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Chapter 1
BOTANY: INTRODUCTION
The word “botany” comes from the Greek word ‘botane’ meaning “plant.”
EVOLUTION OF PLANTS
Plants, algae and some bacteria are capable of photosynthesis.
Life on planet Earth, with a few exceptions, depends on this process that changes radiant energy
into chemical energy that can be utilized by organisms as a source of energy.
LIFE ORIGINATED EARLY IN THE EARTH’S GEOLOGIC HISTORY


Condensation of the nebular material into protoplanets and meteorites.
Solidification of planets about 4.6 billion years ago.
The large condensing mass at the center became the sun.
During condensation, elements scattered according to a density gradient with the heavy masses
forming the planets near the sun and the lighter masses forming the outer planets.
Earth Chronology:
4.6 BY earth formed
4-3.8 BY life originated
3.5 BY oldest known fossils
2.5 BY photosynthesis, oxygen accumulated
2.1 BY first eukaryotes
1.2 BY eukaryotes are well established and diverse
700 MY soft-bodies multicellular life
540 MY hard-bodied multicellular life
"Arrhenius and graduate student Stephen Mojzsis ... recently discovered the oldest chemical
evidence of life in sedimentary rocks from Greenland. The rocks are estimated to be more than
3.85 billion years old. Carbon in these rocks had an isotope profile seen only in remains of
organisms (S.J. Mojzsis et al., Nature, 384:51-9, 1996). "The evidence of the carbon signatures is
crucial in arguing that life on Earth was present before 3.85 billion years ago," maintains
Mojzsis. "Furthermore, the carbonaceous matter was found in intimate association with the
phosphate mineral apatite, a common biologically formed substance." Phosphates exist in cell
membranes, enzymes, genetic material, and biological energy molecules." http://www.thescientist.com/yr1997/mar/research_970331.html ; The Scientist, March 31, 1997.
In 1953, Stanley Miller demonstrated that amino acids and other organic compounds could be
synthesized spontaneously from hydrogen gas, ammonia, methane and other compounds
presumed to have been present in the second atmosphere of the Earth if energy is provided.
Miller found that as much as 10 percent of the carbon in the system was converted to a relatively
small number of identifiable organic compounds, and up to 2 percent of the carbon went to
making amino acids of the kinds that serve as constituents of proteins.
Variants of Miller’s experiment are many. The results have been similar to Miller’s, a large
number of organic molecules, some found in living organisms and others not.
In reproducing Miller’s experiment or its variants, it is important to keep O2 out of the reaction.
Aldehydes and cyanides are first products then more complex organic compounds are
synthesized.
Proteinoids
Fox showed that AA mixtures subject to high temperatures (150 -200ºC) in the absence of water
polymerized to form proteinoids.
Proteinoids have protein-like properties:

Nonrandom proportions of AA: frequency not based on the proportion of AA in the original
mixture.
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Some AA preferentially occupy the N― and C― terminal position.

Proteinoid have enzyme-like activity (low level catalytic activity), and increase the rate of
organic reactions, e. g. split by hydrolysis, catalyzed the condensation of ATP into
nucleotides, remove carboxyl groups from various molecules.

Give positive color tests with the same reagents that proteins do.
Two important characteristics of proteinoids are:
1. They have catalytic activity.
2. They organize into microspheres.
AA are catalytic only in peptide form.
AA can polymerize in certain types of clay, volcanic sediments and hydrothermal currents.
These organic molecules are presently thought to have served as a source of energy for the
earliest forms of life.
Droplets bounded by a double membrane and formed by boiling proteinoids. The hot solution is
then allowed to cool down slowly.
Microspheres may be regarded as a precursor of protocells.

They are uniform in size.

Microspheres can selectively absorb and diffuse some chemicals, grow in size, form junctions
with other microspheres.
They share one important feature with cells: they form a compartment that separates a reaction
from the surrounding.
Microspheres can absorb proteinoids from the surrounding solution, which allows them to grow
and eventually to divide in two by fission or budding
Microspheres grow to a certain size and then produce a bud, which is capable of growing and
budding in turn thus creating several generations of microspheres.
As these early forms of life evolved became more complex and acquired the ability to grow,
reproduce, and pass on their characteristics to subsequent generations (heredity).
Characteristics of living things:
 Ability to grow
 Ability to reproduce
 Ability to pass on their characteristics to subsequent generations
 Have cellular organization
AUTOTROPHIC AND HETEROTROPHIC ORGANISMS
Heterotrophs must obtain food from outside.
Autotrophs make their own energy rich molecules.
Depletion of organic compounds randomly made in nature eventually occurred.
The most successful autotrophs were able to evolve system that made use of direct sun light and
store its energy in organic molecules.
Photosynthesis may have existed 3.5 billion years ago; the evidence for this date is based on
chemical markers, stromatolite fossils and microfossils of cyanobacteria.
About 100 million years after the first signs of life on Earth.
Origin of the mechanism is not known. It is presumed to have been anoxygenic (“no oxygen
involved”).

