Overview

Lesson Procedure

60-65 minutes of class time across 5 phases.

1. Warm-Up5 minutes
2. Direct Instruction15-20 minutes
3. Guided Practice15 minutes
4. Independent Practice20 minutes
5. Closure5 minutes

1. Warm-Up5 minutes

   Write nine lab items on the board: beaker, goggles, balance, flask, gloves, thermometer, test tube, apron, ruler. Give students two minutes.

   Warm-Up Prompt

   Sort the nine items into groups, and then put your groups into one or two larger groups. Name every group, and write the rule that decides who belongs in it.

   Collect two different answers, for example glassware, measuring tools and safety gear, or "things that touch chemicals" and "things that do not." Both are reasonable; the difference is the rule at the top. Tell students that this standard asks them to see how a science text sets up its own categories and levels, what rule each level uses, and what that structure shows about the ideas.

2. Direct Instruction15-20 minutes

   Part 1: What to look for in a classifying text. Keep this table up for the whole lesson.

   How science texts build categories and hierarchies, and the words that signal them

   Feature	Signal words	Question to ask
   Membership	belongs to, comprises, includes, are species of	Which group does this item go in?
   Criterion	according to, distinguished by, decided by	What rule puts items in this group and not another?
   Levels	grade, more comprehensive, subdivision, group of groups	Which groups sit inside which, and how many levels are there?
   Completeness	every, only one, exactly one	Must every item have a place at every level?
   Labels	also called, synonymously, of lower grade	Does the same word name the same level everywhere?
   Boundaries	most, commonly, can look like, unclassified	What does the text do with items that fit badly?

   Part 2: Model with Gray (T1). Asa Gray, a Harvard botanist, wrote this textbook for schools in 1887. Read the excerpt aloud once. On the second reading, box every name of a grade (class, order, genus, species, variety) and underline every example Gray places in one. Diagram 1 shows the result for the Rose order.

   1527. There are, at nearly the lowest computation, as many as one hundred thousand species of phanerogamous plants, and the cryptogamous species are thought to be still more numerous. They are all connected by resemblances or relationships, near and remote, which show that they are all parts of one system, realizations in nature, as we may affirm, of the conception of One Mind. As we survey them, they do not form a single and connected chain, stretching from the lowest to the highest organized species, although there obviously are lower and higher grades. But the species throughout group themselves, as it were, into clusters or constellations, and these into still more comprehensive clusters, and so on, with gaps between. It is this clustering which is the ground of the recognition of kinds of species, that is, of groups of species of successive grades or degree of generality; such as that of similar species into Genera, of genera into Families or Orders, of orders into Classes. In classification the sequence, proceeding from higher or more general to lower or special, is always CLASS, ORDER, GENUS, SPECIES, VARIETY (if need be).

   2528. Genera (in the singular, Genus) are assemblages of closely related species, in which the essential parts are all constructed on the same particular type or plan. White Oak, Red Oak, Scarlet Oak, Live Oak, etc., are so many species of the Oak genus (Latin, Quercus). The Chestnuts compose another genus; the Beeches another. The Apple, Pear, and Crab are species of one genus, the Quince represents another, the various species of Hawthorn a third. [...] Some genera are represented by a vast number of species, others by few, very many by only one known species. For the genus may be as perfectly represented in one species as in several, although, if this were the case throughout, genera and species would of course be identical. The Beech genus and the Chestnut genus would be just as distinct from the Oak genus even if but one Beech and Chestnut were known; as indeed was once the case.

   3529. Orders are groups of genera that resemble each other; that is, they are to genera what genera are to species. As familiar illustrations, the Oak, Chestnut, and Beech genera, along with the Hazel genus and the Hornbeams, all belong to one order. The Birches and the Alders make another; the Poplars and Willows, another; the Walnuts (with the Butternut) and the Hickories, still another. The Apple genus, the Quince and the Hawthorns, along with the Plums and Cherries and the Peach, the Raspberry with the Blackberry, the Strawberry, the Rose, belong to a large order, which takes its name from the Rose. Most botanists use the names "Order" and "Family" synonymously; the latter more popularly, as "the Rose Family," the former more technically, as "Order Rosaceae."

