200 Biology 2-Mark Questions with Answers
For CBSE, ICSE, NIOS & All State Boards
These questions are designed from frequently tested Class 12 Biology concepts and recurring PYQ-style themes relevant to CBSE, ISC, NIOS and State Board examinations. Each question is suitable for a short-answer response of approximately 2 marks.
Chapter 1: Sexual Reproduction in Flowering Plants
1. What is microsporogenesis?
Answer: Microsporogenesis is the process of formation of haploid microspores from diploid microspore mother cells through meiosis inside the anther. The microspores later develop into pollen grains.
2. What is megasporogenesis?
Answer: Megasporogenesis is the formation of haploid megaspores from a diploid megaspore mother cell by meiosis inside the ovule. Usually, one functional megaspore develops into the embryo sac.
3. Distinguish between autogamy and geitonogamy.
Answer: Autogamy is transfer of pollen from the anther to the stigma of the same flower. Geitonogamy is transfer of pollen between two different flowers of the same plant.
4. What is cleistogamy? Give one advantage.
Answer: Cleistogamous flowers remain closed and undergo self-pollination. It ensures seed production even when pollinating agents are absent.
5. What is double fertilisation?
Answer: Double fertilisation involves syngamy and triple fusion. One male gamete fuses with the egg to form the zygote, while the other fuses with two polar nuclei to form the primary endosperm nucleus.
6. What is triple fusion?
Answer: Triple fusion is the fusion of one male gamete with the two polar nuclei in the central cell. It produces the triploid primary endosperm nucleus.
7. What is pollen-pistil interaction?
Answer: It is the interaction between pollen grains and the stigma/style that determines whether a pollen grain is compatible or incompatible. Compatible pollen germinates and forms a pollen tube.
8. What is apomixis?
Answer: Apomixis is a form of asexual reproduction in which seeds are produced without fertilisation. The offspring are generally genetically similar to the parent plant.
9. What is polyembryony?
Answer: Polyembryony is the formation of more than one embryo in a single seed. It is commonly observed in citrus and some other plants.
10. Why are emasculation and bagging performed in artificial hybridisation?
Answer: Emasculation removes anthers before pollen release to prevent self-pollination. Bagging prevents unwanted pollen from reaching the stigma.
Chapter 2: Human Reproduction
11. What is spermatogenesis?
Answer: Spermatogenesis is the formation of spermatozoa from spermatogonia in the seminiferous tubules of the testes. It begins at puberty and is regulated mainly by FSH and testosterone.
12. What is oogenesis?
Answer: Oogenesis is the process of formation and maturation of the female gamete or ovum from oogonia in the ovaries. It begins before birth and resumes cyclically after puberty.
13. State two functions of Sertoli cells.
Answer: Sertoli cells nourish developing sperm cells and help regulate spermatogenesis. They also form the blood-testis barrier and secrete inhibin.
14. What is the role of Leydig cells?
Answer: Leydig cells are present in the interstitial spaces of testes. They secrete androgens, mainly testosterone, which support male reproductive development and spermatogenesis.
15. What is ovulation?
Answer: Ovulation is the release of a secondary oocyte from a mature Graafian follicle. It is triggered mainly by a sudden surge of luteinising hormone.
16. What is implantation?
Answer: Implantation is the attachment and embedding of the blastocyst into the uterine endometrium. It normally occurs about a week after fertilisation.
17. What is the function of the placenta?
Answer: Placenta provides nutrients and oxygen to the developing embryo and removes metabolic wastes. It also acts as an endocrine tissue and produces hormones such as hCG, hPL, oestrogens and progesterone.
18. What is parturition?
Answer: Parturition is the process of childbirth at the end of pregnancy. It involves strong uterine contractions, mainly regulated by oxytocin and positive feedback mechanisms.
19. Differentiate between spermatogenesis and oogenesis.
Answer: Spermatogenesis produces four functional spermatozoa from one primary spermatocyte, whereas oogenesis generally produces one functional ovum and polar bodies. Spermatogenesis begins at puberty, while oogenesis begins during fetal development.
20. What is lactation?
Answer: Lactation is the production and secretion of milk by mammary glands after childbirth. Prolactin promotes milk production, whereas oxytocin helps in milk ejection.
Chapter 3: Reproductive Health
21. What is reproductive health?
Answer: Reproductive health means complete physical, emotional, behavioural and social well-being in matters related to reproduction. It includes awareness, safe reproductive practices and prevention of reproductive disorders.
