BSCI 124 Lecture Notes

Undergraduate Program in Plant Biology, University of Maryland


Part 1. The Origins of Agriculture

I. Introduction

    A. For most of their early history, humans survived as foragers or hunter-gatherers, gathering
    wild plants and hunting animals in their natural environment.

    B. Around 10,000 years ago in many areas of the world, there was a shift in human endeavor
    from foraging to farming. Why this happened is not known, but it appears to have formed the
    basis of advanced civilization in both the old and new worlds.

II. Early foragers

    A. These early foragers knew which plants were edible, which were poisonous, and which had
    medicinal properties. They knew which plants could be used as dyes, which could be used for
    weaving or building materials.

    B. One group, the !Kung have foraged Africa for at least 10,000 years. Their diet consisted of
    2300 calories per day, and two thirds of it was plant based, particularly, fruits, nuts, melons,
    berries, roots, and greenery.

III. Agriculture: revolution or evolution

    A. About 10,000 years ago, human cultures began the practice of agriculture in several
    different areas of the world; the near East, the far East, and in Mesoamerica.

IV. Early sites of agriculture

    A. The Near East: an area known as the "fertile crescent" of Mesopotamia which includes
    parts of Iran, Iraq, Turkey, Syria, Lebanon, and Israel.

    B. The Far East: Southeast Asia in Thailand, and the Yellow and Yangtze river valleys in

    C. The New World:

  D. World recipes reflect origins of agriculture

V. Characteristics of domesticated plants

    A. Plants that have been domesticated are genetically distinct from their wild progenitors.

    B. The wild ancestors of several cultivated crops still exist. As these are often the only sources
    of germ plasm for the continued development of new cultivars, or human-selected kinds of
    domesticated crops, collection of seed and protection of wild populations is now an
    international goal in maintaining genetic diversity of crop plants.

    C. Many of the early explorers were responsible for introducing plants from around the world
    into western European culture

VI. Agriculture today

    A. Now that we have seen how agriculture began, now lets compare some statistics about
    present day agriculture

    B. Since 1950 (45 years) agriculture related research in the US has provided some
    dramatic increases in the yield per acre of many important crops.

    C. Summary of agriculture in the United States for 1992

Part 2. Human Nutrition - Why people need to develop agriculture

I. Examination of a typical nutrition label from a box of breakfast cereal shows the nutrients broken up into several classes, after the general information on servings.

The New Food Label

Nutrition Facts 
Serving Size 1/2 cup (114 g) 
Servings Per Container 4
Amount Per Serving
Calories 90 Calories From Fat 30
% Daily Value*
Total Fat 3g 5%
Saturated Fat 0g 0%
Cholesterol 0 mg 0%
Sodium 300 mg 13%
Total Carbohydrate 13g 4%
Dietary Fiber 3g 12%
Sugars 3g
Protein 3g
Vitamin A 80% Vitamin C 60%
Calcium 4% Iron 4%
* Percent Daily Values are based on a 2,000 calorie diet. Your daily values may be higher or lower, depending on your calorie needs:
Calories 2,000 2,500
Total Fat Less than 65g 80g
Sat Fat Less than 20g 25g
Cholesterol Less than 300mg 300mg
Sodium Less than 2,400mg 2,400mg
Total Carbohydrate 300g 375g
Fiber 25g 30g
Calories per gram:
Fat 9 Carbohydrate 4 Protein 4

By Barbara McLaurin, Ph.D., R.D., L.D., Extension Human Nutrition Specialist, Mississippi State University Click here to see full explanation of parts of label 

II. What does this all mean?  These are important nutritional categories for humans:

    A. Calories
    B. Macronutrients  - required in sufficient amounts
        1. Calories: lipids, carbohydrates
        2. Proteins
    C. Micronutrients - these are essential for proper nutrition, but required in smaller amounts
        1. Vitamins
        2. Minerals

III. Calories

    A. Food nutritional value is measured in the amount of energy supplied from the food source.

        1. The unit of measurement is the calorie. Technically, this is the amount of energy required
        to raise the temperature of one gram of water one degree C.
        2. In humans, two thirds of all calories taken in are used to maintain the body temperature.

