World of Living: Life Processes, Coordination, Reproduction, Heredity and Evolution
The World of Living domain tests life processes, control and coordination, reproduction, and heredity and evolution through descriptive questions, reasoning and genetic crosses.
Life processes
Nutrition may be autotrophic (photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ in chloroplasts) or heterotrophic. Digestion breaks food into absorbable molecules; villi absorb nutrients. Respiration releases ATP: aerobic respiration uses oxygen and gives CO₂ + H₂O, while anaerobic respiration in muscle gives lactic acid. Transport uses xylem for water and minerals and phloem for food; the human heart has four chambers and double circulation. Excretion removes urea through nephrons and urine.
Control, coordination and reproduction
Neurons carry electrical impulses; a reflex arc is receptor → sensory neuron → spinal cord → motor neuron → effector. The brain and spinal cord form the central nervous system. Hormones are chemical messengers: insulin lowers blood glucose, thyroxine controls metabolic rate, adrenaline prepares the body for action. Plants respond by tropisms, e.g. auxin causes phototropism. Reproduction may be asexual (fission, budding, fragmentation, regeneration, vegetative propagation) or sexual. In flowers, pollination precedes fertilisation; in humans, the placenta exchanges materials between mother and fetus. Heredity: Mendel's monohybrid ratio is 3:1; sex in humans is determined by XX female and XY male. Evolution involves variation and natural selection.
Worked example
Cross two heterozygous tall pea plants (Tt × Tt). Each parent gives T or t with equal chance. Punnett square: TT, Tt, Tt, tt. Genotypes are 1 TT : 2 Tt : 1 tt; phenotypes are 3 tall : 1 dwarf. The probability of a dwarf offspring is 1/4, or 25%. Tall appears more often because T is dominant, not because tall alleles are more numerous.
Traps
Dominant does not mean more common in a population. Reflex actions are rapid and involuntary, unlike learned actions. Arteries carry blood away from the heart, not always oxygenated blood. The placenta separates maternal and fetal blood. Homologous organs share ancestry; analogous organs share function only.