus (PEN).
Reason (R): A male gamete fuses with two polar nuclei located in the central cell to produce a triploid primary endosperm nucleus (PEN).
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is NOT the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
✅ (2) Both A and R are true but R is NOT the correct explanation of A
▶️ In double fertilization, one male gamete fuses with the egg cell (syngamy) to form the zygote, while the other male gamete fuses with two polar nuclei in the central cell to form the triploid primary endosperm nucleus (PEN). This triploid nucleus gives rise to the endosperm, which provides nourishment to the developing embryo in angiosperms.
▶️ Since 2 types of fusions (syngamy & triple fusion) take place in an embryo sac, it is called double fertilisation.
▶️ It is an event unique to flowering plants.
Q 3: Assertion (A): Endometrium is necessary for implantation of blastocyst.
Reason (R): In the absence of fertilization, the corpus luteum degenerates that causes disintegration of endometrium.
Reason (R): In the absence of fertilization, the corpus luteum degenerates that causes disintegration of endometrium.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is NOT the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
✅ (2) Both A and R are true but R is NOT the correct explanation of A
▶️ The endometrium is necessary for implantation because it provides the site and support for the embryo to grow.
▶️ The degeneration of the corpus luteum and subsequent disintegration of the endometrium is a result of the absence of fertilization, not a reason why the endometrium is necessary for the implantation of a blastocyst.
Q 4: Assertion (A): During oogenesis, each primary oocyte gives only one ovum.
Reason (R): Oogenesis begins at embryonic stage but suspends up to puberty.
Reason (R): Oogenesis begins at embryonic stage but suspends up to puberty.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is NOT the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
✅ (2) Both A and R are true but R is NOT the correct explanation of A
▶️ During oogenesis, each primary oocyte gives rise to only one ovum due to the process of meiosis. This is because the divisions in oogenesis are unequal, resulting in one large ovum and smaller cells called polar bodies.
▶️ The ovum retains most of the cytoplasm and nutrients, which are vital for the early stages of embryonic development after fertilization.
Q 5: Assertion (A): Amniocentesis for sex determination is one of the strategies of Reproductive and Child Health Care Programme.
Reason (R): Ban on amniocentesis checks increasing menace of female foeticide.
Reason (R): Ban on amniocentesis checks increasing menace of female foeticide.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is NOT the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
✅ (4) A is false but R is true
▶️ Amniocentesis is a prenatal diagnostic technique used to detect genetic disorders in the fetus. However, it is not used as a strategy for sex determination in Reproductive and Child Health Care Programmes.
▶️ There is a statutory ban on the use of amniocentesis for sex determination in many countries, including India, to prevent its misuse for sex-selective abortions.
Q 6: Assertion (A): Haemophilia occurs very rarely in females.
Reason (R): Haemophilia is a sex-linked disorder and in females, it happens only when mother is at least carrier and father haemophilic.
Reason (R): Haemophilia is a sex-linked disorder and in females, it happens only when mother is at least carrier and father haemophilic.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is NOT the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
✅ (1) Both A and R are true and R is the correct explanation of A
▶️ Haemophilia is a sex-linked disorder, more common in males.
▶️ Females have two X chromosomes, so they can be carriers with one affected X chromosome. For a female to have haemophilia, both her X chromosomes must be affected, which is rare as it requires a carrier mother and a haemophilic father.
Q 7: Assertion (A): Colour blindness occurs in 8% of females and only about 0.4% of males.
Reason (R): It happens due to mutation in some genes in X chromosome.
Reason (R): It happens due to mutation in some genes in X chromosome.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is NOT the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
✅ (4) A is false but R is true
▶️ Colour blindness is a sex-linked (X-linked) recessive disorder due to defect in either red or green cone of eye. It results in failure to discriminate between red and green colour.
▶️ It is due to mutation in some genes in X chromosome.
▶️ It occurs in 8% of males and only about 0.4% of females. This is because the genes are X-linked.
Q 8: Assertion (A): A phenylketonuria would be mentally retarded.
Reason (R): In this, phenylalanine converts into phenyl pyruvic acid and other derivatives and accumulates in brain.
Reason (R): In this, phenylalanine converts into phenyl pyruvic acid and other derivatives and accumulates in brain.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is NOT the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
✅ (1) Both A and R are true and R is the correct explanation of A
▶️ Phenylketonuria is an inborn error of metabolism.
