Life Science
What this domain tests
Life Science tests cells and inheritance, evolution and natural selection, ecology and energy flow, and the structure and function of organisms. Items often ask you to trace information, predict offspring ratios, or explain how a population changes over time.
Core rules
- DNA is transcribed to RNA, and mRNA is translated to protein; traits arise from proteins and gene regulation.
- Mitosis produces genetically similar body cells; meiosis produces haploid gametes with genetic variation from crossing over and independent assortment.
- In Mendelian crosses, alleles segregate and assort independently. A monohybrid heterozygote cross gives a 3:1 phenotype ratio and a 1:2:1 genotype ratio.
- Natural selection requires heritable variation, differential reproduction, and change in allele frequencies over generations.
- Ecosystems transfer energy through trophic levels; only a fraction reaches the next level, while nutrients cycle.
Worked example
Cross two heterozygous pea plants, Aa x Aa, where A is dominant and a is recessive. Each parent forms A and a gametes. A Punnett square gives AA, Aa, Aa, aa: genotype ratio 1 AA:2 Aa:1 aa and phenotype ratio 3 dominant:1 recessive. The reasoning is that dominance affects phenotype, not the segregation of alleles. A testcross with aa would reveal whether a dominant-looking parent is AA or Aa.
Traps
Do not equate dominant with most common or 'stronger'; dominance describes expression in heterozygotes. Do not confuse mitosis with meiosis when the question asks about gametes or variation. In ecology, energy flows and is lost as heat, whereas matter cycles. Avoid saying an individual 'evolves'; populations evolve.