Materials Needed for Exercise

Compound microscope

Coverslips

Dissecting needles

Dropper bottle of distilled water

Inulin Artichoke Microscop
FIGURE 13.2 STARCH GRAINS OF (A) BANANA; (B) CROWN OF THORNS. AND (C) POTATO.
Starch Grains Banana

Dropper bottle of iodine solution (IjKI

Glass slides

Plants to examine tor leucoplasts and starch grains

(e.g., white potato, crown of thorns, banana-

Polarizing tiltcrs

Starch of arrowroot, potato, corn, ctc.

Procedure for Exercise B

  1. Place a drop of distilled water on the center of a glass slide. Using a dissecting needle, obtain a very small sample of the starchy flesh of a banana and put this sample in the drop of water. Carefully cover with a cover slip, pressing firmly to spread a thin film of banana flesh on the slide. If the coverslip rocks, you have too much banana flesh. Remove some and try again.
  2. Examine the slide under the low power (10 x objective) of a compound microscope. Look for wide elongated ovals some of which resemble the shape of a banana. In the rable provided in worksheet 13-1 at the end of this laboratory topic, record the name of the plant you are testing and draw a few of the starch grains you see.
  3. Add a drop of iodine solution to the edge of one side of the coverslip. Place a bit of paper towel on the other side of the coverslip to draw the iodine solution across the slide. Observe through the microscopc as the iodine solution diffuses across the slide. What happens when the iodine solution comes in contact with the starch grains of banana? Do you notice a color change? Describe.

The iodine test is the standard test for the presence of starch.

  1. Now try to find the starch grains of crown of thorns (Euphorbia splcndcns). In this case, just pull a leaf from the stem. Note the milky exudate. Squeeze a few drops of this exudate onto a glass slide. Add a drop of water and a drop of iodine solution. Cover with a coverslip.
  2. Observe the slide under the low power (10 x objective) of a compound microscope. Look for the structures stained blue-black. These arc the starch grains. Bring up to high power (40 x objective) to see more clearly. Draw the shape in worksheet 13-1.
  3. Now take a look at the starch grains in a potato. Using a razor blade, slice a small piece from the fleshy part of a white potato.
  4. On a glass slide, cut this slicc into tiny picccs. Add a drop of water and a drop of iodine solution. Care fully cover with a coverslip. If the coverslip rocks, you have too much potato flesh. Remove some and try again.
  5. Observe under the low power (10 x objective) of a compound microscopc. lx>ok for the dark-stained structures. Some should soil be in the cells while others were released when you cut the slicc. Bring up to high power (40 x objective) to sec more clearly. Draw die shape in worksheet 13-1.
  6. Repeat this proccss for any other plants provided for this purpose in the laboratory. Record the shapes of die starch grains in worksheet 13-1.
  7. Add a bit of arrowroot starch to a glass slide. Add a drop of water and cover with a coverslip. Observe under the low power (10 x objective) and of the compound microscope to sec the starch grains of arrowroot. Bring up to high power C40 x objective) to sec more clearly. Obtain two polarizing filters. Place one over the light source below the stage. Hold the second filter in front of the eyepiece lens while looking into the microscope. Slowly rotate this upper filter as you continue to examine the starch grains. Stop when you sec the distinctive Maltese cross. Repeat making slides of other starch grains using corn or potato starch.

EXERCISE C: Storage Organs

At the start of the growing season, stored starch serves as the energy source for new aboveground growth. In stressed environments when conditions arc not favorable for photosynthesis, starch provides the plant with a ready supply of organic solutes. Any part of a plant may be adapted for storage. Some storage organs arc roots, while others are modified underground stems and leaves (fig. 13.3). (Note: For assistance in identifying the plant parts in the following exercise, refer to Laboratory Topic 4.)

Materials Needed for Exercise C

Bulb of daffodil Compound microscope Corm of crocus Covcrslips Dissccting needles

Dropper bottle of iodine solution KI) Dropper bottle of distilled water Glass slides

Iodine Test Starch
(b) Rh!2ome
  • is 'J 1
  • 0 < 'I
  • c) Tuner
  • e) Corm <0 Taproot (g) Tuberous root

FIGURE 13.3 STORAGE STEMS AND ROOTS.