▶️ It is an autosomal recessive disease.
▶️ It is due to mutation of a gene that codes for the enzyme phenylalanine hydroxylase. This enzyme converts an amino acid phenylalanine into tyrosine.
▶️ The affected individual lacks this enzyme. As a result, phenylalanine accumulates and converts into phenyl pyruvic acid and other derivatives.
▶️ They accumulate in brain resulting in mental retardation. These are also excreted through urine because of poor absorption by kidney.
Q 9: Assertion (A): In DNA, Polymorphism is higher in non-coding sequence.
Reason (R): Mutations in these sequences may not affect an individual’s reproductive ability and accumulate over generations.
Reason (R): Mutations in these sequences may not affect an individual’s reproductive ability and accumulate over generations.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is NOT the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
✅ (1) Both A and R are true and R is the correct explanation of A
▶️ Polymorphism is higher in non-coding DNA sequence because mutations in these sequences may not affect an individual’s reproductive ability. These mutations accumulate over generations causing polymorphism.
▶️ Polymorphisms have great role in evolution & speciation.
Q 10: Assertion (A): Replication occurs within a small opening of the DNA helix.
Reason (R): DNA replication happens in Semi-conservative manner.
Reason (R): DNA replication happens in Semi-conservative manner.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is NOT the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
✅ (2) Both A and R are true but R is NOT the correct explanation of A
▶️ The two strands of long DNA molecules cannot be separated in entire length as it needs high energy. So replication occurs within a small opening of the DNA helix. It is called replication fork.
Q 11: Assertion (A): Insertion or deletion of three or its multiple bases in a DNA sequence results in frame-shift mutations.
Reason (R): Codons are read contiguously and are composed of three bases.
Reason (R): Codons are read contiguously and are composed of three bases.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is NOT the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
✅ (4) A is false but R is true
▶️ Insertion or deletion of one or two bases changes the reading frame from the point of insertion or deletion. It is called frame-shift insertion or deletion mutations.
▶️ Insertion/ deletion of three or its multiple bases insert or delete one or multiple codons. The reading frame remains unaltered from that point onwards. Hence one or multiple amino acids are inserted /deleted.
▶️ It proves that codon is a triplet and is read contiguously.
Q 12: Assertion (A): In South America, there were mammals resembling horse, hippopotamus, bear, rabbit etc. but they couldn’t survive.
Reason (R): Due to continental drift, when South America joined North America, these animals were overridden by North American fauna.
Reason (R): Due to continental drift, when South America joined North America, these animals were overridden by North American fauna.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is NOT the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
✅ (1) Both A and R are true and R is the correct explanation of A
▶️ In South America, there were mammals resembling horse, hippopotamus, bear, rabbit etc. Due to continental drift, when South America joined North America, these animals were overridden by North American fauna.
▶️ Due to continental drift, Australian marsupials survived because of lack of competition from any other mammals.
Q 13: Assertion (A): A malaria patient exhibits recurring fever and chills.
Reason (R): The rupture of RBCs is associated with release of a toxic substance, haemozoin.
Reason (R): The rupture of RBCs is associated with release of a toxic substance, haemozoin.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is NOT the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
✅ (1) Both A and R are true and R is the correct explanation of A
▶️ Malaria is caused by Plasmodium sp. (P. vivax, P. malariae & P. falciparum).
▶️ Most serious (malignant) malaria is caused by P. falciparum.
▶️ Mode of transmission: By female Anopheles mosquito.
▶️ Symptoms: Haemozoin (toxin released by Plasmodium) causes chill and high fever recurring every 3-4 days.
Q 14: Assertion (A): Elimination of mosquitoes is a better way to prevent the diseases such as Amoebiasis.
Reason (R): Amoebiasis is transmitted by the bite of female Culex mosquito.
Reason (R): Amoebiasis is transmitted by the bite of female Culex mosquito.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is NOT the correct explanation of A
(3) A is true but R is false
(4) Both A and R are false
✅ (4) Both A and R are false
▶️ Amoebiasis (Amoebic dysentery): Pathogen is Entamoeba histolytica.
▶️ Mode of transmission: Houseflies (mechanical carriers) transmit parasites from faeces to food & water.
