Organismic Lab Lab1- Dichotomous Key Introduction A dichotomous key is a series of paired statements or questions that are used to categorize organisms with their similarities in characteristics and or structure. The word dichotomous comes from two Greek words that translate to “divided in two parts. ” In a Dichotomous key each step has two choices: whether a particular characteristic is present or absent. The questions are arranged into a couplet which directs to another couplet and the process is repeated until a successful identification is reached.
Qualitative descriptions refer to physical attributes such as scent or color, and quantitative descriptions refer to numerical values such as the amount of pedals on a flower. When constructing a dichotomous key, it is important that the questions are very clear and specific so that any two people that use the key will finish the key with the same conclusion. The purpose of this experiment is to demonstrate the use and know how to create a dichotomous key. Materials 1 metric ruler 4 soy beans 4 mung beans 4 kidney beans li’ Fig 4 Wrinkled pea seeds Fig 5. Mung bean seeds Fig 6.
Sweet Corn seeds Fig7. Wheat Seeds Fig8. Soy bean seeds Discussion Our group was successful in creating dichotomous keys in part A and part B. In part A, the dichotomous key will lead any two users to identify the same smiley faces. The dichotomous key of the seeds were to be much more difficult in classifying and separating than the smiley faces because the seeds did not have many simple physical differences like the ones found in the different smiley faces. The first physical difference identified divided the seeds into two different subsets: round and not round.
Although identifying seeds as round or not round could differ from person to person, my group agreed that the soy bean seeds, wrinkled pea seeds, and mung bean seeds were clearly more spherical and could be classified as round. The most difficult seeds to differentiate were the oat seeds, corn seed, and wheat seeds because of the possible things one could mistaken for the wrong seed. My group finally decided to separate them into two different groups: the seeds that were invaginated and the seeds that were not invaginated. The wheat seeds did not have dents or invaginations, but the oat seeds and corn seeds did contain invaginations.
I believe the dichotomous key created by my group was successful because any two users could easily follow our dichotomous key to identify the specified seed. 1b 4b 5a Sunflower seeds. Conclusion The purpose of this lab was to demonstrate how to use and create a dichotomous key. Thought to be very simple, yet this lab proved that even something as simple as identifying just one characteristic to divide a population into two smaller groups can be challenging when dealing with a population of organisms that are physically very similar like the seeds used during the experiment.
It took a combined participation with effort from everyone in my group to create a dichotomous key that successfully identified two different types of seeds. References http://oregonstate. edu/trees/dichotomous_key. html http://www. mhhe. com/biosci/pae/zoology/cladogram/ http://www. saskschools. ca/curr_content/biology20/unit3/unit3_mod1_les2. htm Lab Handout: 2002 Ward’s Natural Science Establishment