22. What are STIs? Give two examples.
Answer: Sexually transmitted infections are diseases transmitted mainly through sexual contact. Examples include gonorrhoea and syphilis.
23. What is IVF?
Answer: In vitro fertilisation is a technique in which fertilisation occurs outside the body under laboratory conditions. The resulting embryo is transferred to the reproductive tract for further development.
24. What is amniocentesis?
Answer: Amniocentesis involves examination of amniotic fluid obtained from the uterus. It can be used for prenatal diagnosis of certain genetic and chromosomal abnormalities, but its misuse for sex determination is illegal.
25. What is contraception?
Answer: Contraception refers to methods used to prevent unwanted pregnancy. Methods include barrier methods, intrauterine devices, hormonal methods and surgical methods.
26. Give two advantages of condoms.
Answer: Condoms prevent sperm from entering the female reproductive tract and thereby reduce the chance of fertilisation. They also help reduce transmission of many sexually transmitted infections.
27. What are copper-releasing IUDs?
Answer: Copper IUDs are intrauterine contraceptive devices that release copper ions. They increase sperm mortality and reduce sperm motility and fertilising capacity.
28. What is medical termination of pregnancy?
Answer: Medical termination of pregnancy is the intentional termination of a pregnancy using medically approved procedures. It is performed under appropriate medical and legal conditions.
29. What is infertility?
Answer: Infertility is the inability of a couple to achieve pregnancy despite regular unprotected intercourse over an appropriate period. It may result from male, female or combined factors.
30. What is ICSI?
Answer: Intracytoplasmic sperm injection is an assisted reproductive technique in which a sperm is directly injected into the cytoplasm of an ovum. It is particularly useful in certain cases of male infertility.
Chapter 4: Principles of Inheritance and Variation
31. State Mendel's law of segregation.
Answer: The two alleles of a gene separate during gamete formation so that each gamete receives only one allele. The alleles reunite during fertilisation.
32. What is a test cross?
Answer: A test cross is the crossing of an individual showing a dominant phenotype with a homozygous recessive individual. It is used to determine the unknown genotype.
33. What is a back cross?
Answer: A back cross is a cross between an offspring and either of its parents or a genetically similar parental type. A test cross is a specific type of back cross.
34. What is incomplete dominance?
Answer: In incomplete dominance, neither allele completely dominates the other. The heterozygote shows an intermediate phenotype, as in flower colour in Snapdragon.
35. What is codominance? Give an example.
Answer: Codominance occurs when both alleles in a heterozygote are expressed simultaneously. The ABO blood group system, particularly the IA and IB alleles, is a classic example.
36. Why is ABO blood grouping an example of multiple allelism?
Answer: The ABO blood group gene has three alleles in the population: IA, IB and i. An individual, however, possesses only two of these alleles.
37. What is pleiotropy?
Answer: Pleiotropy occurs when a single gene influences more than one phenotypic trait. The gene responsible for phenylketonuria is a commonly cited example.
38. What is linkage?
Answer: Linkage is the tendency of genes located close together on the same chromosome to be inherited together. Closely linked genes show less recombination.
39. What is crossing over?
Answer: Crossing over is the exchange of corresponding segments between homologous chromosomes during prophase I of meiosis. It produces genetic recombination.
40. What is mutation?
Answer: Mutation is a sudden heritable change in genetic material. It may involve changes in DNA sequence or chromosome structure/number.
41. What is Down syndrome?
Answer: Down syndrome is a chromosomal disorder caused by an additional copy of chromosome 21. It is therefore called trisomy 21.
42. What is Klinefelter syndrome?
Answer: Klinefelter syndrome generally results from an extra X chromosome in a male, giving the karyotype 47,XXY. Affected individuals may show small testes and reduced fertility.
43. What is Turner's syndrome?
Answer: Turner's syndrome is a chromosomal condition in females in which one X chromosome is absent, commonly represented as 45,X. It is associated with short stature and infertility.
44. What is pedigree analysis?
Answer: Pedigree analysis is the study of inheritance of a trait through several generations of a family. It helps identify patterns such as autosomal or sex-linked inheritance.
45. What is haemophilia?
Answer: Haemophilia is a hereditary bleeding disorder caused by deficiency of certain clotting factors. The common forms are inherited as X-linked recessive traits.
46. Why are males more commonly affected by X-linked recessive disorders?
Answer: Males have only one X chromosome. Therefore, a recessive disease-causing allele on their X chromosome is expressed because there is no second X-linked allele to mask it.
