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Chapters 8 and 1 (Chapter 8: Plant Systematics and Evolution pages 129…
Chapters 8 and 1
Chapter 8: Plant Systematics and Evolution
pages 129-133
Phylocode
Linnaean nomenclature is an artificial system based on the appearance of organisms that often does not reflect their evolutionary relationships, or phylogeny
phylogeny
:
the evolutionary history and relationship of a species
movement to replace this with new system of nomenclature (PhyloCode), that is truly phylogenetic
PhyloCode is based on work of Hennig, proposed that only shared derived characteristics should be used to define a group of related organisms
each group constructed should be monophyletic, composed of only those organisms that can trace their descent from a common ancestor
clade
:
monophyletic group of organisms, i.e., organisms that can trace descent from a common ancestor
as new information that may change a group’s ranking in taxonomic hierarchy is collected, names are not changed
instead of ranks, clades are the only groups recognized
in 1991, the APG (Angiosperm Phylogeny Group) system compared the sequence data of select genes to classify the flowering plants
highest rank is order, higher categories only identified as clades
in APG II (2003), angiosperms are recognized as a clade, sharing several distinct characteristics, such as ovules enclosed in a carpel and double fertilization
within angiosperms, all monocots appear to belong to distinct clade, but molecular data indicate that traditional dicots represent several evolutionary lineages
most dicots constitute clade (true dicots); includes about 75% of all angiosperms
eudicot
:
true dicots; clade of dicotyledonous plants as indicated by phylogenetic analysis
traditional dicots excluded from the clade eudicot include several ancient lineages in the evolution of angiosperms
paleodicot
:
group of dicots from several ancient lineages excluded from the clade eudicot
Barcoding Species
new way of identifying species relies on barcode (a short segment of DNA that is standard for a particular group of organisms)
for animal and algal groups, the nucleotide sequence of one gene (CO1) in the mitochondrial genome has been identified as the standard for distinguishing among species
difference in its nucleotide sequences is greater between species than within species
has not worked as an identifiable genetic DNA segment for land plants and fungi
mitochondrial groups evolve too slowly; different species have similar sequences
use the nuclear ribosomal DNA segment in fungal plants and the gene rbcL in chloroplast for land plants
not enough differences in these genes between closely related species, making identification of species less certain
organellar DNA preferred over nuclear DNA because less likely to occur in multiple copies and it is much easier to sequence, but only uses maternal DNA in plant hybrids
The Influence of Darwin's Theory
The Voyage of the HMS Beagle
in 1831, at age 22, Charles Darwin recommended as companion on ship to help collect and identify specimens during voyage
found that some fossils of extinct species looked very similar to current species
questioned the fixity of species concept, popular at the time, which said that species were acts of Divine Creation, unchanging over time
in 1842, began putting thoughts together on what was to become his theory of evolution by natural selection
Natural Selection
four underlying premises to Darwin’s theory of evolution by natural selection
variation- members within species exhibit individual differences, which are heritable
overproduction- natural populations increase geometrically, producing more offspring than will survive
competition- individuals compete for limited resources (“struggle for existence”)
survival to reproduce- only individuals that are better suited to environment survive and reproduce (survival of the fittest), passing on to a proportion of their offspring the advantageous characteristics
gradually, the species evolves, or changes, as more and more individuals carry these effective traits
in addition to natural selection, humans have used artificial selection, selective breeding as practiced by humans, to shape the characteristics of crop plants to suit the needs of humans
artificial selection
:
selective breeding as practiced by humans on domesticated plants and animals
biggest flaw in Darwin’s theory was mechanism of hereditary; did not understand the means by which traits are passed down from generation to generation
a trait that promotes the survival and reproductive success of an organism in a particular environment is an adaptation
adaptation
:
trait that enhances the survival of an organism in its environment
realized that species are dynamic and variable, continually evolving through the mechanism of natural selection in which adaptations are refined to changing environment
Saving Species through Systematics
about 1.4 million living microbes, fungi, plants, and animals have been identified by systematics
biodiversity is an inventory of the number and variety of organisms that inhabit Earth
biodiversity
:
the sum variety of living organisms on Earth
currently in a biodiversity crisis; variety of living species is declining because of accelerating extinction rate
in 2015, estimated that if global temperature raises by 2°C, global extinction rate for species will also increase from its current rate of 2.8% to 5.2%, will vary by continent
biodiversity is the basis for the necessary essentials to human existence- food, fiber, fuel, and shelter
advances in agriculture are dependent upon the interaction between systematics and biodiversity
with the advent of genetic engineering, nearly any plant species is a potential source of genes for transfer to agricultural crops
however, the the conversion of native ecosystems to agricultural lands in an attempt to accommodate the food demands of an exponentially growing human population may eliminate the very organisms on which agriculture depends for its future
species loss could result in soils unable to support vegetation
knowledge of systematics has many practical applications
