Question 1
The Leydig cells or interstitial cells, which are present in the intertubular spaces of the testis, synthesize and secrete testicular hormones called:
✅ Correct Answer: Androgens
Explanation: According to NCERT, the regions outside the seminiferous tubules called interstitial spaces contain small blood vessels and interstitial cells or Leydig cells. Leydig cells synthesize and secrete testicular hormones called androgens.
Question 2
In a single strand of a nucleic acid, successive nucleotides are linked together by:
✅ Correct Answer: Phosphodiester bonds
Explanation: In a polynucleotide chain, a 3'-5' phosphodiester linkage joins the 3'-hydroxyl group of the sugar of one nucleotide to the 5'-phosphate group of the successive nucleotide's sugar.
Question 3
In which of the following plant groups is the sporophyte completely dependent on the gametophyte for nourishment and support?
✅ Correct Answer: Bryophytes
Explanation: In Bryophytes (like mosses and liverworts), the main plant body is the free-living haploid gametophyte. The multicellular diploid sporophyte is not free-living; it remains attached to the photosynthetic gametophyte and derives nourishment from it.
Question 4
The large holes in 'Swiss cheese' are due to the production of a large amount of CO2 by a bacterium named:
✅ Correct Answer: Propionibacterium sharmanii
Explanation: NCERT explicitly mentions that the large holes in 'Swiss cheese' are due to the production of a large amount of CO2 by a specific bacterium named Propionibacterium sharmanii.
Question 5
A person suffers a deep puncture wound in his chest cavity in a road accident, but the lungs themselves are not directly injured. What will be the immediate physiological effect?
✅ Correct Answer: Cessation of breathing
Explanation: The normal breathing mechanism relies on the negative intrapleural pressure within the sealed, air-tight thoracic cavity. A puncture in the chest wall breaks this seal, equalizing the pressure with the atmosphere, leading to a collapsed lung and the cessation of breathing.
Question 6
If a plant cell is placed in a strongly hypertonic solution, what specific substance fills the space between the cell wall and the shrunken protoplast?
✅ Correct Answer: Hypertonic solution
Explanation: During plasmolysis in a hypertonic solution, water moves out of the cell, and the cell membrane shrinks away from the cell wall. Because the plant cell wall is freely permeable, the external hypertonic solution easily passes through it and fills the gap.
Question 7
Which specific stage of prophase I in meiosis can last for months or years in the primary oocytes of some vertebrate species?
✅ Correct Answer: Diplotene
Explanation: According to NCERT, the diplotene stage of prophase I is characterized by the dissolution of the synaptonemal complex. In the oocytes of some vertebrates, this diplotene stage is prolonged and can last for months or years (dictyotene stage).
Question 8
The wings of a bird and the wings of an insect represent an evolutionary relationship known as:
✅ Correct Answer: Analogous structures and represent convergent evolution
Explanation: Bird wings (modified forelimbs with bones) and insect wings (chitinous extensions) have completely different anatomical origins but perform the same function (flying). This makes them analogous structures, which are a result of convergent evolution adapting to similar environmental pressures.
Question 9
Assertion (A): In gel electrophoresis, DNA fragments move towards the anode when an electric field is applied.
Reason (R): DNA is a positively charged molecule due to the presence of phosphate groups.
✅ Correct Answer: A is true but R is false.
Explanation: The assertion is true because DNA fragments are forced to move towards the positively charged electrode (anode) under an electric field. The reason is false because the phosphate groups give DNA a negative charge, not a positive one.
Question 10
Assertion (A): Sickle-cell anaemia is an autosome-linked recessive trait.
Reason (R): The disease is controlled by a single pair of alleles, HbA and HbS, and only homozygous individuals (HbSHbS) show the diseased phenotype.
✅ Correct Answer: Both A and R are true but R is not the correct explanation of A.
Explanation: Both statements are factually correct. However, Reason (R) merely describes the genetic makeup (genotype) and Mendelian behavior of the trait. It does not explain why it is linked to an "autosome" (which would require stating it is located on chromosome 11, rather than a sex chromosome).
Question 11
Consider the following statements about photosynthesis in higher plants:
Statement I: In C4 plants, the Calvin cycle (C3 pathway) operates exclusively in the bundle sheath cells.
Statement II: The mesophyll cells of C4 plants completely lack the RuBisCO enzyme.
✅ Correct Answer: Both Statement I and Statement II are correct.
