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Maharashtra Board Class 12 Biology Question Paper Solutions Feb 2025

Maharashtra Board Class 12 Biology Question Paper Solutions February 2025
Question Paper Page No. 1 Question Paper Page No. 2 Question Paper Page No. 3 Maharashtra Board Biology Question Paper Header

Board Question Paper: February 2025
BIOLOGY

Time: 3 Hrs.

Max. Marks: 70

SECTION – A

Q.1. Select and write the correct answer for the following multiple choice questions: [10]

i. The aquatic plant ______ is known as "Terror of Bengal".
  • (A) Lotus
  • (B) Pistia
  • (C) Eichhornia
  • (D) Vallisneria
Answer: (C) Eichhornia
ii. A flower shows dull colour, strong fragrance and edible pollen grains. The type of pollination in such flowers is ______.
  • (A) Anemophily
  • (B) Chiropterophily
  • (C) Ornithophily
  • (D) Entomophily
Answer: (D) Entomophily
(Note: While strong fragrance and dull color can suggest bats/Chiropterophily, edible pollen is a specific reward for beetles, which falls under Entomophily).
iii. Part of the sperm containing enzymes for penetration of corona radiata is ______.
  • (A) tail
  • (B) middle part
  • (C) neck
  • (D) head
Answer: (D) head
(Specifically the acrosome located in the head).
iv. In bird population of newly formed volcanic island, a rare allele of a gene was noted to be much more prevalent than the populations of same species on the mainland. This is known as ______ effect.
  • (A) Founder
  • (B) Bohr
  • (C) Bottle neck
  • (D) Haldane
Answer: (A) Founder
v. In a plant, deficiency symptom called 'Die-back of shoots' was observed. This can be rectified by this element –
  • (A) zinc
  • (B) sulphur
  • (C) iron
  • (D) copper
Answer: (D) copper
vi. Insect resistant property in cotton crop is developed by introducing a gene from ______.
  • (A) Bacillus thuringiensis
  • (B) Bacillus subtilis
  • (C) Bacillus polymyxa
  • (D) Escherichia coli
Answer: (A) Bacillus thuringiensis
vii. The type of interspecific interaction in which one species is harmed and other is not affected is termed as ______.
  • (A) commensalism
  • (B) parasitism
  • (C) amensalism
  • (D) mutualism
Answer: (C) amensalism
viii. The small pores present on woody stem surface with bark and which carry out gaseous exchange are ______.
  • (A) stomata
  • (B) hydathode
  • (C) ventricle
  • (D) lenticels
Answer: (D) lenticels
ix. In the given food chain, if plants absorb 1000 Joules of light energy, then how much energy is available for Lion?
Plants \(\rightarrow\) Deer \(\rightarrow\) Lion
(Producer) (Herbivore) (Carnivore)
  • (A) 10 Joules
  • (B) 100 Joules
  • (C) 1000 Joules
  • (D) 0.1 Joule
Answer: (A) 10 Joules
(10% Law: Plants 1000J -> Deer 100J -> Lion 10J).
x. Glucagon is secreted by ______ cells of pancreas.
  • (A) PP
  • (B) alpha
  • (C) delta
  • (D) beta
Answer: (B) alpha

HSC Biology

Q.2. Answer the following questions: [8]

i. What is the effect of excessive transpiration in leaves?
Answer: Excessive transpiration leads to wilting (drooping of leaves due to loss of turgidity).
ii. Which method of plant breeding can be used to obtain many genetically identical saplings of endangered species?
Answer: Tissue Culture or Micropropagation.
iii. Define: Spermatogenesis.
Answer: Spermatogenesis is the process of formation of haploid, microscopic, and functional male gametes (spermatozoa) from the diploid spermatogonial cells in the testes.
iv. What is grand period of growth?
Answer: The phase of rapid growth (exponential phase) in the sigmoid growth curve where maximum growth occurs is called the grand period of growth.
v. Write the anticodon of 5' AUG 3'.
Answer: 3' UAC 5'
vi. Mention pollinating agent for maize flowers.
Answer: Wind (Anemophily).
vii. Which is the first step in the process of absorption of water by roots from soil?
Answer: Imbibition.
viii. Name the hormonal disorder caused due to hyperthyroidism in adults.
Answer: Exophthalmic Goiter (Graves' disease).

SECTION – B

Attempt any EIGHT of the following questions: [16]

Q.3. Enlist any two domesticated species of honeybee and write their role in increasing crop yield.
Answer:

Species: 1. Apis mellifera (European bee) 2. Apis cerana indica (Indian bee).

Role: They act as excellent pollinators. When they visit flowers for nectar/pollen, they transfer pollen grains, resulting in fertilization and significantly increasing crop yield (e.g., in sunflower, mustard).