47. What is thalassemia?
Answer: Thalassemia is an inherited blood disorder caused by reduced synthesis of one or more globin chains of haemoglobin. It results in anaemia of varying severity.
48. What is a dihybrid cross?
Answer: A dihybrid cross studies inheritance of two pairs of contrasting traits simultaneously. In a typical Mendelian case, the F2 phenotypic ratio is 9:3:3:1.
49. State the law of independent assortment.
Answer: During gamete formation, alleles of different genes assort independently of one another when the genes are unlinked. Thus, inheritance of one trait does not necessarily affect inheritance of another.
50. What is chromosomal theory of inheritance?
Answer: The chromosomal theory states that genes are located on chromosomes and that chromosome behaviour during meiosis explains Mendelian inheritance. Sutton and Boveri independently proposed the theory.
Chapter 5: Molecular Basis of Inheritance
51. What is DNA replication?
Answer: DNA replication is the process by which a DNA molecule produces two identical DNA molecules. It is semiconservative, meaning each daughter DNA contains one parental and one newly synthesised strand.
52. What is the role of DNA polymerase?
Answer: DNA polymerase synthesises a new DNA strand by adding nucleotides to the 3′ end of a growing strand. It also has proofreading functions in many organisms.
53. What is transcription?
Answer: Transcription is the synthesis of RNA using DNA as a template. RNA polymerase catalyses this process.
54. What is translation?
Answer: Translation is the synthesis of a polypeptide using the nucleotide sequence of mRNA. Ribosomes, tRNA and amino acids participate in the process.
55. What is the genetic code?
Answer: The genetic code is the sequence of nucleotide triplets in mRNA that specifies amino acids in a protein. It is generally triplet, degenerate and nearly universal.
56. Why is the genetic code called degenerate?
Answer: The genetic code is degenerate because more than one codon can specify the same amino acid. For example, several different codons code for leucine.
57. What are start and stop codons?
Answer: AUG generally acts as the start codon and codes for methionine. UAA, UAG and UGA are stop codons that terminate translation.
58. What is an operon?
Answer: An operon is a functional unit of DNA containing regulatory elements and structural genes that are coordinately regulated. The lac operon of E. coli is a classic example.
59. What is the lac operon?
Answer: The lac operon is an inducible gene-regulatory system in E. coli involved in lactose utilisation. It includes structural genes regulated by a promoter and operator.
60. What is a transcription unit?
Answer: A transcription unit is a segment of DNA involved in transcription. It generally contains a promoter, structural gene region and a terminator.
61. What is hnRNA?
Answer: Heterogeneous nuclear RNA is the primary RNA transcript produced in eukaryotic cells. It undergoes processing such as capping, tailing and splicing to form mature mRNA.
62. What is RNA splicing?
Answer: RNA splicing removes non-coding introns from the primary transcript and joins coding exons. It is an important step in eukaryotic mRNA processing.
63. What is the role of tRNA?
Answer: tRNA carries specific amino acids to ribosomes during translation. Its anticodon pairs with the complementary codon on mRNA.
64. What is DNA fingerprinting?
Answer: DNA fingerprinting is a technique used to identify individuals based on variations in repetitive DNA sequences. It has applications in forensic science, paternity testing and identification.
65. What are VNTRs?
Answer: VNTRs are variable number tandem repeats, consisting of repeated DNA sequences whose copy number varies among individuals. They are useful in DNA fingerprinting.
66. What is the Human Genome Project?
Answer: The Human Genome Project was an international scientific effort to determine the sequence of the human genome and identify its genes. It generated extensive information about human DNA.
67. What are SNPs?
Answer: SNPs are single nucleotide polymorphisms, in which a single nucleotide differs among individuals at a particular genomic position. They are useful genetic markers.
68. What is a nucleosome?
Answer: A nucleosome is the basic unit of eukaryotic chromatin. It consists of DNA wrapped around a histone protein core.
69. What is a point mutation?
Answer: A point mutation is a change involving a single nucleotide pair or a single base position in DNA. It may alter a codon and sometimes change the resulting protein.
70. What is the central dogma of molecular biology?
Answer: The central dogma describes the flow of genetic information from DNA to RNA and from RNA to protein. DNA can also replicate to transmit genetic information.
Chapter 6: Evolution
71. What is evolution?
Answer: Evolution is the gradual change in inherited characteristics of populations over generations. It results from mechanisms such as mutation, recombination, natural selection, genetic drift and gene flow.
72. What is natural selection?
Answer: Natural selection is the process by which individuals with advantageous heritable variations tend to survive and reproduce more successfully. Over generations, such traits may become more common.