    B. Food energy is normally measured in thousands of calories or Kilocalories of kcal. So 1000
    calories = one kilocalorie.

    C. We get calories from four food groups: fat (9 calories per gram), alcohol (7 calories per
    gram), carbohydrate (4 calories per gram), and protein (4 calories per gram).

        1. Typically, humans require between 1200 and 3200 Calories per day to maintain
        themselves. The Percent Daily Values listed in food labels are usually based on a 2,000
        calorie diet.
            a. How many calories do you need?
            b. Facts about calories.
            c. Calories that don't count.

IV. Macronutrients: Lipids - Fat and Cholesterol

    A. These compounds belong to a general class of organic molecule called lipids
    (refer to Lecture 4). Their main chemical feature is that they are insoluble in water. Ninety five
    percent of all lipids in the body are in the form of fats and oils called triglycerides.

        1. Triglycerides: compounds formed from glycerol and fatty acids. Fatty Acids are the
        simplest type of lipid, and are used to also make up phospholipids.
            a. Fatty acids: Each fatty acid has a carbon chain with hydrogen atoms attached. The
            different fatty acids differ in number of carbon and hydrogen atoms.
            b. Essential fatty acids:
                i. the body can make most fatty acids
                ii. however three must be supplied in the diet: linoleic, linolenic, and arachidonic acids,
                designated as the essential fatty acids
                iii. the main source of these is from vegetable oils.
            c. Saturated and unsaturated fatty acids
                i. Fatty acids are separated by whether they are saturated or unsaturated; this refers to
                the amount of single bonds between the carbon atoms, which in turn determines the
                number of hydrogen atoms that can be bound to the carbons
                ii. If all the carbon atoms are joined together by single bonds, and all possible
                hydrogens are attached, the fatty acid is saturated.
                iii. If some double bonds occur between the carbons, then the number of hydrogen
                atoms that can be bound is reduced, and the fatty acid is unsaturated.
                iv. All food fats contain a mixture of saturated and unsaturated fatty acids. Saturated
                fatty acids are solid at room temperature for example butter and beef fat, and
                unsaturated fatty acids are liquid at room temperature, for example corn oil and
                safflower oil.
            d. Fatty acids are long chains of carbon and hydrogen atoms that are a
            major source of body energy.
    B. Cholesterol

        1. This is a sub category of lipids known as steroids. Cholesterol is a vital component of
        cells as a part of cell membranes, as well as being used to synthesized several of the human
        sex and other hormones.
            a. It is synthesized in the liver from saturated fatty acids, or absorbed in the intestine from
            eggs, butter, cheese and meat.
            b. Plant sources do not contribute dietary cholesterol directly, and in fact contain
            unsaturated fats, which are known to lower blood cholesterol levels.
        2. Because cholesterol is insoluble in the blood, it is transported by molecules called
            lipoproteins.  These lipoproteins exist in two forms, high density HDL and low density
            a. LDL forms of cholesterol can be taken up by cells lining the arteries resulting in excess
            cholesterol blockages of the arteries, and a restriction of blood flow. This can lead to a
            heart attack if the coronary arteries are involved.
            b. HDL forms of cholesterol help to reduce the levels of LDL cholesterol.
            c. What levels of cholesterol should you maintain? (from Pacific Health, L.L.C.)
                i. Indications of low risk: These are the most commonly agreed upon observation for
                cholesterol levels that best accommodate the maintenance of a healthy heart.
                      Total cholesterol count below 200 mg/dl
                      LDL cholesterol level 130mg/dl or lower
                      HDL cholesterol levels 35mg/dl or greater
                      LDL to HDL ratio less than 3
                      Total cholesterol to HDL cholesterol ratio 3.5 or lower
                ii. Indications of medium-high risk: Any of these traits indicates medium risk of heart
                      Total cholesterol level from 200mg/dl to 239mg/dl
                      LDL cholesterol level from 130 to 159
                      Total cholesterol to HDL ratio from 3.5 to 4.5
                iii. Indications of high risk: Any of these traits indicates high risk of heart disease.
                      Total cholesterol count 240mg/dl or greater
                      HDL cholesterol level less than 35mg/dl
                      LDL cholesterol to HDL cholesterol ratio of 3 or greater
                      Total cholesterol to HDL cholesterol ratio of 4.5 or greater
                iv. If your cholesterol levels indicate medium or high risk, you should consult your
                physician. Most people can control their cholesterol levels through a healthy low-fat diet
                and regular exercise. Some people will require medicines to control their cholesterol

V. Macronutrients: Carbohydrates

    A. Carbohydrates are grouped together as sugars and starches, but also are classified as to
    how many sugar units are present in the molecule (see Lecture 4).

