First Lab – botany and experimental design lab
Sample Lecture Notes
The genus Achillea, also known as yarrow or milfoil, was originally described by Carol Linneaus in 1753. We now know, there are over 1,000 species of Achillea on several continents from sea level to the highest mountain tops. In low, moist locales, Achillea can be 2-3 feet in height and very broad. In the highest mountains, it is only a few inches tall and manages to complete its life cycle in less than two months.
In the early days of plant identification, the details of genetics were not known. Therefore, organisms were categorized exclusively by their physical appearance, ie their morphology.
However, looks aren’t everything. Organisms can evolve to exhibit similar morphological characteristics because of their similar habitats. Their similarities are the product of convergent evolution and the species bear little genetic similarity. Alternatively, a single population can be permanently separated geographically such that, through generations of sexual reproduction in these now-isolated populations, they evolve into separate species. This is divergent evolution.
We will discuss evolution in greater depth in future weeks after we have identified all the proposed species concepts.
Photo caption: There are over 1000 species of Yarrow (Achillea spp.) in diverse habitats around the world.
Plants defy gravity
Water is a polar molecule in which one side of the molecule is electronegative near the oxygen atom while there is an electropositive force near the hydrogen molecules. This is why water molecules are attracted to each other, which is called cohesion. Water molecules like to stick together due to these cohesive forces. Water molecules also like to stick to other things, like the walls of a thin tube. This is called adhesion. Try it- when you drink with a straw, the liquid in the straw is higher than the liquid in the cup because the straw is thinner, therefore the adhesive forces are stronger.
Photo caption: Water is a polar substance. The delta minus symbol indicates a negative charge near the oxygen and the delta plus symbol indicates a positive charge near the hydrogens.
Capillary rise is the movement of water from plant roots to its other organs, ie the stems and leaves. This is facilitated by the adhesive and cohesive forces within plant tissues. Water, photosynthetic products, and nutrients from the soil move throughout a plant’s vascular system…if it is a vascular plant that is. There are two kinds of vascular tissue. Materials moving up through the roots like minerals and water travel in the xylem. Photosynthetic products move down from the plant leaves in the phloem. A simple way to remember this is that phloem starts with “ph” as does photosynthesis. Plant do photosynthesis in the leaves, therefore the sequestered materials in phloem originated from the above ground parts of the plants. The reverse is true for xylem.
Photo caption: Stoma in a tomato leaf shown via colorized scanning electron microscope. When the stoma open, carbon dioxide is captured, but water is lost.
Transpiration is another important phenomenon to discuss here. Since plants open their stoma to gather carbon dioxide for photosynthetic chemical reactions, water is lost through these openings. This produces a vapor deficit that also facilitates the rise of liquid in the vascular system of plants. The vertical vapor pressure gradient relates to the dryness of the air in which the plant grows. This is described by Dalton’s Law (https://www.khanacademy.org/science/chemistry/gases-and-kinetic-molecular-theory/ideal-gas-laws/a/daltons-law-of-partial-pressure).
The topic of evapotranspiration has many political and social facets. Invasive plants and climate change are two subtopics of evapotranspiration that might interest you for your final research project. Here is one reference to explore this topic more:
Wang, K., & Dickinson, R. E. (2012). A review of global terrestrial evapotranspiration: Observation, modeling, climatology, and climatic variability. Reviews of Geophysics, 50(2). http://onlinelibrary.wiley.com/doi/10.1029/2011RG000373/full
Surface area leads to absorption
Looking at the roots of plants, we see plants exhibit two broad morphologies for root systems. Depending on local environmental factors like climate, prevailing weather, soil types, and aspect, plants can be better served by taproot systems or fibrous root systems.
For example, the majority of floral species in Plains regions are grasses. Their fibrous root systems maximize surface area. This vast surface area facilitates moisture absorption. Since average rain fall in the Plains is so low, plants must be able to absorb as much water as quickly as possible when it is available for brief periods of time. Since the strategy is rapid absorption, there is little need for caloric investment in thick or deep roots.
Photo caption: Grasses have fibrous roots that have lots of surface area, but are not very deep.
In contrasts, some species use a taproot to draw water. This is a relatively wide vertical root that draws a constant supply of moisture from deep in the soil. This root is a storage organ is calorically expensive, but the trade-off is that water resources are more available. Plains Cottonwoods are the only trees native to the Plains. They live only in riparian areas where they can access the water table near streams and lakes using a taproot system.
The nuts and bolts of labs
In this course, we will engage in an at-home laboratory experience. You will receive a lab kit in the mail and it will contain most of the materials you need to perform the labs. There are a few common household items you will need to round up. As soon as you get your kit, unpack it. Check the contents against the packing list. If you are missing any items, contact HOL right away to get them shipped out to you. Tell me if you are missing something so I can support you through this process.
You need a dedicated and secure place in your home where you will do the labs. You would be surprised how many labs fail due to the actions of roommates and pets! Don’t let this happen to you. You will have some on-going lab components to attend to, for example, you need to grow some plants! In general, try to secure at least an end of the counter, or a card table somewhere in the corner of the room where your lab materials can reside. If you have to unpack and pack up every time you want to do labs, your time management might be challenged.
Take lots of pictures. All labs have photo requirements to authenticate your experience in lab at home. Photos also really help me to contextualize what you are doing so if any problems arise, I can help troubleshoot them. Finally, photos help me to get to know you and the stronger our relationship is, the more I can facilitate your learning experience in the course.
Photos need to be small enough to submit to the dropbox in a word document. You can change the photo settings on your camera device or you can use common photo editing tools in your computer to do this. You should plan to submit one document per lab that contains all of the narrative, graphs, and photos required for the lab. Do not submit a word document, a few jpg files and an excel spreadsheet. This challenges my time management and it is not model the most professional and academic product that you can produce. I can’t open a file bigger than 4MB, so plan ahead. Your photos should no more than 500 x 500 pixel and your file should be saved as a pdf. Both of these tips troubleshoot a file size issue.
Finally, if there is math involved, please take the time to share your math work with me. Again, I can sometimes guess where you went wrong when you submit a number that is incorrect, but it is most helpful if you actually tell me what you did, just once so I can help you better. If you use an excel spreadsheet to do math, copy the excel equation you used and I will be able to figure it out.
The majority of my ad-hoc instruction is directed at your lab experience. Use the lab discussion to communicate with me. I recommend you at least read the next lab when you submit a lab so you can ask for help right away if something doesn’t make sense. I can’t give you the best help if you ask for help late at night right before the submission deadline. At the very least, plan to start the lab a few days before it is due so you can ask a question and get a response before the deadline. I will respond, but I also highly recommend that you respond to each other. Always read the lab discussion when there is a new message!