Materials Needed for Exercise A

Forceps

Hand lens or magnifying glass Legume flowers Legume seed mix Mung bean sprouts Peanuts in the shell

Pods of green beans, snowpcas, and others Soy-based foods

Standard

Floral Structure Mung BeanLocust Magnified

Standard

Morphology Mung Bean

Epicotyf

Legume Morphology

FIGURE 12.1 LEGUME MORPHOLOGY: (A) FLOWER; (B) FRUIT; (C) SEED: (D) SEEDLING.

Standard

Standard

First true leaves

Hypccotyt

/-Radicle

Epicotyf

Radicle Leaves

Procedure for Exercise A

1 Obtain a flower of black locust, wisteria, Texas blue-bonnet, garden pea, bean or odier legume flower. (You may want to refer to Laboratory Topic 6 to review flower structure.) Is the legume flower regular (radial symmetry) or irregular (bilateral symmetry)?

What is the number of sepals and petals?

Identify the largest and topmost petal, the standard. Find the two side petals, or wings. Is the standard outside or inside the wings? Arc the petals of the keel fused together or separate?

Till I.OWDOWN ON LliCiUMKS 161

Remove the petals and locate the stamens. What is the number of stamens? Arc the stamens separate all the way to die base of the filaments, or is there some fusion? If the filaments are fused, are all the stamens fused? How many? Are there any solitary stamens? How many?

What is the number of carpels?

In the following space, draw the shape of a carpel.

Examine two other legume flowers and record your observations in tabic 1 ofworksheet 12-1 at die end of this laboratory topic.

2. The shape of the legume carpel that you drew in step 1 hints at the shape of the fruit to come. Obtain several peanuts (Arachis hypogea) in their shells. Observe the shell of a peanut. Carefully apply pressure to the shell. Does the peanut split lengthwise along two seams? Splitting along two scams is typical of a pod also called a legume), the characteristic fruit of the Fabaceac i tig. 12.1 b). Although the peanut matures underground where soil microbes decompose the fruit wall, the ^ancestral scams" of the pod arc still retained.

Within rhe shell, find 2-3 peanuts. The peanuts arc actually seeds tig. 12.1 c). Note the brown papery material surrounding each seed. This is the protective seed coat, or testa. The two large edible structures per seed arc cotyledons. Legumes belong to the class of angiospcrms called dicots (or more formally, dicotyledons) in which each seed is typically equipped with two of these seed leaves. The cotyledons arc rich in protein and oil, and they supply rhe young growing plant with nutrients.

Obtain one peanut seed and carefully pull it apart. Observe die miniature peanut plant, and note the shoot with two foliage leaves and the large radiclc or embryonic root. Examine green beans, snow peas, and other examples of legume pods from the produce aisle and the great outdoors.

3. For a better view of a seedling, obtain a sprout of the mung bean (tig. 12.1 d). Find the two cotyle dons. which may be in the process of shedding the brown seed coat. The embryonic axis above the w cotyledons is called rhe cpicotvl. It develops into the stem and leaves as the seedling grows. You should also be able to find rhe first ser of true leaves, the first photosyntheric organs of the plant. Identify the hypocotyl, the area of the stem below rhe cotyledons. Also find the radiclc, the cmbrvonic root.

  1. In table 2 of worksheet 12-1, you will find dcscrip rions of several common types of edible beans and peas. Obtain a handful of legume seed mix, and as you sort through it, try to match each bean and pea with the descriptions in the tabic. Put a check mark bv the name of diose vou have corrcctly • » «
  2. Note also the prominent hilum on many of the sec.ds. The hilum is the scar that marks the attachment point of the seed to the pod. Also look for a small pore; that is the micropyle, the opening through which the pollen tube enters the ovule in the ovary of the flower during fertilization.

Some legume seeds are processed to make prepared foods. One common example is peanut butter, which in its purest form is simply a paste made from ground-up peanuts. Peanut butter was invented by an American physician from St. Louis in 1888 as a nutritious supplement for his patients.

5. The soybean (Glycinc max) cannot be consumed raw because it contains an inhibitor that interferes with the normal breakdown of protein in the human digestive tract. Despite this drawback, the soybean has been valued for centuries in Asia, where it is the starting ingredient for many processed foods. To make soy sauce, soybeans are fermented in brine. Soy milk is prepared by soaking soybeans in water and then pureeing the mixture. After heating, the liquid that is poured off is soy milk. The remaining solids arc soybean curds, or tofu. Although tofu has little taste on its own, it can readily pick up the flavors and colors of added spices. Soy cheeses, ice crcam, and many other products attest to rhe versatility of tofu. Sample the soy products available in the lab.

