Transcript Plants and Society - University of Windsor

Plants and Society – 03-55-208
Administrative Details:
Lecture Times: Tuesday and Thursday 11:30-12:50
Lecture Room: 361 Dillon Hall
Instructor: Dr. I. Michael Weis
Room 202 Biology Building
phone: ext. 2724
email: [email protected]
Office hours: T, Th afternoons ~2-4PM
Graduate Assistant: David Yurkowski
Counselling/Assistance hours: TBA
Required Text:
Plants and Society (2006) Levetin, E. and K.
McMahon (4th Edition). McGraw-Hill, Toronto,
ON.
Course Website: follow these links
www.uwindsor.ca/courses 
Science 
Biology 
55-208 
Course website
Here you will find the course outline, readings,
and Powerpoint slide set for each lecture as early
as possible.
Exams, marks and marking policy
• Mid-term Exam (25%) tentative date Feb. 17
• Course Project (combined 30%)
(comprised of a research paper (20%) based on the scientific
literature, leading to development of Poster for presentation)
(5% for participation in Poster Session, 5% for
poster quality) poster session date TBA
Bonus Mark (2%) for bringing snacks to the Poster Session
• Final Exam (40%)
Both exams will be comprised of multiple choice
(and other questions of various types requiring
answer choice), short answer (10-25 word
answers), and a small number of essay questions.
Course Topics
• Basics of Plant Biology
• Plants as food
• Plants as spice, stimulants and beverages
• Plants as medicines
• Plants for fibre, oils, building materials etc.
• Plants for aesthetics, habitat
• Plant Biotechnology
Cosmology and The Origin of Life
Science now believes the universe as we know it
originated in a “Big Bang” approximately 14 BYBP.
Very early on stars originated by the accretion of
matter. Lesser amounts of matter in the general
vicinity of our sun accreted into the planets (initially
into small lumps called planetismals, then growing
larger by collisions with asteroids, meteorites or
smaller lumps and by gravitational attraction of
nearby mass). Earth was initially formed 4-5 BYBP.
When earth finally cooled to a surface temperature
<100°C, the energy of volcanic eruptions, lightning,
intense UV, cosmic radiation, and radioactive decay
caused the formation of the basic molecules of life –
amino acids, nucleosides, fatty acids, and simple
carbohydrates.
The atmosphere was also important to formation of
these molecules: it consisted of CO2, H2O, N2, CH4,
and NH3, possibly H2 and H2S, but no O2.
Amino acids and nucleic acids were joined together
abiotically. The various molecules of life were
accumulated together, with various pre-life ‘cellular’
assemblies (called protobionts).
The Miller-Urey experiments showed that all the basic
monomer units could be formed abiotically.
Sidney Fox demonstrated that short chain polypeptides
could form abiotically from amino acid monomers
through dehydration of amino acid solutions on hot
rocks. Fox also showed that simple, proteinoid
microspheres could spontaneously form. Others
showed that lipid-based microcells, called liposomes
would form. Neither of these incorporates the
characteristics by which we define life.
A.I. Oparin showed that completely dissociated
cellular components spontaneously re-organized into
what he called coacervates.
Coacervates have many of the properties of life.
They:
1.Accumulate monomers and polymers from
solution and grow
2.Divide (though only by budding off portions of the
‘cell’
3.Decompose glucose (one form of metabolism)
4.Trap energy (a primitive form of electron transport)
5.Have the potential for self-growth (capable of some
RNA and protein synthesis)
6.Have the potential to undergo a kind of selection
So, are they “living cells”?
According to Cech and Altman, RNA was probably
the first catalyst for protein and nucleic acid synthesis.
The first successful, replicating cells, however, had
DNA, not RNA. Why? (think of molecular stability,
necessary in the harsh, primitive environment and the
requirement for at least relatively faithful inheritance)
Whichever protobionts occurred, they were probably
present approximately 4 BYBP.
The oldest accepted fossil evidence of cellular life
dates back 3.5 billion years. Chemosynthetic bacteria,
found in stromatolites from western Australia, date to
around 3.5 – 3 BYBP.
This is an Australian stromatolite. The layers are
where fine sediment has stuck to ‘sticky’ prokaryotic
cells.
What are the characteristics these cells had to possess
to be considered living?
1. the capacity for growth and reproduction
2. the ability to respond to their environments
3. the ability to adapt and evolve
4. the ability to metabolize – cellular respiration and
(for some) photosynthesis
5. structural (cellular) organization
6. organic composition (based on proteins, nucleic
acids, proteins and lipids)
The first primitive Archaea (anaerobic, nonphotosynthetic, initially probably not even
chemosynthetic) are evident around 3.8 – 3.5 BYBP.
They were clearly present in fossils in chert and in
stromatolites by 3 BYBP.
Non-photosynthetic, anaerobic prokaryotes (but
chemosynthetic, with sulfur-based chemosynthesis)
dominated life until ~2.8 BYBP, when photosynthetic
bacteria evolved.
