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Maharashtra Board Class 12 Biology Question Paper Solutions July 2024

Maharashtra Board Class 12 Biology Question Paper Solutions July 2024
Question Paper Page No. 1 Question Paper Page No. 2 Question Paper Page No. 3 Question Paper Page No. 4 Maharashtra Board Question Paper

BOARD QUESTION PAPER: JULY 2024 - BIOLOGY SOLUTIONS

Max. Marks: 70 | Time: 3 Hrs.

SECTION – A

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

i. In monocot embryo the protective sheath of plumule is called __________.
Answer: (D) coleoptile
ii. The synonymous term for centromere is ________.
Answer: (A) primary constriction
iii. Protein digesting enzyme is ________.
Answer: (B) protease
iv. Spermatids get transformed into a functional spermatozoa by the process of ________.
Answer: (A) spermiogenesis
v. Industrial melanism is one of the best example of ________.
Answer: (B) natural selection
vi. Value of root pressure is +1 to +2 bars which is enough to pump water to a height of ________.
Answer: (B) 10-20 meters
vii. ________ cellular fragments are formed from megakaryocytes.
Answer: (C) Thrombocytes
viii. Degeneration of dopamine producing neurons in the CNS causes ________.
Answer: (D) Parkinson's disease
ix. Choose the correct name of phases A, B and C in the given figure:
Answer: (D) Lag, Log, Stationary
x. Rivet Popper Hypothesis explains
Answer: (A) loss of biodiversity

HSC Biology

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

i. Write the ratio of methane, ammonia and hydrogen respectively in Urey and Miller's experiment.
The ratio of methane ($CH_4$), ammonia ($NH_3$), and hydrogen ($H_2$) in Urey and Miller's experiment is 2:1:2.
ii. What are the cells of Rauber?
The cells of the trophoblast that are in contact with the embryonal knob (inner cell mass) are called cells of Rauber.
iii. Which gene is introduced in tobacco against pest like Zabrotes subfasciatus?
The Arcelin gene (from Phaseolus vulgaris) is introduced in tobacco against Zabrotes subfasciatus.
iv. How many haploid nuclei are present in mature female gametophyte of Angiosperms?
There are 8 haploid nuclei present in a mature female gametophyte of Angiosperms.
v. Name the connection between pulmonary trunk and aortic arch representing remnant of embryonic ductus arteriosus.
Ligamentum arteriosum.
vi. Which endocrine gland plays an important role in the development of immune system?
Thymus gland.
vii. Mention the type of association between sea anemone and clown fish.
Commensalism.
viii. Name the pioneer species in the aquatic habitat during primary succession.
Phytoplanktons.

SECTION – B

Attempt any EIGHT of the following questions: [16]

Q.3. i. Why DNA replication is called semi-conservative replication?
ii. Name the scientist who experimentally proved the same.
i. DNA replication is called semi-conservative because in the newly formed DNA molecule, one strand is old (parental) and conserved, while the other strand is newly synthesized.
ii. Matthew Meselson and Franklin Stahl experimentally proved this.
Q.4. Distinguish between Asexual and Sexual reproduction with reference to:
i. Cell division
ii. Genetic makeup
Feature Asexual Reproduction Sexual Reproduction
i. Cell division It involves only mitosis (or amitosis). It involves both meiosis (during gamete formation) and mitosis.
ii. Genetic makeup Offspring are genetically identical to the parent (Clones). Offspring show genetic variation due to recombination.
Q.5. Arrange the following stages of human evolution in the order of their increasing cranial capacity:
i. Homo sapiens
ii. Neanderthal man
iii. Australopithecus
iv. Homo erectus
Correct Order: iii \(\to\) iv \(\to\) ii \(\to\) i

1. Australopithecus (approx 450-600 cc)
2. Homo erectus (approx 900 cc)
3. Neanderthal man (approx 1400 cc)
4. Homo sapiens (approx 1450 cc)
Q.6. Identify chromosomal disorder caused due to non-disjunction of 21st chromosome and enlist its characteristics.
Disorder: Down's Syndrome (Trisomy 21).
Characteristics:
  • Mild to moderate mental retardation.
  • Flat face with a protruding tongue.
  • Slanting eyes with epicanthal folds.
  • Short stature and stubby fingers.
Q.7. What is radial and tangential translocation of food in plants?
  • Radial Translocation: Transport of food from the phloem to the pith or cortex (in a lateral direction) via medullary rays is called radial translocation.
  • Tangential Translocation: Transport of food in a direction perpendicular to the radius (around the circumference) is called tangential translocation.
Q.8. Explain any two causes of genetic variation.
  1. Gene Mutation: Sudden permanent change in the genetic material (DNA) leads to new traits and variation.
  2. Genetic Recombination (Crossing Over): During meiosis (Prophase I), the exchange of genetic material between non-sister chromatids of homologous chromosomes creates new combinations of genes.
Q.9. Identify A, B, C and D from the following table regarding respiratory system:
OrganismHabitatRespiratory organ
ATerrestrialTracheal tubes and spiracles
ScorpionsTerrestrialB
SpongesCPlasma membrane
TurtlesUnderwaterD