EXERCISE B: The Nitrogen Goes Round and Round

Nitrogen is an essential clement for living organisms. It is a ncccssary ingredient in the making of nucleic acids (such as DNA), proteins and amino acids. All organisms must be able to obtain a usable source of nitrogen. And that's the dilemma. We live in an atmosphere that is rich in nitrogen gas (N2), a form of nitrogen that cannot be uti-

Nitrate Decomposers

N2 fixation

Nj fixation

Denitrifying bacteria

Nodules

Cyanobacteria

Nitrate-producing bacteria ^^

Decomposer

Dead organisms and animal waste

Nitrogen-fixing bacteria In soil

Sediment

Decomposers

Nitrite-producing bacteria

FIGURE 12.2 THE NITROGEN CYCLE. NITROGEN-FIXING BACTERIA LIVING WITHIN NODULES IN THE ROOTS OF LEGUMES CONVERT NITROGEN GAS (N2E) INTO AMMONIUM (NH< + ).

lizcd by most forms of life. Fortunately, several spccics of bacteria and fungi arc capable of utilizing armosphcric nitrogen gas and converting it into ammonium (NH4 ), a form that can be readily absorbed by plants (fig. 12.2). This process is called nitrogen fixation. Luckily for legumes (and humans), many legumes arc in closc association with Rhizobium, one of the nitrogen-fixing bacteria that can convert (or "fix") nitrogen gas to ammonium. Rhizobium lives in the roots of its leguminous host, where it can be seen as visible swellings of the roots called nodules.

Materials Needed for Exercise B

Clover, bean, or other leguminous plant with root nodules

Covcrslips

Dropper botdc of crystal violet stain Dropper bottle of distilled water Glass slides

Procedure for Exercise B

  1. Obtain a clover, bean, or other leguminous plant. Wash the soil awav from the roots and look for nodules. •
  2. Remove a nodule from the root and place it on a glass slide. Chop up the nodule completely with the razor blade.
  3. Add a drop of distilled water and a drop of crystal violet stain. Cover with a covcrslip.
  4. Look for a bacterium that resembles a lcrtcr of the alphabet. This is Rhizobium. the nitrogen-fixing bacterium.
  5. Sketch RJrizobium in the following spacc.

Razor blades, single-edged

Clover Bean Stain

EXERCISE C: Saturated or Unsaturated? You be the Judge

Fats and oils belong to the class of macronutricnts called lipids, which provide us with more than twice the energy content of carbohydrates or proteins- 9 Kcal/g. It is no wonder that animals typically build up energy reserves as fat. While plants with their lower metabolic demands and stationary habit generally store cxccss energy in the form of starch, an cxccption is seen in many seeds and some fruits. Oils arc often the dominant energy store in the mobile packages of plants, their seeds.

Lipids are a diverse group of organic compounds that share one important characteristic; they are insoluble in water. Chemically, fats and oils belong to the class of lipids known as triglycerides. A triglyceride is composed of a molcculc of glycerol with three side chains of fatty acids (tig. 12.3/t). The nature of the fatty acid chain—that is, the number of carbon atoms in the chain and the number of carbon-carbon double bonds—determines die nature of the rriglyccridc.

Generally, fats have longer side chains than oils, and the carbons in the fatty acid side chains are joined to

Fatty acid Fatty acid Fatty acid

Saturated Fatty Acids

Monounsaturated Fatty Acids h h h h h

Fat/ Oil

Polyunsaturated Fatty Acids h h h h h

h oh

Coconut oil Palm kernel otf Chocolate Milk, cheese Butter, cream Beef. vea) Palm oil Lard Pork Chicken

Avocados Flounder Olive oil Almonds Haddock Peanut oil Peanuts Cottonseed oil Canola ch!

Soft margarine (most) Sesame od Mayonnaise Soybean oil Com oil Sunflower oil Safflower oil

FIGURE 12.3 (A) THE STRUCTURE OF A TRIGLYCERIDE. (B) THE STRUCTURES OF SATURATED. MONOUNSATURATED. AND POLYUNSATURATED FATTY ACIDS. AND EXAMPLES OF THE FOODS CONTAINING THEM.

neighboring atoms by single bonds. Fats are solid at room temperature and obtained from animal sources. Tallow (beef fat), lard (pig fat), and butter are all examples of fats. Oils have shorter side chains, and the fatty acids contain some carbon-carbon double bonds, characteristics that lead to a lower melting point, which means that oils arc liquid at room temperature. Oils are generally obtained from plants.

If there is only one carbon double bond, a fatty acid is said to be monounsaturated. If the triglyceride has mainly monounsaturated fatty acids, the oil is also said to be monounsaturated. If the fattv acid has more than one carbon double bond, and if the oil likewise is mostly composed of these kinds of fatty acids, both fatty acid and oil arc said to be polyunsaturated. Fats on the other hand arc described as saturated bccausc thev consist of

fatty acids, the majority of which lack any double carbon bonds. Figure 12.3£shows the chemical structures of saturated, monounsaturëd, and polyunsaturated fatty acids, and lists some common foods belonging to each group.