   4530. But when the two are distinguished, as is common in zoology, Family is of lower grade than Order.

   5531. Classes are still more comprehensive assemblages, or great groups. Thus, in modern botany, the Dicotyledonous plants compose one class, the Monocotyledonous plants another (36-40).

   6532. These four grades, Class, Order, Genus, Species, are of universal use. Variety comes in upon occasion. For, although a species may have no recognized varieties, a genus implies at least one species belonging to it; every genus is of some order, and every order of some class.

   • Reading a hierarchy from general to special (T1, paragraphs 1 and 6)

     Gray gives the White Oak as a species. Use paragraphs 1, 2, 3, 5 and 6 to place it at every grade, and say which sentence tells you the placement must be complete.

     Result: Paragraph 1 gives the sequence: "CLASS, ORDER, GENUS, SPECIES, VARIETY (if need be)." The White Oak is a species of "the Oak genus (Latin, Quercus)" (paragraph 2); the Oak genus belongs to one order with the Chestnut, Beech, Hazel and Hornbeam genera (paragraph 3); and that order, like every order, sits in a class, here the Dicotyledonous plants (paragraph 5). The rule that makes the chain complete is in paragraph 6: "every genus is of some order, and every order of some class." So the text structures plants as a strict hierarchy in which each group has exactly one parent group.

   • Defining a grade by a repeated relationship (T1, paragraph 3)

     Paragraph 3 says orders "are to genera what genera are to species." What does this analogy tell a reader about how the hierarchy is built?

     Result: It says the same relationship repeats at each step: a genus is a group of closely related species, so an order is a group of related genera. Gray does not need a new kind of definition for each grade; each grade is a group of the grade below it, joined by resemblance. Paragraph 1 describes the same structure in other words: species form "clusters or constellations, and these into still more comprehensive clusters." Paragraph 5 finishes the pattern at the top: classes are "still more comprehensive assemblages."

   • When one grade has two names (T1, paragraphs 3-4)

     Is a Family the same grade as an Order? Use paragraphs 3 and 4 to explain Gray's answer.

     Result: It depends on the system. In botany, "Most botanists use the names 'Order' and 'Family' synonymously," one popular and one technical (paragraph 3). "But when the two are distinguished, as is common in zoology, Family is of lower grade than Order" (paragraph 4). A reader must therefore tie a label to its place in the hierarchy, not to the word alone. Modern biology has since adopted the zoologists' usage for plants as well: families are now grouped into orders.

3. Guided Practice15 minutes

   Pairs read the lab guide (T2) and draw its hierarchy before they look at Diagram 2, writing the criterion beside each level. Then check the drawings against Diagram 2 as a class and work the two examples together.

   1Purpose. This guide explains how the lab's rock collection is classified, so that every specimen is placed in the same system. Rocks are sorted in three levels: class, group and rock name. The specimen descriptions used in class activities are written for teaching.

   2Level 1: class, by origin. Every rock belongs to one of three classes, decided by how it formed, not by how it looks. Igneous rocks formed when molten rock, magma underground or lava at the surface, cooled and hardened. Sedimentary rocks formed from sediment, meaning pieces of older rock or material from water or living things, that was laid down in layers and hardened. Metamorphic rocks formed when an existing rock was changed by heat and pressure without melting.

   3Level 2: group, by the clue that records how the rock formed. Igneous rocks are grouped by crystal size. Intrusive rocks cooled slowly underground and have crystals large enough to see; extrusive rocks cooled quickly at the surface and have crystals too small to see, or none at all, as in volcanic glass. Sedimentary rocks are grouped by what they are made of. Clastic rocks are made of fragments of other rocks; chemical and biological rocks formed from minerals that settled out of water or from the remains of living things. Metamorphic rocks are grouped by texture. Foliated rocks have their minerals lined up in parallel bands or sheets; nonfoliated rocks do not.

