Biology (Theory) | Set A1 • Code 71/SS/314

1st Blank: zygote (or embryo / offspring)

2nd Blank: maternal (or cytoplasmic / extra-nuclear)

Scientific Context: During fertilization, only the sperm nucleus enters the ovum while sperm mitochondria located in the neck/middle piece degenerate. All mitochondria in the resulting zygote originate solely from the maternal ooplasm.

• \(\mathbf{A}\): Transcription (Enzymatic synthesis of mRNA from a DNA template directed by RNA Polymerase)

• \(\mathbf{B}\): Translation (Decoding genetic codons on mRNA into an amino acid polypeptide chain on ribosomes)

• Solid Line: Represents Stimulatory / Positive Action (Forward Endocrine Stimulation). Hypothalamus secretes TRH to stimulate the Pituitary, which in turn releases TSH to stimulate the Thyroid gland to secrete thyroxin.

• Broken Line: Represents Inhibitory Feedback (Negative Feedback Mechanism). Elevated circulating levels of thyroxin act back on the anterior pituitary and hypothalamus to suppress further release of TSH and TRH, maintaining homeostatic hormonal equilibrium.

(a) False (F) (The edible portion of coconut is the cellular and liquid endosperm; the endocarp is the hard stony inner shell that is inedible).

(b) True (T) (Apple is a false fruit or pome where the fleshy, edible portion develops from the swollen thalamus surrounding the central ovary core).

(a) Amniocentesis (or Gel Electrophoresis / Micropropagation depending on curriculum diagram).

(b) Significance:
• It allows prenatal detection of chromosomal abnormalities (e.g. Down syndrome, Turner syndrome, Klinefelter syndrome) and metabolic genetic disorders in the developing fetus.
• It assesses fetal health and lung maturity before delivery.

(a) nodules (Root nodules housing symbiotic Rhizobium bacteria)

(b) Nodulins (Special plant-encoded proteins specifically induced during nodule organogenesis and symbiosis)

(a) Kwashiorkor [or Protein-Energy Malnutrition (PEM) / Cretinism].

(b) Reason: Severe deficiency of proteins in the diet despite adequate or marginal caloric/carbohydrate intake. Hypoalbuminemia reduces blood oncotic pressure, resulting in fluid accumulation (edema) in tissues and the abdominal cavity (ascites / pot-belly).

• Graft Rejection Prevention: The recipient's immune system recognizes cell-surface major histocompatibility complex (MHC/HLA) markers on the transplanted organ as non-self foreign antigens.

• Role of Cell-Mediated Immunity: T-lymphocytes (cytotoxic T-cells) initiate a cell-mediated immune response to attack and destroy the foreign donor tissue (graft rejection). Immunosuppressive drugs (such as Cyclosporin A) inhibit T-cell activation, preventing graft rejection and ensuring survival of the transplant.

1st Blank: wings

2nd Blank: analogous

Evolutionary Explanation: Bird wings (feathers attached to forelimb skeleton) and bat wings (membranous patagium stretched between elongated digits) perform identical flight functions but possess fundamentally different structural origins, demonstrating convergent evolution.

1. Statement (a): "Body is covered by hairs"
Correction: Reptilian skin is dry, non-glandular, and covered by epidermal scales or scutes; hair is a diagnostic characteristic exclusive to mammals.

2. Statement (d): "Heart is two chambered"
Correction: Reptiles possess a 3-chambered heart with an incompletely partitioned ventricle (and fully 4-chambered in crocodiles); a 2-chambered venous heart is found in fishes.

• Definition: Commensalism is an interspecific ecological interaction between two organisms of different species in which one species benefits (\(+\)) while the other remains completely unaffected, deriving neither benefit nor harm (\(0\)).

• Example: An epiphytic orchid growing on the bark of a mango tree. The orchid derives physical support, space, and sunlight without extracting water or sap from the mango tree, leaving the tree unharmed.