Solution:
A: Insects (e.g., Cockroach)
B: Book lungs
C: Aquatic
D: Cloaca (or Lungs/Plastron depending on specific context of aquatic respiration modes)
Q.10. Give the function of Nebenkern and Zona pellucida.
  • Nebenkern: It is the spirally arranged mitochondria in the middle piece of the sperm. It provides energy (ATP) for the movement of the sperm.
  • Zona pellucida: It is a glycoprotein layer surrounding the plasma membrane of the mammalian ovum. It ensures species-specific fertilization and prevents polyspermy (along with cortical reaction).
Q.11. Give location of corpus callosum and arbor vitae of human brain.
  • Corpus callosum: Located deep within the longitudinal fissure, connecting the two cerebral hemispheres of the forebrain.
  • Arbor vitae: Located in the cerebellum (hindbrain); it is the tree-like branching pattern of white matter within the cerebellar hemispheres.
Q.12. Match cells of immune system in column-I and their functions in column-II and rewrite it.
Column-I Column-II (Correct Match)
i. Cytotoxic T cells (c) Secretion of perforins
ii. Plasma cells (d) Antibody production
iii. Antigen presenting cells (a) Activation of helper T cells
iv. Red blood cells (b) Blood group antigens
Q.13. Give any two examples of commercially exploited products of transgenic plants.
  1. Bt Cotton: Produces insecticidal protein to resist bollworms.
  2. Golden Rice: Genetically modified to produce Pro-vitamin A (Beta-carotene).
  3. (Alternative) Flavr Savr Tomato: Delayed ripening for longer shelf life.
Q.14. Write causative agent, two symptoms and mode of transmission of typhoid.
  • Causative agent: Salmonella typhi.
  • Symptoms: High fever, stomach pain, loss of appetite, constipation.
  • Mode of transmission: Fecal-oral route (ingestion of contaminated food and water).

SECTION – C

Attempt any EIGHT of the following questions: [24]

Q.15. Suggest the specific term for the following:
i. Both male and female reproductive organs present in same organism.
ii. Y-linked gene.
iii. Unfertilised egg develops into haploid male bee.
i. Hermaphrodite / Bisexual / Monoecious.
ii. Holandric gene.
iii. Arrhenotoky (Parthenogenesis).
Q.16. Explain the role of diazotrophs in nitrification.
Wait, the question asks about diazotrophs in nitrification? Diazotrophs are typically nitrogen fixers ($N_2 \to NH_3$). Nitrification is carried out by nitrifying bacteria (e.g., Nitrosomonas, Nitrobacter).

Clarified Answer:
Diazotrophs (like Azotobacter, Rhizobium, Nostoc) fix atmospheric nitrogen ($N_2$) into ammonia ($NH_3$). This ammonia then becomes the substrate for nitrification.
Nitrification process:
  1. Ammonia is oxidized to Nitrite ($NO_2^-$) by Nitrosomonas.
  2. Nitrite is further oxidized to Nitrate ($NO_3^-$) by Nitrobacter.
Thus, diazotrophs provide the initial fixed nitrogen required for the nitrification process to occur in the soil.
Q.17. Explain the following events of cardiac cycle with respect to type of valves and duration:
i. atrial systole
ii. ventricular systole
iii. joint diastole
Event Duration Valves Status
i. Atrial Systole 0.1 sec Atrioventricular (AV) valves (Tricuspid & Bicuspid) are Open. Semilunar valves are closed. Blood is pumped into ventricles.
ii. Ventricular Systole 0.3 sec AV valves Close (producing 'Lubb' sound). Semilunar valves Open. Blood is pumped into Pulmonary trunk and Aorta.
iii. Joint Diastole 0.4 sec Semilunar valves Close (producing 'Dubb' sound). AV valves Open. All chambers are in relaxed state; passive filling occurs.
Q.18. What is reflex action? Explain with one example each of the types of reflex actions based on previous experiences.
Reflex Action: It is a sudden, spontaneous, automatic, and involuntary response to a stimulus, mediated by the spinal cord or brain stem.

