Detailed Solutions 📝

Explanation: In Basidiomycetes (like mushrooms and bracket fungi), karyogamy and meiosis take place within the club-shaped structure called the basidium. This meiotic division produces four haploid basidiospores, which are borne exogenously (on the outside) of the basidium.

Explanation: In Periplaneta americana, both males and females possess a pair of jointed filamentous structures called anal cerci on the 10th segment. However, only males bear a pair of short, thread-like anal styles on the 9th sternum.

Explanation: According to NCERT, members of Rhodophyceae (red algae) store their food as floridean starch. Structurally, floridean starch is very similar to amylopectin and glycogen, as all are highly branched polymers of glucose.

Explanation: The secretory phase is also known as the luteal phase because it is driven by progesterone secreted by the corpus luteum. In a standard 28-day cycle, this phase is relatively constant and lasts for approximately 14 days following ovulation.

Explanation: Since the couple has a child with blood group O (genotype $i i$), both parents must be heterozygous carrying the recessive allele 'i'. The man's genotype is $I^A i$ and the woman's is $I^B i$. A Punnett square of this cross yields four possible genotypes ($I^A I^B$, $I^A i$, $I^B i$, $i i$) in equal ratios. Thus, the probability of an AB child ($I^A I^B$) is 1/4 or 25%.

Explanation: Stabilizing selection occurs when nature favors the intermediate phenotype over both extremes (long and short wings). This leads to a reduction in variation and a narrower bell curve for the trait.

Explanation: In the tissues, active cellular respiration consumes oxygen and produces $CO_2$ and heat. This creates low $pO_2$, high $pCO_2$, high $H^+$ concentration (low pH), and higher temperature. These conditions shift the oxygen dissociation curve to the right, promoting the release of $O_2$ from haemoglobin (the Bohr effect).

Explanation: Pure water has the highest water potential ($\Psi_w = 0$). As water enters the flaccid cell, hydrostatic pressure builds up against the cell wall, causing the pressure potential ($\Psi_p$) to increase (become more positive). Consequently, the overall water potential ($\Psi_w$) of the cell increases until it reaches zero (equilibrium). The solute amount doesn't change, so $\Psi_s$ remains relatively constant.

Explanation: EcoRI recognizes the 6-base palindromic sequence 5'-GAATTC-3'. Because of its specific catalytic properties tied to this recognition sequence, it cuts the sugar-phosphate backbone specifically between the guanine (G) and adenine (A) residues on both strands, producing sticky ends.

Explanation: The pyramid of energy is always strictly upright. This is a direct consequence of the laws of thermodynamics in ecosystems. As energy is transferred to successive trophic levels, only about 10% is passed on, while the rest is utilized for metabolism or lost as heat, making it impossible for a higher trophic level to have more energy than a lower one.

Explanation: Primary treatment physically removes large and small particles via filtration and sedimentation. Secondary treatment is biological; vigorous growth of aerobic microbes consumes the organic matter, which directly reduces the BOD. A drop in BOD means the water is becoming less polluted.

Explanation: Plasmodium falciparum causes malignant malaria, which is the most dangerous form (Statement I is correct). However, when sporozoites enter the human body, they travel through the blood to the liver first. They multiply asexually in liver cells before they burst out and invade the red blood cells (Statement II is incorrect).

Explanation: The frequency of the recessive phenotype ($q^2$) is $900/10000 = 0.09$. Therefore, the recessive allele frequency ($q$) is $\sqrt{0.09} = 0.3$. The dominant allele frequency ($p$) is $1 - 0.3 = 0.7$. The frequency of heterozygotes (carriers) is $2pq = 2 \times 0.7 \times 0.3 = 0.42$. The number of carriers in the population of 10,000 is $0.42 \times 10000 = 4200$.

Explanation: A 200 base-pair DNA segment contains a total of 400 bases. If Adenine (A) = 60, then Thymine (T) = 60. Total $A+T$ bases = 120. This leaves $400 - 120 = 280$ bases to be Cytosine (C) and Guanine (G). Thus, $C = 140$ and $G = 140$. Since A-T pairs have 2 hydrogen bonds and G-C pairs have 3 hydrogen bonds: Total H-bonds = ($60 \times 2$) + ($140 \times 3$) = $120 + 420 = 540$.

Explanation: One Microspore Mother Cell (MMC) undergoes one meiotic division to produce 4 functional microspores (which become 4 pollen grains). Thus, to get 100 pollen grains, $100/4 = 25$ meiotic divisions are required. One Megaspore Mother Cell undergoes one meiosis to produce 4 megaspores, but 3 degenerate. Only 1 functional megaspore develops into an embryo sac. Thus, 100 embryo sacs require 100 meiotic divisions. Total divisions = $25 + 100 = 125$.

Explanation: Lysosomes are membrane-bound vesicular structures formed by the process of packaging in the Golgi apparatus. They are bound by a single membrane and contain hydrolytic enzymes (hydrolases - lipases, proteases, carbohydrases) that are optimally active at acidic pH.

Explanation: Insulin is a hypoglycemic hormone. It binds to receptors primarily on hepatocytes (liver cells) and adipocytes (fat cells), increasing their permeability to glucose. This rapid uptake clears glucose from the blood. It also promotes glycogenesis (conversion of glucose to glycogen).

Explanation: The ploidy of the male gamete will be half of the male plant's ploidy: $4n/2 = 2n$. The ploidy of the female plant is $2n$. The two polar nuclei in the central cell of the female embryo sac will each be $n$. During double fertilization, the primary endosperm nucleus (PEN) is formed by the fusion of one male gamete ($2n$) with the two polar nuclei ($n+n$). Therefore, Endosperm ploidy = $2n$ (male) + $n$ + $n$ (polar nuclei) = $4n$.

Explanation: In an ECG, the P-wave represents atrial depolarization. The QRS complex represents ventricular depolarization. The T-wave represents the repolarization of the ventricles, marking the end of ventricular systole as the muscle returns to its resting electrical state.

Explanation: Mycoplasma are organisms that completely lack a cell wall. According to NCERT, they are the smallest living cells known and can survive without oxygen. Many Mycoplasma are pathogenic in animals and plants.