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Introduction to Plant Products and Human Affairs


Title: Introduction to Plant Products and Human Affairs Author: Administratr Last modified by: Administratr Created Date: 8/15/2011 1:24:57 PM Document presentation ... – PowerPoint PPT presentation

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Title: Introduction to Plant Products and Human Affairs

Introduction to Plant Products and Human Affairs
How Do We Use Plants?
  • Food and fuel
  • Shelter
  • Medicine
  • Pleasure

  • Plants convert carbon dioxide and water into
    sugar, using energy from sunlight.
  • CO2 H2O ? C6H12O6 (sugar)
  • The chemical bonds in the sugar molecules store
  • Sugar is our primary food sourceeverything else
    is made from it. To get energy, we reverse the
    reaction above
  • C6H12O6 (sugar) ? CO2 H2O
  • This is the same process as burning fuel, but our
    bodies do it in a slower and more controlled way.
  • Plants also use the sugar they make as food.

More Food
  • Plants store sugar as starch, to help survive the
    winter and to help new seedlings get started. We
    take advantage of this process to get our food.
  • About 80 of the human diet is starch
  • To use starch, our bodies convert it back into
  • Starch mostly comes from
  • the seeds of cereal grains like maize (corn),
    wheat, and rice
  • The underground storage organs of potatoes, yams,
    and cassavas
  • Starch molecules are composed of many sugars
    joined together.

  • Proteins are an essential part of all living
  • A fundamental difference between plants and
    animals our bodies are mostly protein, and
    plants are mostly carbohydrate.
  • Carbohydrates are made of carbon, oxygen, and
    hydrogen, but proteins are 1/3 nitrogen (as well
    as C, H, and O).
  • Nitrogen gas in the air must be fixed before it
    can be used. This process is difficult and
  • Bacteria in the root nodules of legumes perform
    nitrogen fixation.
  • We eat legumes (things like beans and peas)
    because they produce lots more protein than other

Root nodules containing nitrogen-fixing bacteria
Plant-derived Materials
  • Wood, fiber, paper, rubber
  • Plants live on land. They need sunlight and
    carbon dioxide (above ground), plus water and
    minerals (below ground) to photosynthesize.
  • The way to satisfy these needs a vascular system
    to transport water up from the roots and sugar
    from the leaves to everywhere else.
  • With mechanical support to hold the plant upright
  • Wood and fibers are derived from the vascular
  • Cellulose is also composed of sugar molecules
    (similar to starch)

  • Plants have to survive whatever predators attack
    themthey cant hide or run away.
  • A major form of defense is chemical many plants
    produce chemical compounds that are poisonous.
  • We have found that in small amounts, many of
    these poisons can be used as medicinal drugs.
  • Also, recreational drugs and spices.
  • Things that are poisonous to organisms like
    bacteria or fungi or insects are often useful for

Estrogen-like molecules produced by plants
  • Most plants rely on animals for reproduction the
    animals spread the pollen from one plant to
    another, and also disperse seeds to new
  • Plants need to attract pollinators, and we often
    benefit perfumes, ornamental flowers, fruits,

Principles of Biology
Principles of Biology
  • Biology is based on two fundamental principles.
    Throughout this class we will constantly be
    referring to these principals.
  • Life is applied chemistry life is a set of
    self-sustaining chemical reactions
  • So we want to know which chemical compounds and
    reactions are involved in the plant products we
  • Life evolves by natural selection
  • So we often ask what advantage some useful trait
    confers on the plant.

1. Chemistry
  • This is the physical reality of life what we are
    made of, the mechanisms used in all living
  • All living things are composed of atoms
  • Mostly carbon, hydrogen, oxygen, and nitrogen.
  • About 20 others used in lesser amounts
  • Atoms consist of a nucleus containing protons and
    neutrons, and a cloud of electrons surrounding
    the nucleus
  • The number of protons determines which element an
    atom is

  • Atoms usually combine together into molecules,
    such as carbon dioxide, water, and glucose.
  • Atoms are connected together by chemical bonds,
    which are shared electrons.
  • All chemical reactions involve the movement of
  • Each type of atom forms a characteristic number
    of bonds carbon has 4, nitrogen has 3, oxygen
    has 2, hydrogen has 1
  • Chemical reactions are used to rearrange the
    atoms in molecules to create different molecules.

  • Atoms can be combined into very large molecules,
    called macromolecules.
  • Macromolecules are built up from smaller
  • Carbohydrates are long chains (sometimes
    branched) of sugars.
  • DNA molecules are millions of nucleotides strung
  • Proteins are chains of 20 different types of
    amino acid. Several hundred amino acids in a
    chain for a typical protein.

  • Energy is needed to do any form of work.
  • Thermodynamics energy is neither created nor
    destroyed, it just changes form. But, disorder
    (entropy) increases.
  • In practice, useful forms of energy get converted
    into waste heat, which cant be used for
  • Chemical bonds contain energy different amounts
    in different molecules. Most chemical reactions
    either need energy added or they release energy.
  • Thus, converting carbon dioxide and water into
    sugar needs energy from sunlight added, and
    metabolizing sugar back into carbon dioxide and
    water releases energy.

