Spring has to be the prettiest season in Bavaria!  Flowers are blooming everywhere. 

This past week I have launched the topic 9 Plant Science unit in time with the botanical events around us.  I started with giving my students some sunflower seeds to inspect.  They took some paper towelling, wrapped the paper inside a beaker, soaked and drained of the excess water and  then placed 2-4 seeds between the paper and glass.  Within two to three days, the seeds had germinated.  This prompted the discussion of the events of germination. Just before the weekend, students dissected dicot flowers to learn (again) the structure and function of flower parts. I took this opportunity to discuss the regulation of flowering in short day and long day plants.

Over the weekend, the seeds had sprouted the hypocotyl and the roots started to branch.  My students are measuring the growth of the seedlings.  The appearance of the fuzzy growth midway on the white roots puzzled some students.  "Is this a fungus?", some asked.  Others thought  about root hairs.  A great time to ask them this question for homework, " Explain the importance and role of root hairs."  Many students went straight to chapter 9.1 to write about the increase of surface area for absorption of water and minerals.  Too many stopped there, rather than go on to explain how this occurs and why an increased surface area would be beneficial.  Had they read chapter 9.2, they would have found the zone of maturation and cell differentiation where root hair cells form.

"But why is the hypocotyl green and the roots white?", again I asked for homework.  Many answered that the hypocotyl was green as it has chlorophyll ( point) in the chloroplasts ( point) used for photosynthesis. No one thought outside the evident answer to what they had studied only a few months back.  In the class discussion today, I finally coaxed out the idea of all the cells in the plant are genetically identical and that cell differentiation by expression of some genes and not others had occurred.  Hypocotyl cells express the genes for chlorophyll and chloroplast production, probably triggered by exposure to light, while roots cells are not stimulated this way and so do not express these genes and remain white.  It was now time to plant the seeds in soil.  Care had to be taken to carefully remove the roots from the paper towelling and not destroy too many root hairs- hopefully the message from the homework had been learned!

My students will continue to measure the hypocotyl growth and subsequent epicotyl growth for the rest of the school term, another 5-6 weeks.  This should reinforce the concept that plant growth occurs at the apical meristem as the hypocotyl will no longer increase and the epicotyl will continue to grow, then the internodal ( between the leaves) growth will increase in steps from one leaf to another.  They will produce a graph of the growth of the various plant parts.  I have told the students that these seedlings are their own "children" now and must be looked after.  Will any student return sunflower seeds?  I hope to answer this question at the term!