73. What is genetic drift?
Answer: Genetic drift is a random change in allele frequencies in a population, especially in small populations. Founder effect and bottleneck effect are examples.
74. What is founder effect?
Answer: Founder effect occurs when a new population is established by a small number of individuals from a larger population. The new population may have different allele frequencies from the original population.
75. What is adaptive radiation?
Answer: Adaptive radiation is the evolution of several species from a common ancestor, each adapted to a different ecological niche. Darwin's finches are a classic example.
76. Differentiate between homologous and analogous organs.
Answer: Homologous organs have a common evolutionary origin but may perform different functions, such as the forelimbs of humans and whales. Analogous organs perform similar functions but have different origins, such as wings of birds and insects.
77. What are fossils?
Answer: Fossils are preserved remains, impressions or traces of ancient organisms found mainly in sedimentary rocks. They provide important evidence for evolution.
78. What is divergent evolution?
Answer: Divergent evolution occurs when related organisms evolve different characteristics due to adaptation to different environments. It commonly produces homologous structures.
79. What is convergent evolution?
Answer: Convergent evolution occurs when unrelated organisms independently develop similar adaptations due to similar environmental pressures. It commonly produces analogous structures.
80. State Hardy-Weinberg principle.
Answer: Hardy-Weinberg principle states that allele frequencies remain constant in an ideal population in the absence of evolutionary forces. Mutation, migration, selection, drift and recombination can disturb equilibrium.
Chapter 7: Human Health and Disease
81. What is immunity?
Answer: Immunity is the ability of the body to recognise and defend itself against pathogens and foreign substances. It may be innate or acquired.
82. Differentiate between innate and acquired immunity.
Answer: Innate immunity is present from birth and provides non-specific defence. Acquired immunity develops after exposure to specific antigens and has immunological memory.
83. What is active immunity?
Answer: Active immunity develops when the person's own immune system produces antibodies and memory cells after exposure to an antigen. It may occur naturally after infection or artificially after vaccination.
84. What is passive immunity?
Answer: Passive immunity occurs when ready-made antibodies are transferred to an individual. It provides immediate but usually temporary protection.
85. What are antibodies?
Answer: Antibodies are specific immunoglobulin proteins produced mainly by plasma cells in response to antigens. They help neutralise or eliminate foreign substances.
86. What is vaccination?
Answer: Vaccination introduces antigenic material that stimulates the immune system to develop a specific immune response and memory. It prepares the body for faster response to future exposure.
87. What is allergy?
Answer: Allergy is an exaggerated immune response to normally harmless substances called allergens. Common examples include reactions to pollen, dust and certain foods.
88. What is AIDS?
Answer: AIDS is a condition caused by infection with HIV that progressively damages the immune system. HIV mainly targets CD4-positive helper T cells.
89. How is HIV transmitted?
Answer: HIV can spread through unprotected sexual contact, contaminated blood or blood products, sharing contaminated needles, and from an infected mother to child under certain circumstances.
90. What is cancer?
Answer: Cancer is uncontrolled and abnormal cell proliferation. Cancer cells may invade surrounding tissues and can spread to distant sites through metastasis.
91. What is metastasis?
Answer: Metastasis is the spread of malignant cancer cells from the primary site to distant organs through blood or lymph. It is a major feature of malignant tumours.
92. What are carcinogens?
Answer: Carcinogens are agents capable of causing or promoting cancer. Certain chemicals, radiation and some infectious agents can act as carcinogens.
93. What is an autoimmune disease?
Answer: An autoimmune disease occurs when the immune system mistakenly attacks the body's own cells or tissues. Rheumatoid arthritis is one example.
94. What is a pathogen?
Answer: A pathogen is a biological agent capable of causing disease. Bacteria, viruses, fungi, protozoans and parasitic worms can act as pathogens.
95. What is an antigen?
Answer: An antigen is a substance recognised by the immune system that can stimulate an immune response. Many antigens are molecules present on pathogens or foreign cells.
Chapter 8: Microbes in Human Welfare
96. What are probiotics?
Answer: Probiotics are beneficial microorganisms consumed as part of food or supplements that can support normal intestinal microbial balance. Certain Lactobacillus strains are commonly used.
97. What is fermentation?
Answer: Fermentation is a microbial biochemical process used to convert substrates into useful products under suitable conditions. It is widely used in food and industrial production.
98. What is the role of Lactobacillus in curd formation?
Answer: Lactobacillus converts lactose into lactic acid. The acid causes milk proteins to coagulate, resulting in formation of curd.
