(A Level) Photosynthesis

Learning objectives

Relate the structure of the chloroplast in diagrams and electron micrographs to its function, with the light-dependent stage on the thylakoid membranes of the grana and the light-independent stage (Calvin cycle) in the stroma, linked by ATP and reduced NADP.

Describe how chlorophyll a, chlorophyll b, carotene and xanthophyll absorb light in the thylakoids, interpret absorption spectra and action spectra, and separate the pigments by chromatography, identifying them from Rf values.

Explain cyclic photophosphorylation (photosystem I only, making ATP) and non-cyclic photophosphorylation (photosystems I and II, photolysis of water by the oxygen-evolving complex, making ATP and reduced NADP), including electron transport and chemiosmosis across the thylakoid membrane.

Outline the Calvin cycle — rubisco fixes CO₂ with RuBP to give two GP, GP is reduced to triose phosphate using ATP and reduced NADP, and RuBP is regenerated using ATP — and state that GP and TP are used to make carbohydrates, lipids and amino acids.

Explain how light intensity, carbon dioxide concentration and temperature act as limiting factors, and interpret graphs showing which factor limits the rate of photosynthesis.

Describe investigations of the rate of photosynthesis using DCPIP or methylene blue with a chloroplast suspension (light intensity and wavelength) and using whole or aquatic plants (light intensity, CO₂ concentration and temperature).