Tahsili (SAAT) Complete Review Guide 2026–2027

4. Mitochondria carry out cellular respiration and make most of the ATP, chloroplasts carry out photosynthesis in plants, and ribosomes make proteins.
5. Photosynthesis equation: \( 6CO_2 + 6H_2O \xrightarrow{\text{light}} C_6H_{12}O_6 + 6O_2 \).
6. The light reactions occur in the thylakoid membranes and make ATP and NADPH and release oxygen; the Calvin cycle occurs in the stroma and builds glucose.
7. Aerobic respiration: glycolysis in the cytoplasm (net 2 ATP), then the Krebs cycle in the mitochondrial matrix, then the electron transport chain in the inner membrane, for a total of about 30 to 32 ATP.
8. Phases of mitosis in order: prophase, metaphase, anaphase, telophase.
9. In meiosis, crossing over occurs in prophase I, and four haploid cells form that carry genetic variation.
10. Mendel's first law (segregation): the two alleles separate when gametes form. A cross of Aa × Aa gives a 3 : 1 phenotypic ratio and a 1 : 2 : 1 genotypic ratio under complete dominance.
11. Base pairing in DNA: A with T, and G with C. In RNA, U replaces T.
12. Transcription makes mRNA from DNA in the nucleus; translation builds protein at the ribosome, and each three bases (a codon) code for one amino acid.
13. PCR amplifies a chosen DNA segment, and gel electrophoresis separates fragments by size, so smaller fragments travel farther.
14. In the circulatory system the left ventricle pumps oxygenated blood to the body through the aorta, and the right atrium receives deoxygenated blood from the body.
15. Gas exchange in the lungs occurs by diffusion in the alveoli, and the kidney forms urine in nephrons through filtration, reabsorption and secretion.
16. Double fertilization occurs in flowering plants: one sperm fertilizes the egg to form the zygote, and the other joins the two polar nuclei to form the endosperm.
17. In a food chain, energy starts with producers, then primary, secondary and tertiary consumers, and only about 10% of the energy passes from one level to the next.
18. Relationships between organisms: parasitism (one benefits, one is harmed), mutualism (both benefit), commensalism (one benefits, the other is unaffected), plus competition and predation.

Common mistakes in this chapter

• ✕ Diffusion versus osmosis: osmosis is the diffusion of water only, across a semipermeable membrane, from higher to lower water concentration.
• ✕ Passive transport needs no energy and follows the concentration gradient; active transport uses ATP and moves against it.
• ✕ Mixing up mitosis and meiosis: mitosis gives two identical diploid (2n) cells; meiosis gives four haploid (n) cells.
• ✕ Confusing genotype with phenotype, and dominant with recessive alleles: dominant does not necessarily mean most common.
• ✕ In RNA, uracil (U) replaces thymine (T); this appears often in transcription and translation questions.
• ✕ Confusing xylem with phloem: xylem carries water and minerals up from the roots; phloem carries sugars made by photosynthesis.
• ✕ Oxygenated blood: arteries usually carry blood away from the heart, but the pulmonary artery carries deoxygenated blood and the pulmonary vein carries oxygenated blood.
• ✕ In the 10% rule only about a tenth of the energy passes to the next level, not all of it; most of the rest is lost as heat.