99. Name two microbes used for industrial products.
Answer: Saccharomyces cerevisiae is used in fermentation, while Aspergillus niger is used for production of citric acid.
100. What is biogas?
Answer: Biogas is a combustible gaseous mixture produced by anaerobic microbial digestion of organic matter. Methane is its major useful component.
101. What are methanogens?
Answer: Methanogens are archaea that produce methane under anaerobic conditions. They occur in environments such as marshes and the digestive tracts of ruminants.
102. What is sewage treatment?
Answer: Sewage treatment removes pollutants and organic matter from wastewater using physical, chemical and biological processes. Microbial treatment plays an important role in secondary treatment.
103. What is BOD?
Answer: Biochemical oxygen demand is the amount of dissolved oxygen required by microorganisms to decompose biodegradable organic matter in water. High BOD generally indicates greater organic pollution.
104. What is activated sludge?
Answer: Activated sludge is the microbial floc formed during secondary sewage treatment. It contains microorganisms that degrade organic matter in wastewater.
105. What is a biofertiliser?
Answer: Biofertilisers contain living microorganisms that improve nutrient availability or soil fertility. Rhizobium and certain cyanobacteria are examples.
Chapter 9: Biotechnology – Principles and Processes
106. What is biotechnology?
Answer: Biotechnology is the application of living organisms, cells or biological molecules to develop useful products and processes. Modern biotechnology often involves genetic engineering.
107. What is recombinant DNA technology?
Answer: Recombinant DNA technology involves joining DNA fragments from different sources and introducing the recombinant DNA into a suitable host. It is used to produce desired genes or proteins.
108. What are restriction enzymes?
Answer: Restriction enzymes are nucleases that cut DNA at specific recognition sequences. They are important tools in recombinant DNA technology.
109. What are sticky ends?
Answer: Sticky ends are short single-stranded DNA overhangs generated when certain restriction enzymes cut DNA in a staggered manner. They can base-pair with complementary ends.
110. What is DNA ligase?
Answer: DNA ligase is an enzyme that joins DNA fragments by forming phosphodiester bonds between adjacent nucleotides. It is used to construct recombinant DNA molecules.
111. What is a cloning vector?
Answer: A cloning vector is a DNA molecule used to carry a foreign DNA fragment into a host cell and allow its replication. Plasmids are commonly used vectors.
112. What is a plasmid?
Answer: A plasmid is a small, usually circular, extrachromosomal DNA molecule found commonly in bacteria. It can replicate independently and is widely used as a cloning vector.
113. What is the origin of replication?
Answer: The origin of replication is a specific DNA sequence where replication begins. In a vector, it helps control the replication of the recombinant DNA molecule inside the host.
114. What is a selectable marker?
Answer: A selectable marker is a gene that helps identify or select host cells containing the desired recombinant DNA. Antibiotic-resistance genes are commonly used examples.
115. What is PCR?
Answer: Polymerase chain reaction is a technique used to amplify a specific DNA sequence. It involves repeated cycles of denaturation, primer annealing and extension.
116. What is the role of Taq polymerase?
Answer: Taq polymerase is a heat-stable DNA polymerase used in PCR. It synthesises new DNA strands during the extension step.
117. What is gel electrophoresis?
Answer: Gel electrophoresis separates DNA fragments according to size by movement through a gel under an electric field. Smaller DNA fragments generally migrate faster than larger ones.
118. What is downstream processing?
Answer: Downstream processing refers to the recovery, purification and formulation of a desired biological product after its production. It ensures that the final product meets required standards.
119. What is a bioreactor?
Answer: A bioreactor is a vessel in which biological processes are carried out under controlled conditions. It provides suitable temperature, pH, oxygen and nutrient conditions for production.
120. Why are restriction enzymes called molecular scissors?
Answer: Restriction enzymes cut DNA molecules at specific recognition sequences. Because of this precise DNA-cutting ability, they are commonly called molecular scissors.
Chapter 10: Biotechnology and Its Applications
121. What is genetically modified organism?
Answer: A genetically modified organism contains genetic material that has been deliberately altered using biotechnology. The modification may introduce, remove or change particular traits.
122. What is Bt cotton?
Answer: Bt cotton is genetically modified cotton containing genes from Bacillus thuringiensis. The genes produce proteins toxic to certain insect pests.
123. What is Bt toxin?
Answer: Bt toxin is an insecticidal protein produced by certain strains of Bacillus thuringiensis. In susceptible insects, the activated toxin damages the midgut and can cause death.