        1. Glucose- The basic building block of all carbohydrates, and the most abundant of all the
        sugars. A single glucose molecule is called a monosaccharide. It is the form of sugar that is
        transported in the blood to all the cells in the body. Cellular respiration converts glucose into
        energy necessary for life.
        2. Fructose and galactose are also common monosaccharides with basically the same
        3. Disaccharides- when two monosaccharides are joined together, they make up a
        disaccharide. For example: One glucose unit and one fructose unit together make up the
        disaccharide called sucrose. This is the form of sugar found on the dinner table. Another
        example of a disaccharide is lactose, the sugar found in cow's milk. These disaccharides are
        broken down into monosaccharides in order to be used by the body.
        4. Polysaccharides- These are also known as complex sugars, contain hundreds or
        thousands of individual sugar units, usually glucose. There are three forms of
        polysaccharides important for human nutrition. The arrangement, number and way the
        glucose units are joined together is what distinguishes one from the other.
            a. Starch- This is the storage form of glucose found in plants. It is found in the seeds,
            fruits, tubers (potato) and roots. The majority of starch in the human diet comes from
            wheat, rice and corn as grain crops, potato, sweet potato, and cassava the underground
            crops, and beans and peas, the legumes. Our body breaks down starch to glucose by
            enzymes in the saliva, and small intestine.
            b. Glycogen- This is the storage form of glucose in the human body found mainly in the
            liver and skeletal muscles. Excess glucose in the blood from food is converted into
            glycogen and stored. Unfortunately, we can only store a day's supply of glycogen in the
            liver, the rest being converted into fat. During exercise this glycogen is converted back
            into glucose to be used for energy. This is why athletes practice "Carbo loading" before
            an athletic event. They eat excess amounts of starch foods to build up muscle glycogen.
            c. Fiber- This is derived from plant sources and is mainly comprised of cellulose,
            lignin, hemicellulose and pectin. It is not digestible, but provides bulk. Cellulose is again
            formed from glucose, but humans do not have the proper enzymes to digest it. Foods
            with fiber include grains, legumes, fruits, and vegetables.  Dietary fiber comes in two
                i. soluble fiber - found in psyllium husks and is the type that makes wet oatmeal sticky,
                shown to reduce levels of cholesterol and appears to be associated with lowered heart
                disease risk
                ii. insoluble fiber - the sponge-like version in bran and in fruit and vegetable skins
                which absorb water, prevent constipation, and may lower colorectal cancer risk

VI. Macronutrients: Proteins

This is a group of large molecules that perform many functions in the body. One type of protein is insulin, a hormone produced by the pancreas to regulate the metabolism of glucose and other carbohydrates.  They are constructed from smaller building blocks called amino acids (see Lecture 4). Usually there are 20 naturally occurring amino acids that are used in protein synthesis.

    A. Essential amino acids: In order to successfully synthesize proteins the human body requires
    the presence of all 20 of the amino acids. However, the human body can only synthesize 11 of
    the 20. Nine others absolutely must be obtained from the diet. These are called the essential
    amino acids. These amino acids cannot be stored by the body, so must be continually
    taken in via the diet. Lack of any of these can result in serious protein deficiency diseases.

    B. Complete Proteins- These proteins contain all the essential amino acids. Proteins obtained
    in the diet from animal sources are complete. Those obtained from plant sources are
    incomplete, deficient in one or more essential amino acids. In order to get all the essential
    amino acids from plant sources it is necessary to combine different plant sources. For example,
    beans and corn, the traditional diet of the Mexican indians provides all the essential amino

    C. Protein digestion requires the use of proteins in the form of digestive enzymes.  Therefore,
    there is a constant turnover in the body's supply of proteins.  For proteins in your diet, see
    proteins for athletes.