movement to reduce our dependence on chemical pesticides and rely more heavily on biological controls to manage nuisance organisms
depends on proper identification of pest, knowledge of its life cycle, and correct identification of its predators and susceptibility to disease
knowledge of systematics can be used to predict economic uses of little known but related species
systematics research is fundamental to learning about the characteristics and dimensions of biodiversity
Chapter 1: Plants in Our Lives
pages 8-15
Molecules of Life
Carbohydrates
carbohydrates include sugars, starches, and cellulose; composed of carbon, hydrogen, and oxygen
sugar
:
a monosaccharide; a carbohydrate with the general formula CnH2nOn
starch
:
a polysaccharide composed of a thousand or more glucose molecules; the chief food-storage material in most plants
cellulose
:
complex carbohydrate that occurs in the cell walls of plants and oomycetes
many carbohydrates, especially glucose, sources of energy for cells; cellulose and others are structural materials
glucose
:
six-carbon monosaccharide; one of the most abundant simple sugars; the building block of both cellulose and starch and important to several metabolic pathways
simplest carbohydrates are simple sugars; contain only one sugar molecule
monosaccharide
:
the simplest carbohydrate, a simple sugar
most familiar examples of monosaccharides are glucose and fructose
fructose
:
six-carbon monosaccharide; often referred to as fruit sugar
although most plants transport carbohydrates from one part of the plant to another in form of sucrose, only a few actually store this molecule
two sugar molecules bonded together known as disaccharide
disaccharide
:
sugar consisting of two monosaccharides; example: sucrose in composed of glucose and fructose
sucrose
:
a disaccharide made from a molecule of glucose linked to a molecule of fructose; table sugar
polysaccharides consist of many thousands of sugar molecules bonded together
polysaccharide
:
a polymer, such as starch or cellulose, composed of thousands of monosaccharides
three most common are starch, glycogen, and cellulose
starch and glycogen are storage molecules
starch occurs in green plants while glycogen found in fungi, bacteria, and animals
cellulose is structural component of plant cell walls, while citing is major structural component of fungal cell walls
Proteins
proteins are large, complex macromolecules composed of small molecules (amino acids)
amino acid
:
nitrogen-containing building block of proteins
composed of carbon, hydrogen, oxygen, nitrogen, and sulfur
amino acids attached to each other by special covalent bond, called a peptide bond, and long chains of amino acids are called polypeptide chains
polypeptide
:
a chain of amino acids connected by peptide bonds
proteins have many functions
can serve as enzymes (biological catalysts), structural materials, regulatory molecules, or transport molecules
Lipids
lipids are diverse group of substances largely composed of only carbon and hydrogen
different types, but all insoluble in water
include such compounds as triglycerides, phospholipids, steroids, and waxes
triglyceride
:
a type of lipid formed from three fatty acids bonded to a molecule of glycerol; a fat to an oil
important source of energy; function as food reserves
phospholipid
:
a type of lipid molecule occurring in a bilayer in biological membranes; a lipid with two fatty acids and a phosphate group attached to glycerol
important structural component of cell membranes
steroid
:
a type of lipid containing four fused rings of carbon atoms with various side chains
important hormone
Nucleic Acids
nucleic acids contain carbon, hydrogen, oxygen, nitrogen, and phosphorus
composed of repeating units of nucleotides, which consist of sugar (either ribose or deoxyribose), a phosphate group, and a nitrogen base (eitehr a purine or a pyrimidine base)
nucleotide
:
a single unit of nucleic acid composed of a phosphate group, a five-carbon sugar (either ribose or deoxyribose), and a purine or pyrimidine base
ribose
:
a pentose sugar present in RNA
deoxyribose
:
five-carmon sugar in DNA
purine
:
one type of nitrogen-containing base found in nucleotides; consisting of adenine and guanine
pyrimidine
:
one type of nitrogen-containing base found in nucleotides; consisting of cytosine, thymine, and uracil
five different types of nucleotides occur, depending on the type of base
two purine bases
adenine
:
one of the purine bases found in nucleotides and nucleic acids
guanine
:
purine base present in both DNA and RNA
three pyrimidine bases
thymine
:
a pyrimidine base occurring in DNA but not in RNA
cytosine
:
a pyrimidine base in DNA and RNA
uracil
:
a pyrimidine found in RNA but not in DNA
DNA and RNA are the two types of nucleic acids
deoxyribonucleic acid (DNA)
:
the genetic material of life
thymine nucleotides occur only in DNA
ribonucleic acid (RNA)
:
the nucleic acid formed from DNA and involved in protein synthesis; nucleotide of chain of phosphates, ribose sugars, and purine and pyrimidines
uracil occurs only in RNA
both DNA and RNA contain four types of nucleotides, two purines and two pyrimidines
DNA is unique in its ability to replicate itself and thus pass on the genetic code from one generation to the next
exists as a double-stranded molecule that is twisted into a helix
double helix:
the form of the DNA molecule; the complementary nucleotide strands of the DNA molecule twisted into a helix
RNA usually consists of single strange, with ribose as part of the sugar-phosphate backbone
involved in the manufacture of proteins, using the instructions coded in the DNA molecule
sequence of bases in DNA makes up a gene, and each gene codes for the formation of a specific product
gene
:
unit of hereditary information on chromosomes
chemical composition of life is based on element carbon and classes of carbon compounds known as carbohydrates, lipids, proteins, and nucleic acids
these four classes of compounds are the most important molecules in living organisms and often exist as large, complex macromolecules
macromolecule
:
complex organic molecule formed by joining smaller molecules; example: proteins are macromolecules formed by joining amino acids
carbohydrates, lipids, and proteins are also major nutrients in human diet