124. What is gene therapy?
Answer: Gene therapy aims to treat a disease by introducing, replacing, modifying or regulating genetic material in a patient's cells. It has been explored for several inherited disorders.
125. What is recombinant insulin?
Answer: Recombinant insulin is insulin produced using genetically engineered microorganisms or cells. Recombinant DNA technology allows large-scale production of human insulin.
126. What are transgenic animals?
Answer: Transgenic animals contain a foreign gene introduced into their genome using genetic engineering techniques. They are used in research, disease studies and production of biological products.
127. What is molecular diagnosis?
Answer: Molecular diagnosis identifies diseases using specific molecules such as DNA, RNA or proteins. Techniques such as PCR can detect pathogens or genetic abnormalities.
128. What is ELISA?
Answer: ELISA is an immunological technique used to detect specific antigens or antibodies. It is widely used in diagnosis of infections and detection of various biological molecules.
129. What is biopiracy?
Answer: Biopiracy refers to unauthorised commercial use or appropriation of biological resources or traditional knowledge, often without proper recognition or benefit sharing with the source communities.
130. What are biosafety concerns?
Answer: Biosafety concerns relate to possible harmful effects of biological research, genetically modified organisms or biotechnology products on humans and the environment. Proper assessment and regulation are therefore important.
Chapter 11: Organisms and Populations
131. What is a population?
Answer: A population is a group of individuals of the same species living in a particular geographical area at a given time. Members can potentially interbreed with one another.
132. What is population density?
Answer: Population density represents the number of individuals of a population per unit area or volume. It can also be expressed through biomass or percentage cover in suitable cases.
133. What is natality?
Answer: Natality is the birth rate of a population. It increases population size by adding new individuals through reproduction.
134. What is mortality?
Answer: Mortality is the death rate in a population. It reduces population size by removing individuals from the population.
135. What is carrying capacity?
Answer: Carrying capacity is the maximum population size that an environment can support sustainably with available resources. It is represented by K in the logistic growth equation.
136. Differentiate between exponential and logistic growth.
Answer: Exponential growth occurs under unlimited resources and produces a J-shaped curve. Logistic growth considers limited resources and produces an S-shaped curve approaching carrying capacity.
137. What is mutualism?
Answer: Mutualism is an interaction in which both participating species benefit. Examples include lichen association and mycorrhiza.
138. What is commensalism?
Answer: Commensalism is an interaction in which one species benefits while the other is neither significantly helped nor harmed. Epiphytic orchids growing on trees are an example.
139. What is parasitism?
Answer: Parasitism is an interaction in which one organism, the parasite, benefits while the host is harmed. Tapeworms living in the human intestine are an example.
140. What is predation?
Answer: Predation is an interaction in which one organism captures and consumes another organism. It can regulate prey populations and influence community structure.
141. What is competition?
Answer: Competition occurs when organisms require the same limited resource. Both competitors may experience reduced access to resources and lower fitness.
142. What is competitive exclusion?
Answer: Competitive exclusion states that two closely related species competing for exactly the same limiting resources cannot coexist indefinitely in the same niche. One may eventually eliminate or displace the other.
143. What is ecological niche?
Answer: An ecological niche describes the functional role of a species and the range of environmental conditions and resources it uses. It is broader than simply the physical place where the species lives.
144. What is adaptation?
Answer: Adaptation is a heritable feature that increases an organism's ability to survive and reproduce in a particular environment. Adaptations develop through evolutionary processes.
145. What is hibernation?
Answer: Hibernation is a state of greatly reduced metabolic activity and body temperature during unfavourable cold conditions. It helps some animals conserve energy.
Chapter 12: Ecosystem
146. What is an ecosystem?
Answer: An ecosystem is a functional unit consisting of living organisms interacting with one another and with the physical environment. It includes biotic and abiotic components.
147. What are producers?
Answer: Producers are organisms that synthesise organic food from inorganic substances, mainly through photosynthesis. Green plants and algae are major producers.
148. What are decomposers?
Answer: Decomposers, mainly bacteria and fungi, break down dead organic matter into simpler substances. They recycle nutrients back into the ecosystem.
149. What is a food chain?
Answer: A food chain represents a sequence of organisms through which food and energy pass. Each step represents a trophic level.
150. What is a food web?
Answer: A food web is a network of interconnected food chains in an ecosystem. It provides multiple pathways for energy transfer.
151. What is an ecological pyramid?
Answer: An ecological pyramid is a graphical representation of the number, biomass or energy present at successive trophic levels of an ecosystem.
