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Biology Board Question Paper Solution March 2020 Maharashtra Board

Biology Board Question Paper Solution

Maharashtra State Board - March 2020 (HSC Class 12)

Max. Marks: 70 | Time: 3 Hours

Question Paper Page No. 1 Question Paper Page No. 2 Question Paper Page No. 3 Question Paper Page No. 4
Section-A
Q.1. i.
Which of the following is most appropriate for thalassemia?
  • (A) decrease of either beta (β) or alpha (α) globin chain of HbA
  • (B) decrease of alpha (α) cells of pancreas
  • (C) decrease of WBC count
  • (D) decrease of blood platelets
Answer: (A) decrease of either beta (β) or alpha (α) globin chain of HbA
Q.1. ii.
Injury to _______ causes sudden death.
  • (A) cerebrum
  • (B) pons varolii
  • (C) medulla oblongata
  • (D) diencephalon
Answer: (C) medulla oblongata
Q.1. iii.
Name the smooth muscle of urinary bladder.
  • (A) cardiac muscle
  • (B) detrusor muscle
  • (C) dartos muscle
  • (D) gubernaculum
Answer: (B) detrusor muscle
Q.1. iv.
Identify the cell labelled 'A' in the T.S. of testis :
[Diagram: T.S. of testis showing seminiferous tubule. Label A points to large pyramidal cells extending from the basement membrane to the lumen, supporting developing sperm.]
  • (A) Leydig cell
  • (B) Basement membrane
  • (C) Sperm
  • (D) Sertoli cell
Answer: (D) Sertoli cell
Q.1. v.
_______ represents connecting link between amphibians and reptiles.
  • (A) Seymouria
  • (B) Archaeopteryx
  • (C) Ichthyostegia
  • (D) Archaeornis
Answer: (A) Seymouria
Q.1. vi.
How many meiotic and mitotic divisions are required for the formation of male gametophyte from pollen mother cell?
  • (A) 2 meiotic and 1 mitotic
  • (B) 1 meiotic and 1 mitotic
  • (C) 1 meiotic and 2 mitotic
  • (D) 2 meiotic and 2 mitotic
Answer: (C) 1 meiotic and 2 mitotic
Q.1. vii.
_______ is the common pathway for aerobic and anaerobic respiration.
  • (A) Krebs’ cycle
  • (B) ETS
  • (C) Calvin cycle
  • (D) Glycolysis
Answer: (D) Glycolysis
Q.1. viii.
Find the odd man out with respect to chemoautotrophs:
  • (A) Nitrosomonas
  • (B) Chromatium
  • (C) Thiobacillus
  • (D) Ferrobacillus
Answer: (B) Chromatium
(Reason: Chromatium is a photoautotroph, while others are chemoautotrophs.)
Q.1. ix.
Genotype of blood group ‘AB’ in human is _______.
  • (A) \(I^A I^B\)
  • (B) \(I^B i\)
  • (C) \(I^A I^A\)
  • (D) ii
Answer: (A) \(I^A I^B\)
Q.1. x.
Linker-DNA, connecting two successive nucleosomes, consists of _______.
  • (A) 146 base pairs
  • (B) 200 base pairs
  • (C) 160 base pairs
  • (D) 54 base pairs
Answer: (D) 54 base pairs

HSC Biology

Q.2.
Answer the following questions:

i. Where were the bones of jaws and teeth of Ramapithecus found?

Answer: The fossils (jaws and teeth) of Ramapithecus were found in the Shivalik Hills of India and in Kenya (Africa).

ii. In electrocardiogram, QRS complex stands for:

In electrocardiogram, QRS complex stands for:
[Diagram: ECG wave P-QRS-T]
Answer: The QRS complex stands for ventricular depolarization (spread of impulse from AV node to the wall of ventricles).

iii. Laxman has low secretion of ADH resulting in _______ type of diabetes.

Answer: Diabetes insipidus

iv. Name the region of retina where rods and cones are absent.

Answer: Blind spot (Optic disc)

v. Among biotic components, the micro consumers are called _______.