VII. Micronutrients:  Vitamins

Vitamins: Molecules that are essential for the normal functioning of certain enzymes in many metabolic pathways of the body. These are called coenzymes. Others are directly involved the synthesis of essential compounds in the body. They are classified into two groups; fat soluble (A, D, E, K) and water soluble (C and B-complex).  For a food guide to vitamins and minerals, see this nutritional science course at Cornell.

    A. Vitamin A

        1. This vitamin is very important in the formation of visual pigments in the retina of the eye.
        Each pigment is made up of a protein molecule, and a form of vitamin A called retinal.
        These pigments are present in the photoreceptor cells of the eye. Night blindness is one of
        the earliest signs of Vitamin A deficiency.
        2. Vitamin A is necessary for the maintenance of epithelial tissues that line both internal and
        external body surfaces, an area equal to one fourth of a football field.
        3. It also helps the body fight infections and helps sustain the immune system.
        4. Food sources of vitamin A is animal liver and is in the form of retinol. Plant sources
        provide beta-carotene found abundantly in many yellow, orange and dark green fruits and
        vegetables. Beta-carotine, when split into two molecules, forms retinol in the body. Unsplit,
        beta-carotine is an antioxidant. Vitamin A deficiency can reduce the health of the skin and
        epithelial tissues, affect digestion and absorption of nutrients, cause infections, and stop
        bone growth.

    B. Vitamin B complex  This is a complex of eight vitamins, which serve as coenzymes in
    literally thousands of chemical reactions in the body. They are water soluble and can be
    leached out of food during preparation if food is prepared in water.

        1. Thiamine (Vitamin B1) is part of the coenzyme thymine pyrophosphate, which
        is involved in the breakdown of carbohydrates by the body. Since its role is metabolic, the
        main signs of deficiency are fatigue, depression, mental confusion etc. Good dietary sources
        of thiamine include meat, especially pork and liver, whole grains, seeds, nuts and legumes.
        2. Niacin (Vitamin B3) collectively this includes two compounds, nicotinic acid and
        nicotinamide. Either are used in the coenzymes NAD+ and NADP+ which are important in
        oxidation-reduction reactions of the body. Without these reactions in the body, release of
        energy from food breakdown cannot occur and cellular death results. The most common
        ailment due to niacin deficiency is called pellagra, the symptoms are referred to as the 4 Ds:
        dermatitis, dementia, diarrhea, and death. In the early years of this century, death was
        surprisingly common in the southern states. Its cause was discovered by Dr. Joseph
        Goldberger in 1914, one of the first efforts of what would eventually become The National
        Institutes of Health. Food sources rich in niacin include meat, poultry, fish, eggs, nuts, seeds
        and legumes.
        3. Vitamin B12 (Cobalamin) - This vitamin does not occur naturally in any food of plant
        origin, but only occurs in animal sources, where it is widely available. It is made from
        bacteria and is only present in foods that contain the bacteria or from animals that have
        ingested the bacteria. Vitamin B12 is involved in energy release from food, and nucleic acid
        synthesis. The most common cause of deficiency is pernicious anemia characterized by the
        production of improperly formed red blood cells. Symptoms include fatigue and weakness.

    C. Vitamin C

        1. Vitamin C or ascorbic acid is obtained from fresh fruits and vegetables. Since they are
        water soluable, they can be leached out of food during preparation.
        2. The most important role of vitamin C is in the synthesis of collagen, a connective tissue
        that holds body cells and tissues together. Collagen is the most abundant protein in the
        body, and is found in bones, teeth and cartilage.
        3. For centuries, sailors on long ocean voyages contracted Scurvy, a disease that could
        cause bleeding of the gums and under the skin, fatigue, brittle bones and even sudden death
        due to internal bleeding. It is now known that scurvy is caused by vitamin C deficiency, and
        is directly traced to the bodies inability to make collagen.