The bulb is a modified stem with storage leaves. These white storage leaves make up die bulk of the bulb. The stem at the base of the bulb gives rise not only to leaves but also to roots. Pick off one white leaf and note its diin, translucent covering (epidermis). Take a small sample from the fleshy middle or mcs-ophvll of a leal" and place the sample on a glass slide. Add a drop of water and iodine solution. Cover with a coverslip. Using a compound microscope, view the slide under the low (10 x objective) power first, and then switch to high i40 x objective) power. Observe the numerous starch grains within each parenchyma ccll of the leaf.

If your bulb has sprouted, it is easy to recognize a third type of leaf. These arc the green foliage leaves, die ones that appear aboveground when the bulb is planted. What would their main function be:

Razor blades, single-edged or knives

Rhizome of ginger

Storage organs from other plants

Taproot of carrot

Tuberous root of spider plant

Tuber of caladium

Procedure for Exercise C

1. Obtain a daffodil bulb and observe the papery brown coverings on the outside of the bulb. These are modified leaves that act as a protective barrier and deterrent to discourage microbes and other soil organisms. Note the veins running through these leaves. What is the venation pattern? Is this a monocot or dicot plant?

Next obtain and examine a crocus corm. As with the bulb, papery leaves on the outside form a protective barrier. Again, it is easy to sec the venation pattern of these leaves. What is the pattern? Is the crocus a monocot or dicot plant?

Now slice the bulb longitudinally. What does this resemble:

Now slice the corm longitudinally. Note that the corm is a solid stem, unlike the stem and storage leaves in the bulb. Take a small piece of the corm flesh and place it on a glass slide. Add a drop of water and a drop of iodine solution. Cover with a coverslip, and look for starch grains first under low (10 x objective) power and then under high (40 x objective» power. Record in worksheet 13-1.

3. The rhizome of ginger is the next storage organ to examine, t'nlike the bulb and corm. which arc vcr-

rically oriented, a rhizome shows a distinctive horizontal orientation. The rhizome is an underground horizontal stem. You mav also find adventitious roots

arising from the rhizome.

You can verify the starch storing capacity of the rhizome by taking a small sample of it and preparing a slide to observe the starch grains. Record in worksheet 13-1

4. Examine the tuber of a caladium. Tubers are enlargements found at the ends of some rhizomes. Examine closclv the "eves" of the tuber. Botanicaliv

speaking, the eyes arc collections of buds.

Would a tuber be a root or a stem? How do you

know?

Sample a piece of the inner storage region of the caladium tuber, and examine it under the microscope for starch grains. Record in worksheet 13-1.

5. Obtain a carrot and cut it horizontallv. Note the ccntral corc of tissue cncircled by a large outer region. Have you seen this arrangement before? In what vegetative organ? What is this corc region called? Would a carrot be a root or a stem? How do vou know?

Sample a piecc of the inner storage region of the taproot of the carrot and examine for starch grains under the microscope. Record in worksheet 13-1.

  1. Examine rhc many enlarged underground structures of the spider plant, or airplane plant ( CbloropJntum comosum). These arc tuberous roots, a type of root that develops in many monocots when fibrous roots enlarge for storage.
  2. Examine the other examples of underground storage organs available in the lab. List the ones you examine^ and determine whether the storage organ is a bulb, corm, tuber, rhizome, taproot, or tuberous root. Record your findings in worksheet 13 2.

EXERCISE D: The Starchy Staples

The crops callcd starchy staples arc equal in food value to the cereals and legumes. But, unlike the cereals and legumes, the starchy staples arc not exclusive to a single family. This vegetable group is so named because of the high quantities of starch sequestered within the underground storage organs. Although most of these crops arc tropical in origin, several are adapted to grow under temperate conditions.

Materials Needed for Exercise D

Cassava

Dropper bottle of distilled water

Dropper bottle of iodine solution ' KJ)

Dropper botde of Sudan III

Potato chips

Sweet potato

Taro

True yam

White potato varieties: round white, russet, long white, round red

Procedure for Exercise D

1. White potatoes (Sola ?j urn tuberosum) originated in the Andean highlands of South America. Although tropical, the growth at the cooler temperatures of higher altitudes allows its widespread cultivation in temperate climates. Obtain and examine a white potato. Note the "eyes," which as discussed in Fxcr-cisc C, arc collections of buds at nodes.

