This includes questions from Class 12 Biology chapters.
Q 1: Assertion (A): Xenogamy is genetically similar to autogamy.
Reason (R): In Xenogamy, the pollen grains come from same plant.
Reason (R): In Xenogamy, the pollen grains come from same plant.
(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
▶️ Geitonogamy: It is the transfer of pollen grains from the anther to the stigma of another flower of the same plant. It is functionally cross-pollination involving a pollinating agent. But it is genetically similar to autogamy since the pollen grains come from same plant.
▶️ Xenogamy: It is the transfer of pollen grains from anther to the stigma of a different plant. It brings genetically different pollen grains to the stigma.
Q 2: Assertion (A): Lack of menstruation is the confirmation for pregnancy.
Reason (R): During pregnancy, the hormone progesterone prevents menstrual cycle.
Reason (R): During pregnancy, the hormone progesterone prevents menstrual cycle.
(1) Both A and R are true but R is NOT the correct explanation of A
(2) A is true but R is false
(3) A is false but R is true
(4) Both A and R are true and R is the correct explanation of A
✅ (3) A is false but R is true
▶️ Menstruation is stopped due to pregnancy. But it may also be caused due to stress, poor health etc. So lack of menstruation does not confirm pregnancy.
▶️ After ovulation, Graafian follicle is transformed to a yellow endocrine mass called Corpus luteum. It secretes progesterone.
▶️ Progesterone helps to maintain the endometrium for implantation and other events of pregnancy.
▶️ If a woman becomes pregnant, all events of menstrual cycle stop and there is no menstruation.
Q 3: Assertion (A): Surgical sterilization methods are typically considered as a last resort for contraception.
Reason (R): Surgical sterilizations are permanent and irreversible or difficult to reverse.
Reason (R): Surgical sterilizations are permanent and irreversible or difficult to reverse.
(1) Both A and R are true but R is NOT the correct explanation of A
(2) A is true but R is false
(3) A is false but R is true
(4) Both A and R are true and R is the correct explanation of A
✅ (4) Both A and R are true and R is the correct explanation of A
Surgical sterilization methods block gamete transport and prevents conception. It is very effective but reversibility is very poor.
2 types:
1. Vasectomy: Sterilization procedure in males. In this, a small part of the vas deferens is removed or tied up through a small incision on the scrotum.
2. Tubectomy: Sterilization procedure in females. In this, a small part of the fallopian tube is removed or tied up through a small incision in abdomen or through vagina.
Q 4: Assertion (A): Sex-linked (X-linked) recessive disorders occur more in males than females.
Reason (R): Males inherit their X chromosome from their mother.
Reason (R): Males inherit their X chromosome from their mother.
(1) Both A and R are true but R is NOT the correct explanation of A
(2) A is true but R is false
(3) A is false but R is true
(4) Both A and R are true and R is the correct explanation of A
✅ (1) Both A and R are true but R is NOT the correct explanation of A
▶️ Sex-linked recessive disorders occur more frequently in males because males have only one X chromosome. If a male inherits a recessive gene associated with a disorder on his X chromosome, he will express the disorder because there is no corresponding gene on the Y chromosome to counteract the recessive gene.
▶️ Females have two X chromosomes, so they would need to inherit two copies of the recessive gene (one on each X chromosome) to express the disorder. If a female inherits only one copy of the recessive gene, she becomes a carrier without expressing the disorder. This is why sex-linked recessive disorders are more common in males.
Q 5: Assertion (A): Tightly linked genes show low recombination.
Reason (R): Because of the proximity of genes, they tend not to segregate independently during meiosis.
Reason (R): Because of the proximity of genes, they tend not to segregate independently during meiosis.
(1) Both A and R are true but R is NOT the correct explanation of A
(2) A is true but R is false
(3) A is false but R is true
(4) Both A and R are true and R is the correct explanation of A
✅ (4) Both A and R are true and R is the correct explanation of A
▶️ During meiosis, recombination or crossing over occur, where segments of DNA are exchanged between homologous chromosomes.
▶️ However, the closely linked genes on a chromosome show lower recombination event between them. Therefore, they do not segregate independently. It leads to lower recombination frequencies for tightly linked genes.
