Biology: Cells, Life Processes, Heredity, Evolution, and Ecosystems
Biology on this exam tests how you link cell structure to function, compare reproduction and life processes, predict inheritance patterns, and explain energy flow and change in ecosystems.
Cells and reproduction
Prokaryotic cells lack a nucleus; eukaryotic cells have a nucleus and membrane-bound organelles. Mitosis produces genetically identical diploid cells for growth and repair. Meiosis produces haploid gametes and introduces variation through crossing over and independent assortment.
Plant and animal life processes
Photosynthesis uses light, carbon dioxide, and water to make glucose and release oxygen. Cellular respiration releases energy from glucose and uses oxygen in aerobic organisms. Plants transport water and minerals through xylem and sugars through phloem.
Heredity and evolution
Genes occur in allele pairs; genotype is the allele combination and phenotype is the observable trait. Dominant alleles are expressed when present; recessive alleles require two copies. Natural selection acts on variation: individuals with favorable inherited traits tend to survive and reproduce more.
Ecosystems
Energy flows from producers to consumers and is lost as heat at each trophic level. Decomposers recycle nutrients. Food webs show feeding relationships; changes to one population can affect others.
Worked example
Cross Bb × Bb. Each parent can pass B or b. Offspring genotypes are BB, Bb, Bb, and bb: genotype ratio 1:2:1. BB and Bb show the dominant phenotype, while bb shows the recessive phenotype, so the phenotype ratio is 3 dominant : 1 recessive.
Traps
Do not confuse mitosis with meiosis. Do not say photosynthesis and respiration are opposites in every way; both involve energy transformation. Dominant does not mean more common. Energy is not recycled in ecosystems, but nutrients are.