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Biology.
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Grade 12 · Lahore Board · 2024 · Group II
Complete objective paper · English questions

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17 questions. 17 marks.

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QUESTION 1 · 1 MARKThe hormone that keeps the flower fresh :

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Correct answer: D — Cytokinins

Cytokinins delay senescence and help maintain freshness in flowers.

  1. Cytokinins are plant hormones that promote cell division and delay aging.
  2. Because they retard senescence, cut flowers stay fresh longer when cytokinin activity is higher.
  3. Auxins mainly promote elongation, ethene promotes ripening/senescence, and gibberellins promote stem elongation and germination.
QUESTION 2 · 1 MARKThe strand which leads towards the replication fork is :

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Correct answer: B — Leading

The leading strand is synthesized continuously in the direction of the replication fork.

  1. DNA polymerase can add nucleotides only in the 5' to 3' direction.
  2. The leading strand is made continuously as the fork opens.
  3. The lagging strand is made discontinuously in Okazaki fragments.
QUESTION 3 · 1 MARKHow many base pairs are present in human genome :

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Correct answer: B — 03 billions

The human haploid genome contains about 3 billion base pairs.

  1. The commonly cited size of the human haploid genome is about 3 × 10^9 base pairs.
  2. That is approximately three billion base pairs.
  3. So the correct option is 03 billions.
QUESTION 4 · 1 MARKCoal, oil and natural gas are examples of which resource :

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Correct answer: D — Both B and C

Fossil fuels are non-renewable and exhaustible resources.

  1. Coal, oil, and natural gas form over millions of years.
  2. They cannot be replaced quickly on a human time scale, so they are non-renewable.
  3. Because supplies can be depleted, they are also exhaustible.
QUESTION 5 · 1 MARKLiver helps to synthesize :

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Correct answer: A — Bile

The liver synthesizes bile.

  1. The liver is the organ responsible for producing bile.
  2. Bile helps in emulsification of fats during digestion.
  3. Citric acid and lactic acid are metabolic products, not liver secretions.
QUESTION 6 · 1 MARKGenes for albinism are located on :

Source note: The expected chromosome 11 answer refers to TYR-related oculocutaneous albinism (OCA1). Other forms of albinism involve different genes and chromosomes.

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Correct answer: C — 11 chromosome

Albinism is commonly associated with a gene on chromosome 11 (especially tyrosinase-related albinism).

  1. Albinism is a group of conditions affecting melanin production, rather than one disease caused by a single universal gene.
  2. The standard textbook example here is TYR-related oculocutaneous albinism, OCA1. TYR is located on chromosome 11.
  3. Therefore C is the expected answer for this example. The statement should not be generalized to all forms of albinism.
QUESTION 7 · 1 MARKThe muscles which have intercalated discs :

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Correct answer: B — Cardiac

Intercalated discs are characteristic of cardiac muscle.

  1. Cardiac muscle fibers are joined by intercalated discs.
  2. These discs help rapid conduction and coordinated contraction.
  3. Smooth and skeletal muscles do not have intercalated discs.
QUESTION 8 · 1 MARKPrinciple of population was published by :

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Correct answer: D — Malthus

Malthus published the principle of population.

  1. Thomas Malthus proposed the principle of population growth exceeding food supply.
  2. His ideas influenced later evolutionary thinkers such as Darwin.
  3. Therefore the correct answer is Malthus.
QUESTION 9 · 1 MARKThe grass-land having no woody plants known as :

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Correct answer: D — Prairies

Prairies are grasslands without woody plants.

  1. Prairies are temperate grasslands dominated by grasses.
  2. They have few or no woody plants.
  3. Savanna usually has scattered trees, so it is not 'no woody plants'.
QUESTION 10 · 1 MARKGray crescent is present in :

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Correct answer: B — Cytoplasm

The gray crescent is a cytoplasmic region in amphibian eggs.

  1. Gray crescent appears in the cytoplasm of the fertilized egg of amphibians.
  2. It helps determine the body axes during development.
  3. It is not a nuclear or membrane structure.
QUESTION 11 · 1 MARKIn plants which are involved in testa formation :

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Correct answer: C — Sclereids

Sclereids are the thick-walled cells associated with seed coat hardness (testa).

  1. Sclereids are a type of sclerenchyma cell with thick, lignified walls.
  2. They contribute to hardness of seed coats and other protective tissues.
  3. Trachea, tracheids, and collenchyma are not the best answer for testa formation.
QUESTION 12 · 1 MARKThe genetic code for methionine is :

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Correct answer: D — AUG

AUG is the start codon and codes for methionine.

  1. Read codons on messenger RNA in the 5′ to 3′ direction.
  2. AUG specifies methionine and usually serves as the start codon. Therefore choose D.
  3. UAA is a stop codon; GGC specifies glycine; UAC specifies tyrosine. Do not confuse UAC, an mRNA codon here, with the complementary tRNA anticodon to AUG.
QUESTION 13 · 1 MARKThe endosperm of angiosperm is :

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Correct answer: A — Triploid

Angiosperm endosperm is usually triploid because of double fertilization.

  1. In the usual angiosperm embryo sac, the central cell contains two haploid polar nuclei, giving n + n.
  2. During double fertilization, one haploid sperm fuses with these polar nuclei.
  3. The resulting primary endosperm nucleus is n + n + n = 3n, so the expected answer is triploid, A.
QUESTION 14 · 1 MARKThe chromosomes become visible, short and thick during :

Source note: Chromosomes first become visible as thin threads in leptotene. “Short and thick” points to their greatest condensation in diakinesis, the expected answer here.

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Correct answer: A — Diakinesis

Chromosomes are maximally condensed and clearly visible during diakinesis.

  1. In prophase I of meiosis, chromosomes condense gradually.
  2. Diakinesis is the final stage of prophase I where chromosomes are shortest and thickest.
  3. Therefore they become very visible at diakinesis.
QUESTION 15 · 1 MARKMSH is secreted from the :

Source note: “Median lobe” is the source’s wording for the intermediate lobe (pars intermedia). In adult humans this region is rudimentary; this is the textbook pituitary-lobe classification.

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Correct answer: A — Median lobe of pituitary gland

MSH (melanocyte-stimulating hormone) is secreted by the pars intermedia (median lobe) of the pituitary.

  1. MSH is associated with the intermediate part of the pituitary gland.
  2. This part is called the median lobe or pars intermedia in many textbooks.
  3. Therefore the correct option is median lobe of pituitary gland.
QUESTION 16 · 1 MARKThe enzyme luciferase is produced in an insect called :

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Correct answer: A — Firefly

Fireflies produce luciferase for bioluminescence.

  1. Luciferase is the enzyme responsible for light production in bioluminescent organisms.
  2. Fireflies are the best-known insects with this enzyme system.
  3. Housefly, butterfly, and tsetse fly are not standard bioluminescent insects.
QUESTION 17 · 1 MARKIn Sindh the desert ecosystem is called :

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Correct answer: A — Thar

The desert ecosystem in Sindh is the Thar Desert.

  1. Thar Desert lies mainly in Sindh and adjoining Rajasthan regions.
  2. It is the known desert ecosystem of Sindh.
  3. Thal and Cholistan are in other areas of Pakistan.

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