Biology
What this section tests
Biology questions span cell structure, cellular processes, genetics, classification, and ecology. Know the prokaryote/eukaryote difference (prokaryotes lack a membrane-bound nucleus), the organelle functions, and the two energy pathways.
Must-know content
- Organelles: mitochondria (ATP production), ribosomes (protein synthesis), rough ER (protein transport), Golgi apparatus (packaging), lysosomes (digestion), chloroplasts (photosynthesis), nucleus (DNA storage).
- Photosynthesis: in chloroplasts; carbon dioxide + water + light yields glucose + oxygen.
- Cellular respiration: mainly in mitochondria; glucose + oxygen yields carbon dioxide + water + ATP.
- Mitosis: one division, two identical diploid cells, for growth and repair.
- Meiosis: two divisions, four haploid gametes, with crossing over - the source of genetic variation.
- DNA: double helix; adenine pairs with thymine, cytosine with guanine. Transcription makes mRNA in the nucleus; translation builds protein at the ribosome.
- Genetics: dominant alleles mask recessive ones; a cross of two heterozygotes gives a 3:1 phenotype ratio.
- Enzymes: proteins that lower activation energy; denatured by high heat or extreme pH.
- Macromolecules: carbohydrates, lipids, proteins, nucleic acids.
- Ecology: producers, consumers, decomposers; energy flows one way and is lost as heat at each level.
Traps to expect
Confusing mitosis with meiosis; calling the ribosome the site of ATP production; assuming a dominant trait is more common in a population; mixing up the products of photosynthesis and respiration.
Worked example
Cross Aa × Aa. Each parent gives A or a with equal chance, producing AA, Aa, Aa, aa - three dominant-phenotype offspring to one recessive, or 3:1. Genotype ratio is 1:2:1.