152. Why is the pyramid of energy always upright?
Answer: Energy is lost as heat at every trophic transfer. Therefore, energy available decreases progressively from producers to higher trophic levels, making the pyramid always upright.
153. State the 10% law of energy transfer.
Answer: According to the 10% law, approximately 10% of the energy at one trophic level is transferred to the next trophic level. Most of the remaining energy is lost through metabolic activities and heat.
154. What is primary productivity?
Answer: Primary productivity is the rate at which producers convert solar or chemical energy into organic matter. Gross primary productivity is total production, while net primary productivity is the amount remaining after producer respiration.
155. What is decomposition?
Answer: Decomposition is the breakdown of complex organic matter into simpler substances by decomposers. It includes processes such as fragmentation, leaching, catabolism, humification and mineralisation.
156. What is humification?
Answer: Humification is the process of formation of humus during decomposition of organic matter. Humus is resistant to microbial decomposition and acts as a reservoir of nutrients.
157. What is mineralisation?
Answer: Mineralisation is the conversion of organic nutrients in detritus into inorganic forms by microbial activity. These inorganic nutrients become available for plant uptake.
158. What is ecological succession?
Answer: Ecological succession is the gradual and orderly change in species composition of a community over time. It eventually leads toward a relatively stable community.
159. Differentiate between primary and secondary succession.
Answer: Primary succession begins on a previously unoccupied surface without soil, such as bare rock. Secondary succession begins in an area where a community existed previously and soil is already present.
160. What is the carbon cycle?
Answer: The carbon cycle describes movement of carbon among atmosphere, organisms, soil, oceans and geological reservoirs. Photosynthesis, respiration and decomposition are major biological processes in this cycle.
Chapter 13: Biodiversity and Conservation
161. What is biodiversity?
Answer: Biodiversity is the variety of living organisms at genetic, species and ecosystem levels. It reflects biological variation within and among ecosystems.
162. What are the three levels of biodiversity?
Answer: The three levels are genetic diversity, species diversity and ecosystem diversity. Together they describe biological variation at different organisational levels.
163. What is species diversity?
Answer: Species diversity refers to the variety and relative abundance of different species in a particular region or ecosystem. It includes species richness and evenness.
164. What is genetic diversity?
Answer: Genetic diversity is variation in genes among individuals and populations of the same species. It helps populations adapt to environmental changes.
165. What is ecosystem diversity?
Answer: Ecosystem diversity refers to the variety of ecosystems, habitats and ecological processes in a region. Forests, wetlands and deserts are examples of different ecosystems.
166. What is a biodiversity hotspot?
Answer: A biodiversity hotspot is a region with exceptionally high endemic biodiversity that is also under significant threat from habitat loss. Hotspots are priority areas for conservation.
167. What is endemism?
Answer: Endemism refers to the occurrence of a species naturally restricted to a particular geographical region. Endemic species are often especially vulnerable to habitat loss.
168. What is in-situ conservation?
Answer: In-situ conservation protects organisms in their natural habitats. National parks, wildlife sanctuaries, biosphere reserves and sacred groves are examples.
169. What is ex-situ conservation?
Answer: Ex-situ conservation protects species outside their natural habitats. Examples include zoos, botanical gardens, seed banks, cryopreservation and captive breeding.
170. What is a sacred grove?
Answer: Sacred groves are patches of natural vegetation protected by local communities because of traditional cultural or religious beliefs. They help conserve biodiversity in natural habitats.
171. What is the Red Data Book?
Answer: The Red Data Book provides information about threatened species and their conservation status. It helps draw attention to species at risk of extinction.
172. What is extinction?
Answer: Extinction is the permanent disappearance of a species from Earth. Habitat loss, overexploitation, invasive species and other pressures can drive species to extinction.
173. What is co-extinction?
Answer: Co-extinction occurs when extinction of one species leads to the extinction of another species that depends strongly on it. Host-parasite and specialised mutualistic relationships can be involved.
174. What is the species-area relationship?
Answer: Species richness generally increases with increasing area of habitat. It is often represented by the relationship S = CAz, where S is species richness and A is area.
175. What is the rivet-popper hypothesis?
Answer: The rivet-popper hypothesis compares species in an ecosystem with rivets in an aircraft. Loss of a few species may have little immediate effect, but continued loss can eventually destabilise the ecosystem.
Chapter 14: Reproduction, Genetics and Applied Biology – Mixed PYQ Practice
176. Why is endosperm important in flowering plants?
Answer: Endosperm provides nourishment to the developing embryo. In most angiosperms it develops after triple fusion and is generally triploid.
