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
FIGURE 12.1 LEGUME MORPHOLOGY: (A) FLOWER; (B) FRUIT; (C) SEED: (D) SEEDLING.
First true leaves
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?
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.
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-producing bacteria ^^
Dead organisms and animal waste
Nitrogen-fixing bacteria In soil
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
Dropper botdc of crystal violet stain Dropper bottle of distilled water Glass slides
Razor blades, single-edged
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
Polyunsaturated Fatty Acids h h h h h
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
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
Plastic pctri dishes Soy milk Sudan IV vial Test rubes Test tube rack Toothpicks Variety of plant oils
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
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)
Soybean oil (substitute for palm oil) Spices for color (optional) Thermometers
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