Answer: Decomposers (or Reducers)

vi. Identify ‘A’ in the chart given below:

Product Plant
(1) Nicotine Nicotiana tabacum
(2) Vincristin, Vinblastin ‘A’
Answer: ‘A’ is Catharanthus roseus (or Vinca rosea).

vii. The genotypic ratio 1:2:2:4:1:2:1:2:1 is obtained in F2 generation. What will be the phenotypic ratio?

Answer: 9 : 3 : 3 : 1

viii. Define the term ‘recessive’.

Answer: A recessive allele is an allele that is not expressed in the presence of an alternative dominant allele. It expresses itself only in the homozygous condition (presence of two identical alleles) or in the absence of a dominant allele.
Section-B

Attempt any eight of the following questions:

Q.3.
Sketch and label angiospermic embryo sac.
Solution: Sketch and label angiospermic embryo sac
[Diagram: Sketch and label angiospermic embryo sac]

(Student should draw the 7-celled, 8-nucleate structure of the female gametophyte)

Labels required:

  • Chalazal end: Contains 3 Antipodal cells.
  • Central part: Large central cell with Secondary nucleus (or two Polar nuclei).
  • Micropylar end: Egg apparatus containing 1 Egg cell (Oosphere) and 2 Synergids.
  • Filiform apparatus: Inside synergids.
Q.4.
To avoid photorespiration, which anatomical peculiarities are shown by C4 plants?
Answer:

C4 plants show a specialized anatomy called Kranz anatomy to avoid photorespiration:

  1. Dimorphic Chloroplasts:
    • Mesophyll cells: Contain granal chloroplasts (with grana).
    • Bundle Sheath cells: Contain large, agranal chloroplasts (without grana).
  2. Concentric Arrangement: The bundle sheath cells form a wreath-like (Kranz) layer around the vascular bundles, surrounded by mesophyll cells.
  3. Thick Walls: Bundle sheath cells have thick walls impervious to gaseous exchange, concentrating CO2 internally.
Q.5.
Enlist the steps involved in rDNA technology.
Answer:
  1. Isolation of DNA (Genetic material) from the donor organism.
  2. Cutting of DNA at specific locations using Restriction Endonuclease enzymes.
  3. Amplification of the gene of interest using PCR (Polymerase Chain Reaction).
  4. Insertion of the Recombinant DNA (rDNA) into the host cell/organism using a vector.
  5. Selection and screening of transformed host cells.
  6. Obtaining the foreign gene product (downstream processing).
Q.6.
Define the terms:
i. Bio-patent
ii. Bio-piracy
Answer:

i. Bio-patent: It is a patent granted by the government to the inventor for biological entities (like strains of microorganisms, cell lines, genetically modified strains), DNA sequences, and biotechnological processes and products.

ii. Bio-piracy: It refers to the use of bio-resources by multinational companies and other organizations without proper authorization from the countries and people concerned without compensatory payment.

Q.7.
Give the flow chart of central dogma.
Answer:
DNA \(\xrightarrow{\text{Transcription}}\) mRNA \(\xrightarrow{\text{Translation}}\) Protein

It can also be represented including Replication:

Replication \(\circlearrowleft\) DNA \(\rightarrow\) mRNA \(\rightarrow\) Polypeptide (Protein)
Q.8.
How will you identify that, F1 hybrid is homozygous or heterozygous? Explain it with a suitable example.
Answer:

We can identify the genotype of an F1 hybrid by performing a Test Cross. In a test cross, the F1 individual is crossed with the homozygous recessive parent.

Example: Consider height in pea plants (T = Tall, t = Dwarf).