  • Chemical reactions in living cells happen because
    of catalysts called enzymes.
  • Technically, enzymes just greatly speed up the
    reactions, which otherwise would occur at an
    impossibly slow rate.
  • Each different reaction in the cell uses a
    different enzyme. Thousands of different enzymes
    in a typical cell.

Enzymes and Proteins
  • Enzymes are made of proteins
  • Enzymes catalyze all chemical reactions in the
  • Proteins are macromolecules made from chains of
    amino acids
  • Enzymes are used to create the amino acid
    subunits and then assemble them into the proteins
    which make up the enzymes. This is the basic
    self-sustaining set of chemical reactions that is

DNA and Proteins
  • The sequence of amino acids in each protein
    determines its function.
  • Information about the sequence is stored in DNA.
  • DNA is a very stable molecule that can be easily
    copied so its information is passed to future
  • Each gene is a short region of DNA that codes for
    a particular protein.

2. Evolution
  • Evolution by natural selection is one of the
    cornerstones of biology nothing makes much sense
    without it.
  • Unfortunately, the concept has been caught up in
    a religious and political fight.
  • This is a science class, so we are only going to
    teach the scientific view. You are welcome to
    believe whatever you like outside of class.

Natural Selection
  • The basic concept is very simple if one organism
    is better able to survive and produce than
    another organism, there will be more descendants
    of the first organism than the second after a few
  • The ability to survive and reproduce is called
    evolutionary fitness.
  • Having greater fitness needs to be inherited, so
    the descendants also have greater fitness.
  • Its like compound interest a little bit better
    to start leads to a much greater result after a
    long time has passed.
  • We can say that a given trait confers a selective
    advantage if it increases the fitness of an

Artificial Selection
  • Artificial selection is when humans decide which
    organisms will survive and reproduce.
  • As opposed to natural selection, when only
    natural forces affect reproduction
  • The point is, artificial and natural selection
    work the same way, by allowing some individuals
    to reproduce more than others.
  • Most of plant (and animal) breeding uses
    artificial selection we choose the best
    individuals to be parents for the next

Genetic Variation
  • For natural selection to work, there needs to be
    genetic variation within a species, so that some
    variants will be more fit than others.
  • Most species have a lot of naturally occurring
    variation differences in their DNA due to random
  • Some mutations are quite small changing a single
    DNA base, for example.
  • Others are quite large genes fused together or
    split in two, for example. Entirely new traits
    can arise from these changes.

Effects of Genetic Variation
  • Most mutations have little or no effect on the
  • More than 95 of the DNA in a typical organism is
    not involved in making proteins or anything else
    needed for life (as far as we know).
  • Even mutations within genes often have little
    effect proteins work quite well with minor
    variations in their amino acid sequence
  • Many mutations that cause minor changes have no
    immediate effect on fitness, but when external
    conditions change, they become important.
  • Called pre-adaptive characteristics
  • For example, a mutation that makes an enzyme work
    better at low temperatures might become very
    important if the climate cools off during an Ice
  • Important point fitness depends on the
    environment you find yourself in.

  • A basic principle of evolution is that genetic
    change is random but natural selection causes
    mutations with greater fitness to increase.
  • Lots of new mutations occur, but only a few
    persist due selective advantage.
  • This is opposed to the false idea that changes
    that occur within the body of an individual
    affect future generations.
  • Reading a lot wont make your children smarter,
    and exercising a lot wont make them stronger
  • This false idea is called inheritance of
    acquired characteristics, and is often
    associated with Jean-Baptiste Lamarck, an
    otherwise excellent scientist from the 1700s.

Exchanging DNA
  • Evolution would be a very slow process if it had
    to depend on mutations alone. It is much faster
    to pick up a new useful trait by getting whole
    genes or groups of genes from another organism.
  • Bacteria and other lower organisms trade random
    pieces of DNA frequently, often between very
    different species. This is called horizontal
    gene transfer, and it is very common.
  • Higher organisms (eukaryotes, including plants
    and animals) have a regular sexual process that
    mixes the DNA from two different individuals to
    produce offspring that are genetically different
    from either parent.
  • This allows several good traits to be combined in
    a single individual
  • Also, some unlucky individuals get several bad
    traits they then fail to reproduce, which
    removes the bad traits from the population.

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  • Most lower organisms have only 1 copy of each
    gene this is called haploid.
  • The sexual process in eukaryotes means that at
    least for a short time, two copies of each gene
    are present one from each parent. This is
    called diploid.
  • Simple eukaryotes (like yeast) quickly go back to
    the haploid state.
  • But, being diploid has a real advantage you have
    a backup copy of every gene, so if one copy gets
    inactivated (by random mutation), there is a
    second copy to take over.
  • This seems to work very well almost all large
    organisms (anything you can see) are diploid,
    including all plants more complicated than mosses
    as well as most animals.