   4Level 3: rock name. Each group is divided again. Clastic rocks are named by grain size: conglomerate has rounded grains larger than 2 mm, sandstone has grains from 1/16 mm to 2 mm, siltstone has grains from 1/256 mm to 1/16 mm, and shale has grains finer than 1/256 mm and splits into thin layers. Intrusive rocks are named mainly by color, which follows their minerals: granite is light-colored and gabbro is dark. Basalt and obsidian are extrusive; rock salt, limestone and coal are chemical or biological; slate, schist and gneiss are foliated; marble and quartzite are nonfoliated.

   5Using the system. Always work from the top: decide the class first, then the group, then the name. A specimen goes in only one box at each level, and each box sits inside exactly one box above it. Appearance can mislead. Quartzite, a metamorphic rock made from sandstone, can look like sandstone, but its grains are fused so tightly that it breaks through the grains instead of around them. Marble can look like limestone, but its crystals interlock. When a specimen's origin cannot be decided, label it "unclassified" and record why, instead of forcing it into a class.

   • Placing a specimen by working down the levels (T2, paragraphs 2-4)

     A specimen is made of rounded pebbles 5-20 mm across, cemented together in a layer of sand. Classify it at every level of the lab guide.

     Result: Level 1: the pebbles are pieces of older rock laid down and hardened, so the rock is sedimentary. Level 2: it is made of fragments, so it is clastic. Level 3: the grains are rounded and every one is larger than 2 mm (5 mm > 2 mm), so it is a conglomerate. Each decision uses only the criterion the guide sets for that level, and each answer limits the choices at the next level: once the rock is clastic, only grain size matters.

   • When appearance and origin disagree (T2, paragraph 5)

     A student labels a pale, sugary-looking rock "sandstone." When it is broken, the fractures run straight through the grains. How should it be classified, and why does the guide's structure decide the case?

     Result: The guide says quartzite "can look like sandstone, but its grains are fused so tightly that it breaks through the grains instead of around them." So the specimen is quartzite: metamorphic at level 1 and nonfoliated at level 2, since it has no parallel bands. The structure decides the case because level 1 is set by origin, "not by how it looks" (paragraph 2): the top criterion outranks any resemblance at the bottom.

   Debrief with one question: How is the lab guide's hierarchy stricter than Gray's? (Every level has a stated criterion, the order of decisions is fixed, and there is an "unclassified" label for doubtful specimens. Gray groups by resemblance and admits that his clusters come "with gaps between.") Students should see that analyzing a classification means naming both its levels and the rule at each level.

4. Independent Practice20 minutes

   Students read the Clerke excerpt below on their own and answer quiz questions 1-20 with the text open. Clerke is describing how the Jesuit astronomer Angelo Secchi sorted stars by their spectra, the patterns of colors and dark lines that a star's light shows when spread out by a prism, and how the German astronomer H. C. Vogel later rearranged Secchi's groups. Remind students to identify the level and the criterion before they choose, and to cite paragraphs in short answers.

   1[...] To Father Secchi is due the merit of having executed the first spectroscopic survey of the heavens. Above 4,000 stars were passed in review by him, and classified according to the varying qualities of their light. His provisional establishment (1863-67) of four types of stellar spectra has proved a genuine aid to knowledge through the facilities afforded by it for the arrangement and comparison of rapidly accumulating facts. Moreover, it is scarcely doubtful that these spectral distinctions correspond to differences in physical condition of a marked kind.