Q.4.
i. Name the vein which carries oxygenated blood.
ii. How does portal vein differ from normal vein?
Answer:

i. Pulmonary vein (carries oxygenated blood from lungs to heart).

ii. A normal vein starts from capillaries in body tissues and ends in the heart. A portal vein starts in capillaries (of one organ) and ends in capillaries (of another organ) without going directly to the heart (e.g., Hepatic portal vein).

Q.5. The health worker in hilly area will advise people to prevent which deficiency disease? Which micronutrient is deficient in the above area?
Answer:

Disease: Simple Goiter.

Micronutrient: Iodine (Hilly areas often have iodine-deficient soil).

Q.6. Name the vector responsible for causing malaria and filariasis respectively.
Answer:
  • Malaria: Female Anopheles mosquito.
  • Filariasis: Female Culex mosquito.
Q.7. Name two chromosomal disorders which show presence of 47 chromosomes. Give their genotypes.
Answer:
  1. Down's Syndrome: Genotype: 45 + XY or 45 + XX (Total 47 due to Trisomy 21).
  2. Klinefelter's Syndrome: Genotype: 44 + XXY (Total 47).
Q.8. Which germinal layer produces following structures?
i. Eustachian tube
ii. Pineal gland
iii. Middle ear
iv. Lining of middle ear
Answer:
  1. Eustachian tube: Endoderm
  2. Pineal gland: Ectoderm
  3. Middle ear (bones/structure): Mesoderm
  4. Lining of middle ear: Endoderm
Q.9. Due to environmental change in area, the fruits were taking more time for ripening. Which gaseous growth regulator can be suggested to fruit merchant? Give the source of the same in plants.
Answer:

Regulator: Ethylene.

Source in plants: It is synthesized in ripening fruits, flowers, and senescent leaves.

Q.10. Explain two-celled stage of pollen grain in angiosperms.
Answer:

The pollen grain (microspore) undergoes the first mitotic division to form two unequal cells:

  1. Vegetative Cell: Larger, has abundant food reserve and a large irregular nucleus.
  2. Generative Cell: Smaller, spindle-shaped, and floats in the cytoplasm of the vegetative cell. It eventually divides to form male gametes.

Most angiosperms shed pollen at this 2-celled stage.

Q.11. What is the difference between Heterocatalytic and Autocatalytic function of DNA?
Answer:
  • Autocatalytic function: When DNA directs the synthesis of its own copy (Replication).
  • Heterocatalytic function: When DNA directs the synthesis of other molecules like RNA and Proteins (Transcription/Translation).
Q.12. What is Transpiration? How does it differ from guttation?
Answer:

Transpiration: The loss of water in the form of vapor from the aerial parts of the plant.

Difference: In transpiration, water is lost as vapor through stomata, while in guttation, water is lost in liquid form through hydathodes (at leaf margins).

Q.13. Give reason: When Rh -ve mother conceives Rh +ve foetus, then she is given injection of anti Rh antibodies.
Answer:

This is done to prevent Erythroblastosis fetalis (HDN). During the first delivery, some Rh+ blood from the fetus may mix with the mother's Rh- blood, causing her to produce anti-Rh antibodies. If not treated, these antibodies can cross the placenta in a subsequent pregnancy and destroy the Rh+ fetus's RBCs. The anti-Rh injection (Rogham) destroys any fetal RBCs entering the mother before her immune system can sensitize.

Q.14. Identify the chromosomal aberrations:
diagrammatic representation of 'decomposition cycle

[Refer to Image Q14]

i. A B C D E F G H → A B C F G H (Loss of D E)

ii. A B C D E F G H → P Q R C D E F G H (Substitution/Translocation)

iii. A B C D E F G H → A B C D C D E F G H (Repeat of C D)

iv. A B C D E F G H → A D C B E F G H (Reversal of B C D)

Answer:
  1. Deletion (Loss of segment DE).
  2. Translocation (Segment AB replaced by PQR from non-homologous chromosome).
  3. Duplication (Segment CD is repeated).
  4. Inversion (Segment BCD is reversed to DCB).

SECTION – C

Attempt any EIGHT of the following questions: [24]

Q.15. Complete the following table –
Organ Region Sympathetic effect Parasympathetic effect
i. Heart beat Increases Decreases
ii. Blood vessels Constricts Dilates
iii. Arterial B.P. Increases Decreases
iv. Pupil of eye Dilates Constricts
v. Gastrointestinal movements Retards peristalsis Increases / Accelerates
vi. Urinary bladder Relaxes Contracts
Q.16. i. Draw neat and labelled diagram to show T.S. of artery.
ii. Name two superficially placed arteries.
Answer:

i. Diagram: (Students should draw T.S. of Artery showing three layers: Tunica Externa, Tunica Media (thick muscular), Tunica Interna, and narrow lumen).

ii. Superficial Arteries: Radial artery (wrist), Carotid artery (neck), or Temporal artery.

