Virginia Biology SOL Module 2 biochemistry: a complete overview of water, macromolecules, enzymes, photosynthesis, and respiration for BIO.2

What Module 2 actually demands

Module 2 is the biochemistry core of the Virginia Biology SOL, standard BIO.2, sitting in the Cell Biology and Cellular Processes reporting category. It runs from the single most important molecule (water), through the molecules of life (the macromolecules), to the proteins that control reactions (enzymes), and finally to the two great energy processes (photosynthesis and respiration). The unifying theme the EOC keeps returning to is energy and matter: how energy is captured, stored, transformed, and released, and how matter is rearranged but conserved.

This guide ties together the matching dot-point pages, each with its own practice questions: water and the chemistry of life, macromolecules of life, enzymes and biochemical reactions, photosynthesis, and cellular respiration.

Water: the molecule of life

Water is polar: its oxygen pulls the shared electrons more strongly than the hydrogens, so the oxygen end is slightly negative and the hydrogen ends slightly positive. That polarity lets water molecules form hydrogen bonds, and almost every special property follows from it. Cohesion (water sticking to itself) gives surface tension and pulls water up tall plants; adhesion (water sticking to other surfaces) helps. A high specific heat means water resists temperature change, stabilizing the temperature of cells, organisms, and climates. As the universal solvent, water dissolves polar and charged substances, so the chemistry of life happens in solution. Water is also a reactant (in photosynthesis and in hydrolysis) and a product (of respiration and dehydration synthesis).

The four macromolecules

Every living thing is built from four classes of macromolecule, each with a monomer and a function. Carbohydrates (monomer: monosaccharides such as glucose) are the main quick energy source and provide structure. Lipids (glycerol and fatty acids) are nonpolar, store energy long-term, and form membranes. Proteins (monomer: amino acids) do most of the cell's work, as enzymes, structures, transporters, and antibodies, with their folded shape determining function. Nucleic acids (monomer: nucleotides) store and carry genetic information. Cells build polymers by dehydration synthesis (remove water) and break them by hydrolysis (add water).

Enzymes

An enzyme is a protein catalyst that speeds up a reaction by lowering its activation energy, without being used up. Each enzyme is specific, because its active site fits only a particular substrate (the lock-and-key idea). Enzyme activity depends on conditions: it rises with temperature (more collisions) to an optimum, then falls as heat denatures the enzyme, changing the active site shape; each enzyme also has an optimum pH. The EOC tests this mostly through graphs, asking you to explain why activity rises, peaks, and then crashes, so connect the curve to collisions and denaturation.

Photosynthesis and respiration

These two processes are reverses of each other, and seeing the link is the key. Photosynthesis happens in chloroplasts, uses chlorophyll to capture light, and converts carbon dioxide and water into glucose and oxygen: $6\text{CO}_2 + 6\text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$, storing energy in glucose. Cellular respiration happens mainly in mitochondria, uses oxygen to break glucose down, and releases the energy as ATP: $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O}$. When oxygen is short, cells use fermentation, which releases far less energy and makes lactic acid (animals) or ethanol and carbon dioxide (yeast). The rate of photosynthesis is set by limiting factors (light, carbon dioxide, temperature), another graph the EOC loves.

Check your knowledge

A mix of recall, reasoning, and interpretation questions covering Module 2. Attempt them under timed conditions, then check against the solutions.

1. Explain why water is described as polar. (2 marks)
2. Name the property of water that lets it be pulled up a tall plant, and the cause. (2 marks)
3. State the monomer and one function of each: carbohydrate, protein, nucleic acid. (3 marks)
4. Define a catalyst and state what an enzyme does to activation energy. (2 marks)
5. Explain why an enzyme stops working above its optimum temperature. (2 marks)
6. Write the word equation for photosynthesis. (2 marks)
7. State the organelle and the energy molecule produced in aerobic respiration. (2 marks)
8. Explain how photosynthesis and respiration are related. (2 marks)