Q 6: Assertion (A): Hydrogen bonds play a crucial role in maintaining the structure of DNA.
Reason (R): Hydrogen bonds form between complementary nitrogenous bases, holding the two strands of DNA together.
Reason (R): Hydrogen bonds form between complementary nitrogenous bases, holding the two strands of DNA together.
(1) Both A and R are true but R is NOT the correct explanation of A
(2) A is true but R is false
(3) A is false but R is true
(4) Both A and R are true and R is the correct explanation of A
✅ (4) Both A and R are true and R is the correct explanation of A
▶️ DNA is made of 2 polynucleotide chains coiled in a right-handed fashion. Its backbone is formed of sugar & phosphates. The bases project inside.
▶️ The 2 chains have anti-parallel polarity, i.e., one chain has the polarity 5’→3’ and the other has 3’→5’.
▶️ The bases in 2 strands are paired through H-bonds forming base pairs (bp).
▶️ A=T (2 hydrogen bonds) C≡G (3 hydrogen bonds)
▶️ Purine comes opposite to a pyrimidine. This generates uniform distance between the 2 strands.
Q 7: Assertion (A): DNA replication occurs semi-conservatively.
Reason (R): During DNA replication, two DNA molecules are synthesised – one with parental strands and other with newly synthesized strands.
Reason (R): During DNA replication, two DNA molecules are synthesised – one with parental strands and other with newly synthesized strands.
(1) Both A and R are true but R is NOT the correct explanation of A
(2) A is true but R is false
(3) A is false but R is true
(4) Both A and R are true and R is the correct explanation of A
✅ (2) A is true but R is false
▶️ There isn’t a new DNA molecule synthesized with only parental strands. Therefore, the reason does not correctly explain the assertion.
▶️ So, the correct statement would be: During DNA replication, two DNA molecules are synthesized, each containing one parental strand and one newly synthesized strand. This is the basis of semi-conservative DNA replication.
Q 8: Assertion (A): Homologous organs are evidence of convergent evolution.
Reason (R): Homologous organs share structural similarities due to common ancestry but may have different functions in different species.
Reason (R): Homologous organs share structural similarities due to common ancestry but may have different functions in different species.
(1) Both A and R are true but R is NOT the correct explanation of A
(2) A is true but R is false
(3) A is false but R is true
(4) Both A and R are true and R is the correct explanation of A
✅ (3) A is false but R is true
▶️ Homologous organs are evidence of divergent evolution, not convergent evolution. They originate from a common ancestor and may have different functions in different species due to adaptation to different environments, which is a process known as divergent evolution.
▶️ Convergent evolution is illustrated by analogous organs, which perform similar functions in different species but do not share a common ancestry. These organs evolve independently, often as a response to similar environmental challenges.
Q 9: Assertion (A): Forelimbs of vertebrates, such as humans, cats, whales and bats, are homologous organs.
Reason (R): Despite differences in function, forelimbs of vertebrates share a common underlying structure inherited from a common ancestor.
Reason (R): Despite differences in function, forelimbs of vertebrates share a common underlying structure inherited from a common ancestor.
(1) Both A and R are true but R is NOT the correct explanation of A
(2) A is true but R is false
(3) A is false but R is true
(4) Both A and R are true and R is the correct explanation of A
✅ (4) Both A and R are true and R is the correct explanation of A
▶️ Homologous organs are the organs having fundamentally similar structure and origin but different functions. E.g.,
1. Human hand, Whale’s flippers, Bat’s wing & Cheetah’s foot. These forelimbs have different functions but similar anatomical structures such as bones.
2. In plants: E.g. Thorns of Bougainvillea and tendrils of Cucurbita.
▶️ Homology indicates common ancestry.
▶️ The origin of homologous organs is due to Divergent evolution. It is the evolution by which same structure evolve in different directions due to adaptations to different needs.
Q 10: Assertion (A): Antibody mediated immunity (AMI) is also known as Humoral immune response.
Reason (R): Antibodies are found in blood plasma.
Reason (R): Antibodies are found in blood plasma.
