Biological Sciences: Cells, Energy, Heredity, and Ecosystems
Core concepts to connect
Life-science questions on this test usually link structure to function. Know that cells are the basic unit of life, that cell theory states all living things are made of cells, that cells come from existing cells, and that cells carry out life processes. Match organelles to jobs: nucleus (genetic instructions), cell membrane (selective boundary), mitochondria (releases energy from food), chloroplasts (capture light for photosynthesis), cell wall (support in plants), vacuole (storage).
Trace energy and matter through ecosystems. Producers capture sunlight; consumers eat; decomposers recycle nutrients. Energy flows one way and is lost as heat at each level, so food pyramids narrow upward, while matter cycles. Know the photosynthesis and respiration relationship as a pair: photosynthesis stores energy in glucose using carbon dioxide and water, and respiration releases that energy using oxygen and glucose.
Heredity questions ask you to use dominant and recessive alleles, genotype versus phenotype, and simple Punnett squares. Traits come from genes on chromosomes, and offspring inherit one allele from each parent. Natural selection explains adaptation: variation exists, some variations aid survival and reproduction, and those traits become more common over generations.
Traps
- Saying energy is recycled. Matter cycles; energy flows and is lost as heat.
- Confusing photosynthesis and respiration direction.
- Mixing genotype (alleles) with phenotype (appearance).
- Believing individual organisms 'try' to adapt; populations change, not individuals.
- Ignoring that biotic and abiotic factors both shape an ecosystem.
Worked example
Cross two heterozygous purple-flowered plants (Bb x Bb). Offspring genotypes are BB, Bb, Bb, bb: three purple to one white. The 3:1 ratio is phenotype; the 1:2:1 ratio is genotype.