Life Science (Biology)
Core concepts to master
Life science questions on the TASC test how organisms are built, how they function, and how they pass traits to offspring. You should be able to describe cell structure and the roles of the nucleus, mitochondria, chloroplasts, ribosomes, and cell membrane, and to distinguish prokaryotic from eukaryotic cells. Know the difference between mitosis (growth and repair, producing identical cells) and meiosis (gamete formation, producing genetically varied cells with half the chromosome number). Understand DNA as the molecule of heredity, the relationship among DNA, genes, chromosomes, and proteins, and the basic logic of dominant and recessive alleles in simple Mendelian crosses. Be ready to trace energy through an ecosystem via photosynthesis, cellular respiration, food chains, and trophic levels, and to explain natural selection as differential survival and reproduction acting on inherited variation.
Traps to watch for
Questions often reverse cause and effect: organisms do not adapt because they need to, and acquired traits are not inherited. Distinguish mitosis from meiosis by purpose and outcome, not just by name. Watch for confusion between photosynthesis (light energy stored in glucose, oxygen released) and cellular respiration (glucose broken down, energy released). In genetics, remember that a recessive trait can appear only when two recessive alleles are present, and that a dominant allele does not mean the trait is more common. Ecosystem questions may ask about energy loss between trophic levels, so recall that roughly 90 percent of energy is lost at each step.
Worked example and rule of thumb
Cross two heterozygous pea plants (Tt x Tt) for tall (T) versus short (t). A Punnett square gives TT, Tt, Tt, tt: three tall to one short, so 75 percent tall and 25 percent short. Rule of thumb: write the alleles each parent can donate first, then fill the square; never assume the phenotype ratio equals the genotype ratio.