(1) Both A and R are true but R is NOT the correct explanation of A
(2) A is true but R is false
(3) A is false but R is true
(4) Both A and R are true and R is the correct explanation of A
✅ (4) Both A and R are true and R is the correct explanation of A
Types of Acquired immune responses:
1. Humoral immune response/ Antibody mediated immunity (AMI): It is the immune response mediated by antibodies. Antibodies are found in blood plasma. So called as Humoral immune response. (Humor means fluid. Plasma is a fluid).
2. Cell-mediated response / cell-mediated immunity (CMI): It is the immune response mediated by T-lymphocytes (T-cells). By this, the body can differentiate ‘self’ and ‘non-self’. CMI causes Graft rejection.
Q 11: Assertion (A): Innate immunity is non-specific.
Reason (R): It is present at the time of birth and various barriers prevent the entry of pathogens.
Reason (R): It is present at the time of birth and various barriers prevent the entry of pathogens.
(1) Both A and R are true but R is NOT the correct explanation of A
(2) A is true but R is false
(3) A is false but R is true
(4) Both A and R are true and R is the correct explanation of A
✅ (1) Both A and R are true but R is NOT the correct explanation of A
▶️ Innate immunity is non-specific because it responds to all pathogens in a similar manner, rather than targeting specific pathogens.
▶️ It includes 4 types of Barriers:
1. Physical barriers: E.g. Skin, Mucus coating.
2. Physiological barriers: E.g. gastric HCl, saliva, tear.
3. Cellular barriers: E.g., Phagocytes like WBC, macrophages etc.
4. Cytokine barriers: E.g., Interferon.
Q 12: Assertion (A): Lactic acid bacteria are used in the fermentation of dairy products.
Reason (R): Lactic acid bacteria produce lactic acid during fermentation, which gives dairy products their characteristic tangy flavor.
Reason (R): Lactic acid bacteria produce lactic acid during fermentation, which gives dairy products their characteristic tangy flavor.
(1) Both A and R are true but R is NOT the correct explanation of A
(2) A is true but R is false
(3) A is false but R is true
(4) Both A and R are true and R is the correct explanation of A
✅ (4) Both A and R are true and R is the correct explanation of A
▶️ Lactobacillus or Lactic acid bacteria (LAB) converts milk to curd by producing acids that coagulate and partially digest the milk proteins.
▶️ Fresh milk can be converted to curd by adding some curd containing LAB. It also increases vitamin B12 in curd.
▶️ In stomach, LAB helps to check pathogens.
Q 13: Assertion (A): Gel electrophoresis is used to separate DNA fragments based on their size.
Reason (R): In gel electrophoresis technique, restriction enzymes are used cut DNA molecules into fragments.
Reason (R): In gel electrophoresis technique, restriction enzymes are used cut DNA molecules into fragments.
(1) Both A and R are true but R is NOT the correct explanation of A
(2) A is true but R is false
(3) A is false but R is true
(4) Both A and R are true and R is the correct explanation of A
✅ (1) Both A and R are true but R is NOT the correct explanation of A
▶️ Purified DNA is incubated with the restriction enzyme. As a result, DNA digests. These DNA fragments are separated by a technique called gel electrophoresis.
▶️ 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. The smaller sized fragment moves farther.
Q 14: Assertion (A): Cloning vectors are used to introduce recombinant DNA into host cells.
Reason (R): Cloning vectors typically contain genes for antibiotic resistance to identify transformed cells.
Reason (R): Cloning vectors typically contain genes for antibiotic resistance to identify transformed cells.
(1) Both A and R are true but R is NOT the correct explanation of A
(2) A is true but R is false
(3) A is false but R is true
(4) Both A and R are true and R is the correct explanation of A
✅ (4) Both A and R are true and R is the correct explanation of A
Features required for cloning into a vector:
1. Origin of Replication (ori): Allows replication within the host.
2. Selectable Markers: Typically antibiotic resistance genes; help identify transformed cells.
3. Cloning Sites: Unique restriction enzyme sites to insert foreign DNA.
Q 15: Assertion (A): Recombinant insulin is produced by genetically engineered bacteria.
Reason (R): Bacteria are transformed with a plasmid containing the human insulin gene, enabling them to produce insulin through protein synthesis.