  • Case 1 (Heterozygous): If F1 is Hybrid Tall (Tt):
    Cross: Tt (F1) × tt (Recessive parent)
    Progeny: 50% Tall (Tt) and 50% Dwarf (tt). Ratio 1:1.
    Conclusion: F1 is Heterozygous.
  • Case 2 (Homozygous): If F1 were Homozygous Tall (TT):
    Cross: TT × tt
    Progeny: 100% Tall (Tt).
    Conclusion: F1 is Homozygous.
Q.9.
Give any two contrasting traits studied by Mendel.
Answer:

(Any two from the seven pairs)

  1. Stem height: Tall vs. Dwarf
  2. Seed colour: Yellow vs. Green
  3. Seed shape: Round vs. Wrinkled
  4. Pod colour: Green vs. Yellow
Q.10.
Match the pairs and rewrite:
Column I Column II
(1) Mechanical means (a) Saheli
(2) Physiological device (b) Jellies
(3) Chemical device (c) Vasectomy
(4) Permanent Method (d) Diaphragm
Answer:
  • (1) Mechanical means — (d) Diaphragm
  • (2) Physiological device — (a) Saheli (Oral Contraceptive Pill)
  • (3) Chemical device — (b) Jellies (Spermicides)
  • (4) Permanent Method — (c) Vasectomy
Q.11.
Redraw, complete and label the diagram given below, which relates to reflex arc:
Redraw, complete and label the diagram given below, which relates to reflex arc:
[Diagram: Cross section of spinal cord with reflex arc pathway]
Solution:

Simplified Exam Diagram

Note: Students are required to draw this in the exam.

Diagram: Cross section of spinal cord with reflex arc pathway
[Diagram: Cross section of spinal cord with reflex arc pathway]

Detailed Diagram (Reference Only)

Note: For understanding purposes only. Not required for the exam.

Diagram: Cross section of spinal cord with reflex arc pathway
[Diagram: Cross section of spinal cord with reflex arc pathway]

The student needs to draw the transverse section of the spinal cord showing the reflex path. Key labels to include:

  1. Receptor: Skin (where pin prick occurs).
  2. Sensory Neuron (Afferent): Enters via Dorsal root.
  3. Dorsal Root Ganglion: Swelling on dorsal root containing cell body of sensory neuron.
  4. Association Neuron (Interneuron): Inside the Grey matter of spinal cord.
  5. Motor Neuron (Efferent): Leaves via Ventral root.
  6. Effector: Muscle (showing contraction).

Arrows should indicate flow: Skin \(\rightarrow\) Sensory Neuron \(\rightarrow\) Spinal Cord \(\rightarrow\) Motor Neuron \(\rightarrow\) Muscle.

Q.12.
Explain Hardy-Weinberg’s principle, with the help of Punnett square.
Answer:

Principle: It states that allele frequencies in a population remain constant from generation to generation in the absence of other evolutionary influences (like mutation, selection, migration).

The sum of allelic frequencies is 1: \(p + q = 1\)

The genotypic frequencies are given by: \((p + q)^2 = p^2 + 2pq + q^2 = 1\)

Punnett Square:

Gametes p (Dominant allele) q (Recessive allele)
p \(p^2\) (AA - Homozygous Dominant) \(pq\) (Aa - Heterozygous)
q \(pq\) (Aa - Heterozygous) \(q^2\) (aa - Homozygous Recessive)
Q.13.
Complete the following chart and rewrite:
S.NO Type Example
1. Vulnerable species Clouded leopard, Musk deer
2. ________________ Great Indian Bustard, Hawaiian monk seal
3. ________________ Three banded armadillo (Brazil), Short eared rabbit (Sumatra)
Answer:
  1. (Given) Vulnerable species
  2. Endangered species
  3. Intermediate species (Note: According to Maharashtra Board Textbook context)
Q.14.
Complete the tree diagram and write examples of (A) and (B):
Redraw, complete and label the diagram given below, which relates to reflex arc:
[Diagram: Complete the tree diagram and write examples of (A) and (B)]
Types of air pollutants
(A) Fine particles | (B) Coarse particles
Answer:

(A) Fine particles:

  • Size: Less than 5 µm (or 2.5 µm depending on specific text edition) in diameter.
  • Ex: (i) Aerosols
  • (ii) Smoke / Soot / Fumes

(B) Coarse particles:

  • Size: Over 5 µm in diameter.
  • Ex: (i) Carbon particles
  • (ii) Dust
Section-C

Attempt any EIGHT of the following questions:

