Lessons 38–39 · 2 lessons · A. G‘afurov, A. Abdukarimov, J. Tolipova, O. Ishankulov, M. Umaraliyeva, I. Abdurahmonova. Biology, Grade 10, 1st edition. “Sharq” publishing and printing joint-stock company, Tashkent, 2017
38
Laboratory work 2
Textbook: p. 155
GoalDescribe and compare two plant species by the morphological criterion and conclude that this criterion is relative.
New words
morphological criterion · morfologik mezonherbarium · gerbariytrait · belgimean value · o‘rtacha qiymat
Explanation
The aim of the laboratory work is to find the external traits of plants of two species and to show whether they belong to the same or to different species. Equipment: 3–5 herbarium specimens of each species, or living plants in the school yard chosen by the teacher (for example leaves of white poplar and black poplar), a magnifier, a ruler, a notebook. Safety: do not put unknown plants in your mouth or taste them, touch them only with the teacher’s permission, and wash your hands after the work. Procedure: 1) number the specimens; 2) for each, write the traits of the root (if on the herbarium sheet), stem, leaf (simple or compound, venation, arrangement, margin), flower and fruit; 3) measure the measurable traits (leaf length, width, number of flowers) and calculate the mean for each species; 4) compare the two species in a table; 5) write a conclusion. Conclusion: individuals of one species also differ in size (variation), so the range of a trait is considered and other criteria (genetic, physiological, ecological) are also taken into account. The morphological criterion is relative: sibling species look the same outwardly, and differences can exist within one species.
Worked examples
Species A: lengths of 5 leaves (cm): 6, 8, 7, 9, 10 – mean (6 + 8 + 7 + 9 + 10) : 5 = 8 cm. Species B: 12, 14, 13, 15, 11 – mean 65 : 5 = 13 cm. The difference is 5 cm and the ranges do not overlap, so this trait separates the two species.
If the ranges of leaf length of two species are 8–14 cm and 10–16 cm, they overlap (10–14 cm): the species cannot be identified by length alone, and other traits (leaf margin, venation) are needed.
Class activity
“Work order”: groups make a table of measurements and check each other’s calculations; whoever finds an error gets a point.
Practice
1
Find the mean of these lengths (cm): 4, 6, 5, 7, 8. (Number only.)
6
2
Why are several specimens measured for one species?
There is variation among individuals; one specimen does not represent the species, while the mean and range are more reliable.
3
Give an example of a wrong conclusion drawn from the morphological criterion alone.
Taking sibling species for one species, or thinking a male and female (sexual dimorphism) are two species.
4
Which safety rules are followed in the laboratory work?
Do not put unknown plants in the mouth or taste them, work with the teacher’s permission, and wash hands afterwards.