Cut the potato in half and note the ring of tissue just inside the skin. This ring of tissue can also be seen in a potato chip. What is it called? WTiar is the large ccntcr region called? What vegetative organ (root, stem, or leaf) of plants has this organization?

What conclusion can you draw about the iden titv of the storage organ of the potato? Record your conclusion by continuing to till oui worksheet 13-2 (begun in Exercise C).

The most familiar varieties of the white potato belong to just four groups: round white, russet, long white, and round red. The round white is a multipurpose variety that works for all preparations—boiling, baking, or converting into chips, fries or flakes. The russet type is the classic baking potato, and its oblong shape is also ideal for processing into French fries. Long whites and round reds are sold as new potatoes because they are harvested early in the growing season while the skins are still thin. New pota toes are used for roasting, steaming, or boiling. View each type on display in the lab.

2. The sweet potato (Ipomea batatas) is the tuberous root of a vine in the morning glory family, llie sweet potato is native to tropical South America, where Christopher Columbus encountered it on his first voyage to the New World. The Arawak people of the Caribbean callcd it batatas, which became -potato" in English; and the same name was bestowed upon Solatium tuberosum because it too was an underground crop from the New World. The sweet potato is also often confused with the true yam, another tropical underground crop. In the United States, sweet potatoes and yarns are simply varieties of Ipomea batatas. The sweet potato has a yellower, drier, and starchier flesh than the yam, whose flesh is sweeter, moistcr, and more orange in color.

Obtain and examine a sweet potato. Note the orange color of its flesh. What orange plant pigment would account for diis color? What vitamin would you

expect to find in abundance in the sweet potato ?

Cut the sweet potato horizontally. Note the inner circle. What inner ring of tissue can be found in roots?

Take a small piece of the sweet potato flesh and prepare a slide to examine its starch grains. Add sweet potato to the chart in worksheet 13 1 (begun in Exercise B), and draw a few of the starch grains.

3. Cassava, Maniboi csculenta, is known by many common names, including manioc, yucca, mandioca, and tapioca. A tropical member of the spurge family, cassava is actually a very large tuberous root from a small tree or bush. Sweet and bitter varieties are classified according to the concentration of cyanogenic glycosides. Cyanogenic glycosides release deadly hydrocyanic acid. Sweet varieties have low levels of these glycosides, while bitter varieties have much higher levels that must be removed dirough extensive preparations to make the cassava safe to cat. Traditional methods of detoxifying bitter varieties vary among cultures, but may include one or more of the following processes: drying, grating, boiling, fermenting, and soaking. Most people are familiar with tapioca, in which the moistened starch of cassava is gently heated to form gelatinized beads. The tapioca pearls are then cooked with milk, eggs, and sugar to make pudding.

Take a sample of cassava or its starch ro view the starch grains. Because the starch grains arc some of the smallest in the plant world, cassava starch and its products are easily digestible and a valuable food for infants and invalids. Record and draw cassava starch grains in worksheet 13-1.

  1. True yam, one of several Dioseorea species and a pantropical native, is an important staple in many tropical countries. The tubers of a vine may reach lengths of 2-3 in (6-9 ft I at the time of harvest. The tuber can be prepared and eaten in ways similar to the white potato. Additionally, the tubers are a source of saponins, or vegetable steroids. Historically, the early research that led to the development of the birth control pill was dependent on extracting inexpensive steroidal precursors from the yam. If available, exam ine the starch grains of yam.
  2. Taro (Colocasia csculenta) grows best in flooded conditions. Native to the tropics of southeast Asia, it was brought along in the canoes of the early migrants who eventually settled Polynesia and the Hawaiian Islands. Poi is the fermented dough of taro, a traditional staple of the Polynesian and Hawaiian peoples. Examine the corm of the close relative of taro, elephant cars, C. ultissima. Take a sample of the corm or its starch to view the starch grains, and draw their shape in worksheet 13-1.

EXERCISE E: What are You Eating?!

