Introduction
The subtopic Biology & Health constitutes a critical pillar of the Science segment in the WBCS examination. Over the years for which PYQs have been analysed, a total of 77 questions have appeared, reflecting its high weightage and the examiners’ consistent focus on bridging theoretical biology with real-world health applications. The questions range from straightforward fact recall (e.g., "Which vitamin aids blood clotting?") to conceptual understanding (e.g., "Why does a short-day plant flower when day length is 12 hours?"). The difficulty level is moderate, but aspirants often falter on nuanced distinctions—such as co‑dominance versus incomplete dominance, or the difference between a living fossil and a merely ancient lineage.
This chapter is designed to be your one-stop resource. It begins with fundamental definitions that every answer builds upon, then dives deep into the major thematic areas repeatedly tested: cell biology and genetics, human physiology and nutrition, health and disease management, plant biology and classification, and animal diversity with ecology. Each section is anchored in actual PYQ occurrences, so you are learning exactly what the exam demands. Worked examples dissect five representative questions step‑by‑step, revealing the logic behind correct answers and the traps in distractors. Finally, trend analysis and forward‑looking predictions help you anticipate what could appear next.
By the end of these notes, you will not only have memorised the facts but internalised the reasoning patterns that separate a high‑scoring aspirant from an average one. Treat this chapter as a living document—revisit it before every mock test and again in the final revision sprint.
Core Concepts & Foundations
Before engaging with specific topics, you must master the vocabulary and first principles. Each key term below is defined in its own blockquote and will be used repeatedly in the deep‑dive sections.
Cell: The fundamental structural and functional unit of all living organisms. Cells can be prokaryotic (no nucleus) or eukaryotic (nucleus present). Human body contains trillions of cells.
Mitochondria: A double‑membrane organelle often called the "powerhouse of the cell" because it generates ATP through cellular respiration. Contains its own DNA and ribosomes.
DNA (Deoxyribonucleic Acid): The hereditary material that carries genetic information. Its structure is a double helix, with base pairs (A‑T, C‑G) held by hydrogen bonds.
Gene: A segment of DNA that codes for a functional product (usually a protein). Genes are the units of inheritance.
Chromosome: Thread‑like structures made of DNA and proteins. Humans have 46 chromosomes (23 pairs) in somatic cells.
Allele: Alternative forms of a gene. For example, the gene for plant height may have a tall allele and a dwarf allele.
Dominance / Recessiveness: In a heterozygote, the dominant allele masks the expression of the recessive allele. This principle was established by Gregor Johann Mendel in his pea plant experiments.
Meiosis: A type of cell division that reduces chromosome number by half, producing four haploid gametes. It involves two successive divisions: Meiosis I and Meiosis II.
Mitosis: A cell division that produces two genetically identical daughter cells, maintaining the diploid chromosome number. Used for growth and repair.
Enzyme: A biological catalyst, usually a protein, that speeds up biochemical reactions without being consumed. Example: Zymase in yeast converts sugars to alcohol.
Hormone: A chemical messenger secreted by an endocrine gland into the bloodstream, affecting target organs. Example: Insulin from the pancreas regulates blood glucose.
Vitamin: An organic micronutrient required in small amounts for normal metabolism. Most vitamins cannot be synthesised by the body and must come from diet.
Deficiency Disease: A disease caused by lack of a specific nutrient. For instance, rickets results from vitamin D deficiency.
Pathogen: A disease‑causing agent, such as bacteria, virus, fungus, or parasite.
Antibody: A protein produced by the immune system in response to an antigen. ELISA (Enzyme‑Linked Immunosorbent Assay) detects antibodies against HIV.
Photosynthesis: The process by which green plants use sunlight, carbon dioxide, and water to produce glucose and oxygen, occurring in chloroplasts.
Transpiration: The loss of water vapour from plant aerial parts, mainly through stomata. It drives water uptake from roots.
Photoperiodism: The response of plants to the relative lengths of light and dark periods. Short‑day plants flower when day length is shorter than a critical period; long‑day plants flower when day length exceeds a critical period.
Ecosystem: A community of interacting organisms and their physical environment. Competitive Exclusion Principle (proposed by Gause) states that two species cannot indefinitely occupy the same niche.
These foundational concepts are the building blocks. Every PYQ you encounter will test either a direct definition or an application of one or more of these ideas. Now we move to the thematic deep‑dives.