Q.17. Write any six characteristics of genetic code.
Answer:
  1. Triplet Nature: Three nucleotides code for one amino acid.
  2. Universality: The code is the same in almost all organisms.
  3. Non-ambiguous: One codon specifies only one amino acid.
  4. Degeneracy: A single amino acid can be coded by multiple codons.
  5. Commaless: Read continuously without punctuation.
  6. Non-overlapping: Adjacent codons do not overlap.
  7. Start/Stop Codons: AUG is start; UAA, UAG, UGA are stop codons.
Q.18. i. In the process of rDNA technology, if two separate restriction enzymes are used to cut the vector and donor DNA, then which problem will arise in the formation of rDNA or chimeric DNA. Explain.
ii. Name any two restriction enzymes and their source organisms.
Answer:

i. Problem: If two different restriction enzymes are used, they will produce different "sticky ends" (overhangs) that are not complementary to each other. Consequently, the vector DNA and donor DNA cannot anneal (base pair), and DNA ligase cannot join them to form recombinant DNA.

ii. Examples:

  • EcoRI from Escherichia coli
  • HindIII from Haemophilus influenzae
  • BamHI from Bacillus amyloliquefaciens
Q.19. i. Explain vestigial organs as evidence of evolution.
ii. Give any two examples of vestigial organs in human beings.
Answer:

i. Explanation: Vestigial organs are rudimentary structures that are non-functional in the current organism but were functional in their ancestors. Their presence suggests that the organism evolved from ancestors where these organs were useful, supporting the theory of descent with modification.

ii. Examples: Vermiform Appendix, Coccyx (tail bone), Nictitating membrane (plica semilunaris), Wisdom teeth.

Q.20. What is water potential? Write any four factors affecting water absorption in plants.
Answer:

Water Potential (\(\Psi_w\)): It is the difference between the free energy of water molecules in pure water and the free energy of water in a solution. It determines the direction of water movement.

Factors affecting water absorption:

  1. Available soil water (Capillary water).
  2. Concentration of soil solution (must be hypotonic).
  3. Soil aeration (Roots need oxygen for respiration).
  4. Temperature of soil (Optimal 20°C - 30°C).
Q.21. Draw the developmental flow chart in plant from seed germination to death of plant.
Answer:

Diagrammatic Representation: (Students are required to draw this diagram only]

diagrammatic representation of 'decomposition cycle

Diagrammatic Representation: (For Better Understanding of the concept. Students are not required to draw this diagram.)

diagrammatic representation of 'decomposition cycle Developmental Flow Chart:

Germination \(\rightarrow\) Juvenile Phase / Vegetative Growth \(\rightarrow\) Reproductive Phase (Flowering) \(\rightarrow\) Maturation (Fruiting/Seed formation) \(\rightarrow\) Senescence (Aging) \(\rightarrow\) Death
Q.22. Which element is mostly fixed by biofertilizer? Write the benefits of biofertilizer.
Answer:

Element: Nitrogen (N2).

Benefits:

  • Cost-effective compared to chemical fertilizers.
  • Eco-friendly and pollution-free.
  • Increases soil fertility and texture.
  • Provides protection against soil-borne pathogens.
Q.23. What is biofortification? Explain with respect to GM food plants.
Answer:

Biofortification: It is the method of breeding crops with higher levels of vitamins, minerals, or higher protein and healthier fats to improve public health.

With GM plants: Genetic modification helps achieve this faster. For example, Golden Rice is a GM crop biofortified with the gene for Pro-vitamin A (Beta-carotene) to combat Vitamin A deficiency (Night blindness).

Q.24. Differentiate between habitat and niche.
Answer:
Habitat Niche
The physical place where an organism lives. (Address) The functional role of an organism in an ecosystem. (Profession)
Can be shared by many species. Specific to a single species.
Example: A pond. Example: Predator of frogs in that pond.
Q.25. What is decomposition? Give diagrammatic representation of 'decomposition cycle.'
Answer:

Decomposition: The process of breaking down complex organic matter into inorganic substances like carbon dioxide, water, and nutrients by decomposers.

Diagrammatic Representation:

diagrammatic representation of 'decomposition cycle Dead Plant/Animal (Detritus)
\(\downarrow\)
1. Fragmentation (Earthworms)
\(\downarrow\)
2. Leaching (Water soluble nutrients go to soil)
\(\downarrow\)
3. Catabolism (Bacteria/Fungal enzymes)
\(\downarrow\)
4. Humification (Humus formation)
\(\downarrow\)
5. Mineralization (Release of inorganic nutrients)
Q.26. What is biomagnification? Draw the flow chart and explain it with respect to DDT.
Answer:

Biomagnification: The increase in concentration of a toxicant/pollutant at successive trophic levels in a food chain.

