FPSC 2025 Zoology Solutions

Solution:

Correct Answer: C) Metamorphosis

Detailed Explanation: Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal’s body structure through cell growth and differentiation. In insects like butterflies, this involves complete metamorphosis (holometabolism) with four distinct stages:

• Egg: The first stage where embryonic development occurs
• Larva (Caterpillar): The feeding and growth stage
• Pupa (Chrysalis): The transformation stage where tissues are broken down and reorganized
• Adult (Butterfly): The reproductive stage

This process is regulated by hormones including juvenile hormone and ecdysone.

Solution:

Correct Answer: A) Fructose

Detailed Explanation: Fructose is absorbed through facilitated diffusion via GLUT5 transporters in the intestinal epithelium, which does not require sodium ions or energy expenditure. In contrast:

• Glucose and Galactose: Absorbed via sodium-dependent glucose transporters (SGLT1) that require sodium ions for active transport against concentration gradient
• Mechanism: SGLT1 co-transports glucose/galactose with sodium ions using the sodium gradient maintained by Na+/K+ ATPase pump

This difference in absorption mechanisms is clinically significant in conditions like glucose-galactose malabsorption.

Solution:

Correct Answer: C) Gamma diversity

Detailed Explanation: In ecology, biodiversity is measured at three spatial scales:

Gamma diversity = Alpha diversity × Beta diversity

Solution:

Correct Answer: B) Relaxation time

Detailed Explanation: Relaxation time is a key concept in island biogeography and conservation biology:

• Definition: The time lag between habitat fragmentation and the eventual decline in species diversity to a new equilibrium level
• Mechanism: When a habitat is fragmented, species don’t disappear immediately but undergo gradual extinction due to reduced habitat area, edge effects, and isolation
• Significance: Explains why extinctions continue even after habitat protection measures are implemented
• Example: In forest fragments, large predators and specialized species may take decades to disappear completely

This concept was developed by Robert MacArthur and E.O. Wilson in their Theory of Island Biogeography.

Solution:

Correct Answer: C) Biotin

Detailed Explanation: The oxidative decarboxylation of pyruvate to acetyl-CoA is catalyzed by the pyruvate dehydrogenase complex (PDC), which involves:

• Three Enzymes:
  • Pyruvate dehydrogenase (E1)
  • Dihydrolipoyl transacetylase (E2)
  • Dihydrolipoyl dehydrogenase (E3)
• Five Coenzymes:
  • Thiamine pyrophosphate (TPP)
  • Lipoamide
  • Coenzyme A (CoA-SH)
  • Flavin adenine dinucleotide (FAD)
  • Nicotinamide adenine dinucleotide (NAD⁺)
• Cofactor: Mg²⁺ (required by E1 component)

Biotin is involved in carboxylation reactions (adding CO₂), not oxidative decarboxylation (removing CO₂).

Solution:

Correct Answer: C) Vertebral column

Detailed Explanation: The notochord is a defining characteristic of chordates:

• Embryonic Structure: Flexible rod of mesodermal cells along dorsal midline
• Function: Provides structural support and signaling center for embryonic development
• Fate in Vertebrates: In most vertebrates, the notochord is replaced by the vertebral column (spine) during development
• Exceptions: In some primitive vertebrates (hagfish, lampreys) and invertebrate chordates (tunicates, lancelets), the notochord persists throughout life

Solution:

Correct Answer: C) Both (A) & (B)

Detailed Explanation: Both hemoglobin and myoglobin are hemoproteins containing iron:

Both contain heme prosthetic groups where iron is in ferrous (Fe²⁺) state for oxygen binding.

Complete Solution:

Part A: Differentiation between Enzymes, Co-enzymes, and Co-factors

Part B: Enzymes and Co-enzymes in Glycolysis and Krebs Cycle

Complete Solution:

Part A: Transcription and mRNA Processing in Nucleus

Transcription Process (3 Stages):

mRNA Processing (Eukaryotes Only):

Part B: Roles of mRNA, tRNA, and rRNA in Polypeptide Synthesis

Complete Solution:

Part A: Structure, Synthesis, and Functions of Thyroid Hormones

1. Structure of Thyroid Hormones:

• Thyroxine (T4): Tetraiodothyronine – 4 iodine atoms
• Triiodothyronine (T3): 3 iodine atoms (more potent)
• Reverse T3 (rT3): Biologically inactive form
• Derived from tyrosine amino acid
• Contain iodine atoms at specific positions

2. Synthesis of Thyroid Hormones (5 Steps):

1. Iodide Uptake: Na+/I- symporter in thyroid follicular cells
2. Oxidation: I- → I₂ by thyroid peroxidase
3. Thyroglobulin Synthesis: Glycoprotein synthesized and secreted into colloid
4. Iodination: Iodine added to tyrosine residues on thyroglobulin
5. Coupling: MIT + DIT → T3; DIT + DIT → T4
6. Proteolysis: Lysosomal enzymes release T3 and T4 into blood

3. Functions of Thyroid Hormones:

• Basal Metabolic Rate: Increase oxygen consumption and heat production
• Carbohydrate Metabolism: Enhance glucose absorption and utilization
• Protein Metabolism: Stimulate protein synthesis (anabolic) in normal levels
• Lipid Metabolism: Enhance lipid mobilization and degradation
• Growth & Development: Essential for normal growth, brain development
• Cardiovascular System: Increase heart rate and cardiac output
• Nervous System: Essential for CNS development and function

Part B: Hypo-and-Hyper-thyroidism