World of Living
What this domain tests
This domain covers life processes, control and coordination, reproduction, and heredity and evolution - how organisms obtain energy, respond to stimuli, reproduce, and change across generations.
Core rules
- Nutrition is autotrophic (photosynthesis using chlorophyll and stomata) or heterotrophic (holozoic, saprophytic, parasitic).
- Respiration: aerobic starts with glycolysis in the cytoplasm and finishes in mitochondria, releasing much more ATP than anaerobic respiration. Yeast gives ethanol + CO₂; overworked muscle gives lactic acid.
- Transport: xylem carries water and minerals upward only; phloem carries food in both directions. Arteries carry blood away from the heart, veins toward it.
- Excretion: in the nephron, filtration happens in the glomerulus and selective reabsorption in the tubule.
- Coordination: the reflex arc runs sensory neuron → relay neuron in the spinal cord → motor neuron → effector, acting before the brain registers the stimulus. Hormones act more slowly but for longer; plants use auxin, gibberellin, cytokinin and abscisic acid.
- Reproduction may be asexual (binary fission, budding, fragmentation, regeneration, vegetative propagation) or sexual. In humans fertilisation is internal, in the oviduct.
- Heredity: genes occur in alleles that may be dominant or recessive; the father's sperm (X or Y) determines the child's sex.
Worked example
Cross two heterozygous tall pea plants, Tt × Tt. A Punnett square gives TT, Tt, Tt, tt. Genotypic ratio 1:2:1; phenotypic ratio 3 tall : 1 short. Reasoning: each parent passes T or t with equal chance, and only tt is short.
Traps
- Dominant does not mean commonest; it means expressed in the heterozygote.
- Acquired traits such as a cut tail or a learned skill are not inherited.
- Write the reflex arc in the correct order; the brain is not the first relay.
- The mother always contributes X; sex determination depends on the father.