   2The first order comprises more than half the visible and probably an overwhelming proportion of the faintest stars. Sirius, Vega, Regulus, Altair, are amongst its leading members. Their spectra are distinguished by the breadth and intensity of the four dark bars due to the absorption of hydrogen, and by the extreme faintness of the metallic lines, of which, nevertheless, hundreds are disclosed by careful examination. The light of these "Sirian" orbs is white or bluish; and it is found to be rich in ultra-violet rays.

   3Capella and Arcturus belong to the second, or solar type of stars, which is about one-sixth less numerously represented than the first. Their spectra are quite closely similar to that of sunlight, in being ruled throughout by innumerable fine dark lines; and they share its yellowish tinge.

   4The third class includes most red and variable stars (commonly synonymous), of which Betelgeux in the shoulder of Orion, and "Mira" in the Whale, are noted examples. Their characteristic spectrum is of the "fluted" description. It shows like a strongly illuminated range of seven or eight variously tinted columns seen in perspective, the light falling from the red end towards the violet. This kind of absorption is produced by the vapours of metalloids or of compound substances.

   5To the fourth order of stars belongs also a colonnaded spectrum, but reversed; the light is thrown the other way. The three broad zones of absorption which interrupt it are sharp towards the red, insensibly gradated towards the violet end. The individuals composing Class IV. are few and apparently insignificant, the brightest of them not exceeding the fifth magnitude. They are commonly distinguished by a deep red tint, and gleam like rubies in the field of the telescope. Father Secchi, who in 1867 detected the peculiarity of their analyzed light, ascribed it to the presence of carbon in some form in their atmospheres; and this was confirmed by the researches of H. C. Vogel, director of the Astro-physical Observatory at Potsdam. [...]

   6The members of all four orders are, however, emphatically suns. They possess, it would appear, photospheres radiating all kinds of light, and differ from each other mainly in the varying qualities of their absorptive atmospheres. [...]

   7[...] The scheme of classification due to the Potsdam astro-physicist differed from Father Secchi's only in presenting his third and fourth types as subdivisions of the same order, and in inserting three subordinate categories; but their variety was "rationalised" by the addition of the seductive idea of progressive development. Thus, the white Sirian stars were represented as the youngest because the hottest of the sidereal family; those of the solar pattern as having already wasted much of their store by radiation, and being well advanced in middle life; while the red stars with banded spectra figured as effete suns, hastening rapidly down the road to final extinction.

5. Closure5 minutes

   Exit ticket: "Pick one of today's classifications. Name its top-level criterion, and explain what would go wrong if a reader used a different criterion at the top." Sort the tickets into "criterion and consequence," "criterion only" and "categories listed without a criterion."

   Teacher note on the historical texts. Both older texts need a modern frame, which students should get after they have analyzed each text on its own terms. Gray's grades are older than today's system: botanists now separate family from order, as zoologists already did in 1887, and later work regrouped several of his examples (Activity 3). His two classes have also changed: the monocots are still one natural group, but the dicots are not, and most of them are now placed in the eudicots. His phrase "the conception of One Mind" in paragraph 1 reflects his own religious view of nature; it is not a scientific claim, and the class need not debate it. In Clerke, Secchi's four types correspond roughly to today's spectral classes: the first order to the A and B stars, the second to F, G and K, the third to M, and the fourth to the carbon stars. Two ideas in the excerpt were later abandoned: a star's color and spectrum depend mainly on the temperature of its surface, not on absorbing vapors alone, and the spectral types are not stages of age, as Vogel proposed. "Betelgeux" is Clerke's spelling of Betelgeuse, and "metalloids" is an old word for nonmetals.

   Homework passage. The homework uses the chemistry reference sheet below. It sorts all matter with a series of questions asked in a fixed order.

   1Classifying matter. Chemists sort every sample of matter with a short series of questions, asked in a fixed order. Each answer sends the sample down one branch, and the branches below it ask a new question.