▶️ Symptoms: Constipation, abdominal pain and cramps, stools with excess mucus and blood clots.
Q 15: Assertion (A): During gel electrophoresis, the DNA fragments move towards the cathode.
Reason (R): DNA fragments are negatively charged molecules.
Reason (R): DNA fragments are negatively charged molecules.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is NOT the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
✅ (4) A is false but R is true
▶️ Gel electrophoresis is a technique to separate DNA fragments based on size.
▶️ Agarose gel electrophoresis is employed to check the progression of a restriction enzyme digestion. DNA is negatively charged. So it moves towards the anode.
▶️ DNA fragments are separated according to their size through sieving effect of the agarose gel (a polymer extracted from sea weeds). The smaller sized fragment moves farther.
Q 16: Assertion (A): The genes encoding resistance to antibiotics are used as selectable markers of E. coli.
Reason (R): They allow researchers to identify and select cells that have successfully taken up a plasmid containing these resistance genes.
Reason (R): They allow researchers to identify and select cells that have successfully taken up a plasmid containing these resistance genes.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is NOT the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
✅ (1) Both A and R are true and R is the correct explanation of A
▶️ Selectable marker (marker gene) is a gene that helps to select the transformants and eliminate the non-transformants.
▶️ If a piece of DNA is introduced in a host bacterium, it is called transformation. Such bacterium is transformant. If transformation does not occur, it is non-transformant.
▶️ Selectable markers of E. coli include the genes encoding resistance to antibiotics like ampicillin, tetracycline, chloramphenicol, kanamycin etc. Normal E. coli cells have no resistance against these antibiotics.
Q 17: Assertion (A): DNA ligase plays an important role in recombinant DNA technology.
Reason (R): The cutting of DNA at specific sites into fragments became possible by enzyme DNA ligase.
Reason (R): The cutting of DNA at specific sites into fragments became possible by enzyme DNA ligase.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is NOT the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
✅ (3) A is true but R is false
▶️ Restriction enzymes are the enzymes that cut DNA at specific sites into fragments.
▶️ DNA ligase plays a crucial role in DNA recombinant technology by joining or ligating DNA fragments together.
Q 18: Assertion (A): Monarch butterfly is highly distasteful to its predator bird.
Reason (R): Monarch butterfly has a special chemical in its body which is acquired during its caterpillar stage by feeding on a poisonous weed.
Reason (R): Monarch butterfly has a special chemical in its body which is acquired during its caterpillar stage by feeding on a poisonous weed.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is NOT the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
✅ (1) Both A and R are true and R is the correct explanation of A
Defenses of prey species to lessen impact of predation:
▶️ Camouflage (cryptic colouration) of some insects & frogs.
▶️ Some are poisonous and so avoided by the predators.
▶️ Monarch butterfly is highly distasteful to its predator bird. It is due to a special chemical in its body. It is acquired during its caterpillar stage by feeding on a poisonous weed.
▶️ Thorns (Acacia, Cactus etc.) are the most common morphological means of defense of plants.
▶️ Many plants produce chemicals that make the herbivore sick, inhibit feeding or digestion, disrupt its reproduction or kill it. E.g. Calotropis produce highly poisonous cardiac glycosides. Therefore cattle or goats do not eat it. Nicotine, caffeine, quinine, strychnine, opium, etc. are defenses against grazers and browsers.
Q 19: Assertion (A): Pyramid of energy is always upright.
Reason (R): Energy at a higher trophic level is always more than at a lower level.
Reason (R): Energy at a higher trophic level is always more than at a lower level.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is NOT the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
✅ (3) A is true but R is false
Pyramid of energy is always upright because some energy is always lost as heat at each trophic level. So energy at a lower trophic level is always more than at a higher level.
Q 20: Assertion (A): Plots with more species shows less year-to-year variation in total biomass.
Reason (R): Increased diversity enhances ecosystem stability, which contributes to higher productivity.
Reason (R): Increased diversity enhances ecosystem stability, which contributes to higher productivity.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is NOT the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
✅ (1) Both A and R are true and R is the correct explanation of A
▶️ According to David Tilman, plots with more species shows less year-to-year variation in total biomass.
▶️ Increased diversity contributes to higher productivity. It is essential for ecosystem health and survival of human race.