Types based on experience:
  1. Unconditioned Reflex (Inborn): Does not require previous experience or learning.
    Example: Salivation on tasting food, withdrawal of hand from a hot object.
  2. Conditioned Reflex (Acquired): Requires previous experience, learning, or training.
    Example: Salivation in a dog just by hearing a bell (Pavlov's experiment), or playing a musical instrument, cycling.
Q.19. Select and fill in the boxes (a) to (f) from given list of options.
List of options: Sickle cell anaemia, Widow’s peak, Flower colour of Mirabilis, Human blood groups, Coat colour of cattle, Klinefelter’s syndrome.

Genetic trait Example
i. Incomplete dominance(a) Flower colour of Mirabilis
ii. Pleiotropy(b) Sickle cell anaemia
iii. Codominance(c) Coat colour of cattle (Roan) (or Human blood groups AB)
iv. Multiple allelism(d) Human blood groups (ABO)
v. Sex chromosomal disorder(e) Klinefelter's syndrome
vi. Autosomal disorder (or trait)(f) Widow's peak
Q.20. Give the role of following mycoherbicides
i. Phytophthora
ii. Alternaria
iii. Fusarium
  • i. Phytophthora palmivora: Controls milkweed vines in citrus orchards. (Commercial name: Devine).
  • ii. Alternaria crassa: Controls water hyacinth.
  • iii. Fusarium sp.: Used to control various weeds.
Q.21. Explain the following terms with respect to survival of an organism in a changed environment.
i. Regulate
ii. Conform
iii. Migrate
  • i. Regulate: Organisms maintain a constant internal environment (homeostasis) despite changes in the external environment (e.g., mammals maintaining body temperature).
  • ii. Conform: Organisms cannot maintain a constant internal environment; their body temperature or osmotic concentration changes with the ambient environment (e.g., most fishes, reptiles).
  • iii. Migrate: Organisms move temporarily from a stressful habitat to a more hospitable area and return when the stressful period is over (e.g., migratory birds).
Q.22. Describe any three causes for loss of biodiversity.
  1. Habitat Loss and Fragmentation: Destruction of natural habitats due to urbanization and deforestation is the primary cause. Breaking large habitats into smaller fragments affects migratory animals.
  2. Over-exploitation: Excessive hunting or harvesting of species by humans for food, medicine, or profit leads to extinction (e.g., Stellar's sea cow).
  3. Invasion of Alien Species: Introduction of non-native species can cause the decline or extinction of indigenous species (e.g., Water hyacinth, Nile Perch).
Q.23. Give physiological effects and applications of cytokinin.
Physiological Effects & Applications:
  • Cell Division: Promotes cytokinesis (cell division) in presence of auxin.
  • Delay of Senescence: Delays the aging of leaves (Richmond-Lang effect) by retaining chlorophyll. Used to increase shelf life of vegetables.
  • Morphogenesis: Promotes shoot formation (caulogenesis) in tissue culture.
  • Breaking Dormancy: Breaks seed and bud dormancy.
Q.24. What is mycorrhiza? Name its types and state any two benefits of mycorrhiza.
Definition: Mycorrhiza is a symbiotic association between a fungus and the roots of higher plants.
Types:
  1. Ectomycorrhiza (Fungal hyphae form a mantle outside the root).
  2. Endomycorrhiza (Fungal hyphae penetrate root cells, e.g., VAM).
Benefits:
  • Enhances absorption of water and minerals (especially Phosphorus).
  • Provides resistance to root-borne pathogens.
Q.25. i. Explain the following:
a. Leaching
b. Humification and mineralization
ii. What is humus?
i. a. Leaching: The process where water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.
i. b. Humification and Mineralization:
  • Humification: Process of formation of a dark-coloured amorphous substance called humus.
  • Mineralization: The process where humus is further degraded by some microbes to release inorganic nutrients.
ii. Humus: It is a dark-coloured, amorphous organic substance that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate. It serves as a reservoir of nutrients.
Q.26. i. What is hematocrit?
ii. Mention the term with respect to –
a. Temporary increase in number of WBCs
b. Decrease in number of RBCs
i. Hematocrit: It is the ratio of the volume of red blood cells to the total volume of blood (also called Packed Cell Volume - PCV).
ii. Terms:
a. Temporary increase in number of WBCs: Leukocytosis.
b. Decrease in number of RBCs: Erythrocytopenia (or Anemia).