Q.15.
Give the location and one function of the following receptors:
(i) Mechanoreceptors
(ii) Statoacoustic receptors
(iii) Baroreceptors
Answer:
  • (i) Mechanoreceptors:
    Location: Skin.
    Function: Detect mechanical stimuli like touch, pressure, and pain.
  • (ii) Statoacoustic receptors:
    Location: Inner ear (Internal ear).
    Function: Hearing (Phonoreceptors) and Body Balance/Equilibrium (Statoreceptors).
  • (iii) Baroreceptors:
    Location: Walls of carotid sinus and aortic arch.
    Function: Detect changes in blood pressure.
Q.16.
Classify the following composition of blood plasma given below as per column ‘A’ and complete column ‘B’.
Answer:
Column A Column B
(1) Plasma Proteins (i) Serum albumin, (v) Fibrinogen
(2) Nitrogenous waste (iii) Urea, (vi) Uric acid
(3) Inorganic Salts (ii) Bicarbonates, (iv) Sulphates of sodium
Q.17.
Name the causative agent of malaria. State any two symptoms and two preventive measures of malaria.
Answer:

Causative agent: Protozoan parasite of the genus Plasmodium (e.g., Plasmodium vivax, P. falciparum).

Symptoms (Any two):

  • High fever with chills and shivering.
  • Severe headache and nausea.
  • Profuse sweating followed by lowering of temperature.

Preventive measures (Any two):

  • Use of mosquito nets and insect repellents to avoid bites.
  • Elimination of mosquito breeding grounds (stagnant water).
  • Spraying insecticides to kill adult mosquitoes and larvae.
Q.18.
Identify ‘1’ and ‘2’ in the following diagram:
[Diagram of Vaccine Production]
Write in brief about production of vaccine.
Redraw, complete and label the diagram given below, which relates to reflex arc:
Answer:

Identification:

  • 1: Isolation of Antigen (Separation of specific antigen from the pathogen).
  • 2: Formulation / Mixing (Mixing of antigen with diluent/adjuvant).

(Note: Interpretation based on standard vaccine production flowchart found in textbooks where step 1 is antigen isolation and step 2 is formulation).

Brief about production of vaccine:

Vaccines are produced using biotechnology. The pathogen is cultured and inactivated or attenuated. The specific antigen (protein) responsible for immunity is isolated ('1'). It is then mixed with a suitable diluent or adjuvant ('2') to increase stability and immune response. This mixture forms the final vaccine.

Q.19.
Satish is a colorblind boy. His mother has normal vision but his maternal grandfather is colourblind. His father and maternal grandmother have normal vision. Explain the pattern of inheritance with a suitable chart.
Answer:

Analysis: Colorblindness is an X-linked recessive disorder.

  • Satish is colorblind (\(X^cY\)).
  • Maternal Grandfather was colorblind (\(X^cY\)). He passed his \(X^c\) chromosome to his daughter (Satish's mother).
  • Satish's Mother is phenotypically normal but must be a carrier (\(X^CX^c\)) because she received the affected X from her father.
  • Satish's Father is normal (\(X^CY\)).

Inheritance Chart:

Parents: Carrier Mother (\(X^CX^c\)) × Normal Father (\(X^CY\))

Gametes \(X^C\) (Sperm) Y (Sperm)
\(X^C\) (Egg) \(X^CX^C\) (Normal Daughter) \(X^CY\) (Normal Son)
\(X^c\) (Egg) \(X^CX^c\) (Carrier Daughter) \(X^cY\) (Colorblind Son - Satish)

Pattern of Inheritance: This is an example of Criss-cross inheritance. The gene for colorblindness was passed from the maternal grandfather to his daughter (carrier), and then from the daughter to her son (Satish).

Q.20.
What are the requirements of dairy management? Give one example of each Indian and exotic breed of cow.
Answer:

Requirements of dairy management:

  • Selection of good breeds with high yielding potential and disease resistance.
  • Proper housing (well-ventilated, sufficient water).
  • Scientific feeding (fodder quantity and quality).
  • Hygiene and cleanliness during milking and handling.
  • Regular veterinary checkups.

