IB Biology SL C1.3 Photosynthesis Notes

Photosynthesis converts light energy into chemical energy in carbon compounds. Photoautotrophs use chlorophyll to capture light; in plants it is in chloroplast thylakoid membranes, while cyanobacteria use chlorophyll in internal membranes instead of chloroplasts.

The photosynthesis equation maps the sources of atoms and products. Carbon dioxide is reduced to carbohydrate using hydrogen from water. Glucose represents the main stored product, though many compounds are synthesized. Oxygen is released from photolysis of water, not directly from CO2; oxygenic photosynthesis occurs in plants, algae, and cyanobacteria.

Paper chromatography separates chlorophylls and accessory pigments because pigments differ in solubility and attraction to the paper. Use Rf as a ratio: distance moved by pigment divided by distance moved by solvent front. A larger Rf means the pigment moved further relative to the solvent.

Spectra questions test whether you know what the graph is measuring. Chlorophyll and accessory pigments absorb specific wavelengths; absorbed light excites electrons for light-dependent reactions. An absorption spectrum shows wavelengths absorbed by pigments, while an action spectrum shows wavelengths most effective for photosynthesis rate, often using oxygen production or CO2 uptake.

Limiting-factor experiments ask what is currently holding photosynthesis back. Light intensity, CO2 concentration, and temperature can limit photosynthesis. Investigations change one variable and estimate rate from O2 production or CO2 uptake per unit time while other variables are controlled. When a graph plateaus, the tested factor is no longer limiting.

CO2 enrichment tests whether increased CO2 raises photosynthesis or growth. Greenhouse experiments are controlled but less natural; FACE experiments enrich CO2 in open air and compare realistic crop and ecosystem responses. The teacher move is to ask: was CO2 really limiting, and were water, nutrients, temperature, and species differences controlled or considered?

Photosynthesis converts light energy into chemical energy in carbon compounds. Carbon dioxide is reduced to carbohydrate using hydrogen from water, glucose is the main stored product, and released oxygen comes from photolysis of water. Pigment evidence is tested with chromatography and Rf, spectra questions separate absorption from action, and rate/evidence questions use limiting factors, controls, and CO2 enrichment context.

Use this for SL/core questions on photosynthesis definition, source of carbohydrate/oxygen, pigment separation, spectra, limiting factors, and CO2 enrichment evidence.