Louisiana LEAP 2025 Biology LS1 (Biochemistry and Energy): a complete overview of the chemistry of life, macromolecules, enzymes, photosynthesis, and cellular respiration

What the biochemistry and energy content demands

Biochemistry and energy is the part of the LS1 core idea on the Louisiana LEAP 2025 Biology test that deals with the molecules of life and the flow of energy through them. This guide runs from the chemistry of carbon and water, through the macromolecules and the enzymes that build and break them, to the two great energy processes: photosynthesis (which stores energy) and cellular respiration (which releases it). The recurring crosscutting concepts are structure and function (water, macromolecules, enzymes) and energy and matter (photosynthesis and respiration).

This guide ties together the matching topic pages, each with its own practice questions: the chemistry of life and water, the macromolecules of life, enzymes and activation energy, photosynthesis, and cellular respiration.

The chemistry of life and water

All matter is made of atoms joined by bonds (covalent share electrons, ionic transfer them). Carbon is central to life because it forms four covalent bonds, building long chains and rings. Water is a polar molecule, and its polarity explains its key properties: it is an excellent solvent, shows cohesion, and resists temperature change, all of which support the chemistry of life and homeostasis.

The macromolecules

The four classes are all carbon-based and built from monomers. Carbohydrates (from monosaccharides) give quick energy and some structure. Lipids (from fatty acids and glycerol) store energy long term, insulate, and form membranes. Proteins (from amino acids) fold into specific shapes to act as enzymes, structures, and transporters. Nucleic acids (from nucleotides) store and carry the genetic information. Match a molecule to its class by its monomer and its function.

Enzymes

An enzyme is a protein catalyst that lowers activation energy, speeding a reaction without being used up. Each enzyme is specific (its active site fits one substrate). Activity rises with temperature to an optimum, then falls as high heat denatures the enzyme; each enzyme also has an optimum pH. Reading and explaining a reaction-rate graph is a common exam skill.

Photosynthesis

Photosynthesis converts light energy into chemical energy stored in glucose, in the chloroplast, using chlorophyll. Reactants are carbon dioxide and water; products are glucose and oxygen: $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$. The key idea is the energy transformation: light energy in, chemical energy stored out.

Cellular respiration

Cellular respiration releases the energy in glucose as ATP. Aerobic respiration uses glucose and oxygen to make carbon dioxide and water: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O$, in the mitochondria. Anaerobic respiration (no oxygen) releases less energy and makes lactic acid (animals) or alcohol and carbon dioxide (yeast). Respiration is the reverse of photosynthesis, and the two cycle matter and move energy.

Check your knowledge

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

1. State how many covalent bonds a carbon atom forms and why this matters for life. (2 marks)
2. Explain why water is a good solvent. (2 marks)
3. Name the monomer of proteins and the monomer of carbohydrates. (2 marks)
4. State the function of lipids in the cell membrane. (1 mark)
5. State what an enzyme does to activation energy. (1 mark)
6. Explain why an enzyme stops working at high temperature. (2 marks)
7. Write the word equation for photosynthesis. (2 marks)
8. State the energy transformation in photosynthesis. (1 mark)
9. Write the word equation for aerobic respiration and state where it mainly occurs. (2 marks)