Although the estimated number of edible plants approaches 50,000 ¿pedes, less than 300 have been widely cultivated. Of these, wheat, rice, and corn con tribute nearly two-thirds of the plant derived calorics in the human diet. This means there arc literally thousands of potent ially useful plants that most of humanity has yet to discover. Government organizations and researchers are constant!) on the lookout for plants that arc little-known but potentially uscftil to bring to die greater attention of consumers in the world's marketplace.

Materials Needed for Exercise E

A variety of little known plant foods (amarandi, arrowroot, chcrimoya, Jerusalem artichoke (sunchoke), jicama. malanga, quinoa, sunchokc and tomatillo)

Procedure for Exercise E

Examine and sample each of the litdc-known food plants available in the lab. Using your knowledge of the anatomy of plants, decide what plant part is represented by die following plants, and record your observations in worksheet 13-3. If ncccssary, refer to Laboratory Topics 4 and 7 to ascertain what part of the plant is eaten. Draw starch grains in worksheet 13-1.

  1. Arrowroot (Maranta arumdinacea) is the sourcc of an easily digested starch because of its tiny starch grains. To the Arawak people, natives of the Caribbean Islands, arrowroot was the dietary staple they called aru-aru or "meal of meals." They also valued it medicinally and used it to draw arrow poisons from wounds. Europeans named it arrowroot after this practice. Examine either the starch or the plant pan. Make a slide to view the starch grains.
  2. The Jerusalem artichoke is neither an artichokc nor from Jersualcm. It is actually the underground storage organ of a sunflower (Heliantbus tuberosus), which is native to North America and was prized by early Native Americans. Once the plant camc to the attention of the early colonists, it was exported to Europe. There, the Italians called the plant jirasole (turning to the sun) because its flowers follow the path of the sun during die course of the day. English speakers soon corrupted jjirasole to Jerusalem. The name artichoke was bestowed by Samuel Champlain, who thought the taste of the vegetable was reminiscent of the globe artichoke. The misnomer Jerusalem artichokc stood until the 1960s, when a campaign to introduce North American consumers to die crop camc up with the name "sunchokc." A versatile vegetable, the sunchokc can be eaten raw, baked, boiled, or fried. Its primary carbohydrate is inulin, a polymer of fructose that, unlike glucose polymers, can be safely consumed by diabetics. Sample the sunchokc, and make a slide to examine its starch grains.
  3. Jicama is a starchy rootstock that is also known as yam bean and Mexican turnip. It is the storage organ of a leguminous vine (Pachyrrhizus erosus), and can be eaten raw or cooked. In Mexico, jicama is usually served raw with a little lime juice, chili pepper, and salt. Native to Mexico, the plant was introduced to China in the seventeenth century, where it is commonly used in stir-fry dishes. Sample jicama, and make a slide to examine its starch grains.
  4. Malanga, also called cocoyam, is a relative of taro. It is the underground storage organ of one of several species of Xanrbosoma from Central and South America. I.ike taro and arrowroot, malanga is valued for its tiny starch grains and easily digestible starch.
  5. Two noncereal grains that have high nutritional potential are quinoa and amaranth. The Incas coined the name quinoa which means "mother grain." High in carbohydrates and quality protein, the ugrain~

(henopodium quinoa) is cooked like ricc or ground into a flour that can be mixed with wheat flour to make bread and other baked goods.

Another noncereal grain is amaranth, one of several species within the genus Amaranthus. These nongrass grains can be toasted, boiled, popped, or ground into a flour that is mixed with wheat to make a variety of baked goods. Its protein content rivals that of the ccrcal grains.

Examine quinoa and amaranth. Botanically, what parts of these plants are actually eaten or ground for flour? Sample foods made from quinoa and amaranth.

6. Two fruits that have been making inroads in North American supermarkets arc the tomatillo and the chcrimoya. Tomatillo, or the husk tomato, is a staple of salsa verde, the green salsa served with Mexican dishes. It can also be sliced and eaten raw. The husk tomato

Pbysalis ixocarpa is so callcd because of its resemblance to a tiny tomato in a papcrlike husk. Sample the tomatillo and determine its fruit type. Chcrimoya, or custard apple, was known by the Incans. The fruit grows on a tree (Annona cherimola) that is native to the uplands of Peru and Ecuador. The fruits are chillcd, and then the custardlikc flesh is scoopcd out and eaten alone or with cream. Sample the delicious chcrimoya, and determine its fruit type.