   2Level 1: pure substance or mixture? A pure substance has a fixed composition: every sample of it, from any source, is made of the same particles in the same proportions, and it has fixed properties such as its boiling point. A mixture contains two or more substances that keep their own properties, can be present in varying amounts and can be separated by physical means, such as filtering, evaporation or distillation.

   3Level 2 for pure substances: element or compound? An element is made of only one kind of atom and cannot be broken down into simpler substances by chemical means; iron, oxygen and copper are elements. A compound is made of two or more elements chemically combined in a fixed ratio, such as water (H₂O) or carbon dioxide (CO₂). It can be broken down into its elements only by a chemical reaction.

   4Level 2 for mixtures: homogeneous or heterogeneous? A homogeneous mixture has the same composition throughout, and its parts cannot be seen even with an ordinary microscope; salt water and air are homogeneous. A homogeneous mixture is also called a solution. A heterogeneous mixture has parts that differ from place to place, such as sand in water or granite, with its visible grains of different minerals.

   5Hard cases. Some samples sit near a boundary. Brass looks like a single metal, but it is copper and zinc in proportions that vary from one brass to another, so it is a homogeneous mixture, not a compound. Milk looks the same throughout to the eye, but under a microscope it shows droplets of fat spread through water, so it is usually classified as heterogeneous. Distilled water and seawater look alike, but only distilled water is a pure substance.

   6Why the order matters. The first question, fixed or varying composition, always comes first, because the questions at the next level only make sense once it is settled. "Element or compound?" is a question about pure substances, and "homogeneous or heterogeneous?" is a question about mixtures. Asking it of the wrong kind of sample gives an answer that means nothing.

Differentiation Strategies

Assessment Guidance

1. Question 1 of 20 · Multiple Choice

   According to paragraph 1, on what basis did Secchi sort the more than 4,000 stars he examined?

   ATheir brightness, as it appears to the unaided eye at night BTheir distances from the earth, measured by parallax CThe constellations in which they appear in the sky DThe qualities of their light, as shown by their spectra

2. Question 2 of 20 · Multiple Choice

   Paragraph 1 says the four types helped "for the arrangement and comparison of rapidly accumulating facts." What does this say a classification is for?

   AOrganizing a growing body of observations so they can be compared BProving that each type of star is made of a different substance CRanking the stars from the most important to the least important ones DReplacing the observations with one simpler theory of the stars

3. Question 3 of 20 · Multiple Choice

   Which features does paragraph 2 use to define the first order?

   AA yellowish tint and innumerable fine dark lines, like sunlight BBroad, intense hydrogen bars and very faint metallic lines CFluted columns of light falling from the red end toward the violet DThree broad zones of absorption that are sharp toward the red

4. Question 4 of 20 · Multiple Choice

   Paragraph 3 calls the second order the "solar type." How does the paragraph define this category?

   ABy listing every star that belongs to it BBy its size, which is exactly one-sixth of the first order CBy comparing its stars' spectra and color with sunlight DBy a chemical element found only in its stars

5. Question 5 of 20 · Multiple Choice

   Paragraph 4 says the third class includes "most red and variable stars (commonly synonymous)." What does the parenthesis claim?

   AThat red stars and variable stars are, as a rule, the same stars BThat every red star is also a member of the fourth order of stars CThat the words red and variable have the same meaning DThat variable stars slowly change from red to white

6. Question 6 of 20 · Multiple Choice

   How does paragraph 5 relate the fourth order to the third?

   AThe fourth order is a smaller group that sits inside the third order BThe fourth order shows no bands at all, unlike the third CThe fourth order holds the brightest of the red stars DBoth show banded spectra, but the fourth's bands face the other way

7. Question 7 of 20 · Multiple Choice

   In paragraph 5, what does "reversed" mean?

   AThe spectrum appears upside down in the telescope BThe bands are shaded the other way, sharp toward the red CThe colors of the spectrum run from violet to red instead DThe dark bars of the spectrum have turned into bright ones

8. Question 8 of 20 · Multiple Choice

   Paragraph 5 reports that Secchi traced the fourth order's light to carbon, and that Vogel confirmed it. What role does this play in the classification?