Prokaryotes were the only life forms until ~1.5 BYBP,
when eukaryotes appeared.
Photosynthetic bacteria (cyanobacteria) and, later,
photosynthetic eukaryotes drastically changed the
earth’s atmosphere. How?
By releasing free oxygen into the atmosphere. Many
anaerobes are intolerant of free oxygen. Other forms
of life could evolve (consumers) once oxygen was
available to support respiratory metabolism.
Aerobic metabolism produces far more energy per
molecule of glucose than does fermentation.
A question for discussion: Do viruses constitute living
organisms?
Go through the conditions that characterize life. Does
a virus fit all these criteria? Does it have, in and of
itself, the ability to grow and reproduce or metabolize?
There are alternative ‘definitions’ of life that might
include viruses: Any entity that exhibits counterentropy and self-replication. Do viruses fit this
definition?
This course is about plants. The current view is to
separate life into three Domains: Archaea, Bacteria,
and Eukarya,
then subdivide Eukarya into: Protista, Fungi,
Plantae and Animalia.
What are the characteristics that permit us to separate
Plantae from the other domains and sub-domains?
Plant cells are encased within cell walls made largely
of cellulose. These are from onion epidermis.
Are cellulose cell walls sufficient to distinguish plants
from all other living organisms? No!
Plants are photosynthetic. Inside their cells are plastids
called chloroplasts.
Is the presence of photosynthetic membranes sufficient
to distinguish plants from other types of living
organisms? No!
Cell walls are present in some prokaryotic cells and in
fungi. Membrane-bound photosynthetic pigments
occur in cyanobacteria.
Even chloroplasts are not exclusively present in
plantae. They are also present in photosynthetic
protists.
Plants are multicellular, photosynthetic,
eukaryotes. Even this is not a perfect discrimination,
since there are large kelps that are usually classed in
the Protista, but are eukaryotic and photosynthetic.
Let’s continue as if we clearly know what plants are,
and consider more about their structure…
How big are plant cells compared to bacteria and
animal cells?
As a eukaryotic cell, plant cells have a membraneenclosed nucleus, as well as other membrane-enclosed
organelles. The largest organelle is frequently the
empty-looking vacuole.
Middle lamella
pits with plasmodesmata
Let’s look on more detail at some of the key
organelles. First, the chloroplast…
Photosynthetic pigments (and
other pigments) are located on
thylakoid membranes, stacked
into grana. Grana are
interconnected, embedded in
stroma. There are two
membranes surrounding the
internal structure of the
chloroplast.
Why are there two membranes surrounding
chloroplasts?
The theory developed by C. Mereschkovsky and Lynn
Margulis is of serial endosymbiosis. Plastids
(mitochondria and chloroplasts) originated as
independent prokaryotes that were engulfed by and
came to live within larger cells as symbionts. The
outer of the two membranes is the cell membrane of
the host cell; the inner membrane is the prokaryotic
membrane of the prokaryotic plastid.
Both the structures and composition of the membranes
and the small ribosomal subunit RNA sequence
support this theory.
There are more pigments than chlorophyll inside
chloroplasts. What are they, and how are they visible?
In the fall, when chlorophyll breaks down, the
phycoerythrin and phycocyanin are visible as the
reds and yellows of fall leaves.
Moving on, the objective is to understand
photosynthesis. First, the anatomy of a leaf (in
particular, one from a C3 plant)…
Leaf water relations and access to atmospheric CO2
are controlled by stomates – openings in the leaf
surface which have guard cells that can close or open
the stomate. When guard cells are turgid (well
hydrated), stomates are open. When guard cells are
flaccid (low water level), stomates close.
Water relations are critical to plant growth and
survival. Plants have adapted different strategies in
different environments…
In cool temperate regions, plants have the structure
and photosynthesis you are probably familiar with,
called C3. Both light and dark reactions occur in the
mesophyll of the leaf. Sugars are then transported to
and through phloem.
In warmer, dryer habitats many plants have adapted a
C4 structure and physiology. Here the light reactions
and carbon fixation occur in the mesophyll, but the
reactions that convert fixed carbon into sugars occur in
the bundle sheath, protected from herbivores by tough
lignin and silica.
In C4 plants, CO2 is concentrated via addition to PEP
(phosphoenolpyruvate) by PEP carboxylase to form
malate, which is then transported to bundle sheath
cells, where it is released and available for
photosynthesis. This makes C4 plants 3-4x more
efficient under hot dry conditions, but they have little
advantage in moderate climates.
There is one more major form of photosynthesis,
called CAM (for Crassulacean Acid Metabolism). It
occurs in succulent desert plants and cacti. In CAM
plants stomata are closed during days (the thermal
stress would cause loss of too much water to
transpiration), but open at night. CO2 is fixed at night
into 4-carbon molecules (like C4 photosynthesis), and
the light reactions and Calvin-Benson cycle reactions
occur during the day with stomates closed.
More about photosynthesis later.