    D. Vitamin D

        1. The primary function of Vitamin D is the regulation of calcium and phosphorous levels,
        especially for normal bone development. The vitamin acts on the absorption, and removal of
        calcium from bones, and retention of calcium by the kidneys.
        2. The human body can synthesize Vitamin D on exposure to sunlight.
        3. Deficiency symptoms are most evident in bone formation.  The most striking is a
        malformed skeleton in children, a disease called rickets.

VIII. Micronutrients: Minerals

    A. Inorganic compounds that exist in the body as ions, or are a part of complex molecules. At
    least 17 minerals are required for normal metabolic activities. They can be major minerals,
    required in amounts greater than 100 mg/day, or trace minerals of which only a few mg are
    required per day.

        1. Calcium: This is the most abundant mineral in the body, with the average adult containing
        800 to 1300 g of the element. 98% is found in the bones and teeth. Its concentration is
        under control of several hormones and vitamin D.
            a. Calcium deficiency leads to osteoporosis, a degenerative bone disease which can be
            easily prevented with a proper level of calcium in the diet. This affects some 15-20 million
            Americans. Bone density is greatly reduced and bones fracture easily.
            b. Milk and milk products are the best sources of calcium, but it is also present in
            dark green leafy vegetables and many seeds. The recommended daily allowance for
            calcium is about 1200 milligrams.  One cup of milk supplies about 300 milligrams of
        2. Iron: Among the trace minerals, iron deficiency is common in women and children and
        care must be taken to insure that the diet supplies sufficient quantities.
            a. Meat, fish, shellfish and poultry are excellent iron sources.
            b. The iron from animal sources is present as heme iron, or nonheme iron.
            c. The most important role of iron is as a component of hemoglobin, the molecule that
            carries oxygen in red blood cells. It is the iron that produces the red color in blood. Iron
            is also found in myoglobin, the oxygen carrier in muscle.
            d. Iron deficiency has its main effect on red blood cells, and leads to iron deficiency
            anemia. This is the most common dietary deficiency disease in the world. Menstruating
            women are often at risk as are those who are pregnant.
            e. Too much iron may also cause health problems, possilby heart attacks.

-Other micronutrients necessary for health? Phytochemicals
                -antioxidants such as carotenoids (e.g. lycopene) and flavonoids

IX. Dietary guidelines

    A. Research has shown that beneficial changes in diet can reduce the risk of developing many
    of these nutritional diseases.

    B. Balancing Nutritional Requirements

        1. Don't become overweight, maintain correct levels of calories consumed.
        2. Reduce overall fat consumption.
        3. Reduce saturated fat consumption.
        4. Reduce cholesterol consumption.
        5. Increase consumption of grains, vegetables, and fruits; high fiber.
        6. Reduce the consumption of refined sugars (sweetners).
        7. Limit intake of sodium (hypernatremia, sodium in foods).
        8. Limit alcoholic consumption.

Links to other sites

    CyberDiet (Commercial site)- shows the nutritional content of specific foods
    Increased life span through nutrition-reduced calorie diet and plant antioxidants
    Nutrition menu
    Dietary guidelines for Americans
    Enjoy a variety of foods
    10 tips to healthy eating
    Importance of a balanced diet
Food labeling
    Food labeling
    Vitamin update
    Benefits of Vitamin E
    Vitamin K: blood clotting
    A major review
    History of food development
    Brief history of agriculture
    Evolution of crop plants
    What is crop evolution: A useful summary and preview
American Indian History
    Brief history of American Indians in New Mexico
    Anasazi: A Southwestern People
    Indian stories about corn:  Sioux, Cherokee, Chippewa, Abnaki
Central American history
    A brief history of Mexico
    A brief history of Central America
European agriculture history
    How agriculture came to central Europe by Peter Bogucki
    Neolithic landscapes in Poland: Technical but informative.
    Neolithic Northern
    European Plains
    Recently discovered Paleolithic cave paintings in France
    A summary of fossil hominids
Agricultural statistics
    Brief history of the U.S. Department of Agriculture
    United States Agricultural Statistics, 1982-1992
    Maryland agriculture census

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 Last revised: March 17, 1999 - Browning