   AIt shows that the fourth order was later merged with the first BIt shows that the fourth order was really defined by brightness CIt links a category defined by its spectrum to a physical cause DIt proves that the stars of the fourth order are really comets

9. Question 9 of 20 · Multiple Choice

   Paragraph 6 opens: "The members of all four orders are, however, emphatically suns." What does this sentence add to the structure?

   AA larger category, suns, that contains all four orders BA fifth order, set apart and reserved for the Sun itself CA reason to abandon the four orders altogether DA new criterion that replaces spectra with brightness

10. Question 10 of 20 · Multiple Choice

    According to paragraph 6, what mainly makes the four orders differ?

    AThe kinds of light their photospheres give out BTheir different distances from the earth and their sizes CTheir ages, from youngest to oldest DThe varying qualities of their absorptive atmospheres

11. Question 11 of 20 · Multiple Choice

    According to paragraph 7, how did Vogel's scheme change the structure of Secchi's?

    AIt split the first order into four new orders of its own BIt joined types III and IV in one order and added lower categories CIt removed the fourth type because its stars were too faint DIt replaced the four types with a list of temperatures and no categories

12. Question 12 of 20 · Multiple Choice

    Counting only the top-level groups, how many orders does Vogel's scheme have, according to paragraph 7?

    ATwo BFour CThree DSeven

13. Question 13 of 20 · Multiple Choice

    Clerke writes that the variety of Vogel's categories was "'rationalised' by the addition of the seductive idea of progressive development." What does her word choice suggest?

    AShe fully accepts that the types are stages in the life of a star BShe thinks Vogel's subordinate categories were far too many CShe thinks Secchi first proposed the idea of development himself DShe doubts that the idea is as sound as it is attractive

14. Question 14 of 20 · Multiple Choice

    Suppose that, of the 4,000 stars in Secchi's survey, 2,100 were of the first order. Using paragraph 3 ("about one-sixth less numerously represented than the first"), about how many would be of the second type?

    A1,750 B350 C2,450 D3,333

15. Question 15 of 20 · Short Answer

    Draw the classification in paragraphs 2-6 as a hierarchy. Show the category that contains all four orders, and for each order give its defining spectral feature, its color and one example star, with the paragraph.

    Show model answer

16. Question 16 of 20 · Short Answer

    Draw Vogel's arrangement from paragraph 7 beside Secchi's. What does making the third and fourth types "subdivisions of the same order" say about which differences between spectra Vogel thought mattered most?

    Show model answer

17. Question 17 of 20 · Short Answer

    Paragraph 1 calls Secchi's scheme "provisional" and also "a genuine aid to knowledge." Use paragraphs 1 and 7 to explain how a classification can be useful while it is still provisional.

    Show model answer

18. Question 18 of 20 · Short Answer

    Vogel's scheme turned the categories into a sequence of age (paragraph 7). Explain the difference between a set of categories and an ordered sequence, what extra claim the sequence makes, and how Clerke signals her view of it.

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19. Question 19 of 20 · Short Answer

    Use the numbers from question 14 (4,000 stars, 2,100 in the first order and the second-type count you found). How many stars are left for the third and fourth orders together, and what fraction of the survey is that? Does the result fit what paragraphs 4 and 5 say about those orders?

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20. Question 20 of 20 · Short Answer

    Clerke names Secchi's groups with several words: "order" (paragraph 2), "type" (paragraph 3), "class" and "Class IV" (paragraphs 4 and 5). In Gray's T1, class and order name two different grades. Explain the difference, and what a reader should conclude about the levels in Clerke's classification.

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These standards connect to RST.11-12.5: prerequisites to review first, parallel standards at the same level, and next steps that build on it.

Standard text: Common Core State Standards for English Language Arts & Literacy. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.