Dandelion life from NatureBridge

Dandelion life from NatureBridge One of the defining characteristics of life is growth and development. Almost all organisms have a predictable developmental cycle. Humans have a predictable cycle of development from birth to death, with only minor variations between individual people. Even plants have a developmental cycle. Most plants outside the tropics have a predictable developmental cycle that follows the seasons. (As an aside, many plants tell the time of year by photoperiod, which is how long the daylight is. In a lab, you can make plants bloom in the dead of winter or lose their leaves in spring by using a timer on their sunlamp). Around the peninsula, there is a lot of variation due to differences in elevation, average temperatures, etc., but for the most part, dandelions bloom in the spring, around April or May. Like almost all species, there will be outliers, which are plants that bloom out of sync with the others. This allows the species to survive in case of some regional calamity during the ordinary time when most of them are blooming. Laminate the following plates. Cut out the individual months. After discussing the concept of plant development with your students, pass out the photoplates and months. Ask the students to: 1. Arrange the plant photoplates in a circle and order that makes sense to them. 2. Around the inside or the outside of the circle, place the months in the spacing that makes the most sense. • Why did you arrange them in this order? Why does this order make sense? (There are multiples of some stages, but there is only one order of development). • Flowers are expensive for a plant to make. Why bother? (Oddly enough, people used to think plants make flowers for the enjoyment of humans!) • Why do plants get pollinated? (Pollination is plant sex. Pollen is the sperm and a fertilized egg cell from another (usually) plant develops into a seed). • Do you think that all the plants will follow this order? (There is only one order and the order I have here is correct). • Do you think all the plants will doing the same thing at the same time? (No. Most of them will be doing the same thing at about the same time, but most species have some variation, which is the key to long term survival of the species). Plates: 1. A germinating seed. 2. A young dandelion 3. Growing dandelions 4. Growing dandelions 5. A flower bud. Flower buds have rounded tips. 6. A look inside a developing flower bud. 7. A flower beginning to emerge. 8. Flower a little further along. 9. Almost fully developed flower. 10. A fully developed flower. 11. A bunch of fully developed flowers. 12. Plant sex via surrogate. Dandelions are both male and female at the same time. For most hermaphroditic flowers, the genders develop at slightly different times to avoid inbreeding. Inbreeding allows negative traits that are normally recessive to become physical traits, which isn’t good. The pollen from other plants is stuck to hairs on the bee. Some of the pollen grains (from the anthers) get stuck to the right female parts of the flower(pistil, or stigma) and grow a tiny tube down which a sperm cell swims to the waiting egg in the ovary. Weirder than science fiction, isn’t it? 13. A fully fertilized flower (actually, dandelions and many other flowers are really mass clusters of tiny flowerets) closed up and developing into parachuted seeds. 14. Developed seeds waiting for wind. 15. Off they go. 16. Off they go. 17. Off they go. 18. Still attached to mama. 19. Mission accomplished. 20. No sense feeding those stalks, their job is done and the plant cuts them off. 21. The object of the whole thing.