Examples:

  • Indian breed: Sahiwal, Gir, or Red Sindhi.
  • Exotic breed: Jersey, Holstein-Friesian, or Brown Swiss.
Q.21.
Distinguish between DNA and RNA.
Answer:
Feature DNA (Deoxyribonucleic Acid) RNA (Ribonucleic Acid)
Sugar Contains Deoxyribose sugar. Contains Ribose sugar.
Strands Usually double-stranded (Double Helix). Usually single-stranded.
Nitrogen Bases Contains Adenine, Guanine, Cytosine, and Thymine. Contains Adenine, Guanine, Cytosine, and Uracil.
Function Stores genetic information. Helps in protein synthesis.
Q.22.
What is ‘green revolution’? Give any two examples each of the improved varieties of wheat and rice.
Answer:

Green Revolution: It refers to the drastic increase in the production of food grains (especially wheat and rice) in developing countries due to the introduction of high-yielding varieties (HYV), use of fertilizers, pesticides, and better irrigation techniques.

Examples:

  • Wheat: Sonalika, Kalyan Sona.
  • Rice: Jaya, Ratna (or Padma).
Q.23.
Give microbial source of the following products in industrial production:
(i) Vitamin B12
(ii) Chloromycetin
(iii) Pectinase
Answer:
  • (i) Vitamin B12: Pseudomonas denitrificans (or Propionibacterium shermanii)
  • (ii) Chloromycetin (Antibiotic): Streptomyces venezuelae
  • (iii) Pectinase (Enzyme): Aspergillus niger (or Sclerotinia libertiana)
Q.24.
State the significance of respiration.
Answer:
  1. Energy Release: It releases energy in the form of ATP, which is essential for various metabolic activities of the cell.
  2. Intermediates: It provides carbon skeleton intermediates required for the synthesis of other biomolecules (like amino acids, fatty acids).
  3. Substrate Activation: It converts insoluble complex food substances into soluble simpler forms.
  4. CO2 Balance: It releases CO2, which is used in photosynthesis, helping maintain the balance of gases in the atmosphere.
Q.25.
Explain the mechanism of anaerobic respiration.
Answer:

Anaerobic respiration occurs in the absence of oxygen. It involves two main steps:

  1. Glycolysis (EMP Pathway):
    • Glucose (6C) is broken down into two molecules of Pyruvate (3C).
    • Net gain: 2 ATP and 2 NADH2.
    • This occurs in the cytoplasm.
  2. Fermentation:
    • The pyruvate produced is reduced to other products depending on the organism.
    • Alcoholic Fermentation (in Yeast): Pyruvate \(\rightarrow\) Acetaldehyde + CO2 \(\rightarrow\) Ethanol (Ethyl Alcohol). NADH2 is reoxidized to NAD.
    • Lactic Acid Fermentation (in Muscle/Bacteria): Pyruvate \(\rightarrow\) Lactic Acid.

Overall, it produces very less energy (2 ATP) compared to aerobic respiration.

Q.26.
Describe the role of citizens in solid waste management.
Answer:

Citizens play a crucial role in solid waste management by adopting the following practices:

  • 3R Principle: Following Reduce, Reuse, and Recycle to minimize waste generation.
  • Segregation: separating waste into biodegradable (wet) and non-biodegradable (dry) waste at the source.
  • Composting: Using wet waste (kitchen scraps) to make compost for home gardens.
  • Avoiding Plastics: Reducing the use of single-use plastics and carrying cloth bags.
  • Safe Disposal: Not littering in public places and disposing of hazardous waste (batteries, medicines) separately.
Section-D

Attempt any THREE of the following questions:

Q.27.
Sketch the internal structure of human heart. Label all the valves present in it. Mention the function of any one valve in the heart.
Solution: Sketch of the internal structure of human heart

Sketch Requirements: Draw a vertical section of the heart showing 4 chambers (RA, RV, LA, LV), major blood vessels (Aorta, Pulmonary Artery, Vena Cavae), and septum.