Explanation: In C4 plants, atmospheric CO2 is initially fixed in the mesophyll cells by PEP carboxylase. The mesophyll cells lack RuBisCO. The resulting 4-carbon acids are transported to the bundle sheath cells, where they are decarboxylated, and the released CO2 enters the Calvin cycle, enabled by the rich presence of RuBisCO there.
Question 12
Consider the following statements regarding human reproduction:
Statement I: In the normal menstrual cycle, menstruation only occurs if the released ovum is not fertilized.
Statement II: The lack of menstruation may be indicative of pregnancy, but it can also be caused by stress or poor health.
✅ Correct Answer: Both Statement I and Statement II are correct.
Explanation: Menstruation is the shedding of the endometrial lining, which is maintained by progesterone if fertilization occurs. Thus, menstruation only happens if fertilization fails (Statement I is true). A missed period is a primary sign of pregnancy, though NCERT explicitly notes that stress and poor health can also delay or stop menstruation (Statement II is true).
Question 13
In a test cross between a male homozygous for recessive alleles (aabb) and a heterozygous female (AaBb), the progeny showed the following phenotypic frequencies: AB (40%), ab (40%), Ab (10%), aB (10%). What is the approximate map distance between genes A and B?
✅ Correct Answer: 20 cM
Explanation: The map distance between two linked genes is equal to the percentage of recombinant progeny. The parental types are AB (40%) and ab (40%), totaling 80%. The recombinant types are Ab (10%) and aB (10%), totaling 20%. Therefore, the recombination frequency is 20%, which equates to 20 centiMorgans (cM) or map units.
Question 14
If the stroke volume of a human heart is 70 mL and the heart rate is 75 beats per minute, what is the cardiac output?
✅ Correct Answer: 5250 mL/min
Explanation: Cardiac output is defined as the volume of blood pumped out by each ventricle per minute. It is calculated as: Cardiac Output = Stroke Volume $\times$ Heart Rate. $70 \text{ mL} \times 75 \text{ beats/min} = 5250 \text{ mL/min}$ (or 5.25 liters/minute).
Question 15
If a linear DNA fragment contains 100 base pairs, what is the approximate physical length of this specific fragment?
✅ Correct Answer: 34 nm
Explanation: According to the Watson-Crick model of B-DNA, the distance between two consecutive base pairs is approximately 0.34 nm (or $3.4 \times 10^{-10}$ meters). For a fragment of 100 base pairs, the length is $100 \times 0.34 \text{ nm} = 34 \text{ nm}$.
Question 16
Which of the following is an in-situ method of biodiversity conservation?
✅ Correct Answer: Biosphere Reserve
Explanation: In-situ (on-site) conservation involves protecting endangered species in their natural habitats. Biosphere reserves, national parks, and wildlife sanctuaries are in-situ methods. Botanical gardens, zoological parks, and cryopreservation are ex-situ (off-site) conservation strategies.
Question 17
The special surface structures that help some bacteria to attach to rocks in streams and also to host tissues are known as:
✅ Correct Answer: Fimbriae
Explanation: According to NCERT, fimbriae are small bristle-like solid fibres sprouting out of the bacterial cell. In some bacteria, they are known to help attach the bacteria to rocks in streams and also to the host tissues.
Question 18
If the loop of Henle were abruptly removed from mammalian nephrons, which of the following outcomes is to be expected?
✅ Correct Answer: The urine formed will be highly dilute.
Explanation: The primary function of the loop of Henle (especially in juxtamedullary nephrons) is the creation of a high osmolarity gradient in the medullary interstitium via the countercurrent mechanism. This gradient allows water to be reabsorbed from the collecting duct. Without it, the urine cannot be concentrated, resulting in the excretion of a large volume of highly dilute urine.
Question 19
When the fat tripalmitin is used completely as a respiratory substrate, the Respiratory Quotient (RQ) is approximately:
✅ Correct Answer: 0.7
Explanation: The Respiratory Quotient (RQ) is the ratio of the volume of CO2 evolved to the volume of O2 consumed. For carbohydrates, the RQ is 1.0. For proteins, it is about 0.9. For fats/lipids, the RQ is less than 1. NCERT provides the specific balanced equation for tripalmitin, yielding an RQ of $102 \text{ CO}_2 / 145 \text{ O}_2 \approx 0.7$.
Question 20
In most of the flowering plants, the haploid structure that develops directly from a microspore is the:
✅ Correct Answer: Pollen grain
Explanation: Microspores are formed by meiosis in the microspore mother cell. Each microspore develops directly into a pollen grain (the male gametophyte). The pollen grain then further undergoes mitosis to eventually produce two male gametes.
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