1. Clean, Non-Polluting Fuel: Biogas (composed of \(50-70\%\) methane) burns with a high calorific value without smoke or residue, preventing household respiratory ailments and deforestation.

2. Enriched Organic Manure: The spent fermented slurry discharged from the biogas digester is rich in nitrogen and phosphorus, serving as high-quality organic biofertilizer for agricultural crops.

1. Promotes Healthy Bowel Movement: Roughage adds bulk to food bolus and retains water, facilitating smooth intestinal peristalsis and preventing chronic constipation.

2. Lowers Cholesterol and Blood Sugar Spikes: Soluble dietary fibres bind to bile acids, aiding in cholesterol excretion and slowing glucose absorption in the small intestine.

(i) For codon \(5'-\text{AGU}-3'\): Complementary anticodon is \(3'-\text{UCA}-5'\) (or \(5'-\text{ACU}-3'\)).

(ii) For codon \(5'-\text{UGC}-3'\): Complementary anticodon is \(3'-\text{ACG}-5'\) (or \(5'-\text{GCA}-3'\)).

• Definition: PEM stands for Protein-Energy Malnutrition, an umbrella term for a spectrum of nutritional deficiency disorders (such as Kwashiorkor and Marasmus) affecting primarily infants and young children.

• Two Main Reasons:
1. Inadequate Nutritional Intake: Chronic deficiency of protein and calories in weaning food due to poverty, lack of balanced dietary resources, and maternal malnutrition.
2. Recurrent Gastrointestinal Infections: Frequent bouts of diarrhea and enteritis impair intestinal absorption of nutrients, rapidly precipitating acute wasting and edema.

Key Stages of the Nitrogen Cycle:

1. Nitrogen Fixation: Conversion of atmospheric \(\text{N}_2\) into \(\text{NH}_3\) by biological fixers (Rhizobium, Azotobacter, Anabaena) or industrial processes.
2. Nitrification: Two-step biological oxidation of ammonia into nitrite by Nitrosomonas, followed by oxidation to nitrate by Nitrobacter: \[2\text{NH}_3 + 3\text{O}_2 \to 2\text{NO}_2^- + 2\text{H}^+ + 2\text{H}_2\text{O}; \quad 2\text{NO}_2^- + \text{O}_2 \to 2\text{NO}_3^-\]
3. Assimilation & Ammonification: Plants absorb \(\text{NO}_3^-\); decomposing organic remains are converted back to ammonia by ammonifying bacteria.
4. Denitrification: Anaerobic reduction of nitrate (\(\text{NO}_3^-\)) back into inert \(\text{N}_2\) gas by Pseudomonas and Thiobacillus.

• Definition: Colostrum is the thick, yellowish initial milk produced and secreted by the maternal mammary glands during the first \(2-4\text{ days}\) postpartum following parturition.

• Essential Significance:
1. Passive Immunization: It contains exceptionally high titers of Secretory Immunoglobulin A (\(\text{IgA}\)), lactoferrin, and lysozyme that coat the newborn's immature gut lining, providing immediate passive immunity against diarrheal and respiratory pathogens.
2. Clears Meconium & Nutritive: It contains mild laxative properties that facilitate the expulsion of meconium (the infant's first stool, clearing fetal bilirubin) and provides concentrated proteins, vitamins, and minerals.

• Definition: The placenta is a temporary, specialized organic structural and physiological disc-like connection established between the chorionic villi of the developing embryo/fetus and the maternal uterine endometrium during pregnancy.

• Two Major Functions:
1. Physiological Exchange (Nutrition, Respiration & Excretion): Mediates the diffusion of oxygen (\(\text{O}_2\)), glucose, amino acids, and antibodies from maternal blood to the fetus, while concurrently transferring fetal metabolic wastes (\(\text{CO}_2\), urea, creatinine) into maternal circulation for maternal elimination.
2. Endocrine Function: Acts as a temporary endocrine gland synthesizing essential pregnancy hormones, including human Chorionic Gonadotropin (hCG), human Placental Lactogen (hPL), progesterone, and estrogens to sustain gestation.