My son is studying chapter 4 of his Standard 5 KSSR Science on Survival of Plants.
Found this as additional reading material for him.
1. Natural Defense Of Plants - Simple explanation from this teacher's blog with pictures to illustrate
2. Seed Dispersal - I especially like the two videos found on this page about seed dispersal that shows how seeds are dispersed by wind and another on explosive seeds dispersal. These videos are an excellent way to explain how seeds are dispersed by this methods.