DDT Flow Chart:

Water (0.003 ppb)
\(\downarrow\)
Zooplankton (0.04 ppm)
\(\downarrow\)
Small Fish (0.5 ppm)
\(\downarrow\)
Large Fish (2 ppm)
\(\downarrow\)
Fish-eating Birds (25 ppm)

Explanation: DDT is non-biodegradable and lipid-soluble. It accumulates in the fat tissues of organisms. As one trophic level eats the next, the DDT accumulates, reaching toxic levels in top carnivores (birds), disturbing calcium metabolism and causing eggshell thinning.

SECTION – D

Attempt any THREE of the following questions: [12]

Q.27. i. What is the location of blind spot in human eye?
ii. Give importance of retina in image formation.
iii. Name the cells which function in dim light and day light.
iv. Which pigment is derived from vitamin A?
Answer:

i. Location: Posterior pole of the eye, medial to and slightly above the posterior pole of the eyeball (where the optic nerve leaves the eye).

ii. Importance of Retina: It acts as the screen where the image is formed. It contains photoreceptor cells that convert light energy into action potentials (nerve impulses) sent to the brain.

iii. Cells: Dim light: Rod cells; Day/Bright light: Cone cells.

iv. Pigment: Retinal (part of Rhodopsin) is an aldehyde derivative of Vitamin A.

Q.28. With the help of a neat and labelled diagram, explain the conducting system of human heart.
Answer:
Diagram of Heart showing SA Node, Internodal pathways, AV Node, Bundle of His, Bundle Branches, Purkinje Fibers [Diagram of Heart showing SA Node, Internodal pathways, AV Node, Bundle of His, Bundle Branches, Purkinje Fibers]

Explanation:

  1. SA Node (Sino-atrial Node): The pacemaker located in the right upper corner of the right atrium. Initiates the impulse.
  2. AV Node (Atrio-ventricular Node): Located in the lower left corner of the right atrium. Receives impulse from SA node and delays it slightly.
  3. Bundle of His: Originates from AV node, divides into right and left bundle branches running through the interventricular septum.
  4. Purkinje Fibers: Fine fibers arising from bundle branches that spread throughout the ventricular walls, causing ventricular contraction.
Q.29. i. Explain incomplete dominance and codominance with suitable example.
ii. Show the genotype with the help of charts.
Answer:

i. Incomplete Dominance: Both alleles express themselves partially. The phenotype is a blend.
Example: Mirabilis jalapa (4 O'clock plant). Red (RR) x White (rr) = Pink (Rr).

ii. Codominance: Both alleles express themselves equally and independently.
Example: Roan coat colour in cattle or AB blood group. Red (RR) x White (WW) = Roan (RW).

Chart for Incomplete Dominance:
P: Red (RR) x White (rr)
F1: Pink (Rr)
F2 (Selfing): 1 Red (RR) : 2 Pink (Rr) : 1 White (rr)

Chart for Codominance:
P: Red (RR) x White (WW)
F1: Roan (RW)
F2: 1 Red (RR) : 2 Roan (RW) : 1 White (WW)
Q.30. i. Define: Siphonogamy.
ii. Differentiate between chalazogamy and porogamy with respect to the entry of the pollen tube.
iii. Draw a neat and labelled diagram to show mesogamy.
Answer:

i. Siphonogamy: The process in which the male gametes are carried to the egg cell through a pollen tube.

ii. Differentiation:

  • Porogamy: Pollen tube enters the ovule through the Micropyle (most common).
  • Chalazogamy: Pollen tube enters the ovule through the Chalaza (basal part).

iii. Diagram (Mesogamy):

Diagram of Ovule showing pollen tube entering laterally through the Integuments (Mesogamy) [Diagram of Ovule showing pollen tube entering laterally through the Integuments (Mesogamy)]
Q.31. i. Define: Infertility.
ii. If woman's fallopian tube is blocked, which treatment can be given to overcome infertility? Explain in brief.
iii. What is sperm bank?
Answer:

i. Infertility: The inability to conceive or produce children even after 1-2 years of unprotected sexual cohabitation.

ii. Treatment: IVF (In Vitro Fertilization).
Brief Explanation: Also known as "Test Tube Baby." Ova from the wife/donor and sperm from the husband/donor are collected and induced to fertilize in the laboratory under simulated conditions. The zygote or early embryo (up to 8 blastomeres) is then transferred into the fallopian tube (ZIFT) or uterus (IUT) for further development.

iii. Sperm Bank: A facility where semen/sperms are collected, frozen, and stored (Cryopreservation) for future use in artificial insemination.

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