Structure and Function of Cells and Organisms
What this domain tests
Structure and Function of Cells and Organisms asks you to connect molecules, organelles, cells, tissues, organs, and organ systems to the life processes they carry out. Expect questions on cell theory, membrane transport, enzymes, photosynthesis and cellular respiration, macromolecules, mitosis, homeostasis, and feedback loops. The exam emphasizes cause-and-effect explanations, not isolated labels.
Core rules
- All living things are made of cells; cells arise from pre-existing cells.
- Prokaryotic cells lack a membrane-bound nucleus; eukaryotic cells have organelles, including mitochondria and chloroplasts.
- The cell membrane is selectively permeable. Diffusion and osmosis are passive; active transport requires energy.
- Enzymes are proteins that lower activation energy; they are specific and can be denatured by heat or pH.
- Photosynthesis stores energy in glucose; cellular respiration releases it as ATP. Matter cycles; energy flows.
- Homeostasis uses negative feedback to keep internal conditions near a set point.
Worked example
A freshwater paramecium is placed in distilled water. Predict the direction of water movement and the effect on the cell. Reasoning: Distilled water has a lower solute concentration than the cytoplasm, so it is hypotonic. Water moves by osmosis from low solute (high water) to high solute (low water) across the membrane. The paramecium gains water and may swell; a contractile vacuole pumps water out. The answer must name osmosis, concentration gradient, and the contractile vacuole.
Traps
- Saying “water moves to the hypertonic side” without identifying which solution is hypertonic.
- Confusing photosynthesis and respiration reactants: photosynthesis uses CO2 and water; respiration uses glucose and oxygen.
- Treating enzymes as consumed; they are reusable catalysts.
- Assuming all transport across a membrane needs ATP.