Molecular and Cell Biology
What this domain tests
Molecular and Cell Biology connects the molecules of life to cell structures and to the processes that keep cells alive. Florida Biology EOC items in this domain ask about macromolecule building blocks, enzyme function, membrane transport, photosynthesis and cellular respiration, and the cell cycle. Questions often change one variable and ask you to predict the result, so trace cause and effect rather than recalling isolated labels.
Core rules and concepts
- Macromolecules. Carbohydrates are built from monosaccharides; lipids from glycerol and fatty acids; proteins from amino acids joined by peptide bonds; nucleic acids from nucleotides. Enzymes are proteins that lower activation energy, are not consumed, and have a specific active site. Temperature and pH can denature them.
- Membranes. The phospholipid bilayer is selectively permeable. Diffusion moves solutes from high to low concentration; osmosis moves water from high water potential (low solute) to low water potential (high solute). Facilitated diffusion uses transport proteins but no ATP. Active transport uses ATP. Endocytosis and exocytosis move bulk materials.
- Energy flow. Photosynthesis in chloroplasts uses light, CO2, and H2O to make glucose and O2. Cellular respiration in mitochondria uses glucose and O2 to make CO2, H2O, and ATP. Plants also respire. Fermentation makes ATP without oxygen.
- Cell cycle. Interphase includes G1, S (DNA replication), and G2. Mitosis separates duplicated chromosomes; cytokinesis divides the cytoplasm. Checkpoints monitor DNA and spindle attachment.
Worked example
An animal cell is placed in a hypertonic solution. Predict water movement and the cell’s fate. Reasoning: “Hypertonic” means the solution has more solute and less water than the cell. Water leaves the cell by osmosis, so the animal cell shrinks and may crenate. A plant cell in the same solution would plasmolyze because its membrane pulls away from the wall.
Traps that cost marks
- Calling diffusion “active transport”; only active transport directly requires ATP.
- Claiming plants do not carry out cellular respiration.
- Saying an enzyme is used up or changes the overall energy yield of a reaction.
- Confusing mitosis with meiosis or forgetting that DNA replication occurs in S phase.