Reason (R): Bacteria are transformed with a plasmid containing the human insulin gene, enabling them to produce insulin through protein synthesis.
(1) Both A and R are true but R is NOT the correct explanation of A
(2) A is true but R is false
(3) A is false but R is true
(4) Both A and R are true and R is the correct explanation of A
✅ (4) Both A and R are true and R is the correct explanation of A
▶️ In 1983, Eli Lilly (an American company) prepared two DNA sequences corresponding to A & B chains of human insulin and introduced them in plasmids of E. coli to produce insulin chains.
▶️ Chains A & B were combined by creating disulfide bonds to form human insulin (Humulin).
Q 16: Assertion (A): All GMOs are harmful to the environment.
Reason (R): GMOs are organisms whose genetic material has been altered using genetic engineering techniques.
Reason (R): GMOs are organisms whose genetic material has been altered using genetic engineering techniques.
(1) Both A and R are true but R is NOT the correct explanation of A
(2) A is true but R is false
(3) A is false but R is true
(4) Both A and R are true and R is the correct explanation of A
✅ (3) A is false but R is true
▶️ Plants, bacteria, fungi & animals whose genes are altered by manipulation are called Genetically Modified Organisms (GMOs).
▶️ In agriculture, GMOs are used to make crops more resistant to harsh conditions like cold, drought, or heat, and to pests.
▶️ GMOs can also be used to improve the nutritional value of food, like making rice richer in Vitamin ‘A’. They can also be used to create plants that can be used in industries to produce things like starches, fuels, and medicines.
▶️ However, there are some concerns about the safety and ethics of using GMOs that need to be carefully considered.
Q 17: Assertion (A): Orchid growing as epiphyte on a mango branch is an example for parasitism.
Reason (R): In this, Orchid is benefitted and the mango tree is harmed.
Reason (R): In this, Orchid is benefitted and the mango tree is harmed.
(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
▶️ Orchid growing as epiphyte on a mango branch is an example for Commensalism. i.e., one species is benefitted (+) and the other is unaffected (0).
▶️ Here Orchid is benefitted (+) and the mango tree is unaffected (0).
Q 18: Assertion (A): Female mosquito is not considered a parasite.
Reason (R): It needs blood only for reproduction, not for its own nutrition.
Reason (R): It needs blood only for reproduction, not for its own nutrition.
(1) Both A and R are true but R is NOT the correct explanation of A
(2) A is true but R is false
(3) A is false but R is true
(4) Both A and R are true and R is the correct explanation of A
✅ (4) Both A and R are true and R is the correct explanation of A
▶️ In parasitism, one species (parasite) is benefitted (+) and the other (host) is harmed (-).
▶️ Many parasites are host-specific (they can parasitize only a single host species). They tend to co-evolve. i.e., if the host evolves special mechanisms against the parasite, the parasite also evolves mechanisms to counteract them to remain with the same host species.
Q 19: Assertion (A): Transfer of energy from one trophic level to another is inefficient.
Reason (R): At each trophic level, the size of the organisms increases.
Reason (R): At each trophic level, the size of the organisms increases.
(1) Both A and R are true but R is NOT the correct explanation of A
(2) A is true but R is false
(3) A is false but R is true
(4) Both A and R are true and R is the correct explanation of A
✅ (1) Both A and R are true but R is NOT the correct explanation of A
▶️ Transfer of energy from one trophic level to another is inefficient because energy is lost as heat at each trophic level, and only a fraction is transferred to the next level due to metabolic processes.
Q 20: Assertion (A): In tropics, Biodiversity (species richness) is highest.
Reason (R): Tropical regions have unstable environment and climate.
Reason (R): Tropical regions have unstable environment and climate.
(1) Both A and R are true but R is NOT the correct explanation of A
(2) A is true but R is false
(3) A is false but R is true
(4) Both A and R are true and R is the correct explanation of A
✅ (2) A is true but R is false
Biodiversity (species richness) is highest in tropics because
1. Tropics had more evolutionary time.
2. Relatively constant environment (less seasonal).
3. They receive more solar energy which contributes to greater productivity.