TERMS TO KNOW

amylopectin 171 amyloplast 172 amvlosc 171 buib 174 condensation reaction 171 corm 174 Icucoplast 172

monomers 171 polymer 171 polymerization 172 rhizome 175 starch grains 172 taproot 175 tubers 175 tuberous roots 175

QUESTIONS FOR REVIEW AND DISCUSSION

  1. What is a polymer? What monomer makes up starch?
  2. How docs amvlose differ from amylopectin?
  3. What is the function of amyloplasts in plant cells?
  4. How can starch grains be used to identify plants?
  5. List the distinguishing characteristics of bulbs, corms, rhizomes, taproots, tubers, and tuberous roots and give examples.
  6. Name the characteristics of the five major starchy staples: white potato, sweet potato, cassava, yam, and taro.
  7. What characteristics of alternative crops mark them as having high potential for tiirthcr development?

ADDITIONAL RESOURCES

Epstein, H. 1996. ('rippling harvest. Natural History 105(7):12-15.

Lcvctin, E., and K. McMahon. 1999. Plants and society 2d ed. New York: McGraw-Hill Companies, Inc.

ON THE WEB

Cal Photos, Berkeley Digital Library Project http://dlp.CSierkeley.EDU/photos

Ethnobotanical Leaflets Starch Research Page http://www.siu.edu/-ebl/amylosc.htm Wayne's word: A Newsletter of Natural History Trivia http://daphne.palomar.edu/waync/wavnc.htm

OTHER ACTIVITIES

  1. Starch can be puffed and made into packing pellets that arc 100% biodegradable. These pellets can be used in a variety of projects and experiments. For example, a homemade glue can be made by making a mixture of water and pellets. Wettencd pellets can be used like papicr-mâché, as a sculpturing material. You could also subject the pellets to different environmental conditions (temperature, light, precipitation) to test biodegradability.
  2. Search your local supermarket or health food store for exotic produce. Research the nutritional value, method of preparation, country of origin and other interesting facts for each novel plant. Be adventurous and prepare an entree, salad, or dessert with these plants that arc new to you. Enjoy!

NAME

DATE

LAB SECTION NUMBER

WORKSHEET 13-1 EXERCISES B. C. AND D: STARCH GRAINS. STORAGE ORGANS

AND STARCHY STAPLES

Draw a few representative starch grains for each plant examined in lab.

COMMON NAME

STARCH GRAINS

ÏST 1 3 ! Si

LAB SECTION NUMBER

WORKSHEET 13-2 EXERCISES C AND D: STORAGE ORGANS AND STARCHY STAPLES

Identify the storage organ (bulb. corm. rhizome, tuber, taproot, tuberous root) for each plant examined in lab.

COMMON NAME

STORAGE ORGAN

Begonia

Canna

Dahlia

Garlic

Ginger

Iris

Onion

Parsnip

Shamrock

Sweet potato

Tulip

Turnip

Water chestnut

White potato

Yam

LAB SECTION NUMBER

WORKSHEET 13-3 EXERCISE E: WHAT ARE YOU EATING?!

COMMON NAME

SCIENTIFIC NAME

PART USED AND USAGE

COMMENTS (TASTE, NUTRITIONAL VALUE. SHAPE OF STARCH GRAINS. ETC.)

Amaranth

Cherimoya

Jerusalem artichoke/sunchoke

Jicama

Malanga/cocoyam

Quinoa

Tomaullo

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Responses

  • Andreas
    How to prepare stem cells to observ starch grainsfor microscope examinations?
    9 years ago
  • martha
    What is the alternative for iodine test kit solution?
    9 years ago
  • Jere
    How to make banana starch grain slide?
    9 years ago
  • matthias
    Why is there more leucoplasts in the fruit of the banana rather than the banana plan leave?
    8 years ago
  • leah
    Does iodine show the presence of starch in fried yam that is pounded?
    7 years ago

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