Unsaturated fats can be converted to saturated fats by the process of hydrogénation. Hydrogénation reduces the number of carbon double bonds as the hydrogen is picked up at these sites and the bonds are converted into single carbon bonds. An a conscqucncc, the unsaturated fat becomes less unsaturated or more saturated and solid at room temperature. Margarine is a good example of a liquid vegetable oil diat has been converted into a solid, spreadable product.

Whether a triglyceride is saturated or unsaturated has important implications in both health and industry. Eating a diet high in saturated fats has been linked to cardiovascular disease. In commercial applications, the degree of saturation determines whether an oil is drying, semidrying, or nondrying. Drying oils are highly unsaturated, and as their name implies, they dry relatively rapidly as atmospheric oxygen reacts with their carbon double bonds. The reaction breaks up the triglycerides and converts them into foul-smelling compounds. This is what happens when an oil spoils or becomcs rancid. If the oil is mixed with paint or varnish, however, the triglycerides are joined to each other by oxygen, forming a protective coating. For this reason drying oils are valued in for making waterproof coatings. Nondrying oils, which have a smaller percentage of unsaturated fatty acids, remain wet for a relatively longer time. Semidrying oils are intermediate in properties and drying times.

The Sudan IV test is one standard for determining the prcscncc of lipids. The red Sudan dye is soluble in lipids but not in nonlipids. Another chemical test uses iodine to determine the amount of saturation in oils. If iodine is added to an oil, it attaches to die carbon-carbon double bond and the reddish brown color of die iodine disappears as it is absorbed. The more unsaturated an oil is, the more iodine it will absorb. The result is expressed in terms of an iodine number; the number is higher for less saturated oils and lower for more saturated oils.

Materials Needed for Exercise C

Avocado extract

Dropper bottle of apple juice

Dropper botde of distilled water

Dropper bottle of iodine solution (I^KJ)

Dropper bottle of soybean oil or other plant oils

Dropper bottle of vinegar

Dropper botde of white grape juice or grape juice

Graduated cylinders or pipets

Liquid margarine

Marker pens

Paintbrushes, small

Parafilm

Plastic pctri dishes Soy milk Sudan IV vial Test rubes Test tube rack Toothpicks Variety of plant oils

Procedure for Exercise C

  1. Obtain a set of S test tubes and a test tube rack. Label the test tubes as follows: avocado extract, apple juice, grape juice, margarine, plant oil, soy milk, water, and vinegar. Add 20 drops of the appropriate solution to each of the labeled test tubes. Using a toothpick, add a scoop of Sudan IV crystals to each test tube. Gently shake. Record any color change and your conclusions in table 1 of worksheet 12 2.
  2. Obtain two plastic petri dishes, 4 paintbrushes, and 4 different vegetable oils.
  3. Isabel the outer surface of each lid with the name of one of die plant oils and the date and time.
  4. With a paintbrush, paint a thin layer of the oil on the inner surface of the lid. Place the lid, with its painted surface exposed to the air. in an undisturbed place.
  5. Check periodically for drying, and record your results in table 2 of worksheet 12-2. From these results, conclude if die oil type is drying, scmidrying, or nondning.
  6. Measure out 5 ml of oil with a graduated cylinder or pipct, and pour it into a labeled test tube. Add

10 drops of iodine solution one drop at a time, to the

011 in the test tube. Cover with a pic cc of parafilm and shake to disperse the color evenly throughout the test tube. Repeat with the second oil. Record the start time and record the time for each oil to clear the iodine color in table 3 of worksheet 12-2.

EXERCISE D: Lather Up

Soaps can be made from a variety of animal and plant fats, and most soaps arc blends of both. The tat or oil selected depends on die characteristics desired in the soap. For example, soaps that contain coconut oil lather up even with scawater. Olive oil also produces a soap thai lathers well and is known to be good for the skin. (It should be noted that ladicring ability is not necessary for a soap to dean.) Most animal fats make a hard soap, which consequently lasts longer.

In this exercise, you will make an all-vegetable soap according to the cold process method, so called bccausc no boiling is required. In-'this method, a strong alkaline substance, sodium hydroxide (NaOH), also known as lyc, is broken down into its component parts, sodium (Na*) and hydroxy (OH ~ ) ions, by the addition of water (tig. 12.4). The lye solution is dicn added to the fats/oil blend chosen, splitting the triglyceride into its component parts— glycerol (an alcohol) and three fatty acids. The glycerol then picks tip hydroxy ions (OH ~ ) and becomes glycerin, which is used to soften skin and is found in many hand and skin products. In commercially prepared soaps, the glycerin is usually removed to make other products, but your soap will contain glycerin. The freed fatty acids now combinc with sodium to form the soap itself. Saponification, or the soap-making reaction, takes placc when acids (in this case, freed fatty acids j combine with a strong base, the sodium hydroxide, to make a salt (a sodium salt in this case).

