Shoot architecture allows plants to spread up (primary growth) and out (branching). Both of these allow leaves to intercept more light by occupying more canopy area. This also allows plants to try to shade out competitors nearby, further locking up light for photosynthesis. The evolution of plants from tiny plants hugging wet ground to massive trees is a race upwards and outwards to collect more and more light.
Work Step by Step
Look through the chapter to pictures of plant architecture as well as reviewing earlier chapters which show earlier- and later-evolving plants. Compare these to see how plant architecture, especially in flowering plants, is greatly advanced in how it interacts with available sunlight.