177. Why is pollen considered a male gametophyte?
Answer: The pollen grain represents the male gametophytic generation of flowering plants. It produces or carries the male gametes required for fertilisation.
178. Why is genetic variation important?
Answer: Genetic variation provides the raw material for natural selection and evolution. It increases the ability of populations to respond to changing environmental conditions.
179. Why are mutations important in evolution?
Answer: Mutations create new genetic variations. Some variations may influence survival or reproduction and can therefore contribute to evolutionary change.
180. Why is DNA considered genetic material?
Answer: DNA stores hereditary information and can replicate accurately. It also contains information required for synthesis and regulation of proteins and can undergo heritable changes.
181. Why is RNA important in gene expression?
Answer: RNA acts as an intermediary and functional molecule in gene expression. mRNA carries genetic information, tRNA carries amino acids and rRNA forms an important part of ribosomes.
182. Why are viruses considered acellular?
Answer: Viruses do not possess a typical cellular structure and lack independent metabolic machinery. They replicate only inside suitable host cells.
183. Why are antibiotics not effective against viruses?
Answer: Antibiotics generally target bacterial structures or metabolic pathways. Viruses lack these independent cellular structures and rely on host-cell machinery for replication.
184. Why are vaccines important?
Answer: Vaccines stimulate specific immune responses and immunological memory without requiring natural disease to establish immunity. They help reduce the incidence and severity of many infectious diseases.
185. Why is biodiversity important?
Answer: Biodiversity supports ecosystem functioning, provides food and other resources, contributes to ecosystem services and has scientific, cultural and ethical value.
Chapter 15: High-Frequency Board Revision Questions
186. What is parthenocarpy?
Answer: Parthenocarpy is the development of fruit without fertilisation. Such fruits are generally seedless, as seen in naturally or artificially induced examples such as banana.
187. What is self-incompatibility?
Answer: Self-incompatibility is a genetically controlled mechanism that prevents self-pollen from successfully fertilising the ovule. It promotes outcrossing and genetic variation.
188. What is a seed bank?
Answer: A seed bank is an ex-situ conservation facility where seeds are stored under suitable conditions for long-term preservation. It helps conserve genetic diversity of plant species.
189. What is cryopreservation?
Answer: Cryopreservation is the preservation of biological material at extremely low temperatures, commonly using liquid nitrogen. It helps maintain cells, tissues, gametes or embryos for long periods.
190. What is tissue culture?
Answer: Tissue culture is the in-vitro growth of plant cells, tissues or organs on a suitable nutrient medium under sterile conditions. It is widely used for micropropagation and conservation.
191. What are somaclones?
Answer: Somaclones are genetically similar or variant plants produced through tissue culture. Variations arising during tissue culture are called somaclonal variations.
192. What is biofortification?
Answer: Biofortification is the improvement of nutritional quality of crops through breeding, biotechnology or agronomic practices. It may increase levels of vitamins, minerals or proteins.
193. What is golden rice?
Answer: Golden rice is a genetically modified rice developed to produce beta-carotene in the edible grain. Beta-carotene can be converted into vitamin A in the body.
194. What is RNA interference?
Answer: RNA interference is a biological mechanism in which small RNA molecules can silence expression of specific genes by interfering with target mRNA. It has applications in biotechnology and research.
195. What is cloning?
Answer: Cloning is the production of genetically identical or nearly identical copies of a biological entity. It may involve genes, cells or whole organisms.
196. What is bioremediation?
Answer: Bioremediation uses living organisms, particularly microorganisms or plants, to remove, degrade or detoxify pollutants from contaminated environments.
197. What is phytoremediation?
Answer: Phytoremediation is the use of plants to remove, immobilise or degrade pollutants in soil or water. Certain plants can accumulate heavy metals and other contaminants.
198. What is eutrophication?
Answer: Eutrophication is excessive nutrient enrichment of a water body, often caused by nitrogen and phosphorus inputs. It can promote algal blooms and reduce dissolved oxygen when organic matter decomposes.
199. What is biomagnification?
Answer: Biomagnification is the increase in concentration of persistent, non-biodegradable toxic substances at successive trophic levels. Top consumers may accumulate the highest concentrations.
200. Why is conservation of biodiversity necessary?
Answer: Biodiversity conservation prevents extinction and maintains ecosystem stability and ecological services. It also preserves genetic resources and biological resources for future generations.
Download PDF 200 Biology 2 Marks Questions with Answers – Class 12 Board Exams