Labels for Valves:

  • Tricuspid Valve: Between Right Atrium and Right Ventricle.
  • Bicuspid (Mitral) Valve: Between Left Atrium and Left Ventricle.
  • Pulmonary Semilunar Valve: At the base of Pulmonary Artery.
  • Aortic Semilunar Valve: At the base of Aorta.
  • Eustachian Valve: (At opening of IVC - usually vestigial).
  • Thebesian Valve: (At opening of coronary sinus).

Function (Any one):

  • Tricuspid Valve: Prevents the backflow of blood from the right ventricle into the right atrium during ventricular contraction.
Q.28.
With the help of a suitable diagrammatic representation explain HSK pathway.
Answer: Sketch of the internal structure of human heart

HSK Pathway (Hatch-Slack Pathway / C4 Cycle):

This pathway occurs in C4 plants (e.g., Maize, Sugarcane) involving two types of cells: Mesophyll and Bundle Sheath.

  1. In Mesophyll Cell:
    • CO2 is accepted by PEP (Phosphoenolpyruvate) in the presence of PEP carboxylase.
    • Product: OAA (Oxaloacetic Acid - 4C compound).
    • OAA is converted to Malic Acid (or Aspartic Acid).
  2. Transport: Malic acid is transported to Bundle Sheath cells.
  3. In Bundle Sheath Cell:
    • Malic acid undergoes decarboxylation to release CO2 and Pyruvate.
    • The released CO2 enters the Calvin Cycle (C3 cycle) to form glucose.
  4. Regeneration: Pyruvate is transported back to Mesophyll cells and regenerated into PEP using ATP.
Q.29.
Describe the process of fertilization in human with the help of four sequential diagrams.
Answer: Process of fertilization in human with the help of four sequential diagrams

Process Description:

  1. Approach of Sperm: Millions of sperms reach the ampulla. Capacitation prepares sperm for fertilization.
  2. Entry of Sperm (Acrosome Reaction): The acrosome releases lysins (Hyaluronidase) to penetrate the Corona Radiata and Zona Pellucida. The sperm head fuses with the oocyte membrane.
  3. Cortical Reaction: Upon entry of one sperm, cortical granules in the egg release enzymes that harden the Zona Pellucida, preventing polyspermy (fertilization membrane formed).
  4. Activation of Ovum: The entry stimulates the secondary oocyte to complete Meiosis II, releasing the second polar body and forming the female pronucleus.
  5. Syngamy (Fusion): The male pronucleus and female pronucleus fuse (Amphimixis) to form a diploid Zygote.

Diagrams required:

  1. Sperms attacking the ovum.
  2. Acrosome reaction and penetration.
  3. Extrusion of polar body and cortical reaction.
  4. Fusion of pronuclei.
Q.30.
What is artificial method of vegetative propagation?
(i) Cutting
(ii) Budding.
Answer:

Artificial Vegetative Propagation: It is the process of growing new plants from vegetative parts of parent plants (root, stem, leaf) using man-made methods.

(i) Cutting:

  • A small piece of any vegetative part of a plant with one or more buds is cut and planted in soil.
  • Stem cutting: e.g., Rose, Sugarcane.
  • Leaf cutting: e.g., Sansevieria.
  • Root cutting: e.g., Blackberry.

(ii) Budding:

  • It is a form of grafting where a single bud (scion) from a desired plant is inserted into a slit in the bark of a rooted stock plant.
  • Common method: T-budding or Shield budding.
  • Example: Rose, Orange, Peach.
Q.31.
Describe the system associated with elimination of urine with the help of a neat, labelled diagram.
Answer:

The system associated with urine elimination is the Human Excretory System.

Components:

  1. Kidneys (Pair): Bean-shaped organs that filter blood to produce urine.
  2. Ureters (Pair): Muscular tubes that carry urine from the renal pelvis of the kidneys to the urinary bladder.
  3. Urinary Bladder: A muscular sac that temporarily stores urine. It has a smooth muscle layer called the Detrusor muscle.
  4. Urethra: A tube leading from the bladder to the exterior for the discharge of urine (micturition).

Diagram Labels Required: Kidney, Renal Artery, Renal Vein, Ureter, Urinary Bladder, Urethra.

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