Present day purple and green bacteria are anoxygenic.
Almost all photosynthetic systems depend on chlorophyll, a derivative of porphyrin.
PHOTOSYNTHESIS ALTERED THE EARTH’S ATMOSPHERE
Molecular oxygen was a byproduct of the splitting of water. An oxidizing aerobic environment
began to form.
We don't know at what speed oxygen began to accumulate in the atmosphere.
3.5 billion-year-old cyanobacteria fossils have been found in Warrawoona, Australia.
Between 2.7 and 2.2 billion years ago, oxygen began to gradually accumulate in the atmosphere.
By the Cambrian (570-510 m.y.a.) the levels of O2 had increased enough to allow the rapid
evolution of aerobic organisms.
Consequences of the increase of oxygen in the atmosphere:
1. Ozone layer also was formed that prevents short wave UV rays from reaching the earth's
surface. By about 450 million years ago, the amount of UV radiation reaching the earth’s
surface was low enough that organisms could live on the surface layers of water and
move onto land.
2. The new aerobic environment caused the development of a new aerobic pathway in which
oxygen was used to produce much more energy from the breakdown of glucose than
anaerobic fermentation could produce.
Only prokaryotic cells existed in the early anoxygenic atmosphere.
According with the fossil record, the accumulation of oxygen was accompanied by the
appearance of eukaryotic cell.
SEASHORE ENVIRONMENT
As cellular colonies multiplied, they quickly depleted the nutrients in the open ocean.
As a consequence, life began to develop more abundantly near the shore where waters were rich
in nitrates and other nutrients brought by rivers and streams.
About 700-650 million years ago, multicellular organisms appeared.
Structures for attachment to the rocky substrate evolved.
COLONIZATION OF THE LAND
1. Roots anchor the plant to the ground.
2. Stems provide support for leaves and transport necessary materials between roots and
leaves.
3. Leaves are the photosynthetic organs.
One of the most significant adaptations to terrestrial habitat was related to coping with
desiccation:
Adaptations for water conservation.
1. Waxy cuticle on the epidermis to protect against desiccation.
2. Stomata (sing. stoma) for gas exchange and control of transpiration.
Adaptations for water transport.
Transport system or vascular tissue:
1. Phloem for the transport of dissolved carbohydrates.
2. Xylem for water and mineral transport.
Conquest of the land by algae probably occurred after the Cambrian (590?-505 m.y.a.).
 http://www.ucmp.berkeley.edu/cambrian/camb.html
Factors that might have played a role in facilitating or causing the journey to the land.
 A fall in sea level during the Ordovician glaciations (505-459).
http://www.ucmp.berkeley.edu/ordovician/ordovician.html
 Increase in oxygen allowed the formation of highly oxygenated polymers cutin and
lignin.
 Formation of ozone protective layer.
Annual plants have a photosynthetic stem.
Perennial plants have their stem covered with cork, which slows down the loss of water.
Plants grow throughout their lifetime.
New tissue is formed in the meristems, which contain embryonic cells capable of adding new
cells to the plant body.
The activity of the apical meristems increases the length of stems and roots, and is called
primary growth.
The activity of lateral meristems or cambium layers increases the girth of the stem and roots and
is called secondary growth.

Vascular cambium and cork cambium
Reproduction on land also required especial adaptations: spores and seeds.
Seeds are multicellular structures that protect and provide food for the embryo.
EVOLUTION OF COMMUNITIES
Plants are most obvious features of the landscape.
Biomes are large and distinctive regional assemblages of plants and animals controlled by
climatic factors.
Ecosystems are stable of associations of plant and animals that depend on photosynthesis and
other factors of the non-living environment for its survival.
Living and non-living environments are integrated into a functional unit.
There is interaction between organisms in the ecosystems: predation, herbivory, competition, etc.
APPEARANCE OF HUMAN BEINGS
Human first appeared about 2 million years ago.
Agriculture started about 10,500 years ago.
Agriculture allowed the support of larger populations of humans that began to gather into towns
and villages.
The increase food supply allowed the development and specialization of human culture.
There are subdivisions of botany: taxonomy, physiology, genetics, etc.
GENETIC ENGINEERING
Genetic engineering has made possible the transfer of genes between entirely different species.
It has resulted in the development of transgenic plants.