The ultimate for all topics.
Year 3 Helping plants grow well and Year 5 Plants – Life-cycles
http://earthguide.ucsd.edu/earthguide/diagrams/photosynthesis/photosynthesis.html
http://www.kew.org/visit-kew-gardens/index.htm
http://www.mbgnet.net/bioplants/parts.html
http://www.ehow.com/how_2109198_do-celery-science-experiment.html
http://www.bbsrc.ac.uk/society/schools/primary/plant-detective-big.aspx
http://www.newtonsapple.tv/video.php?id=915
http://www2.bgfl.org/bgfl2/custom/resources_ftp/client_ftp/ks2/science/plants_pt2/dispersal.htm