SECTION – D

Attempt any THREE of the following questions: [12]

Q.27. Describe mechanism of opening and closing of stomata with reference to:
i. Starch-sugar interconversion theory
ii. Proton transport theory
i. Starch-sugar interconversion theory (Steward/Lloyd):
  • Daytime (Opening): Photosynthesis consumes \(CO_2\), pH rises. Starch phosphorylase converts insoluble Starch into soluble Glucose-1-phosphate. Osmotic pressure of guard cells increases, water enters (endosmosis), guard cells become turgid, and stomata open.
  • Nighttime (Closing): pH drops. Glucose-1-phosphate is reconverted to insoluble Starch. Osmotic pressure decreases, water leaves (exosmosis), guard cells become flaccid, and stomata close.
ii. Proton transport theory (Levitt):
  • Opening: Usually during the day, protons ($H^+$) are actively pumped out of guard cells into subsidiary cells. In exchange, Potassium ions ($K^+$) enter guard cells (Active transport). Malate ions balance the charge. Increased $K^+$ and Malate concentration increases osmotic potential, causing endosmosis and stomatal opening.
  • Closing: Abscisic Acid (ABA) reverses this process. $K^+$ ions flow out, guard cells lose water and become flaccid.
Q.28. i. Define hormone.
ii. Enlist any two properties of hormones.
iii. Give diagrammatic representation of mode of hormone action through membrane bound receptors.
i. Definition: Hormones are chemical messengers (intercellular messengers) produced by endocrine glands in trace amounts, released directly into the blood, and act on specific target organs/cells.
ii. Properties:
  • They are required in very low concentrations.
  • They are highly specific to their target receptors.
iii. Diagrammatic Representation:
Diagram of Mechanism of Hormone Action (Membrane Bound Receptor)
(Diagram showing: Hormone (First messenger) \(\to\) Receptor on Cell Membrane \(\to\) Generation of Second Messenger (e.g., cAMP) \(\to\) Biochemical response \(\to\) Physiological response)
Q.29. With respect to diagram, answer the following:
Anatropous Ovule Diagram from Question Paper
(Refer to the diagram in the question paper image above)

i. Which type of ovule is given in the figure?
ii. Name the first cell of embryo sac.
iii. Identify and write the function of ‘A’ and ‘B’.
i. Type of ovule: Anatropous ovule (Inverted ovule).
ii. First cell of embryo sac: Functional Megaspore.
iii. Identification and Function:
  • A (Funiculus): It is the stalk that attaches the ovule to the placenta. It provides nutrition to the developing ovule.
  • B (Secondary Nucleus / Definitive Nucleus): It is diploid (2n). It fuses with the second male gamete during double fertilization to form the Primary Endosperm Nucleus (PEN), which develops into the nutritive tissue called endosperm.
Q.30. How transgenic pigs and cattle are commercially beneficial?
Transgenic Pigs:
  • Organ Transplantation (Xenotransplantation): Pigs are modified to produce organs that are less likely to be rejected by the human immune system.
  • Meat Production: Modified for leaner meat and faster growth.
Transgenic Cattle:
  • Molecular Pharming: Cows act as bioreactors to produce human therapeutic proteins (e.g., human lactoferrin) in their milk.
  • Increased Production: Modified for increased milk yield (casein variants).
  • Disease Resistance: Engineered to be resistant to specific bovine diseases (e.g., mastitis).
Q.31. With the help of a suitable diagram describe histology of testis.
Histology of Testis (Description):
  • Externally covered by three layers: Tunica vaginalis (outer), Tunica albuginea (middle fibrous), and Tunica vasculosa (inner vascular).
  • The testis contains numerous Seminiferous Tubules.
  • Seminiferous Tubule Structure:
    • Lined by Germinal Epithelium consisting of cuboidal Spermatogonia (male germ cells) and columnar Sertoli cells (Nurse cells).
    • Spermatogonia undergo spermatogenesis to form: Primary Spermatocytes \(\to\) Secondary Spermatocytes \(\to\) Spermatids \(\to\) Spermatozoa (Sperms).
    • Sertoli cells provide nutrition to developing sperms and form the blood-testis barrier.
  • Interstitial Space: The space between tubules contains connective tissue and Leydig cells (Interstitial cells), which secrete testosterone (androgen).
T.S. of Testis Diagram
(Diagram required showing: Seminiferous tubules, Germinal epithelium, Spermatogonia, Sperm bundles, Sertoli cells, and Leydig cells in interstitial space)
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