CBZ (Paper-II): Chemistry, Botany and Zoology Essentials
OSSTET Paper-II CBZ combines Chemistry, Botany and Zoology. The paper tests conceptual understanding, numerical work and the ability to connect structure with function across living and non-living systems.
Core rules and concepts
- Chemistry: mole = mass ÷ molar mass; balance equations before stoichiometry; periodic trends (atomic radius, ionisation energy, electronegativity); pH = −log[H⁺]; Le Chatelier’s principle predicts equilibrium shifts.
- Botany: photosynthesis has light reactions (thylakoid, ATP/NADPH, water splitting) and the Calvin cycle (stroma, CO₂ fixation); transpiration pull moves water; meristems explain primary/secondary growth; taxonomy uses hierarchical ranks.
- Zoology: homeostasis, digestion, circulation, respiration, excretion and nervous coordination; Mendelian inheritance; DNA → RNA → protein.
Worked example
How many molecules are in 4.4 g of CO₂? Molar mass = 12 + 2(16) = 44 g mol⁻¹. Moles = 4.4 ÷ 44 = 0.10 mol. Molecules = 0.10 × 6.022 × 10²³ = 6.022 × 10²². The reasoning is: convert mass to moles first, then multiply by Avogadro’s number; do not multiply grams directly by 6.022 × 10²³.
Traps that cost marks
Using 28 g mol⁻¹ for CO₂; forgetting to balance equations; saying the light reaction fixes CO₂; treating dominance as blending; confusing transpiration with translocation; ignoring units and significant figures.