Materials Needed for Exercise D

Beaker, 400ml Beaker. 800 or 1000 ml

Glycerol

Fatty Acid

Fatty Acid

Fatty Acid

Fatty Acid

Triglyceride - Sodium —> Sodium soap + Glycerin hydroxide

FIGURE 12.4 THE SOAP-MAKING REACTION.

Coconut oil Distilled water

Essential oil for fragrance (optional) Graduated cylinders NaOH or lve

Oatmeal powder (optional) Olive oil

Palm oil (substitute for vegetable shortening)

pH paper

Rubber gloves

Safety goggles

Soap molds

Soybean oil (substitute for palm oil) Spices for color (optional) Thermometers

Vegetable shortening (substitute for palm oil) Wooden or plastic spoons Procedure for Exercise D

  1. All of the plant oils should be warmed and melted beforehand in an oven at 65°C.
  2. Measure 240 ml of distilled water into a 400-ml beaker.
  3. Wearing gloves and goggles, weigh out 85 g of NaOH (lye). LYE IS EXTREMELY CAUSTIC TO SKIN AND CLOTHLNG. If you feel a burning sensation on your skin, procccd immediately to a sink and flush well with water.
  4. In a hood or a well-ventilated area, slowly add, while stirring with a spoon, the NaOH (lye) to the distilled water. NEVER ADD WATER TO LYE OR AN EXPLOSION MAY RESULT!
  5. Stir until the lye is completely dissolved. Note the temperature, and place the beaker in a water bath set at 35°C.
  6. As the lye cools, measure out 225 ml of palm oil (oil that has been expressed from the seeds of a palm tree). You may substitute vegetable shortening, which is partially hydrogenatcd soybean and cottonseed oils, or soybean oil. Add the oil to a 1,000 ml beaker. Add to the palm oil, 210 ml of coconut oil (taken from the seed) and 180 ml of olive oil (taken from the fruit). Stir with a wooden spoon to mix, and set to cool in the 35°C water bath.
  7. When the temperatures of both the fats and die lye arc about 35°C, SLOWLY add the lye solution to the oils while stirring constantly with a wooden spoon. It is important that you continue to stir constantly and vigorously while saponification takes placc. Share the stir ring duties with your lab partner so that the mixture is constantly stirred during the soap-making process. The most common reason a soap fails to form is failure to stir vigorously and continuously.
  8. Observe how the mixture becomcs cloudy and starts to thicken almost immediately. During the saponification process, the lye solution pulls off the fatty acid chains one by one and splits them from the glvccrol. The glycerol is now available to react with the hydroxy ion, and the fatty acids react with the sodium ions. The saponification process is nearly completed when the "soap traces.n A trace is the temporary impression left when you dribble some of die mixture from the spoon onto the surface. For this rccipc, it should take approximately 10-15 minutes.
  9. After the soap traces, colorants and fragrances can be added. Use at about 15 ml of an essential oil for fragrance. and mix thoroughly. If a different color is desired, add a spice such as cinnamon, turmcric, or paprika until you have the desired color. Mix thoroughly. For texture and a mild abrasive, add oatmeal flakes that have been reduced to a powder by a blender.
  10. Your soap is now ready to pour into molds. Let the poured soap set for 24-72 hrs.
  11. After 24-72 hours, remove the soap from the mold. If you have difficulty removing the soap, placc the mold in the freezing compartment of a refrigerator for 10 minutes or so. The soap should then pop out easily.
  12. Wrap the individual soap bars in plastic wrap, or place diem in a scalable plastic bag.
  13. Allow the soap to cure for 2-4 weeks. During the curing, the pH of the soap changes from alkaline to near neutral (pH 7). To test the pH, add a few drops of distilled water to the surface of the soap and touch it with pH paper. You could also perform the rime-honored test of soap-makers by gingerly touching the tip ofyour tongue to the soap. If it burns the tongue, the soap is still too alkaline. If there is no burning sensation, suds up!
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Responses

  • milena
    What happens to the glycerol produced during the saponification?
    8 years ago
  • orlando
    What happens when you stain vegetable specimen with iodine?
    8 years ago
  • julia
    What is inside the bean seed worksheet?
    8 years ago
  • ines
    Where is the hilum and seams of a green bean?
    8 years ago
  • lemlem
    What materials needed for exercise?
    6 years ago

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