CSS GSA — Paper 7, Part-I, Section II (Biological Sciences)

The Basis of Life — Cell Structure and Function

• Cell: basic structural and functional unit of life; two broad types — prokaryotic (no membrane-bound nucleus, e.g., bacteria) and eukaryotic (membrane-bound nucleus, e.g., plant/animal cells)
• Nucleus: control center of the cell; houses DNA/chromosomes; regulates gene expression and cell division
• Mitochondria: "powerhouse of the cell" — site of aerobic respiration and ATP (energy) production; has its own DNA (endosymbiotic theory)
• Ribosomes: site of protein synthesis (translation); can be free-floating in cytoplasm or attached to rough endoplasmic reticulum
• Other key organelles (useful context): Endoplasmic Reticulum (protein/lipid synthesis and transport), Golgi apparatus (packaging/modification), Lysosomes (digestion/waste breakdown), Chloroplasts (photosynthesis, plant cells only), Cell wall (plant cells only, made of cellulose)

Biomolecules

• Proteins: made of amino acid chains (peptide bonds); functions — structural (e.g., keratin, collagen), enzymatic, transport (e.g., hemoglobin), immune (antibodies), hormonal (e.g., insulin)
• Lipids: fats/oils, insoluble in water; functions — energy storage (most energy-dense biomolecule, ~9 kcal/g vs ~4 kcal/g for carbs/proteins), cell membrane structure (phospholipid bilayer), insulation, hormone precursors (steroids)
• Carbohydrates: sugars/starches, made of C, H, O; simple (monosaccharides — glucose, fructose), complex (polysaccharides — starch, glycogen, cellulose); primary/quick energy source
• Enzymes: biological catalysts (mostly proteins) that speed up biochemical reactions without being consumed; highly specific (lock-and-key/induced-fit model); activity affected by temperature and pH

Plant and Animal Kingdom

• Broad classification (Five/Six Kingdom systems commonly referenced): Monera (bacteria), Protista, Fungi, Plantae, Animalia
• Similarities: both are made of cells, require energy, respond to stimuli, reproduce, undergo growth/development, follow genetic inheritance (DNA-based)
• Key diversities:
  • Plants: mostly autotrophic (photosynthesis via chlorophyll), have cell walls, generally immobile, indeterminate growth
  • Animals: mostly heterotrophic (consume other organisms), lack cell walls, generally mobile, determinate growth, nervous coordination
• Animal Kingdom broadly split into Invertebrates (no backbone — e.g., insects, mollusks, worms; ~95% of all animal species) and Vertebrates (backbone — fish, amphibians, reptiles, birds, mammals)

Human Physiology (Brief Overview)

• Circulatory system: heart (4 chambers), blood vessels (arteries carry blood away from heart, veins toward it), blood (RBCs carry oxygen via hemoglobin, WBCs immune defense, platelets clotting)
• Respiratory system: lungs — gas exchange (O₂ in, CO₂ out) at alveoli